Implement fixed-window exponentiation to mitigate hyper-threading
timing attacks.
BN_FLG_EXP_CONSTTIME requests this algorithm, and this done by default for
RSA/DSA/DH private key computations unless
RSA_FLAG_NO_EXP_CONSTTIME/DSA_FLAG_NO_EXP_CONSTTIME/
DH_FLAG_NO_EXP_CONSTTIME is set.
Submitted by: Matthew D Wood
Reviewed by: Bodo Moeller
diff --git a/CHANGES b/CHANGES
index cd3dba1..54df558 100644
--- a/CHANGES
+++ b/CHANGES
@@ -799,6 +799,21 @@
Changes between 0.9.7g and 0.9.7h [XX xxx XXXX]
+ *) Make a new fixed-window mod_exp implementation the default for
+ RSA, DSA, and DH private-key operations to mitigate the
+ hyper-threading timing attacks pointed out by Colin Percival
+ (http://www.daemonology.net/hyperthreading-considered-harmful/),
+ and potential related attacks.
+
+ BN_mod_exp_mont_consttime() is the new exponentiation implementation,
+ and this is automatically used by BN_mod_exp_mont() if the new flag
+ BN_FLG_EXP_CONSTTIME is set for the exponent. RSA, DSA, and DH
+ will use this BN flag for private exponents unless the flag
+ RSA_FLAG_NO_EXP_CONSTTIME, DSA_FLAG_NO_EXP_CONSTTIME, or
+ DH_FLAG_NO_EXP_CONSTTIME, respectively, is set.
+
+ [Matthew D Wood (Intel Corp), with some changes by Bodo Moeller]
+
*) Change the client implementation for SSLv23_method() and
SSLv23_client_method() so that is uses the SSL 3.0/TLS 1.0
Client Hello message format if the SSL_OP_NO_SSLv2 option is set.
