void hmac_sha256_prepare(const uint8_t *key, const uint32_t keylen,
uint32_t *opad_digest, uint32_t *ipad_digest) {
static CONFIDENTIAL uint32_t key_pad[SHA256_BLOCK_LENGTH / sizeof(uint32_t)];
memzero(key_pad, sizeof(key_pad));
if (keylen > SHA256_BLOCK_LENGTH) {
static CONFIDENTIAL SHA256_CTX context;
sha256_Init(&context);
sha256_Update(&context, key, keylen);
sha256_Final(&context, (uint8_t *)key_pad);
} else {
memcpy(key_pad, key, keylen);
}
/* compute o_key_pad and its digest */
for (int i = 0; i < SHA256_BLOCK_LENGTH / (int)sizeof(uint32_t); i++) {
uint32_t data;
#if BYTE_ORDER == LITTLE_ENDIAN
REVERSE32(key_pad[i], data);
#else
data = key_pad[i];
#endif
key_pad[i] = data ^ 0x5c5c5c5c;
}
sha256_Transform(sha256_initial_hash_value, key_pad, opad_digest);
/* convert o_key_pad to i_key_pad and compute its digest */
for (int i = 0; i < SHA256_BLOCK_LENGTH / (int)sizeof(uint32_t); i++) {
key_pad[i] = key_pad[i] ^ 0x5c5c5c5c ^ 0x36363636;
}
sha256_Transform(sha256_initial_hash_value, key_pad, ipad_digest);
memzero(key_pad, sizeof(key_pad));
}
void pbkdf2_hmac_sha256_Update(PBKDF2_HMAC_SHA256_CTX *pctx, uint32_t iterations)
{
for (uint32_t i = pctx->first; i < iterations; i++) {
sha256_Transform(pctx->idig, pctx->g, pctx->g);
sha256_Transform(pctx->odig, pctx->g, pctx->g);
for (uint32_t j = 0; j < SHA256_DIGEST_LENGTH/sizeof(uint32_t); j++) {
pctx->f[j] ^= pctx->g[j];
}
}
pctx->first = 0;
}
void pbkdf2_hmac_sha256_Init(PBKDF2_HMAC_SHA256_CTX *pctx, const uint8_t *pass, int passlen, const uint8_t *salt, int saltlen)
{
SHA256_CTX ctx;
uint32_t blocknr = 1;
#if BYTE_ORDER == LITTLE_ENDIAN
REVERSE32(blocknr, blocknr);
#endif
hmac_sha256_prepare(pass, passlen, pctx->odig, pctx->idig);
memset(pctx->g, 0, sizeof(pctx->g));
pctx->g[8] = 0x80000000;
pctx->g[15] = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH) * 8;
memcpy (ctx.state, pctx->idig, sizeof(pctx->idig));
ctx.bitcount = SHA256_BLOCK_LENGTH * 8;
sha256_Update(&ctx, salt, saltlen);
sha256_Update(&ctx, (uint8_t*)&blocknr, sizeof(blocknr));
sha256_Final(&ctx, (uint8_t*)pctx->g);
#if BYTE_ORDER == LITTLE_ENDIAN
for (uint32_t k = 0; k < SHA256_DIGEST_LENGTH / sizeof(uint32_t); k++) {
REVERSE32(pctx->g[k], pctx->g[k]);
}
#endif
sha256_Transform(pctx->odig, pctx->g, pctx->g);
memcpy(pctx->f, pctx->g, SHA256_DIGEST_LENGTH);
pctx->first = 1;
}
