Network Working Group                                       C. HohendorfInternet-Draft                              University of Duisburg-EssenIntended status: Experimental                               E. UnurkhaanExpires: 1 October 2024                             Mongolian University                                                            T. Dreibholz                                                               SimulaMet                                                           30 March 2024                              Secure SCTP                     draft-hohendorf-secure-sctp-37Abstract   This document explains the reason for the integration of security   functionality into SCTP, and gives a short description of S-SCTP and   its services.  S-SCTP is fully compatible with SCTP defined in   RFC4960, it is designed to integrate cryptographic functions into   SCTP.Status of This Memo   This Internet-Draft is submitted in full conformance with the   provisions of BCP 78 and BCP 79.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF).  Note that other groups may also distribute   working documents as Internet-Drafts.  The list of current Internet-   Drafts is at https://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   This Internet-Draft will expire on 1 October 2024.Copyright Notice   Copyright (c) 2024 IETF Trust and the persons identified as the   document authors.  All rights reserved.Hohendorf, et al.        Expires 1 October 2024                 [Page 1]Internet-Draft                 Secure SCTP                    March 2024   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents (https://trustee.ietf.org/   license-info) in effect on the date of publication of this document.   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.  Code Components   extracted from this document must include Revised BSD License text as   described in Section 4.e of the Trust Legal Provisions and are   provided without warranty as described in the Revised BSD License.Table of Contents   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3   3.  A brief description of S-SCTP . . . . . . . . . . . . . . . .   3   4.  Key terms . . . . . . . . . . . . . . . . . . . . . . . . . .   4   5.  Additional chunks and parameters  . . . . . . . . . . . . . .   4     5.1.  New type chunks and definitions . . . . . . . . . . . . .   4       5.1.1.  Secure Session Open request chunk (SSOpReq) . . . . .   5       5.1.2.  Secure Session Certificate chunk: (SSCert)  . . . . .   9       5.1.3.  Secure Session Open Acknowledge chunk               (SSOpReq_Ack) . . . . . . . . . . . . . . . . . . . .  10       5.1.4.  Secure Session Server Key chunk (SSSerKey)  . . . . .  11       5.1.5.  Secure Session Client Key chunk (SSCliKey)  . . . . .  14       5.1.6.  Secure Session Open Complete chunk (SSOpCom)  . . . .  16       5.1.7.  Secure Session Close chunk (SSClose)  . . . . . . . .  17       5.1.8.  Secure Session Close Acknowledge chunk               (SSClose_Ack) . . . . . . . . . . . . . . . . . . . .  18       5.1.9.  Security Level Changed chunk (SecLevCHD)  . . . . . .  18       5.1.10. Security Level Changed Acknowledged chunk               (SecLevCHD_Ack) . . . . . . . . . . . . . . . . . . .  19       5.1.11. Encrypted Data Chunk (EncData)  . . . . . . . . . . .  19       5.1.12. Padding chunk (PADDING) . . . . . . . . . . . . . . .  20       5.1.13. Authentication chunk (AUTH) . . . . . . . . . . . . .  21   6.  New Error Cause . . . . . . . . . . . . . . . . . . . . . . .  22     6.1.  Secure Session failure  . . . . . . . . . . . . . . . . .  22     6.2.  Secure Session Certificate failure  . . . . . . . . . . .  23     6.3.  Decryption failure  . . . . . . . . . . . . . . . . . . .  24     6.4.  Authentication failure  . . . . . . . . . . . . . . . . .  24     6.5.  Decompression failure . . . . . . . . . . . . . . . . . .  24   7.  S-SCTP packet format and security levels  . . . . . . . . . .  25   8.  S-SCTP data format  . . . . . . . . . . . . . . . . . . . . .  25   9.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .  26     9.1.  Establishment of a secure session . . . . . . . . . . . .  26     9.2.  Choice of cipher suite and compression method . . . . . .  28     9.3.  Data transfer . . . . . . . . . . . . . . . . . . . . . .  29     9.4.  Closing of a secure session . . . . . . . . . . . . . . .  30     9.5.  Generation of the Master secret key . . . . . . . . . . .  30     9.6.  Update of the master secret key . . . . . . . . . . . . .  31Hohendorf, et al.        Expires 1 October 2024                 [Page 2]Internet-Draft                 Secure SCTP                    March 2024     9.7.  Random number generation  . . . . . . . . . . . . . . . .  32     9.8.  HMAC algorithm  . . . . . . . . . . . . . . . . . . . . .  32   10. HMAC algorithm  . . . . . . . . . . . . . . . . . . . . . . .  32   11. S-SCTP to ULP . . . . . . . . . . . . . . . . . . . . . . . .  34   12. Transmission Control Block (TCB) extension  . . . . . . . . .  35   13. Socket API extensions for Secure SCTP . . . . . . . . . . . .  36   14. Testbed Platform  . . . . . . . . . . . . . . . . . . . . . .  38   15. Security Considerations . . . . . . . . . . . . . . . . . . .  38   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38   17. References  . . . . . . . . . . . . . . . . . . . . . . . . .  38     17.1.  Normative References . . . . . . . . . . . . . . . . . .  38     17.2.  Informative References . . . . . . . . . . . . . . . . .  39   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  401.  Introduction   SCTP is a message oriented reliable transmission protocol which works   on top of the IP-based network.  It provides several advantages over   other transmission protocols, such as TCP and UDP over IP.  One of   the advantages is multistreaming -- user data transported by   individual streams.  When multistreaming is used, network blocking   can be avoided in certain cases (e.g. network loss).  Also, SCTP   supports multihoming -- the endpoints support multiple IP addresses.   SCTP provides unordered delivery, so that a receiver immediately   delivers user data to the upper layers upon receipt.  For more   details, see RFC4960 [6].2.  Conventions   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described in BCP   14 [2] [8] when, and only when, they appear in all capitals, as shown   here.3.  A brief description of S-SCTP   S-SCTP provides security functionalities in the transport layer   without the need for any other security protocols (e.g.  TLS or IP-   sec).  Normally, a data transport over SCTP can either be secured   with TLS or can be protected by IPsec.  As both TLS over SCTP and   SCTP over IPsec have disadvantages in certain scenarios, it is   preferable to integrate cryptographic functions into SCTP.   The main issues for the security solutions TLS over SCTP RFC3436 [3]   and SCTP over IPSec RFC3554 [4] is scalability with the number of   streams.  For N secure streams, N TLS connections have to be created,   and N handshakes have to be performed.  If N is small, this is not aHohendorf, et al.        Expires 1 October 2024                 [Page 3]Internet-Draft                 Secure SCTP                    March 2024   big issue, but as N grows larger, it becomes a problem because a   handshake is a slow and expensive process.  So, when an application   performs N handshakes, the load in terms of memory use, CPU use etc.   increases linearly over time.  This problem could be overcome by   using IPsec.  However, IPsec is not so flexible and on the other hand   SCTP over IPsec has to establish new security associations (SA) for   newly added IP addresses in dynamic address reconfiguration scenario.   In this case, the application has to configure a new SA and to   negotiate a new key exchange.4.  Key terms   This part gives the definitions of the key terms, which are used in   this draft:   *  Secure session: This is the session, which provides the security      functionalities for an established SCTP association.   *  Master secret key: S-SCTP uses two kinds of secret keys.  One is      the secret key for the S-SCTP packet authentication, and the other      is the secret key for the data encryption and decryption.   *  Cipher suite: This is the suite of cryptographic algorithms, which      are used for key exchange, data encryption/decryption and the      packet authentication.   *  Pre-enc-data: This is the collection of the data chunks, which      requires encryption.  The data chunks are concatenated together      and create pre-enc-data.  Pre-enc-data may include the padding      chunk.   *  Cipher suite sequence: This is the bundle of cipher suites chosen      by an endpoint from the supported cipher suites.5.  Additional chunks and parameters   Several new chunks and parameters are defined in S-SCTP.  This   section explains those chunks and parameters.  All new chunks can be   bundled with other chunks.  The new parameters follow the Type-   Length-Value format as defined in section 3.2.1 of RFC4960.5.1.  New type chunks and definitions   The following table shows the new chunks.  All new chunks, except for   the Encrypted Data (EncData) chunk, Authentication (AUTH) chunk and   Padding (PADDING) chunk, are used for building the secure session and   to update the master secret key.  The new chunks are to be   interpreted as described in Section 3.2 of RFC 4960, by the receiver.Hohendorf, et al.        Expires 1 October 2024                 [Page 4]Internet-Draft                 Secure SCTP                    March 2024    Chunktype     Chunk name    ---------     ---------------------      0xD0        Secure Session Open Request Chunk      0xD1        Secure Session Certificate Chunk      0xD2        Secure Session Acknowledge Chunk      0xD3        Secure Session Server Key Chunk      0xD4        Secure Session Client Key Chunk      0xD5        Secure Session Open Complete Chunk      0xD6        Secure Session Close Chunk      0xD7        Secure Session Close Acknowledge Chunk      0xD8        Security Level Change Chunk      0xD9        Security Level Change Acknowledge Chunk      0x10        Encrypted Data Chunk      0x11        Authentication Chunk      0x12        Padding Chunk   The new parameters are defined in this section.5.1.1.  