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178 lines
5.2 KiB
178 lines
5.2 KiB
From 6450224f3e3c78fdfa37eadbe6ada8301279f6c1 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
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Date: Mon, 20 Jun 2016 20:04:56 +0200
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Subject: Use mpz_powm_sec.
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Subject: Check for invalid keys, with even p, in dsa_sign.
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Subject: Reject invalid keys, with even moduli, in rsa_compute_root_tr.
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Subject: Reject invalid RSA keys with even modulo.
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diff --git a/bignum.h b/bignum.h
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index 24158e0..0d30534 100644
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--- a/bignum.h
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+++ b/bignum.h
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@@ -53,6 +53,8 @@
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# define mpz_combit mpz_combit
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# define mpz_import mpz_import
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# define mpz_export mpz_export
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+/* Side-channel silent powm not available in mini-gmp. */
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+# define mpz_powm_sec mpz_powm
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#else
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# include <gmp.h>
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#endif
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diff --git a/configure.ac b/configure.ac
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index e1ee64c..1e88477 100644
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--- a/configure.ac
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+++ b/configure.ac
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@@ -236,9 +236,9 @@ fi
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# Checks for libraries
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if test "x$enable_public_key" = "xyes" ; then
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if test "x$enable_mini_gmp" = "xno" ; then
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- AC_CHECK_LIB(gmp, __gmpz_getlimbn,,
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+ AC_CHECK_LIB(gmp, __gmpz_powm_sec,,
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[AC_MSG_WARN(
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- [GNU MP not found, or not 3.1 or up, see http://gmplib.org/.
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+ [GNU MP not found, or too old. GMP-5.0 or later is needed, see http://gmplib.org/.
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Support for public key algorithms will be unavailable.])]
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enable_public_key=no)
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diff --git a/dsa-sign.c b/dsa-sign.c
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index 62c7d4a..b713743 100644
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--- a/dsa-sign.c
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+++ b/dsa-sign.c
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@@ -56,6 +56,11 @@ dsa_sign(const struct dsa_params *params,
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mpz_t tmp;
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int res;
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+ /* Check that p is odd, so that invalid keys don't result in a crash
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+ inside mpz_powm_sec. */
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+ if (mpz_even_p (params->p))
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+ return 0;
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+
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/* Select k, 0<k<q, randomly */
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mpz_init_set(tmp, params->q);
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mpz_sub_ui(tmp, tmp, 1);
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@@ -65,7 +70,7 @@ dsa_sign(const struct dsa_params *params,
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mpz_add_ui(k, k, 1);
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/* Compute r = (g^k (mod p)) (mod q) */
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- mpz_powm(tmp, params->g, k, params->p);
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+ mpz_powm_sec(tmp, params->g, k, params->p);
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mpz_fdiv_r(signature->r, tmp, params->q);
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/* Compute hash */
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diff --git a/rsa-blind.c b/rsa-blind.c
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index 7662f50..16b03d7 100644
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--- a/rsa-blind.c
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+++ b/rsa-blind.c
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@@ -61,7 +61,7 @@ _rsa_blind (const struct rsa_public_key *pub,
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while (!mpz_invert (ri, r, pub->n));
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/* c = c*(r^e) mod n */
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- mpz_powm(r, r, pub->e, pub->n);
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+ mpz_powm_sec(r, r, pub->e, pub->n);
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mpz_mul(c, c, r);
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mpz_fdiv_r(c, c, pub->n);
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diff --git a/rsa-sign-tr.c b/rsa-sign-tr.c
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index 3d80ed4..8542cae 100644
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--- a/rsa-sign-tr.c
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+++ b/rsa-sign-tr.c
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@@ -60,7 +60,7 @@ rsa_blind (const struct rsa_public_key *pub,
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while (!mpz_invert (ri, r, pub->n));
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/* c = c*(r^e) mod n */
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- mpz_powm(r, r, pub->e, pub->n);
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+ mpz_powm_sec(r, r, pub->e, pub->n);
