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)
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index 6f68816..547dc76 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -215,6 +215,15 @@
*((c)++)=(unsigned char)(((l)>> 8)&0xff), \
*((c)++)=(unsigned char)(((l) )&0xff))
+#define l2n8(l,c) (*((c)++)=(unsigned char)(((l)>>56)&0xff), \
+ *((c)++)=(unsigned char)(((l)>>48)&0xff), \
+ *((c)++)=(unsigned char)(((l)>>40)&0xff), \
+ *((c)++)=(unsigned char)(((l)>>32)&0xff), \
+ *((c)++)=(unsigned char)(((l)>>24)&0xff), \
+ *((c)++)=(unsigned char)(((l)>>16)&0xff), \
+ *((c)++)=(unsigned char)(((l)>> 8)&0xff), \
+ *((c)++)=(unsigned char)(((l) )&0xff))
+
#define n2l6(c,l) (l =((BN_ULLONG)(*((c)++)))<<40, \
l|=((BN_ULLONG)(*((c)++)))<<32, \
l|=((BN_ULLONG)(*((c)++)))<<24, \
@@ -1263,4 +1272,29 @@
int ssl_add_serverhello_use_srtp_ext(SSL *s, unsigned char *p, int *len, int maxlen);
int ssl_parse_serverhello_use_srtp_ext(SSL *s, unsigned char *d, int len,int *al);
+/* s3_cbc.c */
+void ssl3_cbc_copy_mac(unsigned char* out,
+ const SSL3_RECORD *rec,
+ unsigned md_size);
+int ssl3_cbc_remove_padding(const SSL* s,
+ SSL3_RECORD *rec,
+ unsigned block_size,
+ unsigned mac_size);
+int tls1_cbc_remove_padding(const SSL* s,
+ SSL3_RECORD *rec,
+ unsigned block_size,
+ unsigned mac_size);
+char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx);
+void ssl3_cbc_digest_record(
+ const EVP_MD_CTX *ctx,
+ unsigned char* md_out,
+ size_t* md_out_size,
+ const unsigned char header[13],
+ const unsigned char *data,
+ size_t data_plus_mac_size,
+ size_t data_plus_mac_plus_padding_size,
+ const unsigned char *mac_secret,
+ unsigned mac_secret_length,
+ char is_sslv3);
+
#endif