Secure Session Open request chunk (SSOpReq)   An endpoint creates the Secure Session Open Request chunk (see next   table)when it wishes to establish a secure session.  The chunk can be   bundled with other chunks.  The SSOpReq chunk can also be used to   update the master secret key or cipher suite after a secure session   establishment.  During the association lifetime, both associated   endpoints can request an update of the master secret key or cipher   suite; in this case, the requesting endpoint sends the SSSOpReq chunk   immediately to the other endpoint.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD0   | Reserved=0  |CF|           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |            Version             |     Key material length       |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                                \    /                     Optional parameters                        /    \                                                                \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   CF: Certificate flag: 1 bit   This flag indicates whether or not the client will send a   certificate.  It is set to 1 when the client sends a certificate.  If   a receiver receives SSOpReq chunk with CF=1 and does not receive a   certificate it raises an error and terminates the secure session   initialisation.Hohendorf, et al.        Expires 1 October 2024                 [Page 5]Internet-Draft                 Secure SCTP                    March 2024   Length: 16 bits unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header, version, random number length and optional   parameter(s).   Version: 16 bits unsigned integer   This field indicates the S-SCTP version 1.0.  The high eight bits   indicate the major version, the low eight bits indicate minor   version.   Key material length: 16 bits unsigned integer   This number has two meanings:   *  when the handshake is made using the RSA key exchange protocol,      the key material length defines the random number length, which is      generated by the server and client to calculate a master secret      key (see RSA parameters of the SSSerKey and SSCliKey chunks)   *  when the handshake is made using the DH key exchange protocol, the      key material length defines the DH prime number length (see DH      parameters of the SSSerKey and SSCliKey chunks).  For security      reasons, the key material length MUST be 512 bits (default) or      longer when the key exchange mechanism uses RSA, and 1024 bits      (default) or longer when the key exchange mechanism uses DH.  The      key material length is increased in steps of 64 bits.  If a user      defines the key material length to be shorter than the default      value, S-SCTP automatically sets it to the default.   Parameter(S):   SSOpReq chunk includes the cipher suite and compression method   parameters, which are described below:   Cipher suite parameter:   This parameter contains the cipher suites, which are chosen from all   supported cipher suites by the client.  One of them is used for the   secure session.  The user can choose certain cipher suites from the   cipher suites supported by the client.Hohendorf, et al.        Expires 1 October 2024                 [Page 6]Internet-Draft                 Secure SCTP                    March 2024    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |         Type=30               |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |      Cipher suite 1           |      Cipher suite 2           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |      ..............           |      ..............           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |      Cipher suite N-1         |      Cipher suite N           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Cipher suite: 16 bits unsigned integer:   This field indicates a cipher suite, which is supported by the   client.  The next table includes cipher suites supported in S-SCTP.   Additional cipher suites can be specified.   Value  Cipher suite               Key exchange  Encryption  Hash   -----  -------------------------  ------------  ----------  ---------     1    RSA_with_DES_CBC_MD5       RSA           DES_CBC     MD5     2    RSA_with_DES_CBC_SHA-1     RSA           DES_CBC     SHA-1     3    RSA_with_3DES_CBC_MD5      RSA           3DES_CBC    MD5     4    RSA_with_3DES_CBC_SHA-1    RSA           3DES_CBC    SHA-1     5    RSA_with_AES-128_CBC_MD5   RSA           AES-128     MD5     6    RSA_with_AES-128_CBC_SHA-1 RSA           AES-128     SHA-1     7    DH_with_DES_CBC_MD5        DH            DES_CBC     MD5     8    DH_with_DES_CBC_SHA-1      DH            DES_CBC     SHA-1     9    DH_with_3DES_CBC_MD5       DH            3DES_CBC    MD5    10    DH_with_3DES_CBC_SHA-1     DH            3DES_CBC    SHA-1    11    DH_with_AES-128_CBC_MD5    DH            AES-128     MD5    12    DH_with_AES-128_CBC_SHA-1  DH            AES-128     SHA-1    13    RSA_with_NULL_MD5          RSA           NULL        MD5    14    RSA_with_NULL_SHA-1        RSA           NULL        SHA-1    15    DH_with_NULL_MD5           DH            NULL        MD5    16    DH_with_NULL_SHA-1         DH            NULL        SHA-1    17    RSA_with_AES-192_CBC_MD5   RSA           AES-192     MD5    18    RSA_with_AES-192_CBC_SHA-1 RSA           AES-192     SHA-1    19    RSA_with_AES-256_CBC_MD5   RSA           AES-256     MD5    20    RSA_with_AES-256_CBC_SHA-1 RSA           AES-256     SHA-1    21    DH_with_AES-192_CBC_MD5    DH            AES-192     MD5    22    DH_with_AES-192_CBC_SHA-1  DH            AES-192     SHA-1    23    DH_with_AES-256_CBC_MD5    DH            AES-256     MD5    24    DH_with_AES-256_CBC_SHA-1  DH            AES-256     SHA-1Hohendorf, et al.        Expires 1 October 2024                 [Page 7]Internet-Draft                 Secure SCTP                    March 2024   The hash algorithms, defined in cipher suites, are used only for the   S-SCTP packet authentication, and not for the signature of the   handshake messages.  An S-SCTP implementation MUST at least support   the default cipher suite, DH_with_3DES_CBC_SHA-1 (value=0).  If the   SSOpReq chunk does not contain a cipher suite parameter, then:   a.)  S-SCTP will use the default, or:   b.)  S-SCTP will use the old cipher suite.   The case "a" will be used at the beginning of the secure session.   The case "b" will be used when the SSOpReq chunk is created after a   secure session establishment.  The signature schemes are derived from   both the client and server certificates, and may be different.   Compression method parameter   This parameter contains compression methods, which are used for data   compression.  The data compression uses lossless compression methods.   The user chooses several compression methods and sends it to the   receiver.  The receiver chooses one compression method.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    | Compression   | Compression   | Compression   | Compression   |    |  method 1     |  method 2     |  method 3     |  method 4     |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |    ....       |    ....       | Compression   | Compression   |    |               |               | method N-1    |  method N     |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Compression method: 8 bits unsigned char   This field indicates a compression method, which is supported by the   client.  The next table includes compression methods supported in   S-SCTP.  Additional compression methods can be specified.    Value  Compression method    -----  ---------------------       1   Huffman Code       2   Lempel-Ziv Code   The secure session uses null compression when the SSOpReq chunk   contains no compression parameters.Hohendorf, et al.        Expires 1 October 2024                 [Page 8]Internet-Draft                 Secure SCTP                    March 20245.1.2.  Secure Session Certificate chunk: (SSCert)   This chunk can be sent by both endpoints.  The certificate helps to   authenticate the endpoint, that establishes a S-SCTP session.  This   chunk contains only one parameter, the certificate parameter.  The   SSCert chunk is optional.  For security reasons, both endpoints   SHOULD use a certificate to authenticate each other.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD1   | Reserved=0    |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                           Certificate                         /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                        Optional parameter                     /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bits unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header and parameter.   Certificate: Variable length   The certificate field contains the certificate of the endpoint.   S-SCTP uses the X.509v3 certificate which is defined in RFC5280 [7].   Optional parameter   SSCert chunk has only one optional parameter.   Certificate parameter   The SSCert chunk uses the certificate parameter for additional   certificates, when the endpoint has two or more certificates.Hohendorf, et al.        Expires 1 October 2024                 [Page 9]Internet-Draft                 Secure SCTP                    March 2024    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |         Type=33               |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                          Certificate                          /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Certificate: Variable length   The endpoint can send two or more certificates.  In this case the   certificate field contains the endpoint's additional certificate.   