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Network Working Group                                            J. ParkRequest for Comments: 4683                                        J. LeeCategory: Standards Track                                         H. Lee                                                                    KISA                                                                 S. Park                                                                   BCQRE                                                                 T. Polk                                                                    NIST                                                            October 2006Internet X.509 Public Key InfrastructureSubject Identification Method (SIM)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   This document defines the Subject Identification Method (SIM) for   including a privacy-sensitive identifier in the subjectAltName   extension of a certificate.   The SIM is an optional feature that may be used by relying parties to   determine whether the subject of a particular certificate is also the   person corresponding to a particular sensitive identifier.Park, et al.                Standards Track                     [Page 1]

RFC 4683             Subject Identification Method          October 2006Table of Contents1. Introduction ....................................................21.1. Key Words ..................................................52. Symbols .........................................................63. Requirements ....................................................63.1. Security Requirements ......................................63.2. Usability Requirements .....................................73.3. Solution ...................................................74. Procedures ......................................................84.1. SII and SIItype ............................................84.2. User Chosen Password .......................................94.3. Random Number Generation ...................................94.4. Generation of SIM ..........................................94.5. Encryption of PEPSI .......................................104.6. Certification Request .....................................104.7. Certification .............................................115. Definition .....................................................115.1. SIM Syntax ................................................115.2. PEPSI .....................................................125.3. Encrypted PEPSI ...........................................126. Example Usage of SIM ...........................................137. Name Constraints ...............................................138. Security Considerations ........................................149. Acknowledgements ...............................................1510. IANA Considerations ...........................................1511. References ....................................................1511.1. Normative References .....................................1511.2. Informative References ...................................15Appendix A.  "Compilable" ASN.1 Module, 1988 Syntax ...............181.  Introduction   A Certification Authority (CA) issues X.509 public key certificates   to bind a public key to a subject.  The subject is specified through   one or more subject names in the "subject" or "subjectAltName" fields   of a certificate.  The "subject" field contains a hierarchically   structured distinguished name.  The "subjectAltName field" may   contain an electronic mail address, IP address, or other name forms   that correspond to the subject.   For each particular CA, a subject name corresponds to a unique   person, device, group, or role.  The CA will not knowingly issue   certificates to multiple entities under the same subject name.  That   is, for a particular certificate issuer, all currently valid   certificates asserting the same subject name(s) are bound to the same   entity.Park, et al.                Standards Track                     [Page 2]

RFC 4683             Subject Identification Method          October 2006   Where the subject is a person, the name that is specified in the   subject field of the certificate may reflect the name of the   individual and affiliated entities (e.g., their corporate   affiliation).  In reality, however, there are individuals or   corporations that have the same or similar names.  It may be   difficult for a relying party (e.g., a person or application) to   associate the certificate with a specific person or organization   based solely on the subject name.  This ambiguity presents a problem   for many applications.   In some cases, applications or relying parties need to ensure that   the subject of certificates issued by different CAs are in fact the   same entity.  This requirement may be met by including a "permanent   identifier" in all certificates issued to the same subject, which is   unique across multiple CAs.  By comparing the "permanent identifier",   the relying party may identify certificates from different CAs that   are bound to the same subject.  This solution is defined in [RFC   4043].   In many cases, a person's or corporation's identifier (e.g., a Social   Security Number) is regarded as sensitive, private, or personal data.   Such an identifier cannot simply be included as part of the subject   field, since its disclosure may lead to misuse.  Therefore, privacy-   sensitive identifiers of this sort should not be included in   certificates in plaintext form.   On the other hand, such an identifier is not actually a secret.   People choose to disclose these identifiers for certain classes of   transactions.  For example, a person may disclose a Social Security   Number to open a bank account or obtain a loan.  This is typically   corroborated by presenting physical credentials (e.g., a driver's   license) that confirm the person's name or address.   To support such applications in an online environment, relying   parties need to determine whether the subject of a particular   certificate is also the person corresponding to a particular   sensitive identifier.  Ideally, applications would leverage the   applicants' electronic credential (e.g., the X.509 public key   certificate) to corroborate this identifier, but the subject field of   a certificate often does not provide sufficient information.   To fulfill these demands, this specification defines the Subject   Identification Method (SIM) and the Privacy-Enhanced Protected   Subject Information (PEPSI) format for including a privacy sensitive   identifier in a certificate.  Although other solutions for binding   privacy-sensitive identifiers to a certificate could be developed,   the method specified in this document has especially attractive   properties.  This specification extends common PKI practices andPark, et al.                Standards Track                     [Page 3]

