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Internet Engineering Task Force (IETF)                       C. PercivalRequest for Comments: 7914                                       TarsnapCategory: Informational                                     S. JosefssonISSN: 2070-1721                                                   SJD AB                                                             August 2016The scrypt Password-Based Key Derivation FunctionAbstract   This document specifies the password-based key derivation function   scrypt.  The function derives one or more secret keys from a secret   string.  It is based on memory-hard functions, which offer added   protection against attacks using custom hardware.  The document also   provides an ASN.1 schema.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7914.Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://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 Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Percival & Josefsson          Informational                     [Page 1]

RFC 7914                      scrypt PBKDF                   August 2016Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  scrypt Parameters . . . . . . . . . . . . . . . . . . . . . .33.  The Salsa20/8 Core Function . . . . . . . . . . . . . . . . .44.  The scryptBlockMix Algorithm  . . . . . . . . . . . . . . . .55.  The scryptROMix Algorithm . . . . . . . . . . . . . . . . . .66.  The scrypt Algorithm  . . . . . . . . . . . . . . . . . . . .77.  ASN.1 Syntax  . . . . . . . . . . . . . . . . . . . . . . . .87.1.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . .98.  Test Vectors for Salsa20/8 Core . . . . . . . . . . . . . . .99.  Test Vectors for scryptBlockMix . . . . . . . . . . . . . . .1010. Test Vectors for scryptROMix  . . . . . . . . . . . . . . . .1111. Test Vectors for PBKDF2 with HMAC-SHA-256 . . . . . . . . . .1212. Test Vectors for scrypt . . . . . . . . . . . . . . . . . . .1313. Test Vectors for PKCS#8 . . . . . . . . . . . . . . . . . . .1414. Security Considerations . . . . . . . . . . . . . . . . . . .1415. References  . . . . . . . . . . . . . . . . . . . . . . . . .1515.1.  Normative References . . . . . . . . . . . . . . . . . .1515.2.  Informative References . . . . . . . . . . . . . . . . .15   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .16   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .161.  Introduction   Password-based key derivation functions are used in cryptography and   security protocols for deriving one or more secret keys from a secret   value.  Over the years, several password-based key derivation   functions have been used, including the original DES-based UNIX   Crypt-function, FreeBSD MD5 crypt, Public-Key Cryptography   Standards#5 (PKCS#5) PBKDF2 [RFC2898] (typically used with SHA-1),   GNU SHA-256/512 crypt [SHA2CRYPT], Windows NT LAN Manager (NTLM)   [NTLM] hash, and the Blowfish-based bcrypt [BCRYPT].  These   algorithms are all based on a cryptographic primitive combined with   salting and/or iteration.  The iteration count is used to slow down   the computation, and the salt is used to make pre-computation   costlier.   All password-based key derivation functions mentioned above share the   same weakness against powerful attackers.  Provided that the number   of iterations used is increased as computer systems get faster, this   allows legitimate users to spend a constant amount of time on key   derivation without losing ground to attackers' ever-increasing   computing power -- as long as attackers are limited to the same   software implementations as legitimate users.  While parallelized   hardware implementations may not change the number of operations   performed compared to software implementations, this does not prevent   them from dramatically changing the asymptotic cost, since in manyPercival & Josefsson          Informational                     [Page 2]