S-SCTP uses the X.509v3 certificate, which is defined in RFC5280 [7].5.1.3.  Secure Session Open Acknowledge chunk (SSOpReq_Ack)   The Secure Session Open Acknowledge chunk is sent by the server to   tell the client that the secure session open request is accepted.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD2   | Reserved=0  |CF|           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |             Version            |        Cipher suite           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |    Compression method          |        Reserved = 0           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   CF: Certificate flag: 1 bit   This flag indicates whether or not the server has a certificate.   This flag is set to 1 when the server has a certificate, else it is   zero.   Length: 16 bits unsigned integer   The chunk length is 8 bytes, including the chunk header, version and   cipher suite field.   Version: 16 bits unsigned integer   This field indicates the S-SCTP version 1.0.  The high eight bits   indicate the major version, the low eight bits indicate the minor   version.Hohendorf, et al.        Expires 1 October 2024                [Page 10]Internet-Draft                 Secure SCTP                    March 2024   Cipher suite: 16 bits unsigned integer   This field indicates the cipher suite, which is used for a secure   session.  The cipher suite includes necessary information for the key   derivation, message encoding and MAC computation.  The server uses   the following rules to choose the cipher suite:   *  Client and Server do not have a certificate: Use DH key exchange.   *  Client or Server has a certificate: Use DH key exchange.   *  Client and Server have a RSA certificate: Use RSA key exchange.   *  Client and Server have a DSS certificate: Use DH key exchange.   Compression method: 16 bits unsigned char   This field indicates the compression method, which is used for data   compression in the secure session.5.1.4.  Secure Session Server Key chunk (SSSerKey)   This chunk includes the parameter which is used for the key exchange   algorithm.  The Server Key Exchange chunk consists of the chunk   header and one parameter.  The parameter type depends on the key   exchange algorithm.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD3   | Reserved=0  |SL|           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                                \    /                           Parameter                            /    \                                                                \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Security level (SL): 2 bits   This 2-bit value indicates a server's security level of the reserved   flags.   Length: 16 bit unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header and parameter.   Parameters:Hohendorf, et al.        Expires 1 October 2024                [Page 11]Internet-Draft                 Secure SCTP                    March 2024   The following two parameters define the key exchange protocols.   Their parameter formats are shown in the next two tables.  When a   user specifies a new cipher suite with a new key exchange algorithm,   then they must define a new parameter.   Diffie-Hellman parameter   The SSSerKey chunk uses this parameter when the handshake is done via   the DH key exchange algorithm.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Type=0xD001             |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |  Length of DH prime number, P | Length of DH prmitive root, R |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Length of DH public key, Y  |         Reserved=0            |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                      DH prime number, P                       /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                     DH primitive root, R                      /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                         DH value, Y                           /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                          Signature                            /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bit unsigned integer   The length field contains the size of the parameter in bytes,   including the parameter header, length of DH prime number, length of   DH primitive root, length of DH public key, reserved, DH prime   number, DH primitive root, DH public key and signature.   Length of DH prime number, P: 16 bits unsigned integer   This field contains the size of the DH prime number.   Length of DH primitive root, Q: 16 bits unsigned integerHohendorf, et al.        Expires 1 October 2024                [Page 12]Internet-Draft                 Secure SCTP                    March 2024   This field contains the size of the DH primitive root.  The size of   the prime number is equal R, where R is a random number defined in   the SSOpReq chunk.   Length of DH value, Y: 16 bits unsigned integer   This field contains the size of the DH public key.   DH value, P: Variable length   This is the prime number of the DH key exchange protocol.   DH value, Q: Variable length   This is the primitive root of the prime number P.   DH value, Y: Variable length   This is the public key of the DH key exchange protocol.   Signature: Variable length   The field contains the signature which is derived from the chunk   header and the whole parameter except the signature field.  The   signature computation uses the signature algorithm which is defined   in the server certificate.  If the server does not have a   certificate, this field does not exist in the parameter.   RSA parameter   The SSSerKey chunk uses this parameter when the handshake uses the   RSA key exchange algorithm.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Type=0xD002             |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                 Encrypted (random number, R)                  /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                          Signature                            /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bits unsigned integerHohendorf, et al.        Expires 1 October 2024                [Page 13]Internet-Draft                 Secure SCTP                    March 2024   The length field contains the size of the parameter in bytes,   including the parameter header, the encrypted random number and the   signature.   Encrypted (Random number, R): Variable length   The random number is used to generate the secret keys for user data   encryption and authentication.  The random number encryption uses the   client public key.   Signature: Variable length   The field contains the signature, which is derived from the chunk   header and the whole parameter except the signature field.  The   signature computation uses the signature algorithm which is defined   in the server certificate.5.1.5.  Secure Session Client Key chunk (SSCliKey)   This chunk includes the parameters which are used for the key   exchange algorithm.  The Secure Session Client Key Exchange chunk   consists of the chunk header and one parameter.  The parameter format   depends on the key exchange algorithm.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD4   | Reserved=0  |SL|           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                                \    /                           Parameter                            /    \                                                                \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Security level (SL): 2 bits   This 2-bit value indicates a client's security level.   Length: 16 bit unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header and parameter.   Parameters:   Two new parameters are defined here that can appear in the SSCliKey   chunk.  Their parameter formats are shown in the next two tables.Hohendorf, et al.        Expires 1 October 2024                [Page 14]Internet-Draft                 Secure SCTP                    March 2024   Diffie-Hellman parameter   The SSCliKey chunk uses this parameter when the handshake uses the DH   key exchange algorithm.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Type=0xD003             |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                         DH value, Y                           /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                          Signature                            /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bit unsigned integer   The length field contains the size of the parameter in bytes,   including the parameter header, the DH public key and the signature.   DH value, Y: Variable length   This field contains the public key of the DH key exchange protocol.   Signature: Variable length   The field contains a signature which is derived from the chunk header   and the whole parameter except the signature field.  The signature   computation uses the signature algorithm defined in the client   certificate.  If the client does not have a certificate, then this   field does not exist in the parameter.   RSA parameter   The SSCliKey chunk uses this parameter when the handshake uses RSA   key exchange algorithm.Hohendorf, et al.        Expires 1 October 2024                [Page 15]Internet-Draft                 Secure SCTP                    March 2024    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Type=0xD003             |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                 Encrypted (random number, R)                  /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                          Signature                            /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bits unsigned integer   The length field contains the size of the parameter in bytes,   including the parameter header, the encrypted random number and a   signature.   Encrypted (Random number): Variable length   This field contains the random number, encrypted by the server's   public key, which is used to generate the master secret key for   encryption and authentication.   