From 9010d1576e278a4274ad3f4aa15776c28f6ba965 Mon Sep 17 00:00:00 2001 From: NIIBE Yutaka Date: Wed, 13 Jun 2018 15:28:58 +0900 Subject: [PATCH] ecc: Add blinding for ECDSA. * cipher/ecc-ecdsa.c (_gcry_ecc_ecdsa_sign): Blind secret D with randomized nonce B. -- Reported-by: Keegan Ryan CVE-id: CVE-2018-0495 Upstream-Status: Backport [http://git.gnupg.org/cgi-bin/gitweb.cgi?p=libgcrypt.git;a=commit;h=9010d1576e278a4274ad3f4aa15776c28f6ba965] Signed-off-by: NIIBE Yutaka Signed-off-by: Jagadeesh Krishnanjanappa --- cipher/ecc-ecdsa.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/cipher/ecc-ecdsa.c b/cipher/ecc-ecdsa.c index 1484830b..140e8c09 100644 --- a/cipher/ecc-ecdsa.c +++ b/cipher/ecc-ecdsa.c @@ -50,6 +50,8 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey, const void *abuf; unsigned int abits, qbits; mpi_ec_t ctx; + gcry_mpi_t b; /* Random number needed for blinding. */ + gcry_mpi_t bi; /* multiplicative inverse of B. */ if (DBG_CIPHER) log_mpidump ("ecdsa sign hash ", input ); @@ -61,6 +63,15 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey, if (rc) return rc; + b = mpi_snew (qbits); + bi = mpi_snew (qbits); + do + { + _gcry_mpi_randomize (b, qbits, GCRY_WEAK_RANDOM); + mpi_mod (b, b, skey->E.n); + } + while (!mpi_invm (bi, b, skey->E.n)); + k = NULL; dr = mpi_alloc (0); sum = mpi_alloc (0); @@ -115,8 +126,11 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey, } while (!mpi_cmp_ui (r, 0)); - mpi_mulm (dr, skey->d, r, skey->E.n); /* dr = d*r mod n */ - mpi_addm (sum, hash, dr, skey->E.n); /* sum = hash + (d*r) mod n */ + mpi_mulm (dr, b, skey->d, skey->E.n); + mpi_mulm (dr, dr, r, skey->E.n); /* dr = d*r mod n (blinded with b) */ + mpi_mulm (sum, b, hash, skey->E.n); + mpi_addm (sum, sum, dr, skey->E.n); /* sum = hash + (d*r) mod n (blinded with b) */ + mpi_mulm (sum, bi, sum, skey->E.n); /* undo blinding by b^-1 */ mpi_invm (k_1, k, skey->E.n); /* k_1 = k^(-1) mod n */ mpi_mulm (s, k_1, sum, skey->E.n); /* s = k^(-1)*(hash+(d*r)) mod n */ } @@ -129,6 +143,8 @@ _gcry_ecc_ecdsa_sign (gcry_mpi_t input, ECC_secret_key *skey, } leave: + mpi_free (b); + mpi_free (bi); _gcry_mpi_ec_free (ctx); point_free (&I); mpi_free (x); -- 2.13.3