RFC 7914                      scrypt PBKDF                   August 2016   contexts -- including the embarrassingly parallel task of performing   a brute-force search for a passphrase -- dollar-seconds are the most   appropriate units for measuring the cost of a computation.  As   semiconductor technology develops, circuits do not merely become   faster; they also become smaller, allowing for a larger amount of   parallelism at the same cost.   Consequently, with existing key derivation algorithms, even when the   iteration count is increased so that the time taken to verify a   password remains constant, the cost of finding a password by using a   brute-force attack implemented in hardware drops each year.   The scrypt function aims to reduce the advantage that attackers can   gain by using custom-designed parallel circuits for breaking   password-based key derivation functions.   This document does not introduce scrypt for the first time.  The   original scrypt paper [SCRYPT] was published as a peer-reviewed   scientific paper and contains further background and discussions.   The purpose of this document is to serve as a stable reference for   documents making use of scrypt.  The rest of this document is divided   into sections that each describe parameter choices and algorithm   steps needed for the final "scrypt" algorithm.2.  scrypt Parameters   The scrypt function takes several parameters.  The passphrase P is   typically a human-chosen password.  The salt is normally uniquely and   randomly generated [RFC4086].  The parameter r ("blockSize")   specifies the block size.  The CPU/Memory cost parameter N   ("costParameter") must be larger than 1, a power of 2, and less than   2^(128 * r / 8).  The parallelization parameter p   ("parallelizationParameter") is a positive integer less than or equal   to ((2^32-1) * 32) / (128 * r).  The intended output length dkLen is   the length in octets of the key to be derived ("keyLength"); it is a   positive integer less than or equal to (2^32 - 1) * 32.   Users of scrypt can tune the parameters N, r, and p according to the   amount of memory and computing power available, the latency-bandwidth   product of the memory subsystem, and the amount of parallelism   desired.  At the current time, r=8 and p=1 appears to yield good   results, but as memory latency and CPU parallelism increase, it is   likely that the optimum values for both r and p will increase.  Note   also that since the computations of SMix are independent, a large   value of p can be used to increase the computational cost of scryptPercival & Josefsson          Informational                     [Page 3]

RFC 7914                      scrypt PBKDF                   August 2016   without increasing the memory usage; so we can expect scrypt to   remain useful even if the growth rates of CPU power and memory   capacity diverge.3.  The Salsa20/8 Core Function   Salsa20/8 Core is a round-reduced variant of the Salsa20 Core.  It is   a hash function from 64-octet strings to 64-octet strings.  Note that   Salsa20/8 Core is not a cryptographic hash function since it is not   collision resistant.  See Section 8 of [SALSA20SPEC] for its   specification and [SALSA20CORE] for more information.  The algorithm   description, in C language, is included below as a stable reference,   without endianness conversion and alignment.   #define R(a,b) (((a) << (b)) | ((a) >> (32 - (b))))   void salsa20_word_specification(uint32 out[16],uint32 in[16])   {     int i;     uint32 x[16];     for (i = 0;i < 16;++i) x[i] = in[i];     for (i = 8;i > 0;i -= 2) {       x[ 4] ^= R(x[ 0]+x[12], 7);  x[ 8] ^= R(x[ 4]+x[ 0], 9);       x[12] ^= R(x[ 8]+x[ 4],13);  x[ 0] ^= R(x[12]+x[ 8],18);       x[ 9] ^= R(x[ 5]+x[ 1], 7);  x[13] ^= R(x[ 9]+x[ 5], 9);       x[ 1] ^= R(x[13]+x[ 9],13);  x[ 5] ^= R(x[ 1]+x[13],18);       x[14] ^= R(x[10]+x[ 6], 7);  x[ 2] ^= R(x[14]+x[10], 9);       x[ 6] ^= R(x[ 2]+x[14],13);  x[10] ^= R(x[ 6]+x[ 2],18);       x[ 3] ^= R(x[15]+x[11], 7);  x[ 7] ^= R(x[ 3]+x[15], 9);       x[11] ^= R(x[ 7]+x[ 3],13);  x[15] ^= R(x[11]+x[ 7],18);       x[ 1] ^= R(x[ 0]+x[ 3], 7);  x[ 2] ^= R(x[ 1]+x[ 0], 9);       x[ 3] ^= R(x[ 2]+x[ 1],13);  x[ 0] ^= R(x[ 3]+x[ 2],18);       x[ 6] ^= R(x[ 5]+x[ 4], 7);  x[ 7] ^= R(x[ 6]+x[ 5], 9);       x[ 4] ^= R(x[ 7]+x[ 6],13);  x[ 5] ^= R(x[ 4]+x[ 7],18);       x[11] ^= R(x[10]+x[ 9], 7);  x[ 8] ^= R(x[11]+x[10], 9);       x[ 9] ^= R(x[ 8]+x[11],13);  x[10] ^= R(x[ 9]+x[ 8],18);       x[12] ^= R(x[15]+x[14], 7);  x[13] ^= R(x[12]+x[15], 9);       x[14] ^= R(x[13]+x[12],13);  x[15] ^= R(x[14]+x[13],18);     }     for (i = 0;i < 16;++i) out[i] = x[i] + in[i];   }Percival & Josefsson          Informational                     [Page 4]

