From 89d1db9116738da5ed5de417c63da5e8be214b4d Mon Sep 17 00:00:00 2001 From: Dmitry Belyavskiy Date: Thu, 4 Apr 2019 18:45:36 +0300 Subject: [PATCH] Cofactor should be taken into account in VKO --- gost_ec_keyx.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/gost_ec_keyx.c b/gost_ec_keyx.c index 6efa3e8..cc94d67 100644 --- a/gost_ec_keyx.c +++ b/gost_ec_keyx.c @@ -24,7 +24,7 @@ static int VKO_compute_key(unsigned char *shared_key, const int vko_dgst_nid) { unsigned char *databuf = NULL; - BIGNUM *UKM = NULL, *p = NULL, *order = NULL, *X = NULL, *Y = NULL; + BIGNUM *UKM = NULL, *p = NULL, *order = NULL, *X = NULL, *Y = NULL, *cofactor = NULL; const BIGNUM *key = EC_KEY_get0_private_key(priv_key); EC_POINT *pnt = EC_POINT_new(EC_KEY_get0_group(priv_key)); BN_CTX *ctx = BN_CTX_new(); @@ -48,9 +48,12 @@ static int VKO_compute_key(unsigned char *shared_key, UKM = hashsum2bn(ukm, ukm_size); p = BN_CTX_get(ctx); order = BN_CTX_get(ctx); + cofactor = BN_CTX_get(ctx); X = BN_CTX_get(ctx); Y = BN_CTX_get(ctx); EC_GROUP_get_order(EC_KEY_get0_group(priv_key), order, ctx); + EC_GROUP_get_cofactor(EC_KEY_get0_group(priv_key), cofactor, ctx); + BN_mod_mul(UKM, UKM, cofactor, order, ctx); BN_mod_mul(p, key, UKM, order, ctx); if (!EC_POINT_mul(EC_KEY_get0_group(priv_key), pnt, NULL, pub_key, p, ctx)) { GOSTerr(GOST_F_VKO_COMPUTE_KEY, GOST_R_ERROR_POINT_MUL); -- 2.39.2