From d911097d7c93e4cfeab624b34d73fe51da158b69 Mon Sep 17 00:00:00 2001 From: Emilia Kasper Date: Mon, 14 Dec 2015 16:38:15 +0100 Subject: Fix a ** 0 mod 1 = 0 for real this time. Commit 2b0180c37fa6ffc48ee40caa831ca398b828e680 attempted to do this but only hit one of many BN_mod_exp codepaths. Fix remaining variants and add a test for each method. Thanks to Hanno Boeck for reporting this issue. Reviewed-by: Rich Salz Reviewed-by: Dr. Stephen Henson --- crypto/bn/bn_exp.c | 39 +++++++++++++++++++++++++++++++-------- 1 file changed, 31 insertions(+), 8 deletions(-) (limited to 'crypto/bn/bn_exp.c') diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c index 66feddcf96..e252593594 100644 --- a/crypto/bn/bn_exp.c +++ b/crypto/bn/bn_exp.c @@ -282,9 +282,14 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, } bits = BN_num_bits(p); - if (bits == 0) { - ret = BN_one(r); + /* x**0 mod 1 is still zero. */ + if (BN_is_one(m)) { + ret = 1; + BN_zero(r); + } else { + ret = BN_one(r); + } return ret; } @@ -418,7 +423,13 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, } bits = BN_num_bits(p); if (bits == 0) { - ret = BN_one(rr); + /* x**0 mod 1 is still zero. */ + if (BN_is_one(m)) { + ret = 1; + BN_zero(rr); + } else { + ret = BN_one(rr); + } return ret; } @@ -671,7 +682,13 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, bits = BN_num_bits(p); if (bits == 0) { - ret = BN_one(rr); + /* x**0 mod 1 is still zero. */ + if (BN_is_one(m)) { + ret = 1; + BN_zero(rr); + } else { + ret = BN_one(rr); + } return ret; } @@ -1180,8 +1197,9 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, if (BN_is_one(m)) { ret = 1; BN_zero(rr); - } else + } else { ret = BN_one(rr); + } return ret; } if (a == 0) { @@ -1295,9 +1313,14 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, } bits = BN_num_bits(p); - - if (bits == 0) { - ret = BN_one(r); + if (bits == 0) { + /* x**0 mod 1 is still zero. */ + if (BN_is_one(m)) { + ret = 1; + BN_zero(r); + } else { + ret = BN_one(r); + } return ret; } -- cgit v1.2.3