RFC 7914                      scrypt PBKDF                   August 20164.  The scryptBlockMix Algorithm   The scryptBlockMix algorithm is the same as the BlockMix algorithm   described in [SCRYPT] but with Salsa20/8 Core used as the hash   function H.  Below, Salsa(T) corresponds to the Salsa20/8 Core   function applied to the octet vector T.   Algorithm scryptBlockMix   Parameters:            r       Block size parameter.   Input:            B[0] || B[1] || ... || B[2 * r - 1]                   Input octet string (of size 128 * r octets),                   treated as 2 * r 64-octet blocks,                   where each element in B is a 64-octet block.   Output:            B'[0] || B'[1] || ... || B'[2 * r - 1]                   Output octet string.   Steps:     1. X = B[2 * r - 1]     2. for i = 0 to 2 * r - 1 do          T = X xor B[i]          X = Salsa (T)          Y[i] = X        end for     3. B' = (Y[0], Y[2], ..., Y[2 * r - 2],              Y[1], Y[3], ..., Y[2 * r - 1])Percival & Josefsson          Informational                     [Page 5]

RFC 7914                      scrypt PBKDF                   August 20165.  The scryptROMix Algorithm   The scryptROMix algorithm is the same as the ROMix algorithm   described in [SCRYPT] but with scryptBlockMix used as the hash   function H and the Integerify function explained inline.   Algorithm scryptROMix   Input:            r       Block size parameter.            B       Input octet vector of length 128 * r octets.            N       CPU/Memory cost parameter, must be larger than 1,                    a power of 2, and less than 2^(128 * r / 8).   Output:            B'      Output octet vector of length 128 * r octets.   Steps:     1. X = B     2. for i = 0 to N - 1 do          V[i] = X          X = scryptBlockMix (X)        end for     3. for i = 0 to N - 1 do          j = Integerify (X) mod N                 where Integerify (B[0] ... B[2 * r - 1]) is defined                 as the result of interpreting B[2 * r - 1] as a                 little-endian integer.          T = X xor V[j]          X = scryptBlockMix (T)        end for     4. B' = XPercival & Josefsson          Informational                     [Page 6]

RFC 7914                      scrypt PBKDF                   August 20166.  The scrypt Algorithm   The PBKDF2-HMAC-SHA-256 function used below denotes the PBKDF2   algorithm [RFC2898] used with HMAC-SHA-256 [RFC6234] as the   Pseudorandom Function (PRF).  The HMAC-SHA-256 function generates   32-octet outputs.   Algorithm scrypt   Input:            P       Passphrase, an octet string.            S       Salt, an octet string.            N       CPU/Memory cost parameter, must be larger than 1,                    a power of 2, and less than 2^(128 * r / 8).            r       Block size parameter.            p       Parallelization parameter, a positive integer                    less than or equal to ((2^32-1) * hLen) / MFLen                    where hLen is 32 and MFlen is 128 * r.            dkLen   Intended output length in octets of the derived                    key; a positive integer less than or equal to                    (2^32 - 1) * hLen where hLen is 32.   Output:            DK      Derived key, of length dkLen octets.   Steps:    1. Initialize an array B consisting of p blocks of 128 * r octets       each:        B[0] || B[1] || ... || B[p - 1] =          PBKDF2-HMAC-SHA256 (P, S, 1, p * 128 * r)    2. for i = 0 to p - 1 do          B[i] = scryptROMix (r, B[i], N)        end for    3. DK = PBKDF2-HMAC-SHA256 (P, B[0] || B[1] || ... || B[p - 1],                                 1, dkLen)Percival & Josefsson          Informational                     [Page 7]

