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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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3
ssl/ssl_algs.c
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@@ -90,10 +90,13 @@ int SSL_library_init(void)
EVP_add_cipher(EVP_aes_256_cbc());
EVP_add_cipher(EVP_aes_128_gcm());
EVP_add_cipher(EVP_aes_256_gcm());
#if 0 /* Disabled because of timing side-channel leaks. */
#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
EVP_add_cipher(EVP_aes_128_cbc_hmac_sha1());
EVP_add_cipher(EVP_aes_256_cbc_hmac_sha1());
#endif
#endif
#endif
#ifndef OPENSSL_NO_CAMELLIA
EVP_add_cipher(EVP_camellia_128_cbc());