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89 lines
3.3 KiB
Diff
89 lines
3.3 KiB
Diff
From d42c477cc794163a3757956bbffca5cea000923c Mon Sep 17 00:00:00 2001
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From: Jouni Malinen <jouni@codeaurora.org>
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Date: Tue, 26 Feb 2019 11:43:03 +0200
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Subject: [PATCH 01/14] OpenSSL: Use constant time operations for private
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bignums
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This helps in reducing measurable timing differences in operations
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involving private information. BoringSSL has removed BN_FLG_CONSTTIME
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and expects specific constant time functions to be called instead, so a
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bit different approach is needed depending on which library is used.
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The main operation that needs protection against side channel attacks is
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BN_mod_exp() that depends on private keys (the public key validation
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step in crypto_dh_derive_secret() is an exception that can use the
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faster version since it does not depend on private keys).
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crypto_bignum_div() is currently used only in SAE FFC case with not
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safe-prime groups and only with values that do not depend on private
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keys, so it is not critical to protect it.
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crypto_bignum_inverse() is currently used only in SAE FFC PWE
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derivation. The additional protection here is targeting only OpenSSL.
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BoringSSL may need conversion to using BN_mod_inverse_blinded().
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This is related to CVE-2019-9494 and CVE-2019-9495.
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Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
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---
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src/crypto/crypto_openssl.c | 20 +++++++++++++++-----
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1 file changed, 15 insertions(+), 5 deletions(-)
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--- a/src/crypto/crypto_openssl.c
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+++ b/src/crypto/crypto_openssl.c
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@@ -549,7 +549,8 @@ int crypto_mod_exp(const u8 *base, size_
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bn_result == NULL)
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goto error;
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- if (BN_mod_exp(bn_result, bn_base, bn_exp, bn_modulus, ctx) != 1)
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+ if (BN_mod_exp_mont_consttime(bn_result, bn_base, bn_exp, bn_modulus,
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+ ctx, NULL) != 1)
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goto error;
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*result_len = BN_bn2bin(bn_result, result);
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@@ -1295,8 +1296,9 @@ int crypto_bignum_exptmod(const struct c
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bnctx = BN_CTX_new();
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if (bnctx == NULL)
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return -1;
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- res = BN_mod_exp((BIGNUM *) d, (const BIGNUM *) a, (const BIGNUM *) b,
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- (const BIGNUM *) c, bnctx);
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+ res = BN_mod_exp_mont_consttime((BIGNUM *) d, (const BIGNUM *) a,
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+ (const BIGNUM *) b, (const BIGNUM *) c,
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+ bnctx, NULL);
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BN_CTX_free(bnctx);
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return res ? 0 : -1;
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@@ -1315,6 +1317,11 @@ int crypto_bignum_inverse(const struct c
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bnctx = BN_CTX_new();
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if (bnctx == NULL)
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return -1;
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+#ifdef OPENSSL_IS_BORINGSSL
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+ /* TODO: use BN_mod_inverse_blinded() ? */
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+#else /* OPENSSL_IS_BORINGSSL */
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+ BN_set_flags((BIGNUM *) a, BN_FLG_CONSTTIME);
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+#endif /* OPENSSL_IS_BORINGSSL */
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res = BN_mod_inverse((BIGNUM *) c, (const BIGNUM *) a,
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(const BIGNUM *) b, bnctx);
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BN_CTX_free(bnctx);
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@@ -1348,6 +1355,9 @@ int crypto_bignum_div(const struct crypt
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bnctx = BN_CTX_new();
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if (bnctx == NULL)
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return -1;
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+#ifndef OPENSSL_IS_BORINGSSL
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+ BN_set_flags((BIGNUM *) a, BN_FLG_CONSTTIME);
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+#endif /* OPENSSL_IS_BORINGSSL */
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res = BN_div((BIGNUM *) c, NULL, (const BIGNUM *) a,
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(const BIGNUM *) b, bnctx);
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BN_CTX_free(bnctx);
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@@ -1439,8 +1449,8 @@ int crypto_bignum_legendre(const struct
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/* exp = (p-1) / 2 */
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!BN_sub(exp, (const BIGNUM *) p, BN_value_one()) ||
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!BN_rshift1(exp, exp) ||
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- !BN_mod_exp(tmp, (const BIGNUM *) a, exp, (const BIGNUM *) p,
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- bnctx))
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+ !BN_mod_exp_mont_consttime(tmp, (const BIGNUM *) a, exp,
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+ (const BIGNUM *) p, bnctx, NULL))
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goto fail;
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if (BN_is_word(tmp, 1))
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