RFC 7914                      scrypt PBKDF                   August 20167.  ASN.1 Syntax   This section defines ASN.1 syntax for the scrypt key derivation   function (KDF).  This is intended to operate on the same abstraction   level as PKCS#5's PBKDF2.  The OID id-scrypt below can be used where   id-PBKDF2 is used, with scrypt-params corresponding to PBKDF2-params.   The intended application of these definitions includes PKCS #8 and   other syntax for key management.   The object identifier id-scrypt identifies the scrypt key derivation   function.   id-scrypt OBJECT IDENTIFIER ::= {1 3 6 1 4 1 11591 4 11}   The parameters field associated with this OID in an   AlgorithmIdentifier shall have type scrypt-params:   scrypt-params ::= SEQUENCE {          salt OCTET STRING,          costParameter INTEGER (1..MAX),          blockSize INTEGER (1..MAX),          parallelizationParameter INTEGER (1..MAX),          keyLength INTEGER (1..MAX) OPTIONAL }   The fields of type scrypt-params have the following meanings:   - salt specifies the salt value.  It shall be an octet string.   - costParameter specifies the CPU/Memory cost parameter N.   - blockSize specifies the block size parameter r.   - parallelizationParameter specifies the parallelization parameter.   - keyLength, an optional field, is the length in octets of the   derived key.  The maximum key length allowed depends on the   implementation; it is expected that implementation profiles may   further constrain the bounds.  This field only provides convenience;   the key length is not cryptographically protected.   To be usable in PKCS#8 [RFC5208] and Asymmetric Key Packages   [RFC5958], the following extension of the PBES2-KDFs type is needed:      PBES2-KDFs ALGORITHM-IDENTIFIER ::=          { {scrypt-params IDENTIFIED BY id-scrypt}, ... }Percival & Josefsson          Informational                     [Page 8]

RFC 7914                      scrypt PBKDF                   August 20167.1.  ASN.1 Module   For reference purposes, the ASN.1 syntax is presented as an ASN.1   module here.   -- scrypt ASN.1 Module   scrypt-0 {1 3 6 1 4 1 11591 4 10}   DEFINITIONS ::= BEGIN   id-scrypt OBJECT IDENTIFIER ::= {1 3 6 1 4 1 11591 4 11}   scrypt-params ::= SEQUENCE {       salt OCTET STRING,       costParameter INTEGER (1..MAX),       blockSize INTEGER (1..MAX),       parallelizationParameter INTEGER (1..MAX),       keyLength INTEGER (1..MAX) OPTIONAL   }   PBES2-KDFs ALGORITHM-IDENTIFIER ::=          { {scrypt-params IDENTIFIED BY id-scrypt}, ... }   END8.  Test Vectors for Salsa20/8 Core   Below is a sequence of octets that illustrate input and output values   for the Salsa20/8 Core.  The octets are hex encoded and whitespace is   inserted for readability.  The value corresponds to the first input   and output pair generated by the first scrypt test vector below.   INPUT:   7e 87 9a 21 4f 3e c9 86 7c a9 40 e6 41 71 8f 26   ba ee 55 5b 8c 61 c1 b5 0d f8 46 11 6d cd 3b 1d   ee 24 f3 19 df 9b 3d 85 14 12 1e 4b 5a c5 aa 32   76 02 1d 29 09 c7 48 29 ed eb c6 8d b8 b8 c2 5e   OUTPUT:   a4 1f 85 9c 66 08 cc 99 3b 81 ca cb 02 0c ef 05   04 4b 21 81 a2 fd 33 7d fd 7b 1c 63 96 68 2f 29   b4 39 31 68 e3 c9 e6 bc fe 6b c5 b7 a0 6d 96 ba   e4 24 cc 10 2c 91 74 5c 24 ad 67 3d c7 61 8f 81Percival & Josefsson          Informational                     [Page 9]

RFC 7914                      scrypt PBKDF                   August 20169.  Test Vectors for scryptBlockMix   Below is a sequence of octets that illustrate input and output values   for scryptBlockMix.  The test vector uses an r value of 1.  The   octets are hex encoded and whitespace is inserted for readability.   The value corresponds to the first input and output pair generated by   the first scrypt test vector below.   INPUT   B[0] =  f7 ce 0b 65 3d 2d 72 a4 10 8c f5 ab e9 12 ff dd           77 76 16 db bb 27 a7 0e 82 04 f3 ae 2d 0f 6f ad           89 f6 8f 48 11 d1 e8 7b cc 3b d7 40 0a 9f fd 29           09 4f 01 84 63 95 74 f3 9a e5 a1 31 52 17 bc d7   B[1] =  89 49 91 44 72 13 bb 22 6c 25 b5 4d a8 63 70 fb           cd 98 43 80 37 46 66 bb 8f fc b5 bf 40 c2 54 b0           67 d2 7c 51 ce 4a d5 fe d8 29 c9 0b 50 5a 57 1b           7f 4d 1c ad 6a 52 3c da 77 0e 67 bc ea af 7e 89   OUTPUT   B'[0] = a4 1f 85 9c 66 08 cc 99 3b 81 ca cb 02 0c ef 05           04 4b 21 81 a2 fd 33 7d fd 7b 1c 63 96 68 2f 29           b4 39 31 68 e3 c9 e6 bc fe 6b c5 b7 a0 6d 96 ba           e4 24 cc 10 2c 91 74 5c 24 ad 67 3d c7 61 8f 81   B'[1] = 20 ed c9 75 32 38 81 a8 05 40 f6 4c 16 2d cd 3c           21 07 7c fe 5f 8d 5f e2 b1 a4 16 8f 95 36 78 b7           7d 3b 3d 80 3b 60 e4 ab 92 09 96 e5 9b 4d 53 b6           5d 2a 22 58 77 d5 ed f5 84 2c b9 f1 4e ef e4 25Percival & Josefsson          Informational                    [Page 10]