RFC 4683             Subject Identification Method          October 2006   mechanisms to allow privacy-sensitive identifiers to be included in   the certificate as well.  The SIM mechanism also permits the subject   to control exposure of the sensitive identifier; when the subject   chooses to expose the sensitive identifier, relying parties can   verify the binding.  Specifically:   (1) A Public Key Infrastructure (PKI) depends upon a trusted third   party -- the CA -- to bind one or more identities to a public key.   Traditional PKI implementations bind X.501 distinguished names to the   public key, but identity may also be specified in terms ofRFC 822   addresses or DNS names.  The SIM specification allows the same   trusted third party -- the CA -- that binds a name to the public key   to include a privacy-sensitive identifier in the certificate as well.   Since the relying party (RP) already trusts the CA to issue   certificates, it is a simple extension to cover verification and   binding of a sensitive identifier as well.  This binding could be   established separately, by another trusted third party, but this   would complicate the infrastructure.   (2) This specification leverages standard PKI extensions to achieve   new functional goals with a minimum of new code.  This specification   encodes the sensitive identifier in the otherName field in the   alternative subject name extension.  Since otherName field is widely   used, this solution leverages a certificate field that is often   populated and processed.  (For example, smart card logon   implementations generally rely upon names encoded in this field.)   Whereas implementations of this specification will require some SIM-   specific code, an alternative format would increase cost without   enhancing security.  In addition, that has no impact on   implementations that do not process sensitive identifiers.   (3) By explicitly binding the public key to the identifier, this   specification allows the relying party to confirm the claimant's   identifier and confirm that the claimant is the subject of that   identifier.  That is, proof of possession of the private key confirms   that the claimant is the same person whose identity was confirmed by   the PKI (CA or RA, depending upon the architecture).   To achieve the same goal in a separate message (e.g., a signed and   encrypted Secure MIME (S/MIME) object), the message would need to be   bound to the certificate or an identity in the certificate (e.g., the   X.501 distinguished name).  The former solution is problematic, since   certificates expire.  The latter solution may cause problems if names   are ever reused in the infrastructure.  An explicit binding in the   certificate is a simpler solution, and more reliable.Park, et al.                Standards Track                     [Page 4]

RFC 4683             Subject Identification Method          October 2006   (4) This specification allows the subject of the privacy-sensitive   identifier to control the distribution and level of security applied   to the identifier.  The identifier is only disclosed when the subject   chooses to disclose it, even if the certificate is posted in a public   directory.  By choosing a strong password, the subject can ensure   that the identifier is protected against brute force attacks.  This   specification permits subjects to selectively disclose an identifier   where they deem it appropriate, which is consistent with common use   of such identifiers.   (5) Certificates that contain a sensitive identifier may still be   used to support other applications.  A party that obtains a   certificate containing a sensitive identifier, but to whom the   subject does not choose to disclose the identifier, must perform a   brute force attack to obtain the identifier.  By selecting a strong   hash algorithm, this attack becomes computationally infeasible.   Moreover, when certificates include privacy-sensitive identifiers as   described in this specification, each certificate must be attacked   separately.  Finally, the subjects can use this mechanism to prove   they possess a certificate containing a particular type of identifier   without actually disclosing it to the relying party.   This feature MUST be used only in conjunction with protocols that   make use of digital signatures generated using the subject's private   key.   In addition, this document defines an Encrypted PEPSI (EPEPSI) so   that sensitive identifier information can be exchanged during   certificate issuance processes without disclosing the identifier to   an eavesdropper.   This document is organized as follows:   -Section 3 establishes security and usability requirements;   -Section 4 provides an overview of the mechanism;   -Section 5 defines syntax and generation rules; and   -Section 6 provides example use cases.1.1.  Key Words   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].Park, et al.                Standards Track                     [Page 5]

