diff options
author | Ben Laurie <ben@links.org> | 2013-01-28 17:31:49 +0000 |
---|---|---|
committer | Dr. Stephen Henson <steve@openssl.org> | 2013-02-05 16:46:16 +0000 |
commit | e5420be6cd09af2550b128575a675490cfba0483 (patch) | |
tree | 9644929986afe97f94d37c02b2d77d7fad1335b4 /ssl/s3_enc.c | |
parent | 9c00a950604aca819cee977f1dcb4b45f2af3aa6 (diff) |
Make CBC decoding constant time.
This patch makes the decoding of SSLv3 and TLS CBC records constant
time. Without this, a timing side-channel can be used to build a padding
oracle and mount Vaudenay's attack.
This patch also disables the stitched AESNI+SHA mode pending a similar
fix to that code.
In order to be easy to backport, this change is implemented in ssl/,
rather than as a generic AEAD mode. In the future this should be changed
around so that HMAC isn't in ssl/, but crypto/ as FIPS expects.
(cherry picked from commit e130841bccfc0bb9da254dc84e23bc6a1c78a64e)
Conflicts:
crypto/evp/c_allc.c
ssl/ssl_algs.c
ssl/ssl_locl.h
ssl/t1_enc.c
Diffstat (limited to 'ssl/s3_enc.c')
-rw-r--r-- | ssl/s3_enc.c | 108 |
1 files changed, 69 insertions, 39 deletions
diff --git a/ssl/s3_enc.c b/ssl/s3_enc.c index b14597076d..de5354aefd 100644 --- a/ssl/s3_enc.c +++ b/ssl/s3_enc.c @@ -470,7 +470,7 @@ int ssl3_enc(SSL *s, int send) SSL3_RECORD *rec; EVP_CIPHER_CTX *ds; unsigned long l; - int bs,i; + int bs,i,mac_size=0; const EVP_CIPHER *enc; if (send) @@ -531,22 +531,12 @@ int ssl3_enc(SSL *s, int send) EVP_Cipher(ds,rec->data,rec->input,l); + rec->orig_len = rec->length; + + if (EVP_MD_CTX_md(s->read_hash) != NULL) + mac_size = EVP_MD_CTX_size(s->read_hash); if ((bs != 1) && !send) - { - i=rec->data[l-1]+1; - /* SSL 3.0 bounds the number of padding bytes by the block size; - * padding bytes (except the last one) are arbitrary */ - if (i > bs) - { - /* Incorrect padding. SSLerr() and ssl3_alert are done - * by caller: we don't want to reveal whether this is - * a decryption error or a MAC verification failure - * (see http://www.openssl.org/~bodo/tls-cbc.txt) */ - return -1; - } - /* now i <= bs <= rec->length */ - rec->length-=i; - } + return ssl3_cbc_remove_padding(s, rec, bs, mac_size); } return(1); } @@ -704,7 +694,7 @@ int n_ssl3_mac(SSL *ssl, unsigned char *md, int send) EVP_MD_CTX md_ctx; const EVP_MD_CTX *hash; unsigned char *p,rec_char; - unsigned int md_size; + size_t md_size; int npad; int t; @@ -729,28 +719,68 @@ int n_ssl3_mac(SSL *ssl, unsigned char *md, int send) md_size=t; npad=(48/md_size)*md_size; - /* Chop the digest off the end :-) */ - EVP_MD_CTX_init(&md_ctx); - - EVP_MD_CTX_copy_ex( &md_ctx,hash); - EVP_DigestUpdate(&md_ctx,mac_sec,md_size); - EVP_DigestUpdate(&md_ctx,ssl3_pad_1,npad); - EVP_DigestUpdate(&md_ctx,seq,8); - rec_char=rec->type; - EVP_DigestUpdate(&md_ctx,&rec_char,1); - p=md; - s2n(rec->length,p); - EVP_DigestUpdate(&md_ctx,md,2); - EVP_DigestUpdate(&md_ctx,rec->input,rec->length); - EVP_DigestFinal_ex( &md_ctx,md,NULL); - - EVP_MD_CTX_copy_ex( &md_ctx,hash); - EVP_DigestUpdate(&md_ctx,mac_sec,md_size); - EVP_DigestUpdate(&md_ctx,ssl3_pad_2,npad); - EVP_DigestUpdate(&md_ctx,md,md_size); - EVP_DigestFinal_ex( &md_ctx,md,&md_size); - - EVP_MD_CTX_cleanup(&md_ctx); + if (!send && + EVP_CIPHER_CTX_mode(ssl->enc_read_ctx) == EVP_CIPH_CBC_MODE && + ssl3_cbc_record_digest_supported(hash)) + { + /* This is a CBC-encrypted record. We must avoid leaking any + * timing-side channel information about how many blocks of + * data we are hashing because that gives an attacker a + * timing-oracle. */ + + /* npad is, at most, 48 bytes and that's with MD5: + * 16 + 48 + 8 (sequence bytes) + 1 + 2 = 75. + * + * With SHA-1 (the largest hash speced for SSLv3) the hash size + * goes up 4, but npad goes down by 8, resulting in a smaller + * total size. */ + unsigned char header[75]; + unsigned j = 0; + memcpy(header+j, mac_sec, md_size); + j += md_size; + memcpy(header+j, ssl3_pad_1, npad); + j += npad; + memcpy(header+j, seq, 8); + j += 8; + header[j++] = rec->type; + header[j++] = rec->length >> 8; + header[j++] = rec->length & 0xff; + + ssl3_cbc_digest_record( + hash, + md, &md_size, + header, rec->input, + rec->length + md_size, rec->orig_len, + mac_sec, md_size, + 1 /* is SSLv3 */); + } + else + { + unsigned int md_size_u; + /* Chop the digest off the end :-) */ + EVP_MD_CTX_init(&md_ctx); + + EVP_MD_CTX_copy_ex( &md_ctx,hash); + EVP_DigestUpdate(&md_ctx,mac_sec,md_size); + EVP_DigestUpdate(&md_ctx,ssl3_pad_1,npad); + EVP_DigestUpdate(&md_ctx,seq,8); + rec_char=rec->type; + EVP_DigestUpdate(&md_ctx,&rec_char,1); + p=md; + s2n(rec->length,p); + EVP_DigestUpdate(&md_ctx,md,2); + EVP_DigestUpdate(&md_ctx,rec->input,rec->length); + EVP_DigestFinal_ex( &md_ctx,md,NULL); + + EVP_MD_CTX_copy_ex( &md_ctx,hash); + EVP_DigestUpdate(&md_ctx,mac_sec,md_size); + EVP_DigestUpdate(&md_ctx,ssl3_pad_2,npad); + EVP_DigestUpdate(&md_ctx,md,md_size); + EVP_DigestFinal_ex( &md_ctx,md,&md_size_u); + md_size = md_size_u; + + EVP_MD_CTX_cleanup(&md_ctx); + } ssl3_record_sequence_update(seq); return(md_size); |