osfmk/corecrypto/cchmac/src/cchmac_init.c

   1 /*
   2  *  cchmac_init.c
   3  *  corecrypto
   4  *
   5  *  Created by Michael Brouwer on 12/7/10.
   6  *  Copyright 2010,2011 Apple Inc. All rights reserved.
   7  *
   8  */
   9
  10 #include <corecrypto/cchmac.h>
  11 #include <corecrypto/ccn.h>
  12 #include <pexpert/pexpert.h>
  13
  14 /* The HMAC_<DIG> transform looks like:
  15    <DIG> (K XOR opad || <DIG> (K XOR ipad || text))
  16    Where K is a n byte key
  17    ipad is the byte 0x36 repeated 64 times.
  18    opad is the byte 0x5c repeated 64 times.
  19    text is the data being protected.
  20  */
  21 void cchmac_init(const struct ccdigest_info *di, cchmac_ctx_t hc,
  22                  unsigned long key_len, const void *key_data) {
  23     const unsigned char *key = key_data;
  24
  25     /* Set cchmac_data(di, hc) to key ^ opad. */
  26     unsigned long byte = 0;
  27         if (key_len <= di->block_size) {
  28         for (;byte < key_len; ++byte) {
  29             cchmac_data(di, hc)[byte] = key[byte] ^ 0x5c;
  30         }
  31     } else {
  32         /* Key is longer than di->block size, reset it to key=digest(key) */
  33         ccdigest_init(di, cchmac_digest_ctx(di, hc));
  34         ccdigest_update(di, cchmac_digest_ctx(di, hc), key_len, key);
  35         ccdigest_final(di, cchmac_digest_ctx(di, hc), cchmac_data(di, hc));
  36         key_len = di->output_size;
  37         for (;byte < key_len; ++byte) {
  38             cchmac_data(di, hc)[byte] ^= 0x5c;
  39         }
  40     }
  41     /* Fill remainder of cchmac_data(di, hc) with opad. */
  42         if (key_len < di->block_size) {
  43                 CC_MEMSET(cchmac_data(di, hc) + key_len, 0x5c, di->block_size - key_len);
  44         }
  45
  46     /* Set cchmac_ostate32(di, hc) to the state of the first round of the
  47        outer digest. */
  48     ccdigest_copy_state(di, cchmac_ostate32(di, hc), di->initial_state);
  49     di->compress(cchmac_ostate(di, hc), 1, cchmac_data(di, hc));
  50
  51     /* Set cchmac_data(di, hc) to key ^ ipad. */
  52     for (byte = 0; byte < di->block_size; ++byte) {
  53         cchmac_data(di, hc)[byte] ^= (0x5c ^ 0x36);
  54     }
  55     ccdigest_copy_state(di, cchmac_istate32(di, hc), di->initial_state);
  56     di->compress(cchmac_istate(di, hc), 1, cchmac_data(di, hc));
  57     cchmac_num(di, hc) = 0;
  58     cchmac_nbits(di, hc) = di->block_size * 8;
  59 }