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Make CBC decoding constant time.

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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.
This commit is contained in:
Ben Laurie
2013-01-28 17:31:49 +00:00
parent 2ee798880a
commit e130841bcc
9 changed files with 214 additions and 197 deletions
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34
ssl/ssl_locl.h
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@@ -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, \
@@ -1133,4 +1142,29 @@ int ssl_parse_clienthello_use_srtp_ext(SSL *s, unsigned char *d, int len,int *al
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