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From db4e9976cc31b314aafad6626b2894e86ee44d60 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Thu, 8 Aug 2019 17:42:02 +0900
Subject: [PATCH] dsa,ecdsa: Fix use of nonce, use larger one.
Upstream-Status: Backport [https://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git;a=commit;h=db4e9976cc3]
CVE: CVE-2019-13627
Signed-off-by: Trevor Gamblin <trevor.gamblin@windriver.com>
* cipher/dsa-common.c (_gcry_dsa_modify_k): New.
* cipher/pubkey-internal.h (_gcry_dsa_modify_k): New.
* cipher/dsa.c (sign): Use _gcry_dsa_modify_k.
* cipher/ecc-ecdsa.c (_gcry_ecc_ecdsa_sign): Likewise.
* cipher/ecc-gost.c (_gcry_ecc_gost_sign): Likewise.
--
Cherry-picked master commit of:
7c2943309d14407b51c8166c4dcecb56a3628567
CVE-id: CVE-2019-13627
GnuPG-bug-id: 4626
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
cipher/dsa-common.c | 24 ++++++++++++++++++++++++
cipher/dsa.c | 2 ++
cipher/ecc-ecdsa.c | 10 +---------
cipher/ecc-gost.c | 2 ++
cipher/pubkey-internal.h | 1 +
5 files changed, 30 insertions(+), 9 deletions(-)
diff --git a/cipher/dsa-common.c b/cipher/dsa-common.c
index 8c0a6843..fe49248d 100644
--- a/cipher/dsa-common.c
+++ b/cipher/dsa-common.c
@@ -29,6 +29,30 @@
#include "pubkey-internal.h"
+/*
+ * Modify K, so that computation time difference can be small,
+ * by making K large enough.
+ *
+ * Originally, (EC)DSA computation requires k where 0 < k < q. Here,
+ * we add q (the order), to keep k in a range: q < k < 2*q (or,
+ * addming more q, to keep k in a range: 2*q < k < 3*q), so that
+ * timing difference of the EC multiply (or exponentiation) operation
+ * can be small. The result of (EC)DSA computation is same.
+ */
+void
+_gcry_dsa_modify_k (gcry_mpi_t k, gcry_mpi_t q, int qbits)
+{
+ gcry_mpi_t k1 = mpi_new (qbits+2);
+
+ mpi_resize (k, (qbits+2+BITS_PER_MPI_LIMB-1) / BITS_PER_MPI_LIMB);
+ k->nlimbs = k->alloced;
+ mpi_add (k, k, q);
+ mpi_add (k1, k, q);
+ mpi_set_cond (k, k1, !mpi_test_bit (k, qbits));
+
+ mpi_free (k1);
+}
+
/*
* Generate a random secret exponent K less than Q.
* Note that ECDSA uses this code also to generate D.
diff --git a/cipher/dsa.c b/cipher/dsa.c
index 22d8d782..24a53528 100644
--- a/cipher/dsa.c
+++ b/cipher/dsa.c
@@ -635,6 +635,8 @@ sign (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t input, DSA_secret_key *skey,
k = _gcry_dsa_gen_k (skey->q, GCRY_STRONG_RANDOM);
}
+ _gcry_dsa_modify_k (k, skey->q, qbits);
+
/* r = (a^k mod p) mod q */
mpi_powm( r, skey->g, k, skey->p );
mpi_fdiv_r( r, r, skey->q );
diff --git a/cipher/ecc-ecdsa.c b/cipher/ecc-ecdsa.c
index 84a1cf84..97966c3a 100644
--- a/cipher/ecc-ecdsa.c
+++ b/cipher/ecc-ecdsa.c
@@ -114,15 +114,7 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
else
k = _gcry_dsa_gen_k (skey->E.n, GCRY_STRONG_RANDOM);
- /* Originally, ECDSA computation requires k where 0 < k < n.
- * Here, we add n (the order of curve), to keep k in a
- * range: n < k < 2*n, or, addming more n, keep k in a range:
- * 2*n < k < 3*n, so that timing difference of the EC
- * multiply operation can be small. The result is same.
- */
- mpi_add (k, k, skey->E.n);
- if (!mpi_test_bit (k, qbits))
- mpi_add (k, k, skey->E.n);
+ _gcry_dsa_modify_k (k, skey->E.n, qbits);
_gcry_mpi_ec_mul_point (&I, k, &skey->E.G, ctx);
if (_gcry_mpi_ec_get_affine (x, NULL, &I, ctx))
diff --git a/cipher/ecc-gost.c b/cipher/ecc-gost.c
index a34fa084..0362a6c7 100644
--- a/cipher/ecc-gost.c
+++ b/cipher/ecc-gost.c
@@ -94,6 +94,8 @@ _gcry_ecc_gost_sign (gcry_mpi_t input, ECC_secret_key *skey,
mpi_free (k);
k = _gcry_dsa_gen_k (skey->E.n, GCRY_STRONG_RANDOM);
+ _gcry_dsa_modify_k (k, skey->E.n, qbits);
+
_gcry_mpi_ec_mul_point (&I, k, &skey->E.G, ctx);
if (_gcry_mpi_ec_get_affine (x, NULL, &I, ctx))
{
diff --git a/cipher/pubkey-internal.h b/cipher/pubkey-internal.h
index b8167c77..d31e26f3 100644
--- a/cipher/pubkey-internal.h
+++ b/cipher/pubkey-internal.h
@@ -84,6 +84,7 @@ _gcry_rsa_pss_verify (gcry_mpi_t value, gcry_mpi_t encoded,
/*-- dsa-common.c --*/
+void _gcry_dsa_modify_k (gcry_mpi_t k, gcry_mpi_t q, int qbits);
gcry_mpi_t _gcry_dsa_gen_k (gcry_mpi_t q, int security_level);
gpg_err_code_t _gcry_dsa_gen_rfc6979_k (gcry_mpi_t *r_k,
gcry_mpi_t dsa_q, gcry_mpi_t dsa_x,
--
2.23.0
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