1 /* gc-pbkdf2-sha1.c --- Password-Based Key Derivation Function a'la PKCS#5
2 Copyright (C) 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2, or (at your option)
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software Foundation,
16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18 /* Written by Simon Josefsson. The comments in this file are taken
31 * PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
32 * example) to derive keys. The length of the derived key is essentially
33 * unbounded. (However, the maximum effective search space for the
34 * derived key may be limited by the structure of the underlying
35 * pseudorandom function. See Appendix B.1 for further discussion.)
36 * PBKDF2 is recommended for new applications.
38 * PBKDF2 (P, S, c, dkLen)
40 * Options: PRF underlying pseudorandom function (hLen
41 * denotes the length in octets of the
42 * pseudorandom function output)
44 * Input: P password, an octet string (ASCII or UTF-8)
45 * S salt, an octet string
46 * c iteration count, a positive integer
47 * dkLen intended length in octets of the derived
48 * key, a positive integer, at most
51 * Output: DK derived key, a dkLen-octet string
55 gc_pbkdf2_sha1 (const char *P, size_t Plen,
56 const char *S, size_t Slen,
58 char *DK, size_t dkLen)
60 unsigned int hLen = 20;
70 size_t tmplen = Slen + 4;
73 return GC_PKCS5_INVALID_ITERATION_COUNT;
76 return GC_PKCS5_INVALID_DERIVED_KEY_LENGTH;
82 * 1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
86 if (dkLen > 4294967295U)
87 return GC_PKCS5_DERIVED_KEY_TOO_LONG;
90 * 2. Let l be the number of hLen-octet blocks in the derived key,
91 * rounding up, and let r be the number of octets in the last
94 * l = CEIL (dkLen / hLen) ,
95 * r = dkLen - (l - 1) * hLen .
97 * Here, CEIL (x) is the "ceiling" function, i.e. the smallest
98 * integer greater than, or equal to, x.
101 l = ((dkLen - 1) / hLen) + 1;
102 r = dkLen - (l - 1) * hLen;
105 * 3. For each block of the derived key apply the function F defined
106 * below to the password P, the salt S, the iteration count c, and
107 * the block index to compute the block:
109 * T_1 = F (P, S, c, 1) ,
110 * T_2 = F (P, S, c, 2) ,
112 * T_l = F (P, S, c, l) ,
114 * where the function F is defined as the exclusive-or sum of the
115 * first c iterates of the underlying pseudorandom function PRF
116 * applied to the password P and the concatenation of the salt S
117 * and the block index i:
119 * F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
123 * U_1 = PRF (P, S || INT (i)) ,
124 * U_2 = PRF (P, U_1) ,
126 * U_c = PRF (P, U_{c-1}) .
128 * Here, INT (i) is a four-octet encoding of the integer i, most
129 * significant octet first.
131 * 4. Concatenate the blocks and extract the first dkLen octets to
132 * produce a derived key DK:
134 * DK = T_1 || T_2 || ... || T_l<0..r-1>
136 * 5. Output the derived key DK.
138 * Note. The construction of the function F follows a "belt-and-
139 * suspenders" approach. The iterates U_i are computed recursively to
140 * remove a degree of parallelism from an opponent; they are exclusive-
141 * ored together to reduce concerns about the recursion degenerating
142 * into a small set of values.
146 tmp = malloc (tmplen);
148 return GC_MALLOC_ERROR;
150 memcpy (tmp, S, Slen);
152 for (i = 1; i <= l; i++)
156 for (u = 1; u <= c; u++)
160 tmp[Slen + 0] = (i & 0xff000000) >> 24;
161 tmp[Slen + 1] = (i & 0x00ff0000) >> 16;
162 tmp[Slen + 2] = (i & 0x0000ff00) >> 8;
163 tmp[Slen + 3] = (i & 0x000000ff) >> 0;
165 rc = gc_hmac_sha1 (P, Plen, tmp, tmplen, U);
168 rc = gc_hmac_sha1 (P, Plen, U, hLen, U);
176 for (k = 0; k < hLen; k++)
180 memcpy (DK + (i - 1) * hLen, T, i == l ? r : hLen);