139 lines
5.5 KiB
Diff
139 lines
5.5 KiB
Diff
Fix CVE-2020-12399 (Timing attack on DSA signature generation: NSS has
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shown timing differences when performing DSA signatures, which was
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exploitable and could eventually leak private keys.)
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Copied from upstream:
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<https://hg.mozilla.org/projects/nss/rev/daa823a4a29bcef0fec33a379ec83857429aea2e>
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but with "nss/" inserted into the file name to patch.
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# HG changeset patch
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# User Robert Relyea <rrelyea@redhat.com>
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# Date 1589907685 0
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# Node ID daa823a4a29bcef0fec33a379ec83857429aea2e
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# Parent d2cfb4ccdf167e5ea06d2bb5bc39c50f789929c8
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Bug 1631576 - Force a fixed length for DSA exponentiation r=pereida,bbrumley
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Differential Revision: https://phabricator.services.mozilla.com/D72011
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diff --git a/nss/lib/freebl/dsa.c b/nss/lib/freebl/dsa.c
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--- a/nss/lib/freebl/dsa.c
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+++ b/nss/lib/freebl/dsa.c
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@@ -308,23 +308,24 @@ DSA_NewKeyFromSeed(const PQGParams *para
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SECItem seedItem;
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seedItem.data = (unsigned char *)seed;
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seedItem.len = PQG_GetLength(¶ms->subPrime);
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return dsa_NewKeyExtended(params, &seedItem, privKey);
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}
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static SECStatus
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dsa_SignDigest(DSAPrivateKey *key, SECItem *signature, const SECItem *digest,
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- const unsigned char *kb)
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+ const unsigned char *kbytes)
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{
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mp_int p, q, g; /* PQG parameters */
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mp_int x, k; /* private key & pseudo-random integer */
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mp_int r, s; /* tuple (r, s) is signature) */
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mp_int t; /* holding tmp values */
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mp_int ar; /* holding blinding values */
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+ mp_digit fuzz; /* blinding multiplier for q */
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mp_err err = MP_OKAY;
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SECStatus rv = SECSuccess;
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unsigned int dsa_subprime_len, dsa_signature_len, offset;
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SECItem localDigest;
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unsigned char localDigestData[DSA_MAX_SUBPRIME_LEN];
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SECItem t2 = { siBuffer, NULL, 0 };
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/* FIPS-compliance dictates that digest is a SHA hash. */
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@@ -368,31 +369,46 @@ dsa_SignDigest(DSAPrivateKey *key, SECIt
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CHECK_MPI_OK(mp_init(&q));
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CHECK_MPI_OK(mp_init(&g));
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CHECK_MPI_OK(mp_init(&x));
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CHECK_MPI_OK(mp_init(&k));
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CHECK_MPI_OK(mp_init(&r));
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CHECK_MPI_OK(mp_init(&s));
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CHECK_MPI_OK(mp_init(&t));
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CHECK_MPI_OK(mp_init(&ar));
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+
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/*
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** Convert stored PQG and private key into MPI integers.
