diff options
author | Ben Laurie <ben@links.org> | 2013-01-28 17:31:49 +0000 |
---|---|---|
committer | Ben Laurie <ben@links.org> | 2013-01-28 17:31:49 +0000 |
commit | e130841bccfc0bb9da254dc84e23bc6a1c78a64e (patch) | |
tree | 025095b97a98c1bfac9ad6eb32a3b4a23a5a1d81 /ssl/t1_enc.c | |
parent | 2ee798880a246d648ecddadc5b91367bee4a5d98 (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.
Diffstat (limited to 'ssl/t1_enc.c')
-rw-r--r-- | ssl/t1_enc.c | 131 |
1 files changed, 55 insertions, 76 deletions
diff --git a/ssl/t1_enc.c b/ssl/t1_enc.c index b37678f2b5..a46c42143c 100644 --- a/ssl/t1_enc.c +++ b/ssl/t1_enc.c @@ -672,7 +672,7 @@ int tls1_enc(SSL *s, int send) SSL3_RECORD *rec; EVP_CIPHER_CTX *ds; unsigned long l; - int bs,i,ii,j,k,pad=0; + int bs,i,j,k,pad=0,ret,mac_size=0; const EVP_CIPHER *enc; if (send) @@ -729,11 +729,11 @@ int tls1_enc(SSL *s, int send) printf("tls1_enc(%d)\n", send); #endif /* KSSL_DEBUG */ - if ((s->session == NULL) || (ds == NULL) || - (enc == NULL)) + if ((s->session == NULL) || (ds == NULL) || (enc == NULL)) { memmove(rec->data,rec->input,rec->length); rec->input=rec->data; + ret = 1; } else { @@ -797,13 +797,13 @@ int tls1_enc(SSL *s, int send) #ifdef KSSL_DEBUG { - unsigned long ui; + unsigned long ui; printf("EVP_Cipher(ds=%p,rec->data=%p,rec->input=%p,l=%ld) ==>\n", - ds,rec->data,rec->input,l); + ds,rec->data,rec->input,l); printf("\tEVP_CIPHER_CTX: %d buf_len, %d key_len [%d %d], %d iv_len\n", - ds->buf_len, ds->cipher->key_len, - DES_KEY_SZ, DES_SCHEDULE_SZ, - ds->cipher->iv_len); + ds->buf_len, ds->cipher->key_len, + DES_KEY_SZ, DES_SCHEDULE_SZ, + ds->cipher->iv_len); printf("\t\tIV: "); for (i=0; i<ds->cipher->iv_len; i++) printf("%02X", ds->iv[i]); printf("\n"); @@ -839,68 +839,26 @@ int tls1_enc(SSL *s, int send) #ifdef KSSL_DEBUG { - unsigned long i; - printf("\trec->data="); + unsigned long i; + printf("\trec->data="); for (i=0; i<l; i++) - printf(" %02x", rec->data[i]); printf("\n"); - } + printf(" %02x", rec->data[i]); printf("\n"); + } #endif /* KSSL_DEBUG */ + rec->orig_len = rec->length; + + ret = 1; + if (EVP_MD_CTX_md(s->read_hash) != NULL) + mac_size = EVP_MD_CTX_size(s->read_hash); if ((bs != 1) && !send) - { - ii=i=rec->data[l-1]; /* padding_length */ - i++; - /* NB: if compression is in operation the first packet - * may not be of even length so the padding bug check - * cannot be performed. This bug workaround has been - * around since SSLeay so hopefully it is either fixed - * now or no buggy implementation supports compression - * [steve] - */ - if ( (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG) - && !s->expand) - { - /* First packet is even in size, so check */ - if ((memcmp(s->s3->read_sequence, - "\0\0\0\0\0\0\0\0",8) == 0) && !