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| author |   tb <tb@openbsd.org> | 2018-07-13 08:43:31 +0000 |
|---|---|---|
| committer | tb <tb@openbsd.org> | 2018-07-13 08:43:31 +0000 |
| commit | 9563ccbc0da9ed3dce9f38cd4d9d134dfc2138fe (patch) | |
| tree | 383f3fd2b615fd88994759fc85c1f556bf9c6b9d | |
| parent | Add "allow instance" option. (diff) | |
| download | wireguard-openbsd-9563ccbc0da9ed3dce9f38cd4d9d134dfc2138fe.tar.xz wireguard-openbsd-9563ccbc0da9ed3dce9f38cd4d9d134dfc2138fe.zip | |
Eliminate the weird condition in the BN_swap_ct() API that at most one bit
be set in condition. This makes the constant time bit-twiddling a bit
trickier, but it's not too bad. Thanks to halex for an extensive rubber
ducking session over a non-spicy spicy tabouleh falafel..
ok jsing, kn
| -rw-r--r-- | lib/libcrypto/bn/bn_lib.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/lib/libcrypto/bn/bn_lib.c b/lib/libcrypto/bn/bn_lib.c index d3ec00413f3..3a468a1285c 100644 --- a/lib/libcrypto/bn/bn_lib.c +++ b/lib/libcrypto/bn/bn_lib.c @@ -1,4 +1,4 @@ -/* $OpenBSD: bn_lib.c,v 1.43 2018/07/11 13:57:53 kn Exp $ */ +/* $OpenBSD: bn_lib.c,v 1.44 2018/07/13 08:43:31 tb Exp $ */ /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com) * All rights reserved. * @@ -894,7 +894,6 @@ BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords) /* * Constant-time conditional swap of a and b. * a and b are swapped if condition is not 0. - * The code assumes that at most one bit of condition is set. XXX add check? * nwords is the number of words to swap. */ int @@ -912,7 +911,8 @@ BN_swap_ct(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords) return 0; } - condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1; + /* Set condition to 0 (if it was zero) or all 1s otherwise. */ + condition = ((~condition & (condition - 1)) >> (BN_BITS2 - 1)) - 1; /* swap top field */ t = (a->top ^ b->top) & condition; |