Signature: Variable length   The field contains the signature which is derived from the chunk   header and the whole parameter except the signature field.  The   signature computation uses the signature algorithm defined in the   server certificate.5.1.6.  Secure Session Open Complete chunk (SSOpCom)   This chunk is the last chunk of the handshake and it indicates the   completion of the secure session establishment.  After receiving this   chunk the endpoint verifies the verification data which is contained   in the chunk.  The secure session procedure is complete when the   verification is successful.  Otherwise the secure session will be   closed.Hohendorf, et al.        Expires 1 October 2024                [Page 16]Internet-Draft                 Secure SCTP                    March 2024    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD5   | Reserved=0    |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                       Verification data                       /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bits unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header and verification data.   Verification data: Variable length   The verification data contains a hashed value which is an output of   the HMAC function.  The HMAC uses the authentication secret key,   which is individually generated by the endpoints.  The HMAC input   contains all received secure session handshake chunks of the current   endpoint.  Both endpoints compute the hash value individually and   exchange it using the SSOpCom chunk.  The receiver computes the hash   value using the same algorithm as the sender, and compares it with   the verification data.  If the receiver's computed value is the same   as the sender's verification data, then the receiver assures that the   secure session open is successfully completed.  If it is not the   same, then the receiver sends an ERROR message to the sender, and   immediately closes the secure session.5.1.7.  Secure Session Close chunk (SSClose)   This chunk indicates a request to close the current secure session.   The sender MUST NOT send any encrypted or authenticated chunks after   it has sent this chunk.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD6   | Reserved=0  |OF|           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |                               TSN                              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Outstanding flag (OF): 1 bit   This flag indicates that the endpoint has sent the SSClose chunk and   has no outstanding secured data.Hohendorf, et al.        Expires 1 October 2024                [Page 17]Internet-Draft                 Secure SCTP                    March 2024   Length: 16 bits unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header and TSN.   Transmission sequence number (TSN): 16 bits unsigned integer   This is the transmission sequence number of the data chunk that was   last encrypted and sent.  The TSN helps the server to detect   outstanding EncData chunks.5.1.8.  Secure Session Close Acknowledge chunk (SSClose_Ack)   This chunk is used to acknowledge the receipt of the secure session   close chunk.  When the endpoint receives the secure session close   chunk, it immediately stops sending encrypted or authenticated   chunks.  The Secure Session Close Acknowledge chunk only consists of   the chunk header.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD7   |   Reserved=0  |          Length=4             |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+5.1.9.  Security Level Changed chunk (SecLevCHD)   This chunk is used to convey the other associated endpoint of the   endpoint's new security level.  The endpoint sends SecLevCHD chunk   every time it selects a new security level.  The endpoint uses the   new selected security level when it receives the Security Level   Changed Acknowledged chunk.  The sender MUST NOT send a new SecLevCHD   chunk when an unacknowledged SecLevCHD chunk exists.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD8   | Reserved=0  |SL|          Length=4             |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Security level (SL): 2 bits   This 2-bit value indicates the sender's new security level.Hohendorf, et al.        Expires 1 October 2024                [Page 18]Internet-Draft                 Secure SCTP                    March 20245.1.10.  Security Level Changed Acknowledged chunk (SecLevCHD_Ack)   This chunk is used to acknowledge the receipt of the SecLevCHD chunk.   When the endpoint receives the SecLevCHD chunk, it immediately sends   the SecLevCHD_Ack chunk.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0xD9   |   Reserved=0  |          Length=4             |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+5.1.11.  Encrypted Data Chunk (EncData)   Each S-SCTP packet includes at most one encrypted data chunk, and the   packet could also include several (normal, unencrypted) data chunks.   The encrypted data chunk may contain one or several data chunks.  The   EncData chunk includes a padding chunk when it is needed.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0x10   | Reserved=0    |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    | Master secret key reference # |     Random number length      |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                         Random number                         /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                         Encrypted data                        /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bits unsigned integer   The length field contains the size of the chunk in bytes,including   the chunk header and encrypted data.   Master secret key reference number: 16 bits unsigned integerHohendorf, et al.        Expires 1 October 2024                [Page 19]Internet-Draft                 Secure SCTP                    March 2024   The association can be updated by changing the master secret key   several times during the association lifetime.  The association keeps   old secret keys.  The number of the kept old secret keys depends on   the implementation.  This field helps to identify which key (old or   new) has been used for encryption.  That means the endpoint is able   to receive messages, which were encrypted with an old key, after the   update of a master secret key.   Random number length: 16 bits unsigned integer   This field contains the size of the random number which is defined   below.   Random number: Variable length   This field indicates the random number which is used as   initialisation vector of the cipher block chaining (CBC) mode for   encryption.   Encrypted data: Variable length   Contains a byte vector that consists of the encrypted data chunks.   Before encryption, the chunk(s) MUST fulfil the following conditions.   If encryption is performed using the DES or 3DES algorithm, the total   size of the chunk(s) MUST be a multiple of 8 bytes.  If encryption is   performed using the AES algorithm, the total size of the chunk(s)   MUST be a multiple of 16 bytes.  If the total size of the chunk(s) is   not a multiple of 8 bytes or 16 bytes, the sender MUST add   appropriate padding at the chunk's end.5.1.12.  Padding chunk (PADDING)   This padding chunk is used with an EncData chunk.  The symmetric   encryption algorithms use a block oriented encryption of the user   data.  For example DES uses 64 bit blocks, and AES uses 128 bit   blocks.  Before encryption, the user data which has to be encrypted   has to be formatted according to the required block size.  If the   last block is not completely full, padding has to be added.  If less   than 4 bytes padding are required, the block is filled up will all   zeros.  The receiver can calculate the number of padding bytes based   on the length field of the original data chunks.  If 4 bytes or more   are required, a padding chunk of appropriate length is added.   The algorithms split user data into blocks when the data length is   greater than the block size.  The blocks MUST be full.  If 104 bits   are to be encrypted using DES algorithm with 64 bit block size, user   data is split into two blocks of 64 and 40 bits.  The second block   must be padded with 24 bits up to the full block size of 64 bits.Hohendorf, et al.        Expires 1 October 2024                [Page 20]Internet-Draft                 Secure SCTP                    March 2024    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0x12   | Reserved=0    |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |                            Padding                            |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: Variable length   This field indicates the padding size.  The padding follows the   padding chunk.  The length includes the padding chunk and padding.   Padding: Variable length   The padding is a random number.  The random number generation is   implementation specific.5.1.13.  Authentication chunk (AUTH)   This chunk is dedicated to the authentication of an S-SCTP packet.   S-SCTP inserts this chunk into the packet when the security level   requires authentication.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |   Type=0x11   | Reserved=0    |           Length              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    | Master secret key reference # |          Reserved=0           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    \                                                               \    /                              HMAC                             /    \                                                               \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Length: 16 bits unsigned integer   The length field contains the size of the chunk in bytes, including   the chunk header, master secret key reference, reserved field and   MAC.   Master secret key reference number: 16 bits unsigned integer   The association can update the secret keys several times during the   association lifetime.  