RFC 7914                      scrypt PBKDF                   August 201610.  Test Vectors for scryptROMix   Below is a sequence of octets that illustrate input and output values   for scryptROMix.  The test vector uses an r value of 1 and an N value   of 16.  The octets are hex encoded and whitespace is inserted for   readability.  The value corresponds to the first input and output   pair generated by the first scrypt test vector below.   INPUT:   B = f7 ce 0b 65 3d 2d 72 a4 10 8c f5 ab e9 12 ff dd       77 76 16 db bb 27 a7 0e 82 04 f3 ae 2d 0f 6f ad       89 f6 8f 48 11 d1 e8 7b cc 3b d7 40 0a 9f fd 29       09 4f 01 84 63 95 74 f3 9a e5 a1 31 52 17 bc d7       89 49 91 44 72 13 bb 22 6c 25 b5 4d a8 63 70 fb       cd 98 43 80 37 46 66 bb 8f fc b5 bf 40 c2 54 b0       67 d2 7c 51 ce 4a d5 fe d8 29 c9 0b 50 5a 57 1b       7f 4d 1c ad 6a 52 3c da 77 0e 67 bc ea af 7e 89   OUTPUT:   B = 79 cc c1 93 62 9d eb ca 04 7f 0b 70 60 4b f6 b6       2c e3 dd 4a 96 26 e3 55 fa fc 61 98 e6 ea 2b 46       d5 84 13 67 3b 99 b0 29 d6 65 c3 57 60 1f b4 26       a0 b2 f4 bb a2 00 ee 9f 0a 43 d1 9b 57 1a 9c 71       ef 11 42 e6 5d 5a 26 6f dd ca 83 2c e5 9f aa 7c       ac 0b 9c f1 be 2b ff ca 30 0d 01 ee 38 76 19 c4       ae 12 fd 44 38 f2 03 a0 e4 e1 c4 7e c3 14 86 1f       4e 90 87 cb 33 39 6a 68 73 e8 f9 d2 53 9a 4b 8ePercival & Josefsson          Informational                    [Page 11]

RFC 7914                      scrypt PBKDF                   August 201611.  Test Vectors for PBKDF2 with HMAC-SHA-256   Below is a sequence of octets that illustrate input and output values   for PBKDF2-HMAC-SHA-256.  The octets are hex encoded and whitespace   is inserted for readability.  The test vectors below can be used to   verify the PBKDF2-HMAC-SHA-256 [RFC2898] function.  The password and   salt strings are passed as sequences of ASCII [RFC20] octets.   PBKDF2-HMAC-SHA-256 (P="passwd", S="salt",                       c=1, dkLen=64) =   55 ac 04 6e 56 e3 08 9f ec 16 91 c2 25 44 b6 05   f9 41 85 21 6d de 04 65 e6 8b 9d 57 c2 0d ac bc   49 ca 9c cc f1 79 b6 45 99 16 64 b3 9d 77 ef 31   7c 71 b8 45 b1 e3 0b d5 09 11 20 41 d3 a1 97 83   PBKDF2-HMAC-SHA-256 (P="Password", S="NaCl",                        c=80000, dkLen=64) =   4d dc d8 f6 0b 98 be 21 83 0c ee 5e f2 27 01 f9   64 1a 44 18 d0 4c 04 14 ae ff 08 87 6b 34 ab 56   a1 d4 25 a1 22 58 33 54 9a db 84 1b 51 c9 b3 17   6a 27 2b de bb a1 d0 78 47 8f 62 b3 97 f3 3c 8dPercival & Josefsson          Informational                    [Page 12]