RFC 4683             Subject Identification Method          October 20062.  Symbols   The following cryptography symbols are defined in this document.       H()        Cryptographically secure hash algorithm.                  SHA-1 [FIPS 180-1] or a more secure hash function is                  required.       SII        Sensitive Identification Information                  (e.g., Social Security Number).       SIItype    Object Identifier that identifies the type of SII.       P          A user-chosen password.       R          The random number value generated by a Registration                  Authority (RA).       PEPSI      Privacy-Enhanced Protected Subject Information.                  Calculated from the input value P, R, SIItype, SII                  using two iteration of H().       E()        The encryption algorithm to encrypt the PEPSI value.       EPEPSI     Encrypted PEPSI.       D()        The decryption algorithm to decrypt the EPEPSI.3.  Requirements3.1.  Security Requirements   We make the following assumptions about the context in which SIM and   PEPSI are to be employed:     - Alice, a certificate holder, with a sensitive identifier SIIa       (such as her Social Security Number)     - Bob, a relying party who will require knowledge of Alice's SIIa     - Eve, an attacker who acquires Alice's certificate     - An RA to whom Alice must divulge her SIIa     - A CA who will issue Alice's certificate   We wish to design SIM and PEPSI, using a password that Alice chooses,   that has the following properties:     - Alice can prove her SII, SIIa to Bob.Park, et al.                Standards Track                     [Page 6]

RFC 4683             Subject Identification Method          October 2006     - Eve has a large work factor to determine Alice's SIIa from       Alice's certificate, even if Alice chooses a weak password, and a       very large work factor if Alice chooses a good password.     - Even if Eve can determine SIIa, she has an equally hard problem       to find any other SII values from any other PEPSI; that is, there       is nothing she can pre-compute that helps her attack PEPSIs in       other certificates, and nothing she learns from a successful       attack that helps in any other attack.     - The CA does not learn Alice's SIIa except in the case where the       CA needs to validate the SII passed by the RA.     - The CA can treat the SIM as an additional name form in the       "subjectAltName" extension with no special processing.     - Alice cannot find another SII (SIIx), and a password (P), that       will allow her to use her certificate to assert a false SII.3.2.  Usability Requirements   In addition to the security properties stated above, we have the   following usability requirements:     - When SIM and PEPSI are used, any custom processing occurs at the       relying party.  Alice can use commercial off-the-shelf software       (e.g., a standard browser) without modification in conjunction       with a certificate containing a SIM value.3.3.  Solution   We define SIM as: R || PEPSI             where PEPSI = H(H( P || R || SIItype || SII))   The following steps describe construction and use of SIM:   1.      Alice picks a password P, and gives P, SIItype, and SII to           the RA (via a secure channel).   2.      The RA validates SIItype and SII; i.e., it determines that           the SII value is correctly associated with the subject and           the SIItype is correct.   3.      The RA generates a random value R.   4.      The RA generates the SIM = (R || PEPSI) where PEPSI = H(H(P           || R || SIItype || SII)).   5.      The RA sends the SIM to Alice by some out-of-band means and           also passes it to the CA.   6.      Alice sends a certRequest to CA.  The CA generates Alice's           certificate including the SIM as a form of otherName from the           GeneralName structure in the subjectAltName extension.   7.      Alice sends Bob her Cert, as well as P, SIItype, and SII.           The latter values must be communicated via a secure           communication channel, to preserve their confidentiality.Park, et al.                Standards Track                     [Page 7]

RFC 4683             Subject Identification Method          October 2006   8.      Bob can compute PEPSI' = H(H(P || R || SIItype || SII)) and           compare SIM' = R || PEPSI' to the SIM value in Alice's           certificate, thereby verifying SII.   If Alice's SII value is not required by Bob (Bob already knows   Alice's SII and does not require it), then steps 7 and 8 are as   follows:   7.      Alice sends Bob her Cert and P.  P must be sent via a secure           communication channel, to preserve its confidentiality.   8.      Bob can compute PEPSI' = H(H(P || R || SIItype || SII)) and           compare SIM' = R || PEPSI' to the value in the SIM, thereby           verifying SII.   If Alice wishes to prove she is the subject of an RA-validated   identifier, without disclosing her identifier to Bob, then steps 7   and 8 are as follows:   7.      Alice sends the intermediate value H(P || R || SIItype ||           SII) and her certificate to Bob.   8.      Bob can get R from the SIM in the certificate, then compute H           (intermediate value) and compare it to the value in SIM,           thereby verifying Alice's knowledge of P and SII.   Eve has to exhaustively search the H(P || R || SIItype || SII) space   to find Alice's SII.  This is a fairly hard problem even if Alice   uses a poor password, because of the size of R (as specified later),   and a really hard problem if Alice uses a fairly good password (seeSection 8).   Even if Eve finds Alice's P and SII, or constructs a massive   dictionary of P and SII values, it does not help find any other SII   values, because a new R is used for each PEPSI and SIM.4.  Procedures4.1.  SII and SIItype   The user presents evidence that a particular SII has been assigned to   him/her.  The SIItype is an Object Identifier (OID) that defines the   format and scope of the SII value.  For example, in Korea, one   SIItype is defined as follows:   -- KISA specific arc   id-KISA OBJECT IDENTIFIER ::=     {iso(1) member-body(2) korea(410) kisa(200004)}Park, et al.                Standards Track                     [Page 8]