The association keeps old secret keys.  The   number of the kept old secret keys depends on the implementation.   This field identifies the key which is used for authentication.  IfHohendorf, et al.        Expires 1 October 2024                [Page 21]Internet-Draft                 Secure SCTP                    March 2024   the endpoint receives a message which was authenticated by an old   key, this message can still be authenticated after an update of the   master secret key.   HMAC: Variable length   This field contains the authentication code for the SCTP packet.  The   message authentication uses the HMAC algorithm defined in RFC 2104.   The hash function used in the HMAC algorithm is derived from the   negotiated cipher suite, which was chosen by the server.6.  New Error Cause   This part explains the new error causes defined for S-SCTP.  When a   secure session or certificate failure is detected in the secure   session open process, the S-SCTP association immediately stops the   process.  However, the association continues (without any security   functionality).  When the secure session failure happens during an   update of the master secret key the association stops the update   operation and closes the secure session.  The following table shows   four general failure groups.    Cause Code Value  Cause Code    ----------------  ---------------------------------------          0x20        Secure Session failure          0x21        Secure Session Certificate failure          0x22        Secure Session Decryption failure          0x23        Secure Session Authentication failure          0x24        Secure Session Decompression failure6.1.  Secure Session failure    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Cause Code=0x20         |     Cause length = 8          |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |          Error Code           |          Reserved=0           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   If any error happens in the secure session open and update process,   endpoints alert their peers with these error codes.  The next table   shows error codes for what can happen.Hohendorf, et al.        Expires 1 October 2024                [Page 22]Internet-Draft                 Secure SCTP                    March 2024    Error Code Value  Error Code    ----------------  -------------------------------------         0            Timer expired         1            Signature failure         2            Secure Session Open Complete failure   *  Timer expired: The sender starts a timer when it sends the secure      session message.  When the sender receives no response from the      receiver before the timer expires, it sends this error code.   *  Signature failure: Some secure session chunks include a signature,      which identifies and protects the secure session message.  If the      receiver checks the signature and cannot identify the chunk, this      error code is used in the error chunk.   *  Secure Session Open Complete failure: This chunk is a very      important part of the secure session.  Both server and client      individually compute the master secret and HMAC secret keys.  Both      sides check these secret keys and parameters (i.e. secure session      chunks exchanged before, source and destination ports).  If these      keys are not identical, an error chunk is sent containing this      error code.6.2.  Secure Session Certificate failure    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Cause Code=0x21         |     Cause length = 8          |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |          Error Code           |          Reserved=0           |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   The certificate failure signals that an error has occurred in   processing the certificates.  The next table shows error codes for   what can happen.    Error Code Value  Error Code    ----------------  -------------------------------------           0          No certificate           1          Bad certificate           2          Certificate expired           3          Unknown certificate   *  No certificate: This error happens when the sender sets the CF      flag and the receiver does not receive the certificate.Hohendorf, et al.        Expires 1 October 2024                [Page 23]Internet-Draft                 Secure SCTP                    March 2024   *  Bad certificate: The signature of the certificate is bad and the      certificate could not be verified.   *  Certificate expired: The certificate is no longer valid.   *  Unknown certificate: The received certificate a X.509v3      certificate.6.3.  Decryption failure   This error happens when the EncData chunk cannot be decrypted or the   data chunk(s) cannot be identified after decryption.  The receiver   discards the EncData and increases a counter by 1.  This counter   counts errors.  If the number of errors reaches a limit, the secure   session is terminated.  The limit of the errors depends on the   implementation.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Cause Code=0x22         |     Cause length = 4          |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+6.4.  Authentication failure   In the event of a HMAC error, the packet is discarded by the   receiver.  To check for an error, the receiver computes the HMAC and   compares it to the HMAC field of the packet.  If they do not match,   an error is reported back.    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Cause Code=0x23         |     Cause length = 4          |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+6.5.  Decompression failure   This error happens when the compressed chunk(s) cannot be   decompressed or the data chunk(s) cannot be identified after   decompression.  The receiver discards the decompressed chunk(s).    0                   1                    2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4  5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |       Cause Code=0x24         |     Cause length = 4          |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Hohendorf, et al.        Expires 1 October 2024                [Page 24]Internet-Draft                 Secure SCTP                    March 20247.  S-SCTP packet format and security levels   S-SCTP has four different security levels, which cover privacy   settings of an S-SCTP association.  The S-SCTP application can change   the security levels at any time during the security session lifetime.   *  Security level 0: This is the null security level.  S-SCTP does      use neither data chunk encryption nor authentication.  The S-SCTP      packet is the same as the SCTP packet (this level is fully      compatible to SCTP).   *  Security level 1: This security level requires packet      authentication but does not use encryption.  Every outgoing packet      (including the SCTP common header) is authenticated.   *  Security level 2: In this security level, data chunks may be      encrypted.  When an S-SCTP packet contains an encrypted data      chunk, it MUST include an AUTH chunk as well.  That means every      chunk and the packet header are authenticated.  When a packet      includes only unencrypted data chunks or control chunks or both      unencrypted data chunks and control chunks, the packet will not be      authenticated.   *  Security level 3: This is the highest security level.  S-SCTP      requires both encryption and authentication.  Every outgoing chunk      is encrypted and the packet is authenticated.   Both endpoints can use different security levels, e.g. the   association can use security functions only for one direction, e.g.   from server to client.  In this case the server uses security level 3   and the client uses security level 0.  The transmission control block   (TCB) of the association includes the security level as a new   parameter.8.  S-SCTP data format   S-SCTP sorts data chunks before bundling them into the outgoing SCTP   packet.  The data chunks are sorted according to whether they have to   be encrypted or not.  The chunks belonging to the encryption group   are concatenated and encrypted into an EncData chunk.  May be a   PADDING chunk is inserted into the encryption group.  Insertion of a   PADDING chunk is done depending on data length and encryption block   size.   An assortment of encrypted and non-encrypted chunks are bundled in   the packet.  The control chunk(s) are placed first in the packet when   bundled with other chunks.  Finally, an AUTH chunk may be added to   the packet.Hohendorf, et al.        Expires 1 October 2024                [Page 25]Internet-Draft                 Secure SCTP                    March 2024   HMAC computation is performed over all chunks and the SCTP common   header with a 0 checksum.  The checksum is then computed over the   complete packet (including AUTH chunk).  The HMAC length depends on   the hash function in the cipher suite.  In every security level, the   SCTP packet construction is slightly different.  In security level 0   the packet format is same as the SCTP packet format.9.  Procedures   In this section an explanation of the procedures of secure session:   initialisation, termination, update and etc., is given.9.1.  Establishment of a secure session   The following process is used to establish the S-SCTP secure session.   The handshake process runs in parallel with the data transmission.   The secure session start and close is controlled by the user.  The   user can establish and close a secure session at any time during the   association lifetime.  Each time a secure session is established, a   new set of keys is generated.  It is not possible to create a new   secure session when a secure session already exists.  The following   describes secure session establishment, which makes use of a   handshake timer and retransmissions in case packets are lost during   transmission.  S-SCTP uses a four-way handshake.  