From 2ee798880a246d648ecddadc5b91367bee4a5d98 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. --- 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 a7cb4202e8..304c6b7062 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 61605769bb..f92fc5182d 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 553d212ebe..af4d24a56e 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 987af60835..5e2c56c983 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 76b690ea13..03b6cf9673 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 ac963b2d47..8bb6ab8baa 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 918da350e0..ead01c82a1 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 dca345865a..3e111406ba 100644 --- a/ssl/s3_pkt.c +++ b/ssl/s3_pkt.c @@ -463,7 +463,7 @@ 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 d8df062a80..27010dd50d 100644 --- a/ssl/t1_lib.c +++ b/ssl/t1_lib.c @@ -2226,7 +2226,7 @@ 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 */ -- 2.25.1