--- /dev/null
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ */
+#include "tomcrypt.h"
+
+/**
+ @file dsa_verify_hash.c
+ DSA implementation, verify a signature, Tom St Denis
+*/
+
+
+#ifdef LTC_MDSA
+
+/**
+ Verify a DSA signature
+ @param r DSA "r" parameter
+ @param s DSA "s" parameter
+ @param hash The hash that was signed
+ @param hashlen The length of the hash that was signed
+ @param stat [out] The result of the signature verification, 1==valid, 0==invalid
+ @param key The corresponding public DSA key
+ @return CRYPT_OK if successful (even if the signature is invalid)
+*/
+int dsa_verify_hash_raw( void *r, void *s,
+ const unsigned char *hash, unsigned long hashlen,
+ int *stat, dsa_key *key)
+{
+ void *w, *v, *u1, *u2;
+ int err;
+
+ LTC_ARGCHK(r != NULL);
+ LTC_ARGCHK(s != NULL);
+ LTC_ARGCHK(stat != NULL);
+ LTC_ARGCHK(key != NULL);
+
+ /* default to invalid signature */
+ *stat = 0;
+
+ /* init our variables */
+ if ((err = mp_init_multi(&w, &v, &u1, &u2, NULL)) != CRYPT_OK) {
+ return err;
+ }
+
+ /* neither r or s can be null or >q*/
+ if (mp_cmp_d(r, 0) != LTC_MP_GT || mp_cmp_d(s, 0) != LTC_MP_GT || mp_cmp(r, key->q) != LTC_MP_LT || mp_cmp(s, key->q) != LTC_MP_LT) {
+ err = CRYPT_INVALID_PACKET;
+ goto error;
+ }
+
+ /* FIPS 186-4 4.7: use leftmost min(bitlen(q), bitlen(hash)) bits of 'hash' */
+ hashlen = MIN(hashlen, (unsigned long)(key->qord));
+
+ /* w = 1/s mod q */
+ if ((err = mp_invmod(s, key->q, w)) != CRYPT_OK) { goto error; }
+
+ /* u1 = m * w mod q */
+ if ((err = mp_read_unsigned_bin(u1, (unsigned char *)hash, hashlen)) != CRYPT_OK) { goto error; }
+ if ((err = mp_mulmod(u1, w, key->q, u1)) != CRYPT_OK) { goto error; }
+
+ /* u2 = r*w mod q */
+ if ((err = mp_mulmod(r, w, key->q, u2)) != CRYPT_OK) { goto error; }
+
+ /* v = g^u1 * y^u2 mod p mod q */
+ if ((err = mp_exptmod(key->g, u1, key->p, u1)) != CRYPT_OK) { goto error; }
+ if ((err = mp_exptmod(key->y, u2, key->p, u2)) != CRYPT_OK) { goto error; }
+ if ((err = mp_mulmod(u1, u2, key->p, v)) != CRYPT_OK) { goto error; }
+ if ((err = mp_mod(v, key->q, v)) != CRYPT_OK) { goto error; }
+
+ /* if r = v then we're set */
+ if (mp_cmp(r, v) == LTC_MP_EQ) {
+ *stat = 1;
+ }
+
+ err = CRYPT_OK;
+error:
+ mp_clear_multi(w, v, u1, u2, NULL);
+ return err;
+}
+
+/**
+ Verify a DSA signature
+ @param sig The signature
+ @param siglen The length of the signature (octets)
+ @param hash The hash that was signed
+ @param hashlen The length of the hash that was signed
+ @param stat [out] The result of the signature verification, 1==valid, 0==invalid
+ @param key The corresponding public DSA key
+ @return CRYPT_OK if successful (even if the signature is invalid)
+*/
+int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
+ const unsigned char *hash, unsigned long hashlen,
+ int *stat, dsa_key *key)
+{
+ int err;
+ void *r, *s;
+ ltc_asn1_list sig_seq[2];
+ unsigned long reallen = 0;
+
+ LTC_ARGCHK(stat != NULL);
+ *stat = 0; /* must be set before the first return */
+
+ if ((err = mp_init_multi(&r, &s, NULL)) != CRYPT_OK) {
+ return err;
+ }
+
+ LTC_SET_ASN1(sig_seq, 0, LTC_ASN1_INTEGER, r, 1UL);
+ LTC_SET_ASN1(sig_seq, 1, LTC_ASN1_INTEGER, s, 1UL);
+
+ err = der_decode_sequence(sig, siglen, sig_seq, 2);
+ if (err != CRYPT_OK) {
+ goto LBL_ERR;
+ }
+
+ err = der_length_sequence(sig_seq, 2, &reallen);
+ if (err != CRYPT_OK || reallen != siglen) {
+ goto LBL_ERR;
+ }
+
+ /* do the op */
+ err = dsa_verify_hash_raw(r, s, hash, hashlen, stat, key);
+
+LBL_ERR:
+ mp_clear_multi(r, s, NULL);
+ return err;
+}
+
+#endif
+
+
+/* ref: $Format:%D$ */
+/* git commit: $Format:%H$ */
+/* commit time: $Format:%ai$ */