After all messages   of one of the connection "legs" have been sent, client or server   starts a RTO.hand (handshake retransmission time out) timer.  For   example, the secure session certificate is the last handshake message   of the first leg.  The sender waits for a response from the receiver   until the RTO.hand timer expires.  The sender stops the RTO.hand   timer when it receives the expected message(s).  If the RTO.hand   timer expires before all expected messages have been received, the   sender retransmits the handshake message(s).   The retransmission uses the following algorithm.  The RTO.hand timer   gets a value from RTO of the path where the message is sent to, which   is defined in RFC4960.  Before a retransmission, the sender checks   RTN.hand.max (handshake maximum retransmission number).  This initial   value is dependent upon specific implementations.  The suggested   value for RTN.hand.max is Path.Max.Retrans (see RFC 4960).   RTN.hand.max should be a constant parameter.  We introduce a counter   for the number of retransmissions, and if that counter exceeds the   parameter RTN.hand.max, the timer expired error message is sent to   the peer.  If a retransmission is required then S-SCTP uses the same   retransmission rules as defined in RFC4960.  If the receiver receives   a retransmission of a handshake message that was already received,   the message last received MUST be dropped.  The endpoint discards the   message(s) when they are unexpected.  A secure session initialisationHohendorf, et al.        Expires 1 October 2024                [Page 26]Internet-Draft                 Secure SCTP                    March 2024   begins when one of the associated endpoints sets the security level   to a value higher than 0.  The endpoint starting a secure session   initialisation is called client and the other associated endpoint is   called server.   *  The client sends the SSOpReq chunk to the server.  If the client      has a certificate, it sets the CF flag of the SSOPReq chunk to 1.      The client sends the SSCert chunk immediately after the SSOpReq      chunk.  The SSCert chunk can be bundled with the SSOpReq chunk or      with other chunk(s).  When the CF flag is set to 0, the client      sends only the SSOpReq chunk.   *  The server receives a SSOpReq chunk and checks the CF flag.  If      the CF flag is set to 1, the server waits for the SSCert chunk.      Upon receipt, the server checks the certificate and if there is a      problem with it, the server stops the handshake and goes to an      error state, aborts secure session setup and reports the cause to      its peer.  It there is no error, the server chooses the cipher      suite and sends the SSOpReq_Ack chunk with CF=1 flag to the client      when the server has a certificate.  The server immediately sends      the certificate and the SSSerKey chunks after the SSOpReq_Ack      chunk.  All three chunks may be bundled together or with other      chunks.  The server sends only the SSOpReq_Ack chunk with the      SSSerKey chunk if CF=0.  Before sending the server key exchange      chunk, the server generates key material.  The server starts the      update master secret key operation when it receives the SSOpReq      chunk after secure session establishment.  If the server receives      the SSCert chunk before the SSOpReq chunk, it stores the SSCert      chunk and waits until it receives the SSOpReq chunk.  But the      server drops a second SSCert chunk.   *  The client receives the handshake messages and checks the      certificate in the SSSerKey chunk.  If the client detects any      errors, it stops the handshake and goes to an error state, aborts      secure session setup and reports the cause to its peer.  The      client generates key material and sends the SSCliKey chunk to the      server.  The client sends the SSOpCom chunk immediately after the      client key exchange chunk.  Before sending the handshake-finished      chunk, the client computes the encryption secret and MAC secret      keys.   *  The server receives the SSCliKey chunk and computes the master      secret and the MAC secret keys.  It then computes the SSOpCom      chunk and sends it to the client.  Finally, the server checks the      SSOpCom chunk of the client.  If the server detects any error, it      reports a secure session open complete error and closes the      handshake.  The secure session is established only when both sides      detect no errors.  The server is ready for secure transmissionHohendorf, et al.        Expires 1 October 2024                [Page 27]Internet-Draft                 Secure SCTP                    March 2024      when it detects no errors, but the client must wait for the      SSOpCom chunk of the server.  When this is received, the client      checks it and reports to the peer a secure session open complete      error if any error is detected before aborting secure session      setup.  The handshake may run simultaneously with normal SCTP data      transmission.  If the client receives encrypted or authenticated      data chunks before it receives the server's SSOpCom chunk, then      those chunks MUST be discarded.   When both associated endpoints request the initialisation of a secure   session simultaneously (both endpoints send an SSOpReq message), both   ignore the received SSOpReq message and wait a random time before   resending the SSOpReq message.  Each endpoint generates the random   time independently.  The random number must be small, e.g. 120   seconds maximum.9.2.  Choice of cipher suite and compression method   This section explains how to choose the cipher suite and compression   method which are used for the secure session.  Each endpoint   maintains an ordered list of supported cipher suites (cipher suite   list).  The ordering in the list indicates the preference with which   a cipher suite should be used (first in the list have higher   preference).  The order in the list is defined by the retrospective   S-SCTP user.   S-SCTP users on both sides can allow all cipher suited in the list   when establishing a secure session or limit the allowed cipher suites   to a subset.  The complete list or the selected subset can be   indicated to the server in the SSOpReq.  If the complete list is   sent, the default cipher suite list must be located first in the   list.  The server uses the following rules to choose the cipher suite   to be used for the secure session:   The server chooses the default cipher suite, if the SSOpReq chunk   does not contain any cipher suite.   The server gets the first cipher suites from SSOpReq chunk and   server's cipher suite sequence.  When both cipher suites are   identical the server chooses this cipher suite for the secure   session.  Otherwise, the server takes its first cipher suite and   looks for a match in the cipher suite sequence of the client.  When   there is no matche, the server takes the client's first cipher suite   and searches for match in its cipher suite sequence.  S-SCTP checks   the first cipher suite in the SSOpReq chunk against all cipher suites   in the cipher suite list of the server.  If no match is found, all   subsequent cipher suites in the SSOpReq are checked sequentially in   the order they appear in the SSOPReq until a match is found.  TheHohendorf, et al.        Expires 1 October 2024                [Page 28]Internet-Draft                 Secure SCTP                    March 2024   first cipher suite supported by both endpoints is chosen.  When two   cipher suites match each other then this cipher suite is selected for   the secure session.  If not, the server looks, its second cipher   suite, for a match in the cipher suite sequence of the client.   Furthermore, the server uses the same mechanism to look a cipher   suite for the secure session.   The server chooses the default cipher suite, when the cipher suites   in the SSOpReq chunk are not supported by the server.   Both client and server also maintain a list of compression methods.   The choice of the compression mechanism works similarly to the cipher   suite selection mechanism described above.  S-SCTP uses a NULL   compression method as default compression method.9.3.  Data transfer   Before transporting the packet over the network, S-SCTP takes the   following steps.  First, it checks the security level.  If the   security level is:   *  0, jump to step "d"   *  1, jump to step "c"   *  2, check the user data.  If the user data requires encryption,      jump to step "a" . If the user data does not require encryption,      jump to step "c"   *  3, jump to step "a"      a) S-SCTP sorts data chunks in two groups, which are encrypted and      unencrypted.  The encrypted group consists of those data chunks      requiring encryption.  The unencrypted group consists of those      data chunks not requiring encryption.  If the secure session's      security level is set to 3, all chunks are sorted into the      encrypted group.      b) The data chunks in the encrypted group are concatenated.  After      this, S-SCTP calculates the padding chunk and inserts the padding      chunk on the last position into pre-enc-data if necessary.  The      Pre-enc-data size MUST be smaller than the current MTU.  If the      pre-enc-data is bigger than the current MTU, S-SCTP must create      two pre-enc-datas.  Every pre-enc-data is encrypted and stored in      the encryption data field of the EncData chunk.      c) SCTP builds the packet according to the security level and      inserts the AUTH chunk in the last position in the packet.Hohendorf, et al.        Expires 1 October 2024                [Page 29]Internet-Draft                 Secure SCTP                    March 2024      d) S-SCTP sends the packet.9.4.  Closing of a secure session   The termination of a secure session begins when one of the endpoints   sends the secure session close chunk.  This chunk includes the last   encrypted data TSN and OF.  The endpoint (sender) stops the   encryption or authentication of all chunks or packets after it has   sent the secure session close chunk.  