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[NSS] Force a fixed length for DSA exponentiation.

master
Fedor 2020-06-10 21:12:46 +03:00
parent 853897d5ca
commit 905ba19715
1 changed files with 35 additions and 10 deletions
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45
security/nss/lib/freebl/dsa.c
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@ -313,13 +313,14 @@ DSA_NewKeyFromSeed(const PQGParams *params,
static SECStatus
dsa_SignDigest(DSAPrivateKey *key, SECItem *signature, const SECItem *digest,
const unsigned char *kb)
const unsigned char *kbytes)
{
mp_int p, q, g; /* PQG parameters */
mp_int x, k; /* private key & pseudo-random integer */
mp_int r, s; /* tuple (r, s) is signature) */
mp_int t; /* holding tmp values */
mp_int ar; /* holding blinding values */
mp_digit fuzz; /* blinding multiplier for q */
mp_err err = MP_OKAY;
SECStatus rv = SECSuccess;
unsigned int dsa_subprime_len, dsa_signature_len, offset;
@ -373,6 +374,7 @@ dsa_SignDigest(DSAPrivateKey *key, SECItem *signature, const SECItem *digest,
CHECK_MPI_OK(mp_init(&s));
CHECK_MPI_OK(mp_init(&t));
CHECK_MPI_OK(mp_init(&ar));
/*
** Convert stored PQG and private key into MPI integers.
*/
@ -380,14 +382,28 @@ dsa_SignDigest(DSAPrivateKey *key, SECItem *signature, const SECItem *digest,
SECITEM_TO_MPINT(key->params.subPrime, &q);
SECITEM_TO_MPINT(key->params.base, &g);
SECITEM_TO_MPINT(key->privateValue, &x);
OCTETS_TO_MPINT(kb, &k, dsa_subprime_len);
OCTETS_TO_MPINT(kbytes, &k, dsa_subprime_len);
/* k blinding create a single value that has the high bit set in
* the mp_digit*/
if (RNG_GenerateGlobalRandomBytes(&fuzz, sizeof(mp_digit)) != SECSuccess) {
PORT_SetError(SEC_ERROR_NEED_RANDOM);
rv = SECFailure;
goto cleanup;
}
fuzz |= 1ULL << ((sizeof(mp_digit) * PR_BITS_PER_BYTE - 1));
/*
** FIPS 186-1, Section 5, Step 1
**
** r = (g**k mod p) mod q
*/
CHECK_MPI_OK(mp_exptmod(&g, &k, &p, &r)); /* r = g**k mod p */
CHECK_MPI_OK(mp_mod(&r, &q, &r)); /* r = r mod q */
CHECK_MPI_OK(mp_mul_d(&q, fuzz, &t)); /* t = q*fuzz */
CHECK_MPI_OK(mp_add(&k, &t, &t)); /* t = k+q*fuzz */
/* length of t is now fixed, bits in k have been blinded */
CHECK_MPI_OK(mp_exptmod(&g, &t, &p, &r)); /* r = g**t mod p */
/* r is now g**(k+q*fuzz) == g**k mod p */
CHECK_MPI_OK(mp_mod(&r, &q, &r)); /* r = r mod q */
/*
** FIPS 186-1, Section 5, Step 2
**
@ -411,15 +427,24 @@ dsa_SignDigest(DSAPrivateKey *key, SECItem *signature, const SECItem *digest,
/* Using mp_invmod on k directly would leak bits from k. */
CHECK_MPI_OK(mp_mul(&k, &ar, &k)); /* k = k * ar */
CHECK_MPI_OK(mp_mulmod(&k, &t, &q, &k)); /* k = k * t mod q */
CHECK_MPI_OK(mp_invmod(&k, &q, &k)); /* k = k**-1 mod q */
/* k is now k*t*ar */
CHECK_MPI_OK(mp_invmod(&k, &q, &k)); /* k = k**-1 mod q */
/* k is now (k*t*ar)**-1 */
CHECK_MPI_OK(mp_mulmod(&k, &t, &q, &k)); /* k = k * t mod q */
SECITEM_TO_MPINT(localDigest, &s); /* s = HASH(M) */
/* k is now (k*ar)**-1 */
SECITEM_TO_MPINT(localDigest, &s); /* s = HASH(M) */
/* To avoid leaking secret bits here the addition is blinded. */
CHECK_MPI_OK(mp_mul(&x, &ar, &x)); /* x = x * ar */
CHECK_MPI_OK(mp_mulmod(&x, &r, &q, &x)); /* x = x * r mod q */
CHECK_MPI_OK(mp_mul(&x, &ar, &x)); /* x = x * ar */
/* x is now x*ar */
CHECK_MPI_OK(mp_mulmod(&x, &r, &q, &x)); /* x = x * r mod q */
/* x is now x*r*ar */
CHECK_MPI_OK(mp_mulmod(&s, &ar, &q, &t)); /* t = s * ar mod q */
CHECK_MPI_OK(mp_add(&t, &x, &s)); /* s = t + x */
CHECK_MPI_OK(mp_mulmod(&s, &k, &q, &s)); /* s = s * k mod q */
/* t is now hash(M)*ar */
CHECK_MPI_OK(mp_add(&t, &x, &s)); /* s = t + x */
/* s is now (HASH(M)+x*r)*ar */
CHECK_MPI_OK(mp_mulmod(&s, &k, &q, &s)); /* s = s * k mod q */
/* s is now (HASH(M)+x*r)*ar*(k*ar)**-1 = (k**-1)*(HASH(M)+x*r) */
/*
** verify r != 0 and s != 0
** mentioned as optional in FIPS 186-1.