(ii & 1)) - s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG; - if (s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) - i--; - } - /* TLS 1.0 does not bound the number of padding bytes by the block size. - * All of them must have value 'padding_length'. */ - if (i > (int)rec->length) - { - /* 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; - } - for (j=(int)(l-i); j<(int)l; j++) - { - if (rec->data[j] != ii) - { - /* Incorrect padding */ - return -1; - } - } - rec->length -=i; - if (s->version >= TLS1_1_VERSION - && EVP_CIPHER_CTX_mode(ds) == EVP_CIPH_CBC_MODE) - { - if (bs > (int)rec->length) - return -1; - rec->data += bs; /* skip the explicit IV */ - rec->input += bs; - rec->length -= bs; - } - } + ret = tls1_cbc_remove_padding(s, rec, bs, mac_size); if (pad && !send) rec->length -= pad; } - return(1); + return ret; } + int tls1_cert_verify_mac(SSL *s, int md_nid, unsigned char *out) { unsigned int ret; @@ -993,7 +951,7 @@ int tls1_mac(SSL *ssl, unsigned char *md, int send) size_t md_size; int i; EVP_MD_CTX hmac, *mac_ctx; - unsigned char buf[5]; + unsigned char header[13]; int stream_mac = (send?(ssl->mac_flags & SSL_MAC_FLAG_WRITE_MAC_STREAM):(ssl->mac_flags&SSL_MAC_FLAG_READ_MAC_STREAM)); int t; @@ -1014,12 +972,6 @@ int tls1_mac(SSL *ssl, unsigned char *md, int send) OPENSSL_assert(t >= 0); md_size=t; - buf[0]=rec->type; - buf[1]=(unsigned char)(ssl->version>>8); - buf[2]=(unsigned char)(ssl->version); - buf[3]=rec->length>>8; - buf[4]=rec->length&0xff; - /* I should fix this up TLS TLS TLS TLS TLS XXXXXXXX */ if (stream_mac) { @@ -1038,17 +990,44 @@ int tls1_mac(SSL *ssl, unsigned char *md, int send) s2n(send?ssl->d1->w_epoch:ssl->d1->r_epoch, p); memcpy (p,&seq[2],6); - EVP_DigestSignUpdate(mac_ctx,dtlsseq,8); + memcpy(header, dtlsseq, 8); } else - EVP_DigestSignUpdate(mac_ctx,seq,8); + memcpy(header, seq, 8); + + header[8]=rec->type; + header[9]=(unsigned char)(ssl->version>>8); + header[10]=(unsigned char)(ssl->version); + header[11]=(rec->length)>>8; + header[12]=(rec->length)&0xff; - EVP_DigestSignUpdate(mac_ctx,buf,5); - EVP_DigestSignUpdate(mac_ctx,rec->input,rec->length); - t=EVP_DigestSignFinal(mac_ctx,md,&md_size); - OPENSSL_assert(t > 0); + if (!send && + EVP_CIPHER_CTX_mode(ssl->enc_read_ctx) == EVP_CIPH_CBC_MODE && + ssl3_cbc_record_digest_supported(mac_ctx)) + { + /* 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. */ + ssl3_cbc_digest_record( + mac_ctx, + md, &md_size, + header, rec->input, + rec->length + md_size, rec->orig_len, + ssl->s3->read_mac_secret, + ssl->s3->read_mac_secret_size, + 0 /* not SSLv3 */); + } + else + { + EVP_DigestSignUpdate(mac_ctx,header,sizeof(header)); + EVP_DigestSignUpdate(mac_ctx,rec->input,rec->length); + t=EVP_DigestSignFinal(mac_ctx,md,&md_size); + OPENSSL_assert(t > 0); + } - if (!stream_mac) EVP_MD_CTX_cleanup(&hmac); + if (!stream_mac) + EVP_MD_CTX_cleanup(&hmac); #ifdef TLS_DEBUG printf("sec="); {unsigned int z; for (z=0; z<md_size; z++) printf("%02X ",mac_sec[z]); printf("\n"); } |