But normal (unsecured) data   transfer will continue.  The endpoint then waits until it receives   the SSClose_Ack chunk.  After receiving the SSClose_Ack chunk, the   association clears the TCB parameters belonging to the secure   session.  The receiver (other endpoint) immediately stops encryption   and authentication of all chunks or packets after it receives the   secure session close chunk.  Before sending the SSClose_Ack, the   receiver waits for outstanding data (encrypted or authenticated   data), which are the receiver's unacknowledged data chunks and   sender's data chunks that have a TSN less than the last encrypted   data TSN in the SSClose chunk.  If the receiver does not receive the   outstanding data chunks before RTO.hand timer expires, the S-SCTP   association closes the secure session and outstanding data chunks   will be dropped.  The receiver ignores the last TSN of SSClose chunk   and waits only for the receiver's unacknowledged data chunks when   SSClose chunk's OF=1.  The SSClose and SSClose_Ack chunks may be   bundled with other chunks.  If the sender does not receive the   acknowledge chunk, the client follows the standard retransmission   rule for messages.  After the termination of the secure session, the   TCB parameters belonging to the secure session MUST be set to zero.   If the SCTP association begins to close the current association, the   SSClose chunk is sent.  If the SCTP association creates an ABORT   chunk, the secure session closes immediately and the TCB parameters   belonging to the secure session MUST be set to zero.9.5.  Generation of the Master secret key   Secret key generation uses the 3DES_CBC algorithm.  Both server and   client compute the master secret key separately.  The key material is   split into 64 bit blocks.  Every block will be input to the 3DES_CBC   encryption.  The key material is as follows:   *  If the secure session key exchange algorithm uses DH, the key      material consists of the DH's secret key.   *  If the secure session key exchange algorithm uses RSA, the key      material consists of random numbers of both client and server.Hohendorf, et al.        Expires 1 October 2024                [Page 30]Internet-Draft                 Secure SCTP                    March 20249.6.  Update of the master secret key   A secure update mechanism of the secret keys is a very important   requirement for a secure session.  The secret keys consist of the   master secret key, which is used for data chunk encryption, and the   HMAC secret key, which is used for packet authentication.  If an   association exists for a long time, the S-SCTP association needs to   update the secret keys.  Both the client and the server can request   an update of the secret keys.  A three way handshake, called an   abbreviated handshake, is used to update the master secret keys.  All   actions of the handshake are encrypted by the current master secret   key.  The current security level does not affect the packets, which   contain the handshake messages.  The key update handshake works   similar to the first establishment handshake (e.g. the endpoints   start an RTO.hand timer when sending handshake chunks).  Format and   function of the chunks used to update keys are the same as for the   handshake.  When an endpoint receives a SSOpReq chunk (after a secure   session establishment) it begins to update secret keys.  Both the   server and client key exchange chunks always use the RSA key exchange   algorithm.  The random numbers in SSSerKey and SSCliKey chunks are   encrypted by the current master secret key.  The following describes   the method used to update the master secret key:   The client generates a random number and sends the SSopReq chunk with   the SSCliKey chunk.  The key material length in the handshake request   chunk may be equal to 0.  If not, the number indicates the size of   the new key material.  If 0, both sides will use the key material   length which was used in the last handshake.  The server sends the   SSop_Ack, the SSSerKey and the SSOpCom chunks immediately after   receiving the SSOpReq and the SSCliKey chunks.  After receiving the   handshake messages from the server, the client computes a new master   secret key and checks the SSOpCom chunk of the server.  If it detects   any error, the client closes the secure session and reports an error   to the peer.  The client computes the SSOpCom chunk and sends it to   the server.  After sending the SSOpCom chunk the client is ready to   use the new master secret key.  The server receives the SSOpCom chunk   of the client and checks the new keys.  If it detects any error, the   server closes the secure session and reports an error to the peer.   Before receiving the client's SSOpCom chunk, the server discards any   encrypted or authenticated chunk that make use of the new master   secret key.Hohendorf, et al.        Expires 1 October 2024                [Page 31]Internet-Draft                 Secure SCTP                    March 2024   The encrypted and unencrypted user data transmission works in   parallel with the update operation.  After the update operation, the   new master secret key is used for data encryption and authentication.   When both client and server receive an SSOpReq chunk simultaneously,   the client ignores the server's SSopReq chunk and the server accepts   the client's SSOpReq chunk.  The next steps are the same as for the   secure session initialisation.   The new master secret key generation uses the same algorithm as   described above.  The secure session includes one parameter which is   called secure session lifetime.  This parameter is used to initialise   a timer which indicates the secure session secret key's lifetime in   seconds.  When the timer expires, the association automatically   updates the secret keys.  The user can define this parameter.  If the   user does not define it, the parameter assumes a default value.  This   default value depends on the implementation.  The implementation MUST   define secure session's lifetime initial value.  We suggest a value   of 600 seconds for the lifetime as a compromise between security and   overhead.9.7.  Random number generation   As the security of S-SCTP depends on the quality of the random number   generator, we suggest to use one according to RFC4086 [5].9.8.  HMAC algorithm   S-SCTP uses the HMAC algorithm which is defined in RFC2104 [1] for   the packet authentication.10.  HMAC algorithm   ULP-to-SCTP primitives deliver upper layer requests to S-SCTP.  The   following part describes new ULP-to-SCTP primitives and thus enhances   the section 10 of RFC4960.  All new ULP-to-SCTP primitives described   below are defined in the ssctp.h header file.   INITSECSESS: This primitive initialises a new secure session.   Format: {initSecSess(secure session ID, key material length, cipher   suites list, compression methods list, certiticate(s) ) --> result}   *  secure session ID: This parameter identifies a secure session.   *  key material length: This defines the key material length which is      used in the SSOPReq chunk.Hohendorf, et al.        Expires 1 October 2024                [Page 32]Internet-Draft                 Secure SCTP                    March 2024   *  cipher suite list: Eligible cipher suites for a new secure      session.   *  compression method list: Eligible compression methods for a new      secure session.   *  certificate(s): Local endpoint certificate(s).   SETSECLEVEL: This primitive sets a new security level for an existing   secure session.   Format: {setSecLevel(secure session ID, security level) --> result}   *  secure session ID: local handle to the secure session   *  security level: This parameter indicates the new security level   GETSECLEVEL: This primitive gets the current security level of a   secure session.   Format: {getSecLevel(secure session ID) --> security level}   *  secure session ID: local handle to the secure session   SENDSEC: This primitive sends secure data via S-SCTP.   Format: {sctp_send_enc(association id, buffer address, byte count,   context, stream id, life time, destination transport address, unorder   flag, no-bundle flag, payload protocol-id, encryption flag,   compression flag) --> result}   Every parameter, except the encryption and compression flags, defined   in this function is the same as the corresponding parameter defined   in the SEND function of RFC4960 section 10.   *  encryption flag: This flag defines if a current user data message      needs encryption or not.   *  compression flag: This flag defines if a current user data message      needs compression or not.   GETSECSTATUS: This primitive gets the security status of an   association.  The security status indicates if the SCTP association   is using a secure session or not.   Format: {setSecStatus(association ID) --> status}   *  association ID: local handle to the SCTP association.Hohendorf, et al.        Expires 1 October 2024                [Page 33]Internet-Draft                 Secure SCTP                    March 2024   SETSECSESSTTL: This primitive sets a new lifetime for a secure   session.   Format: {setSecSessTTL(secure session ID, Time) --> result}   *  secure session ID: local handle to the secure session.   *  time: The new lifetime in seconds.   SHUTSECSESS: This primitive deletes a secure session.   Format: {shutSecSess(secure session ID) --> result}   *  secure session ID: local handle to the secure session.   *  security level: This parameter indicates the new security level.11.  S-SCTP to ULP   S-SCTP defines new notifications to deliver information to the upper   layer.  The notifications extend the section 10.2 of RFC4960 [6].   All new notifications are defined in the ssctp.h header file.   SECSESSUP:   This notification indicates that S-SCTP is ready to send or receive   secure data ({secsessUpNotif()}).   SECSESSDOWN:   This notification indicates that an association has lost a secure   session ({secsessdownNotif()}).   