RFC 4683             Subject Identification Method          October 2006   -- KISA specific OIDs   id-npki OBJECT IDENTIFIER ::= {id-KISA 10}   id-attribute OBJECT IDENTIFIER ::= {id-npki 1}   id-kisa-identifyData OBJECT IDENTIFIER ::= {id-attribute 1}   id-VID OBJECT IDENTIFIER ::= {id-kisa-identifyData 10}   id-SII OBJECT IDENTIFIER ::= {id-VID 1}   For closed communities, the SIItype value may be assigned by the CA   itself, but it is still recommended that the OID be registered.4.2.  User Chosen Password   The user selects a password as one of the input values for computing   the SIM.  The strength of the password is critical to protection of   the user's SII, in the following sense.  If an attacker has a   candidate SII value, and wants to determine whether the SIM value in   a specific subject certificate, P is the only protection for the SIM.   The user should be encouraged to select passwords that will be   difficult to be guessed, and long enough to protect against brute   force attacks.   Implementations of this specification MUST permit a user to select   passwords of up to 28 characters.  RAs SHOULD implement password   filter rules to prevent user selection of trivial passwords.  See   [FIPS 112] and [FIPS 180-1] for security criteria for passwords and   an automated password generator algorithm that randomly creates   simple pronounceable syllables as passwords.4.3.  Random Number Generation   The RA generates a random number, R.  A new R MUST be generated for   each SIM.  The length of R MUST be the same as the length of the   output of the hash algorithm H.  For example, if H is SHA-1, the   random number MUST be 160 bits.   A Random Number Generator (RNG) that meets the requirements defined   in [FIPS 140-2] and its use is strongly recommended.4.4.  Generation of SIM   The SIM in the subjectAltName extension within a certificate   identifies an entity, even if multiple subjectAltNames appear in a   certificate.  RAs MUST calculate the SIM value with the designated   inputs according to the following algorithm:   SIM = R || PEPSI      where PEPSI = H(H(P || R || SIItype || SII))Park, et al.                Standards Track                     [Page 9]

RFC 4683             Subject Identification Method          October 2006   The SII is made known to an RA at user enrollment.  Both SHA-1 and   SHA-256 MUST be supported for generation and verification of PEPSI   values.  This specification does not preclude use of other one-way   hash functions, but SHA-1 or SHA-256 SHOULD be used wherever   interoperability is a concern.   Note that a secure communication channel MUST be used to pass P and   SII passing from the end entity to the RA, to protect them from   disclosure or modification.   The syntax and the associated OID for SIM are also provided in the   ASN.1 modules inSection 5.1.  Also,Section 5.2 describes the syntax   for PEPSI in the ASN.1 modules.4.5.  Encryption of PEPSI   It may be required that the CA (not just the RA) verifies SII before   issuing a certificate.  To meet this requirement, RA SHOULD encrypt   the SIItype, SII, and SIM and send the result to the CA by a secure   channel.  The user SHOULD also encrypt the same values and send the   result to the CA in his or her certificate request message.  Then the   CA compares these two results for verifying the user's SII.   Where the results from RA and the user are the EPEPSI.      EPEPSI = E(SIItype || SII || SIM)   When the EPEPSI is used in a user certificate request, it is in   regInfo of [RFC4211] and [RFC2986].   Note: Specific encryption/decryption methods are not defined in this         document.  For transmission of the PEPSI value from a user to a         CA, the certificate request protocol employed defines how         encryption is performed.  For transmission of this data between         an RA and a CA, the details of how encryption is performed is a         local matter.   The syntax and the associated OID for EPEPSI is provided in the ASN.1   modules inSection 5.3.4.6.  Certification Request   As described above, a certificate request message MAY contain the   SIM.  [RFC2986] and [RFC4211] are widely used message syntaxes for   certificate requests.   Basically, a PKCS#10 message consists of a distinguished name, a   public key, and an optional set of attributes, collectively signed byPark, et al.                Standards Track                    [Page 10]