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mpz_mul(c, m, r);
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mpz_fdiv_r(c, c, pub->n);
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@@ -88,6 +88,14 @@ rsa_compute_root_tr(const struct rsa_public_key *pub,
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int res;
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mpz_t t, mb, xb, ri;
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+ /* mpz_powm_sec handles only odd moduli. If p, q or n is even, the
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+ key is invalid and rejected by rsa_private_key_prepare. However,
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+ some applications, notably gnutls, don't use this function, and
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+ we don't want an invalid key to lead to a crash down inside
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+ mpz_powm_sec. So do an additional check here. */
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+ if (mpz_even_p (pub->n) || mpz_even_p (key->p) || mpz_even_p (key->q))
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+ return 0;
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+
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mpz_init (mb);
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mpz_init (xb);
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mpz_init (ri);
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@@ -97,7 +105,7 @@ rsa_compute_root_tr(const struct rsa_public_key *pub,
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rsa_compute_root (key, xb, mb);
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- mpz_powm(t, xb, pub->e, pub->n);
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+ mpz_powm_sec(t, xb, pub->e, pub->n);
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res = (mpz_cmp(mb, t) == 0);
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if (res)
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diff --git a/rsa-sign.c b/rsa-sign.c
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index eba7388..4832352 100644
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--- a/rsa-sign.c
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+++ b/rsa-sign.c
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@@ -96,11 +96,11 @@ rsa_compute_root(const struct rsa_private_key *key,
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/* Compute xq = m^d % q = (m%q)^b % q */
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mpz_fdiv_r(xq, m, key->q);
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- mpz_powm(xq, xq, key->b, key->q);
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+ mpz_powm_sec(xq, xq, key->b, key->q);
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/* Compute xp = m^d % p = (m%p)^a % p */
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mpz_fdiv_r(xp, m, key->p);
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- mpz_powm(xp, xp, key->a, key->p);
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+ mpz_powm_sec(xp, xp, key->a, key->p);
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/* Set xp' = (xp - xq) c % p. */
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mpz_sub(xp, xp, xq);
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diff --git a/rsa.c b/rsa.c
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index 19d93de..f594140 100644
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--- a/rsa.c
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+++ b/rsa.c
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@@ -58,13 +58,18 @@ rsa_public_key_clear(struct rsa_public_key *key)
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}
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/* Computes the size, in octets, of a the modulo. Returns 0 if the
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- * modulo is too small to be useful. */
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-
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+ * modulo is too small to be useful, or otherwise appears invalid. */
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size_t
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_rsa_check_size(mpz_t n)
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{
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/* Round upwards */
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- size_t size = (mpz_sizeinbase(n, 2) + 7) / 8;
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+ size_t size;
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+
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+ /* Even moduli are invalid, and not supported by mpz_powm_sec. */
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+ if (mpz_even_p (n))
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+ return 0;
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+
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+ size = (mpz_sizeinbase(n, 2) + 7) / 8;
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if (size < RSA_MINIMUM_N_OCTETS)
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return 0;
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diff --git a/testsuite/rsa-test.c b/testsuite/rsa-test.c
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index e9b1c03..a429664 100644
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--- a/testsuite/rsa-test.c
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+++ b/testsuite/rsa-test.c
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@@ -57,6 +57,13 @@ test_main(void)
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test_rsa_sha512(&pub, &key, expected);
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+ /* Test detection of invalid keys with even modulo */
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+ mpz_clrbit (pub.n, 0);
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+ ASSERT (!rsa_public_key_prepare (&pub));
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+
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+ mpz_clrbit (key.p, 0);
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+ ASSERT (!rsa_private_key_prepare (&key));
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+
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/* 777-bit key, generated by
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*
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* lsh-keygen -a rsa -l 777 -f advanced-hex
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--
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2.7.3
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