SECSESSREKEY:   This notification indicates that a secure session updated the secret   keys ({secsessrekeyNotif()}).   Additional changes had to be made in the socket API implementation to   access the new sctplib functions described above.  A user calls the   same socket API functions as in standard SCTP to send and receive   user data, but has to set an additional encryption flag (MSG_ENC) to   request encryption of user data.  Also, a compression flag (MSG_COMP)   has to be set in ext_send, ext_sendto, ext_sendmsg to request   compression of user data.  S-SCTP compression performs per user   message not per chunk or per packet.  In the SCTP DATA chunk, a new   flag is defined, which indicates if the data is compressed or not.   On the receiver side there are no changes.Hohendorf, et al.        Expires 1 October 2024                [Page 34]Internet-Draft                 Secure SCTP                    March 202412.  Transmission Control Block (TCB) extension   A SCTP TCB contains parameters which are related to an association   (e.g. an association id, port number, IP address list...).  S-SCTP   defines several parameters which are related to a secure session and   it extends the TCB defined in section 12 of RFC4960.   Security level:   This parameter contains the association's current security level.   Second security level:   This is the security level of the associated second endpoint.   Key material length:   The size of the key material, which was last used for key generation.   Secure session status:   This parameter indicates whether the association is using a secure   session or not.   Secure session lifetime:   This parameter indicates the lifetime of the secret keys of a secure   session.   Server indication:   This parameter indicates if an endpoint is server or client.  If the   parameter is equal to 1 then it is a server, otherwise it is a   client.   Secure session ID:   This parameter indicates the local secure session ID.   Master secret key reference:   This is an "array of secret data" collection and every array element   includes the following parameters.   *  Selected cipher suite: This parameter indicates the encryption and      authentication algorithms that are used in a secure session.Hohendorf, et al.        Expires 1 October 2024                [Page 35]Internet-Draft                 Secure SCTP                    March 2024   *  Selected compression: This parameter indicates the compression      method that is used in a secure session.   *  Encryption key: This is a secret key which is used for encryption.   *  Authentication key: This is a secret key which is used for      authentication.   This information is used in EncData and AUTH chunks.13.  Socket API extensions for Secure SCTP   S-SCTP defines new socket options for the ext_setsockopt() and   ext_getsockopt() socket functions to initialise, delete and rekey a   secure session.  A user calls the ext_setsockopt or ext_getsockopt   functions with a new option.  It is not necessary to define new   socket API functions, as this is a more standard socket API fashion.   The following paragraphs describe the new socket options.   SSCTP-INIT:   This socket option is used to initialise or update a secure session.   The following structure is used to access these parameters.   struct ssctp_init {          uint16_t  secsessID;          uint16_t  key_length;          uint8_t   num_cipher;          uint8_t   *cipher_suites;          uint8_t   num_comp;          uint8_t   *comp_methods;          uint8_t   *certificate;   };   *  secsessID: This parameter indicates a current secure session ID.   *  key_length: This parameter defines the length of a key material.   *  num_cipher: This parameter defines the number of cipher suites.   *  cipher_suites: This parameter includes a list of cipher suites.   *  num_comp: This parameter defines the number of compression      methods.   *  comp_methods: This parameter includes a list of compression      methods.Hohendorf, et al.        Expires 1 October 2024                [Page 36]Internet-Draft                 Secure SCTP                    March 2024   *  certificate: This parameter includes a certificate of the      endpoint.   SSCTP-SECLEVEL:   This socket option is used to set and get a secure session security   level.  The following structure is used to access and modify these   parameters.   struct ssctp_seclevel {          uint16_t  secsessID;          uint8_t  seclevel;   };   *  secsessID: This parameter indicates a current secure session ID.      This parameter MUST be zero when beginning a secure session      initialisation.   *  seclevel: This parameter contains a new security level before      socket write access or contains the current security level after      socket read access.   SSCTP-SECSTATUS:   This socket option is used to get the secure session status and   secure session ID when a secure session exists.  The following   structure is used to access these parameters.   struct ssctp_secstatus {          uint16_t secsessID;          uint8_t sec_status;   };   *  secsessID: This parameter contains the current secure session ID.      This parameter MUST be zero when a secure session does not exist.   *  sec_status: This parameter contains a security status.  This      parameter MUST be zero when a secure session does not exist.  This      parameter is equal to 1 when a secure session exists.   SSCTP-SECSESSTTL:   This socket option is used to set and get the secure session   lifetime.  The following structure is used to access and modify these   parameters.Hohendorf, et al.        Expires 1 October 2024                [Page 37]Internet-Draft                 Secure SCTP                    March 2024   struct ssctp_secsessTTL {          uint16_t secsessID;          uint16_t secsessTTL;   };   *  secsessID: This parameter indicates the current secure session ID.   *  secsessTTL (seconds): This parameter contains a new secure session      lifetime before socket write access or contains a current secure      session lifetime after socket read access.   SSCTP-CLOSE:   This socket option is used to close an existing secure session.  The   following structure is used to access these parameters.   struct ssctp_secclose {          uint16_t  secsessID;   };   *  secsessID: This parameter contains the current secure session ID.14.  Testbed Platform   A large-scale and realistic Internet testbed platform with support   for the multi-homing feature of the underlying SCTP protocol is   NorNet.  A description of NorNet is provided in [9], some further   information can be found on the project website [10].15.  Security Considerations   Security has been described in the previous sections.16.  IANA Considerations   This document introduces no additional considerations for IANA.17.  References17.1.  Normative References   [1]        Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-              Hashing for Message Authentication", RFC 2104,              DOI 10.17487/RFC2104, February 1997,              <https://www.rfc-editor.org/info/rfc2104>.Hohendorf, et al.        Expires 1 October 2024                [Page 38]Internet-Draft                 Secure SCTP                    March 2024   [2]        Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [3]        Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport              Layer Security over Stream Control Transmission Protocol",              RFC 3436, DOI 10.17487/RFC3436, December 2002,              <https://www.rfc-editor.org/info/rfc3436>.   [4]        Bellovin, S., Ioannidis, J., Keromytis, A., and R.              Stewart, "On the Use of Stream Control Transmission              Protocol (SCTP) with IPsec", RFC 3554,              DOI 10.17487/RFC3554, July 2003,              <https://www.rfc-editor.org/info/rfc3554>.   [5]        Eastlake 3rd, D., Schiller, J., and S. Crocker,              "Randomness Requirements for Security", BCP 106, RFC 4086,              DOI 10.17487/RFC4086, June 2005,              <https://www.rfc-editor.org/info/rfc4086>.   [6]        Stewart, R., Ed., "Stream Control Transmission Protocol",              RFC 4960, DOI 10.17487/RFC4960, September 2007,              <https://www.rfc-editor.org/info/rfc4960>.   [7]        Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,              Housley, R., and W. Polk, "Internet X.509 Public Key              Infrastructure Certificate and Certificate Revocation List              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,              <https://www.rfc-editor.org/info/rfc5280>.   [8]        Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/info/rfc8174>.17.2.  Informative References   [9]        Dreibholz, T. and E. G. Gran, "Design and Implementation              of the NorNet Core Research Testbed for Multi-Homed              Systems", Proceedings of the 3nd International Workshop on              Protocols and Applications with Multi-Homing              Support (PAMS) Pages 1094-1100, ISBN 978-0-7695-4952-1,              DOI 10.1109/WAINA.2013.71, 27 March 2013,              <https://www.simula.no/file/              threfereedinproceedingsreference2012-12-207643198512pdf/              download>.Hohendorf, et al.        Expires 1 October 2024                [Page 39]Internet-Draft                 Secure SCTP                    March 2024   [10]       Dreibholz, T., "NorNet – A Real-World, Large-Scale Multi-              Homing Testbed", 2022, <https://www.nntb.no/>.Authors' Addresses   Carsten Hohendorf   University of Duisburg-Essen, Institute for Experimental Mathematics   Ellernstraße 29   45326 Essen   Germany   Email: hohend@iem.uni-due.de   Esbold Unurkhaan   Mongolian University of Science and Technology   Bayanzurkh duureg, 2-nd khoroo   313/49 Ulaanbaatar   Mongolia   Email: esbold@csms.edu.mn   Thomas Dreibholz   Simula Metropolitan Centre for Digital Engineering   Pilestredet 52   0167 Oslo   Norway   Email: dreibh@simula.no   URI:   https://www.simula.no/people/dreibhHohendorf, et al.        Expires 1 October 2024                [Page 40]