RFC 4683             Subject Identification Method          October 2006   the end entity.  The SIM alternative name MUST be placed in the   subjectAltName extension if this certificate request format is used.   If a CA verifies SII before issuing the certificate, the value of SIM   in the certification request MUST be conveyed in the EPEPSI form and   provided by the subject.4.7.  Certification   A CA that issues certificates containing the SIM includes the SIM as   a form of otherName from the GeneralName structure in the   "subjectAltName" extension.   In an environment where a CA verifies SII before issuing the   certificate, a CA decrypts the EPEPSI values it receives from both   the user and the RA, and compares them.  It then validates that the   SII value is correctly bound to the subject.      SIItype, SII, SIM = D(EPEPSI)5.  Definition5.1.  SIM Syntax   This section specifies the syntax for the SIM name form included in   the subjectAltName extension.  The SIM is composed of the three   fields:  the hash algorithm identifier, the authority-chosen random   value, and the value of the PEPSI itself.      id-pkix     OBJECT IDENTIFIER  ::=            { iso(1) identified-organization(3) dod(6) internet(1)              security(5) mechanisms(5) pkix(7) }      id-on       OBJECT IDENTIFIER ::= { id-pkix 8 }      id-on-SIM   OBJECT IDENTIFIER ::= { id-on 6 }        SIM ::= SEQUENCE {            hashAlg          AlgorithmIdentifier,            authorityRandom  OCTET STRING,   -- RA-chosen random number                                             -- used in computation of                                             -- pEPSI            pEPSI            OCTET STRING    -- hash of HashContent                                             -- with algorithm hashAlg        }Park, et al.                Standards Track                    [Page 11]

RFC 4683             Subject Identification Method          October 20065.2.  PEPSI   This section specifies the syntax for the PEPSI.  The PEPSI is   generated by performing the same hash function twice.  The PEPSI is   generated over the ASN.1 structure HashContent.  HashContent has four   values:  the user-selected password, the authority-chosen random   number, the identifier type, and the identifier itself.        HashContent ::= SEQUENCE {           userPassword     UTF8String,                            -- user-supplied password           authorityRandom  OCTET STRING,                            -- RA-chosen random number           identifierType   OBJECT IDENTIFIER,  -- SIItype           identifier       UTF8String          -- SII        }   Before calculating a PEPSI, conforming implementations MUST process   the userPassword with the six-step [LDAPBIS STRPREP] string   preparation algorithm, with the following changes:      * In step 2, Map, the mapping shall include processing of        characters commonly mapped to nothing, as specified inAppendixB.1 of [RFC3454].      * Omit step 6, Insignificant Character Removal.5.3.  Encrypted PEPSI   This section describes the syntax for the Encrypted PEPSI.  The   Encrypted PEPSI has three fields: identifierType, identifier, and   SIM.        EncryptedPEPSI ::= SEQUENCE {           identifierType  OBJECT IDENTIFIER, -- SIItype           identifier      UTF8String,        -- SII           sIM             SIM                -- Value of the SIM        }   When it is used in a certificate request, the OID in 'regInfo' of   [RFC4211] and [RFC2986] is as follows:   id-regEPEPSI OBJECT IDENTIFIER ::= { id-pkip 3 }Park, et al.                Standards Track                    [Page 12]

RFC 4683             Subject Identification Method          October 20066.  Example Usage of SIM   Depending on different security environments, there are three   possible use cases with SIM.     1.     When a relying party does not have any information about the            certificate user.     2.     When a relying party already knows the SII of the            certificate user.     3.     When the certificate user does not want to disclose his SII.   For the use case 1, the SII and a user-chosen password P (which only   the user knows) must be sent to a relying party via a secure   communication channel; the certificate including the SIM also must be   transmitted.  The relying party acquires R from the certificate.  The   relying party can verify that the SII was validated by the CA (or RA)   and is associated with the entity that presented the password and   certificate.  In this case, the RP learns which SII is bound to the   subject as a result of the procedure.   In case 2, a certificate user transmits only the password, P, and the   certificate.  The rest of the detailed procedure is the same as case   1, but here the relying party supplies the SII value, based on its   external knowledge of that value.  The purpose in this case is to   enable the RP to verify that the subject is bound to the SII,   presumably because the RP identifies the subject based on this SII.   In the last case, the certificate user does not want to disclose his   or her SII because of privacy concerns.  Here the only information   sent by a certificate subject is the intermediate value of the PEPSI,   H(R || P || SIItype || SII).  This value MUST be transmitted via a   secure channel, to preserve its confidentiality.  Upon receiving this   value, the relying party applies the hash function to the   intermediate PEPSI value sent by the user, and matches it against the   SIM value in the user's certificate.  The relying party does not   learn the user's SII value as a result of this processing, but the   relying party can verify the fact that the user knows the right SII   and password.  This gives the relying party more confidence that the   user is the certificate subject.  Note that this form of user   identity verification is NOT to be used in lieu of standard   certificate validation procedures, but rather in addition to such   procedures.7.  Name Constraints   The SIM value is stored as an otherName of a subject alternative   name; however, there are no constraints that can be placed on this   form of the name.Park, et al.                Standards Track                    [Page 13]