RFC 7914                      scrypt PBKDF                   August 201612.  Test Vectors for scrypt   For reference purposes, we provide the following test vectors for   scrypt, where the password and salt strings are passed as sequences   of ASCII [RFC20] octets.   The parameters to the scrypt function below are, in order, the   password P (octet string), the salt S (octet string), the CPU/Memory   cost parameter N, the block size parameter r, the parallelization   parameter p, and the output size dkLen.  The output is hex encoded   and whitespace is inserted for readability.   scrypt (P="", S="",           N=16, r=1, p=1, dklen=64) =   77 d6 57 62 38 65 7b 20 3b 19 ca 42 c1 8a 04 97   f1 6b 48 44 e3 07 4a e8 df df fa 3f ed e2 14 42   fc d0 06 9d ed 09 48 f8 32 6a 75 3a 0f c8 1f 17   e8 d3 e0 fb 2e 0d 36 28 cf 35 e2 0c 38 d1 89 06   scrypt (P="password", S="NaCl",           N=1024, r=8, p=16, dkLen=64) =   fd ba be 1c 9d 34 72 00 78 56 e7 19 0d 01 e9 fe   7c 6a d7 cb c8 23 78 30 e7 73 76 63 4b 37 31 62   2e af 30 d9 2e 22 a3 88 6f f1 09 27 9d 98 30 da   c7 27 af b9 4a 83 ee 6d 83 60 cb df a2 cc 06 40   scrypt (P="pleaseletmein", S="SodiumChloride",           N=16384, r=8, p=1, dkLen=64) =   70 23 bd cb 3a fd 73 48 46 1c 06 cd 81 fd 38 eb   fd a8 fb ba 90 4f 8e 3e a9 b5 43 f6 54 5d a1 f2   d5 43 29 55 61 3f 0f cf 62 d4 97 05 24 2a 9a f9   e6 1e 85 dc 0d 65 1e 40 df cf 01 7b 45 57 58 87   scrypt (P="pleaseletmein", S="SodiumChloride",           N=1048576, r=8, p=1, dkLen=64) =   21 01 cb 9b 6a 51 1a ae ad db be 09 cf 70 f8 81   ec 56 8d 57 4a 2f fd 4d ab e5 ee 98 20 ad aa 47   8e 56 fd 8f 4b a5 d0 9f fa 1c 6d 92 7c 40 f4 c3   37 30 40 49 e8 a9 52 fb cb f4 5c 6f a7 7a 41 a4Percival & Josefsson          Informational                    [Page 13]

RFC 7914                      scrypt PBKDF                   August 201613.  Test Vectors for PKCS#8   PKCS#8 [RFC5208] and Asymmetric Key Packages [RFC5958] encode   encrypted private-keys.  Using PBES2 with scrypt as the KDF, the   following illustrates an example of a PKCS#8-encoded private-key.   The password is "Rabbit" (without the quotes) with N=1048576, r=8,   and p=1.  The salt is "Mouse" and the encryption algorithm used is   aes256-CBC.  The derived key is: E2 77 EA 2C AC B2 3E DA-FC 03 9D 22   9B 79 DC 13 EC ED B6 01 D9 9B 18 2A-9F ED BA 1E 2B FB 4F 58.   -----BEGIN ENCRYPTED PRIVATE KEY-----   MIHiME0GCSqGSIb3DQEFDTBAMB8GCSsGAQQB2kcECzASBAVNb3VzZQIDEAAAAgEI   AgEBMB0GCWCGSAFlAwQBKgQQyYmguHMsOwzGMPoyObk/JgSBkJb47EWd5iAqJlyy   +ni5ftd6gZgOPaLQClL7mEZc2KQay0VhjZm/7MbBUNbqOAXNM6OGebXxVp6sHUAL   iBGY/Dls7B1TsWeGObE0sS1MXEpuREuloZjcsNVcNXWPlLdZtkSH6uwWzR0PyG/Z   +ZXfNodZtd/voKlvLOw5B3opGIFaLkbtLZQwMiGtl42AS89lZg==   -----END ENCRYPTED PRIVATE KEY-----14.  Security Considerations   This document specifies a cryptographic algorithm, and there is   always a risk that someone will find a weakness in it.  By following   the cryptographic research area, you may learn of publications   relevant to scrypt.   ROMix has been proven sequential memory-hard under the random oracle   model for the hash function.  The security of scrypt relies on the   assumption that BlockMix with Salsa20/8 Core does not exhibit any   "shortcuts" that would allow it to be iterated more easily than a   random oracle.  For other claims about the security properties, see   [SCRYPT].   Passwords and other sensitive data, such as intermediate values, may   continue to be stored in memory, core dumps, swap areas, etc., for a   long time after the implementation has processed them.  This makes   attacks on the implementation easier.  Thus, implementation should   consider storing sensitive data in protected memory areas.  How to   achieve this is system dependent.   By nature and depending on parameters, running the scrypt algorithm   may require large amounts of memory.  Systems should protect against   a denial-of-service attack resulting from attackers presenting   unreasonably large parameters.   Poor parameter choices can be harmful for security; for example, if   you tune the parameters so that memory use is reduced to small   amounts that will affect the properties of the algorithm.Percival & Josefsson          Informational                    [Page 14]