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*/
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SECITEM_TO_MPINT(key->params.prime, &p);
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SECITEM_TO_MPINT(key->params.subPrime, &q);
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SECITEM_TO_MPINT(key->params.base, &g);
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SECITEM_TO_MPINT(key->privateValue, &x);
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- OCTETS_TO_MPINT(kb, &k, dsa_subprime_len);
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+ OCTETS_TO_MPINT(kbytes, &k, dsa_subprime_len);
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+
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+ /* k blinding create a single value that has the high bit set in
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+ * the mp_digit*/
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+ if (RNG_GenerateGlobalRandomBytes(&fuzz, sizeof(mp_digit)) != SECSuccess) {
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+ PORT_SetError(SEC_ERROR_NEED_RANDOM);
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+ rv = SECFailure;
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+ goto cleanup;
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+ }
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+ fuzz |= 1ULL << ((sizeof(mp_digit) * PR_BITS_PER_BYTE - 1));
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/*
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** FIPS 186-1, Section 5, Step 1
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**
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** r = (g**k mod p) mod q
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*/
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- CHECK_MPI_OK(mp_exptmod(&g, &k, &p, &r)); /* r = g**k mod p */
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- CHECK_MPI_OK(mp_mod(&r, &q, &r)); /* r = r mod q */
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+ CHECK_MPI_OK(mp_mul_d(&q, fuzz, &t)); /* t = q*fuzz */
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+ CHECK_MPI_OK(mp_add(&k, &t, &t)); /* t = k+q*fuzz */
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+ /* length of t is now fixed, bits in k have been blinded */
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+ CHECK_MPI_OK(mp_exptmod(&g, &t, &p, &r)); /* r = g**t mod p */
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+ /* r is now g**(k+q*fuzz) == g**k mod p */
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+ CHECK_MPI_OK(mp_mod(&r, &q, &r)); /* r = r mod q */
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+
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/*
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** FIPS 186-1, Section 5, Step 2
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**
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** s = (k**-1 * (HASH(M) + x*r)) mod q
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*/
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if (DSA_NewRandom(NULL, &key->params.subPrime, &t2) != SECSuccess) {
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PORT_SetError(SEC_ERROR_NEED_RANDOM);
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rv = SECFailure;
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@@ -406,25 +422,34 @@ dsa_SignDigest(DSAPrivateKey *key, SECIt
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goto cleanup;
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}
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SECITEM_TO_MPINT(t2, &ar); /* ar <-$ Zq */
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SECITEM_FreeItem(&t2, PR_FALSE);
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/* Using mp_invmod on k directly would leak bits from k. */
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CHECK_MPI_OK(mp_mul(&k, &ar, &k)); /* k = k * ar */
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CHECK_MPI_OK(mp_mulmod(&k, &t, &q, &k)); /* k = k * t mod q */
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- CHECK_MPI_OK(mp_invmod(&k, &q, &k)); /* k = k**-1 mod q */
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+ /* k is now k*t*ar */
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+ CHECK_MPI_OK(mp_invmod(&k, &q, &k)); /* k = k**-1 mod q */
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+ /* k is now (k*t*ar)**-1 */
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CHECK_MPI_OK(mp_mulmod(&k, &t, &q, &k)); /* k = k * t mod q */
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- SECITEM_TO_MPINT(localDigest, &s); /* s = HASH(M) */
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+ /* k is now (k*ar)**-1 */
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+ SECITEM_TO_MPINT(localDigest, &s); /* s = HASH(M) */
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/* To avoid leaking secret bits here the addition is blinded. */
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- CHECK_MPI_OK(mp_mul(&x, &ar, &x)); /* x = x * ar */
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- CHECK_MPI_OK(mp_mulmod(&x, &r, &q, &x)); /* x = x * r mod q */
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+ CHECK_MPI_OK(mp_mul(&x, &ar, &x)); /* x = x * ar */
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+ /* x is now x*ar */
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+ CHECK_MPI_OK(mp_mulmod(&x, &r, &q, &x)); /* x = x * r mod q */
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+ /* x is now x*r*ar */
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CHECK_MPI_OK(mp_mulmod(&s, &ar, &q, &t)); /* t = s * ar mod q */
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- CHECK_MPI_OK(mp_add(&t, &x, &s)); /* s = t + x */
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- CHECK_MPI_OK(mp_mulmod(&s, &k, &q, &s)); /* s = s * k mod q */
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+ /* t is now hash(M)*ar */
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+ CHECK_MPI_OK(mp_add(&t, &x, &s)); /* s = t + x */
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+ /* s is now (HASH(M)+x*r)*ar */
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+ CHECK_MPI_OK(mp_mulmod(&s, &k, &q, &s)); /* s = s * k mod q */
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+ /* s is now (HASH(M)+x*r)*ar*(k*ar)**-1 = (k**-1)*(HASH(M)+x*r) */
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+
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/*
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** verify r != 0 and s != 0
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** mentioned as optional in FIPS 186-1.
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*/
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if (mp_cmp_z(&r) == 0 || mp_cmp_z(&s) == 0) {
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PORT_SetError(SEC_ERROR_NEED_RANDOM);
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rv = SECFailure;
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goto cleanup;
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