RFC 4683             Subject Identification Method          October 20068.  Security Considerations   Confidentiality for a SIM value is created by the iterated hashing of   the R, P, and SII values.  A SIM value depends on two properties of a   hash function: the fact that it cannot be inverted and the fact that   collisions (especially with formatted data) are rare.  The current   attacks by [WANG] are not applicable to SIM values since the end   entity supplying the SII and SIItype values does not supply all of   the data being hashed; i.e., the RA provides the R value.   In addition, a fairly good password is needed to protect against   guessing attacks on SIMs.  Due to the short length of many SIIs, it   is possible that an attacker may be able to guess it with partial   information about gender, age, and date of birth.  SIItype values are   very limited.  Therefore, it is important for users to select a   fairly good password to prevent an attacker from determining whether   a guessed SII is accurate.   This protocol assumes that Bob is a trustworthy relying party who   will not reuse the Alice's information.  Otherwise, Bob could   "impersonate" Alice if only knowledge of P and SII were used to   verify a subject's claimed identity.  Thus, this protocol MUST be   used only with the protocols that make use of digital signatures   generated using the subject's private key.   Digital signatures are used by a message sender to demonstrate   knowledge of the private key corresponding to the public key in a   certificate, and thus to authenticate and bind his or her identity to   a signed message.  However, managing a private key is vulnerable   under certain circumstances.  It is not fully guaranteed that the   claimed private key is bound to the subject of a certificate.  So,   the SIM can enhance verification of user identity.   Whenever a certificate needs to be updated, a new R SHOULD be   generated and the SIM SHOULD be recomputed.  Repeating the value of   the SIM from a previous certificate permits an attacker to identify   certificates associated with the same individual, which may be   undesirable for personal privacy purposes.Park, et al.                Standards Track                    [Page 14]

RFC 4683             Subject Identification Method          October 20069.  Acknowledgements   Jim Schaad (Soaring Hawk Consulting), Seungjoo Kim, Jaeho Yoon,   Baehyo Park (KISA), Bill Burr, Morrie Dworkin (NIST), and the   Internet Security Technology Forum (ISTF) have significantly   contributed to work on the SIM and PEPSI concept and identified a   potential security attack.  Also their comments on the set of   desirable properties for the PEPSI and enhancements to the PEPSI were   most illumination.  Also, thanks to Russell Housley, Stephen Kent,   and Denis Pinkas for their contributions to this document.10.  IANA Considerations   In the future, IANA may be asked to establish a registry of object   identifiers to promote interoperability in the specification of SII   types.11.  References11.1.  Normative References   [RFC2119]         Bradner, S., "Key words for use in RFCs to Indicate                     Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2986]         Nystrom, M. and B. Kaliski, "PKCS #10:                     Certification Request Syntax Specification Version                     1.7",RFC 2986, November 2000.   [RFC3454]         Hoffman, P. and M. Blanchet, "Preparation of                     Internationalized Strings ("stringprep")",RFC3454, December 2002.   [RFC4043]         Pinkas, D. and T. Gindin, "Internet X.509 Public                     Key Infrastructure Permanent Identifier",RFC 4043,                     May 2005.   [RFC4211]         Schaad, J., "Internet X.509 Public Key                     Infrastructure Certificate Request Message Format                     (CRMF)",RFC 4211, September 2005.11.2.  Informative References   [LDAPBIS STRPREP] Zeilenga, K., "LDAP: Internationalized String                     Preparation", Work in Progress.   [FIPS 112]        Fedreal Information Processing Standards                     Publication (FIPS PUB) 112, "Password Usage", 30                     May 1985.Park, et al.                Standards Track                    [Page 15]

