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Simplify some constant-time code

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Some people recommend using bit operations to avoid the compiler producing a
branch on `ret != 0`, but:
- this makes the code less readable,
- here I got a warning from some compilers about unsigned unary minus
- and anyway modern compilers don't produce a branch here, checked on x64 and
  arm with various -O values.
This commit is contained in:
Manuel Pégourié-Gonnard 2015-02-11 15:29:15 +00:00
parent 06d7519697
commit 2ee8d24ca2
1 changed files with 1 additions and 5 deletions
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6
library/ssl_srv.c
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@ -2887,7 +2887,6 @@ static int ssl_parse_encrypted_pms( ssl_context *ssl,
unsigned char *pms = ssl->handshake->premaster + pms_offset;
unsigned char fake_pms[48], peer_pms[48];
unsigned char mask;
unsigned int uret;
size_t i;
if( ! pk_can_do( ssl_own_key( ssl ), POLARSSL_PK_RSA ) )
@ -2951,10 +2950,7 @@ static int ssl_parse_encrypted_pms( ssl_context *ssl,
}
ssl->handshake->pmslen = 48;
uret = (unsigned) ret;
uret |= -uret; /* msb = ( ret != 0 ) */
uret >>= 8 * sizeof( uret ) - 1; /* uret = ( ret != 0 ) */
mask = (unsigned char)( -uret ) ; /* ret ? 0xff : 0x00 */
mask = (unsigned char)( - ( ret != 0 ) ); /* ret ? 0xff : 0x00 */
for( i = 0; i < ssl->handshake->pmslen; i++ )
pms[i] = ( mask & fake_pms[i] ) | ( (~mask) & peer_pms[i] );