From f5cd3561ba9363e6bcc58fcb6b1e94930f81967d Mon Sep 17 00:00:00 2001 From: Ben Laurie Date: Mon, 28 Jan 2013 17:30:38 +0000 Subject: [PATCH] Add and use a constant-time memcmp. This change adds CRYPTO_memcmp, which compares two vectors of bytes in an amount of time that's independent of their contents. It also changes several MAC compares in the code to use this over the standard memcmp, which may leak information about the size of a matching prefix. (cherry picked from commit 2ee798880a246d648ecddadc5b91367bee4a5d98) --- crypto/cryptlib.c | 13 +++++++++++++ crypto/crypto.h | 7 +++++++ crypto/rsa/rsa_oaep.c | 2 +- ssl/d1_pkt.c | 2 +- ssl/s2_clnt.c | 2 +- ssl/s2_pkt.c | 3 +-- ssl/s3_both.c | 2 +- ssl/s3_pkt.c | 2 +- ssl/t1_lib.c | 2 +- 9 files changed, 27 insertions(+), 8 deletions(-) diff --git a/crypto/cryptlib.c b/crypto/cryptlib.c index a7cb4202e..304c6b706 100644 --- a/crypto/cryptlib.c +++ b/crypto/cryptlib.c @@ -925,3 +925,16 @@ void OpenSSLDie(const char *file,int line,const char *assertion) } void *OPENSSL_stderr(void) { return stderr; } + +int CRYPTO_memcmp(const void *in_a, const void *in_b, size_t len) + { + size_t i; + const unsigned char *a = in_a; + const unsigned char *b = in_b; + unsigned char x = 0; + + for (i = 0; i < len; i++) + x |= a[i] ^ b[i]; + + return x; + } diff --git a/crypto/crypto.h b/crypto/crypto.h index 61605769b..f92fc5182 100644 --- a/crypto/crypto.h +++ b/crypto/crypto.h @@ -574,6 +574,13 @@ void OPENSSL_init(void); #define fips_cipher_abort(alg) while(0) #endif +/* CRYPTO_memcmp returns zero iff the |len| bytes at |a| and |b| are equal. It + * takes an amount of time dependent on |len|, but independent of the contents + * of |a| and |b|. Unlike memcmp, it cannot be used to put elements into a + * defined order as the return value when a != b is undefined, other than to be + * non-zero. */ +int CRYPTO_memcmp(const void *a, const void *b, size_t len); + /* BEGIN ERROR CODES */ /* The following lines are auto generated by the script mkerr.pl. Any changes * made after this point may be overwritten when the script is next run. diff --git a/crypto/rsa/rsa_oaep.c b/crypto/rsa/rsa_oaep.c index 553d212eb..af4d24a56 100644 --- a/crypto/rsa/rsa_oaep.c +++ b/crypto/rsa/rsa_oaep.c @@ -149,7 +149,7 @@ int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) return -1; - if (memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) + if (CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) goto decoding_err; else { diff --git a/ssl/d1_pkt.c b/ssl/d1_pkt.c index 987af6083..5e2c56c98 100644 --- a/ssl/d1_pkt.c +++ b/ssl/d1_pkt.c @@ -463,7 +463,7 @@ printf("\n"); else rr->length = 0; i=s->method->ssl3_enc->mac(s,md,0); - if (i < 0 || mac == NULL || memcmp(md, mac, mac_size) != 0) + if (i < 0 || mac == NULL || CRYPTO_memcmp(md,mac,mac_size) != 0) { decryption_failed_or_bad_record_mac = 1; } diff --git a/ssl/s2_clnt.c b/ssl/s2_clnt.c index 76b690ea1..03b6cf967 100644 --- a/ssl/s2_clnt.c +++ b/ssl/s2_clnt.c @@ -939,7 +939,7 @@ static int get_server_verify(SSL *s) s->msg_callback(0, s->version, 0, p, len, s, s->msg_callback_arg); /* SERVER-VERIFY */ p += 1; - if (memcmp(p,s->s2->challenge,s->s2->challenge_length) != 0) + if (CRYPTO_memcmp(p,s->s2->challenge,s->s2->challenge_length) != 0) { ssl2_return_error(s,SSL2_PE_UNDEFINED_ERROR); SSLerr(SSL_F_GET_SERVER_VERIFY,SSL_R_CHALLENGE_IS_DIFFERENT); diff --git a/ssl/s2_pkt.c b/ssl/s2_pkt.c index ac963b2d4..8bb6ab8ba 100644 --- a/ssl/s2_pkt.c +++ b/ssl/s2_pkt.c @@ -269,8 +269,7 @@ static int ssl2_read_internal(SSL *s, void *buf, int len, int peek) s->s2->ract_data_length-=mac_size; ssl2_mac(s,mac,0); s->s2->ract_data_length-=s->s2->padding; - if ( (memcmp(mac,s->s2->mac_data, - (unsigned int)mac_size) != 0) || + if ( (CRYPTO_memcmp(mac,s->s2->mac_data,mac_size) != 0) || (s->s2->rlength%EVP_CIPHER_CTX_block_size(s->enc_read_ctx) != 0)) { SSLerr(SSL_F_SSL2_READ_INTERNAL,SSL_R_BAD_MAC_DECODE); diff --git a/ssl/s3_both.c b/ssl/s3_both.c index 349531460..a537738f4 100644 --- a/ssl/s3_both.c +++ b/ssl/s3_both.c @@ -265,7 +265,7 @@ int ssl3_get_finished(SSL *s, int a, int b) goto f_err; } - if (memcmp(p, s->s3->tmp.peer_finish_md, i) != 0) + if (CRYPTO_memcmp(p, s->s3->tmp.peer_finish_md, i) != 0) { al=SSL_AD_DECRYPT_ERROR; SSLerr(SSL_F_SSL3_GET_FINISHED,SSL_R_DIGEST_CHECK_FAILED); diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c index 4299af1e7..9246ff295 100644 --- a/ssl/s3_pkt.c +++ b/ssl/s3_pkt.c @@ -465,7 +465,7 @@ printf("\n"); #endif } i=s->method->ssl3_enc->mac(s,md,0); - if (i < 0 || mac == NULL || memcmp(md, mac, (size_t)mac_size) != 0) + if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0) { decryption_failed_or_bad_record_mac = 1; } diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c index 512045f31..88570201a 100644 --- a/ssl/t1_lib.c +++ b/ssl/t1_lib.c @@ -3123,7 +3123,7 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick, int eticklen, HMAC_Update(&hctx, etick, eticklen); HMAC_Final(&hctx, tick_hmac, NULL); HMAC_CTX_cleanup(&hctx); - if (memcmp(tick_hmac, etick + eticklen, mlen)) + if (CRYPTO_memcmp(tick_hmac, etick + eticklen, mlen)) return 2; /* Attempt to decrypt session data */ /* Move p after IV to start of encrypted ticket, update length */