RFC 7914                      scrypt PBKDF                   August 201615.  References15.1.  Normative References   [RFC2898]  Kaliski, B., "PKCS #5: Password-Based Cryptography              Specification Version 2.0",RFC 2898,              DOI 10.17487/RFC2898, September 2000,              <http://www.rfc-editor.org/info/rfc2898>.   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms              (SHA and SHA-based HMAC and HKDF)",RFC 6234,              DOI 10.17487/RFC6234, May 2011,              <http://www.rfc-editor.org/info/rfc6234>.15.2.  Informative References   [BCRYPT]   Provos, N. and D. Mazieres, "A Future-Adaptable Password              Scheme", USENIX 1999, June 1999,              <https://www.usenix.org/legacy/event/usenix99/provos/provos.pdf>.   [NTLM]     Microsoft, "[MS-NLMP]: NT LAN Manager (NTLM)              Authentication Protocol", 2015,              <https://msdn.microsoft.com/en-us/library/cc236621.aspx>.   [RFC20]    Cerf, V., "ASCII format for network interchange", STD 80,RFC 20, DOI 10.17487/RFC0020, October 1969,              <http://www.rfc-editor.org/info/rfc20>.   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,              "Randomness Requirements for Security",BCP 106,RFC 4086,              DOI 10.17487/RFC4086, June 2005,              <http://www.rfc-editor.org/info/rfc4086>.   [RFC5208]  Kaliski, B., "Public-Key Cryptography Standards (PKCS) #8:              Private-Key Information Syntax Specification Version 1.2",RFC 5208, DOI 10.17487/RFC5208, May 2008,              <http://www.rfc-editor.org/info/rfc5208>.   [RFC5958]  Turner, S., "Asymmetric Key Packages",RFC 5958,              DOI 10.17487/RFC5958, August 2010,              <http://www.rfc-editor.org/info/rfc5958>.   [SALSA20CORE]              Bernstein, D., "The Salsa20 Core", March 2005,              <http://cr.yp.to/salsa20.html>.Percival & Josefsson          Informational                    [Page 15]

RFC 7914                      scrypt PBKDF                   August 2016   [SALSA20SPEC]              Bernstein, D., "Salsa20 specification", April 2005,              <http://cr.yp.to/snuffle/spec.pdf>.   [SCRYPT]   Percival, C., "STRONGER KEY DERIVATION VIA SEQUENTIAL              MEMORY-HARD FUNCTIONS",  BSDCan'09, May 2009,              <http://www.tarsnap.com/scrypt/scrypt.pdf>.   [SHA2CRYPT]              Drepper, U., "Unix crypt using SHA-256 and SHA-512", April              2008, <http://www.akkadia.org/drepper/SHA-crypt.txt>.Acknowledgements   Text in this document was borrowed from [SCRYPT] and [RFC2898].  The   PKCS#8 test vector was provided by Stephen N. Henson.   Feedback on this document was received from Dmitry Chestnykh,   Alexander Klink, Rob Kendrick, Royce Williams, Ted Rolle, Jr., Eitan   Adler, Stephen Farrel, Nikos Mavrogiannopoulos, and Paul Kyzivat.Authors' Addresses   Colin Percival   Tarsnap   Email: cperciva@tarsnap.com   Simon Josefsson   SJD AB   Email: simon@josefsson.org   URI:http://josefsson.org/Percival & Josefsson          Informational                    [Page 16]