--- /dev/null
+/* gc-pbkdf2-sha1.c --- Password-Based Key Derivation Function a'la PKCS#5
+ Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2, or (at your option)
+ any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software Foundation,
+ Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+/* Written by Simon Josefsson. The comments in this file are taken
+ from RFC 2898. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "gc.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+/*
+ * 5.2 PBKDF2
+ *
+ * PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
+ * example) to derive keys. The length of the derived key is essentially
+ * unbounded. (However, the maximum effective search space for the
+ * derived key may be limited by the structure of the underlying
+ * pseudorandom function. See Appendix B.1 for further discussion.)
+ * PBKDF2 is recommended for new applications.
+ *
+ * PBKDF2 (P, S, c, dkLen)
+ *
+ * Options: PRF underlying pseudorandom function (hLen
+ * denotes the length in octets of the
+ * pseudorandom function output)
+ *
+ * Input: P password, an octet string (ASCII or UTF-8)
+ * S salt, an octet string
+ * c iteration count, a positive integer
+ * dkLen intended length in octets of the derived
+ * key, a positive integer, at most
+ * (2^32 - 1) * hLen
+ *
+ * Output: DK derived key, a dkLen-octet string
+ */
+
+Gc_rc
+gc_pbkdf2_sha1 (const char *P, size_t Plen,
+ const char *S, size_t Slen,
+ unsigned int c,
+ char *DK, size_t dkLen)
+{
+ unsigned int hLen = 20;
+ char U[20];
+ char T[20];
+ unsigned int u;
+ unsigned int l;
+ unsigned int r;
+ unsigned int i;
+ unsigned int k;
+ int rc;
+
+ if (c == 0)
+ return GC_PKCS5_INVALID_ITERATION_COUNT;
+
+ if (dkLen == 0)
+ return GC_PKCS5_INVALID_DERIVED_KEY_LENGTH;
+
+ /*
+ *
+ * Steps:
+ *
+ * 1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
+ * stop.
+ */
+
+ if (dkLen > 4294967295U)
+ return GC_PKCS5_DERIVED_KEY_TOO_LONG;
+
+ /*
+ * 2. Let l be the number of hLen-octet blocks in the derived key,
+ * rounding up, and let r be the number of octets in the last
+ * block:
+ *
+ * l = CEIL (dkLen / hLen) ,
+ * r = dkLen - (l - 1) * hLen .
+ *
+ * Here, CEIL (x) is the "ceiling" function, i.e. the smallest
+ * integer greater than, or equal to, x.
+ */
+
+ l = dkLen / hLen;
+ if (dkLen % hLen)
+ l++;
+ r = dkLen - (l - 1) * hLen;
+
+ /*
+ * 3. For each block of the derived key apply the function F defined
+ * below to the password P, the salt S, the iteration count c, and
+ * the block index to compute the block:
+ *
+ * T_1 = F (P, S, c, 1) ,
+ * T_2 = F (P, S, c, 2) ,
+ * ...
+ * T_l = F (P, S, c, l) ,
+ *
+ * where the function F is defined as the exclusive-or sum of the
+ * first c iterates of the underlying pseudorandom function PRF
+ * applied to the password P and the concatenation of the salt S
+ * and the block index i:
+ *
+ * F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
+ *
+ * where
+ *
+ * U_1 = PRF (P, S || INT (i)) ,
+ * U_2 = PRF (P, U_1) ,
+ * ...
+ * U_c = PRF (P, U_{c-1}) .
+ *
+ * Here, INT (i) is a four-octet encoding of the integer i, most
+ * significant octet first.
+ *
+ * 4. Concatenate the blocks and extract the first dkLen octets to
+ * produce a derived key DK:
+ *
+ * DK = T_1 || T_2 || ... || T_l<0..r-1>
+ *
+ * 5. Output the derived key DK.
+ *
+ * Note. The construction of the function F follows a "belt-and-
+ * suspenders" approach. The iterates U_i are computed recursively to
+ * remove a degree of parallelism from an opponent; they are exclusive-
+ * ored together to reduce concerns about the recursion degenerating
+ * into a small set of values.
+ *
+ */
+
+ for (i = 1; i <= l; i++)
+ {
+ memset (T, 0, hLen);
+
+ for (u = 1; u <= c; u++)
+ {
+ if (u == 1)
+ {
+ char *tmp;
+ size_t tmplen = Slen + 4;
+
+ tmp = malloc (tmplen);
+ if (tmp == NULL)
+ return GC_MALLOC_ERROR;
+
+ memcpy (tmp, S, Slen);
+ tmp[Slen + 0] = (i & 0xff000000) >> 24;
+ tmp[Slen + 1] = (i & 0x00ff0000) >> 16;
+ tmp[Slen + 2] = (i & 0x0000ff00) >> 8;
+ tmp[Slen + 3] = (i & 0x000000ff) >> 0;
+
+ rc = gc_hmac_sha1 (P, Plen, tmp, tmplen, U);
+
+ free (tmp);
+ }
+ else
+ rc = gc_hmac_sha1 (P, Plen, U, hLen, U);
+
+ if (rc != GC_OK)
+ return rc;
+
+ for (k = 0; k < hLen; k++)
+ T[k] ^= U[k];
+ }
+
+ memcpy (DK + (i - 1) * hLen, T, i == l ? r : hLen);
+ }
+
+ return GC_OK;
+}
projects / gnulib.git / blobdiff