RFC 4683             Subject Identification Method          October 2006   [FIPS 180-1]      Federal Information Processing Standards                     Publication (FIPS PUB) 180-1, "Secure Hash                     Standard", 17 April 1995.   [FIPS 140-2]      Federal Information Processing Standards                     Publication (FIPS PUB) 140-2, "Security                     Requirements for Cryptographic Modules", 25 May                     2001.   [WANG]            Xiaoyun Wang, Yiqun Lisa Yin, and Hongbo Yu,                     "Finding Collisions in the Full SHA-1", Crypto'05.                     <http://www.infosec.sdu.edu.cn/paper/sha1-crypto-auth-new-2-yao.pdf>Authors' Addresses   Jongwook Park   Korea Information Security Agency   78, Garak-Dong, Songpa-Gu, Seoul, 138-803   REPUBLIC OF KOREA   Phone: 2-405-5432   EMail: khopri@kisa.or.kr   Jaeil Lee   78, Garak-Dong, Songpa-Gu, Seoul, 138-803   REPUBLIC OF KOREA   Korea Information Security Agency   Phone: 2-405-5300   EMail: jilee@kisa.or.kr   Hongsub Lee   Korea Information Security Agency   78, Garak-Dong, Songpa-Gu, Seoul, 138-803   REPUBLIC OF KOREA   Phone: 2-405-5100   EMail: hslee@kisa.or.krPark, et al.                Standards Track                    [Page 16]

RFC 4683             Subject Identification Method          October 2006   Sangjoon Park   BCQRE Co.,Ltd   Yuil Bldg. Dogok-dong 411-14, Kangnam-ku, Seoul, 135-270   REPUBLIC OF KOREA   EMail: sjpark@bcqre.com   Tim Polk   National Institute of Standards and Technology   100 Bureau Drive, MS 8930   Gaithersburg, MD 20899   EMail: tim.polk@nist.govPark, et al.                Standards Track                    [Page 17]

RFC 4683             Subject Identification Method          October 2006Appendix A.  "Compilable" ASN.1 Module, 1988 Syntax   PKIXSIM {iso(1) identified-organization(3) dod(6) internet(1)      security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-sim2005(38) }   DEFINITIONS EXPLICIT TAGS ::=   BEGIN   -- EXPORTS ALL    IMPORTS    AlgorithmIdentifier, AttributeTypeAndValue FROM PKIX1Explicit88      {iso(1) identified-organization(3) dod(6) internet(1) security(5)       mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18)}   -- SIM   -- SIM certificate OID       id-pkix    OBJECT IDENTIFIER  ::=            { iso(1) identified-organization(3) dod(6) internet(1)              security(5) mechanisms(5) pkix(7) }      id-on       OBJECT IDENTIFIER ::= { id-pkix 8 }       id-on-SIM  OBJECT IDENTIFIER ::= { id-on 6 }   -- Certificate Syntax       SIM ::= SEQUENCE {             hashAlg          AlgorithmIdentifier,             authorityRandom  OCTET STRING,   -- RA-chosen random number                                              -- used in computation of                                              -- pEPSI             pEPSI            OCTET STRING    -- hash of HashContent                                              -- with algorithm hashAlg         }   -- PEPSI       UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING       -- The content of this type conforms toRFC 2279       HashContent ::= SEQUENCE {            userPassword     UTF8String,                             -- user-supplied password            authorityRandom  OCTET STRING,Park, et al.                Standards Track                    [Page 18]

RFC 4683             Subject Identification Method          October 2006                             -- RA-chosen random number            identifierType   OBJECT IDENTIFIER,  -- SIItype            identifier       UTF8String          -- SII         }   -- Encrypted PEPSI   -- OID for encapsulated content type       id-regEPEPSI OBJECT IDENTIFIER ::= { id-pkip 3 }         EncryptedPEPSI ::= SEQUENCE {            identifierType  OBJECT IDENTIFIER, -- SIItype            identifier      UTF8String,        -- SII            sIM             SIM                -- Value of the SIM         }   ENDPark, et al.                Standards Track                    [Page 19]

RFC 4683             Subject Identification Method          October 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Park, et al.                Standards Track                    [Page 20]