[openssl-commits] [openssl] master update

[Matt Caswell]

The branch master has been updated
       via  b336ce57f2d5cca803a920d2a9e622b588cead3c (commit)
      from  c22365b399f62af4a81e9202500cd2cbd9c23a9d (commit)


- Log -----------------------------------------------------------------
commit b336ce57f2d5cca803a920d2a9e622b588cead3c
Author: Matt Caswell <matt at openssl.org>
Date:   Wed May 16 09:58:27 2018 +0100

    Make BN_GF2m_mod_arr more constant time
    
    Experiments have shown that the lookup table used by BN_GF2m_mod_arr
    introduces sufficient timing signal to recover the private key for an
    attacker with access to cache timing information on the victim's host.
    This only affects binary curves (which are less frequently used).
    
    No CVE is considered necessary for this issue.
    
    The fix is to replace the lookup table with an on-the-fly calculation of
    the value from the table instead, which can be performed in constant time.
    
    Thanks to Youngjoo Shin for reporting this issue.
    
    Reviewed-by: Rich Salz <rsalz at openssl.org>
    (Merged from https://github.com/openssl/openssl/pull/6270)

-----------------------------------------------------------------------

Summary of changes:
 crypto/bn/bn_gf2m.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/crypto/bn/bn_gf2m.c b/crypto/bn/bn_gf2m.c
index 287adf3..0fc4460 100644
--- a/crypto/bn/bn_gf2m.c
+++ b/crypto/bn/bn_gf2m.c
@@ -22,30 +22,32 @@
  */
 # define MAX_ITERATIONS 50
 
-static const BN_ULONG SQR_tb[16] = { 0, 1, 4, 5, 16, 17, 20, 21,
-    64, 65, 68, 69, 80, 81, 84, 85
-};
+# define SQR_nibble(w)   ((((w) & 8) << 3) \
+                       |  (((w) & 4) << 2) \
+                       |  (((w) & 2) << 1) \
+                       |   ((w) & 1))
+
 
 /* Platform-specific macros to accelerate squaring. */
 # if defined(SIXTY_FOUR_BIT) || defined(SIXTY_FOUR_BIT_LONG)
 #  define SQR1(w) \
-    SQR_tb[(w) >> 60 & 0xF] << 56 | SQR_tb[(w) >> 56 & 0xF] << 48 | \
-    SQR_tb[(w) >> 52 & 0xF] << 40 | SQR_tb[(w) >> 48 & 0xF] << 32 | \
-    SQR_tb[(w) >> 44 & 0xF] << 24 | SQR_tb[(w) >> 40 & 0xF] << 16 | \
-    SQR_tb[(w) >> 36 & 0xF] <<  8 | SQR_tb[(w) >> 32 & 0xF]
+    SQR_nibble((w) >> 60) << 56 | SQR_nibble((w) >> 56) << 48 | \
+    SQR_nibble((w) >> 52) << 40 | SQR_nibble((w) >> 48) << 32 | \
+    SQR_nibble((w) >> 44) << 24 | SQR_nibble((w) >> 40) << 16 | \
+    SQR_nibble((w) >> 36) <<  8 | SQR_nibble((w) >> 32)
 #  define SQR0(w) \
-    SQR_tb[(w) >> 28 & 0xF] << 56 | SQR_tb[(w) >> 24 & 0xF] << 48 | \
-    SQR_tb[(w) >> 20 & 0xF] << 40 | SQR_tb[(w) >> 16 & 0xF] << 32 | \
-    SQR_tb[(w) >> 12 & 0xF] << 24 | SQR_tb[(w) >>  8 & 0xF] << 16 | \
-    SQR_tb[(w) >>  4 & 0xF] <<  8 | SQR_tb[(w)       & 0xF]
+    SQR_nibble((w) >> 28) << 56 | SQR_nibble((w) >> 24) << 48 | \
+    SQR_nibble((w) >> 20) << 40 | SQR_nibble((w) >> 16) << 32 | \
+    SQR_nibble((w) >> 12) << 24 | SQR_nibble((w) >>  8) << 16 | \
+    SQR_nibble((w) >>  4) <<  8 | SQR_nibble((w)      )
 # endif
 # ifdef THIRTY_TWO_BIT
 #  define SQR1(w) \
-    SQR_tb[(w) >> 28 & 0xF] << 24 | SQR_tb[(w) >> 24 & 0xF] << 16 | \
-    SQR_tb[(w) >> 20 & 0xF] <<  8 | SQR_tb[(w) >> 16 & 0xF]
+    SQR_nibble((w) >> 28) << 24 | SQR_nibble((w) >> 24) << 16 | \
+    SQR_nibble((w) >> 20) <<  8 | SQR_nibble((w) >> 16)
 #  define SQR0(w) \
-    SQR_tb[(w) >> 12 & 0xF] << 24 | SQR_tb[(w) >>  8 & 0xF] << 16 | \
-    SQR_tb[(w) >>  4 & 0xF] <<  8 | SQR_tb[(w)       & 0xF]
+    SQR_nibble((w) >> 12) << 24 | SQR_nibble((w) >>  8) << 16 | \
+    SQR_nibble((w) >>  4) <<  8 | SQR_nibble((w)      )
 # endif
 
 # if !defined(OPENSSL_BN_ASM_GF2m)