File openssl-CVE-2016-0702.patch of Package openssl.4634
From: Andy Polyakov <appro@openssl.org>
Date: Tue, 26 Jan 2016 11:34:41 +0100
Subject: bn/bn_exp.c: constant-time
MOD_EXP_CTIME_COPY_FROM_PREBUF.
Patch-mainline: OpenSSL_1_0_1s
Git-commit: d7a854c055ff22fb7da80c3b0e7cb08d248591d0
References: CVE-2016-0702 bsc#968050
Performance penalty varies from platform to platform, and even
key length. For rsa2048 sign it was observed to reach almost 10%.
CVE-2016-0702
Reviewed-by: Richard Levitte <levitte@openssl.org>
---
crypto/bn/bn_exp.c | 75 +++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 57 insertions(+), 18 deletions(-)
diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index 27146c89e740..52ab0b23f756 100644
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -110,6 +110,7 @@
*/
#include "cryptlib.h"
+#include "constant_time_locl.h"
#include "bn_lcl.h"
#include <stdlib.h>
@@ -535,15 +536,17 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
static int MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top,
unsigned char *buf, int idx,
- int width)
+ int window)
{
- size_t i, j;
+ int i, j;
+ int width = 1 << window;
+ BN_ULONG *table = (BN_ULONG *)buf;
if (top > b->top)
top = b->top; /* this works because 'buf' is explicitly
* zeroed */
- for (i = 0, j = idx; i < top * sizeof b->d[0]; i++, j += width) {
- buf[j] = ((unsigned char *)b->d)[i];
+ for (i = 0, j = idx; i < top; i++, j += width) {
+ table[j] = b->d[i];
}
return 1;
@@ -551,15 +554,51 @@ static int MOD_EXP_CTIME_COPY_TO_PREBUF(const BIGNUM *b, int top,
static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top,
unsigned char *buf, int idx,
- int width)
+ int window)
{
- size_t i, j;
+ int i, j;
+ int width = 1 << window;
+ volatile BN_ULONG *table = (volatile BN_ULONG *)buf;
if (bn_wexpand(b, top) == NULL)
return 0;
- for (i = 0, j = idx; i < top * sizeof b->d[0]; i++, j += width) {
- ((unsigned char *)b->d)[i] = buf[j];
+ if (window <= 3) {
+ for (i = 0; i < top; i++, table += width) {
+ BN_ULONG acc = 0;
+
+ for (j = 0; j < width; j++) {
+ acc |= table[j] &
+ ((BN_ULONG)0 - (constant_time_eq_int(j,idx)&1));
+ }
+
+ b->d[i] = acc;
+ }
+ } else {
+ int xstride = 1 << (window - 2);
+ BN_ULONG y0, y1, y2, y3;
+
+ i = idx >> (window - 2); /* equivalent of idx / xstride */
+ idx &= xstride - 1; /* equivalent of idx % xstride */
+
+ y0 = (BN_ULONG)0 - (constant_time_eq_int(i,0)&1);
+ y1 = (BN_ULONG)0 - (constant_time_eq_int(i,1)&1);
+ y2 = (BN_ULONG)0 - (constant_time_eq_int(i,2)&1);
+ y3 = (BN_ULONG)0 - (constant_time_eq_int(i,3)&1);
+
+ for (i = 0; i < top; i++, table += width) {
+ BN_ULONG acc = 0;
+
+ for (j = 0; j < xstride; j++) {
+ acc |= ( (table[j + 0 * xstride] & y0) |
+ (table[j + 1 * xstride] & y1) |
+ (table[j + 2 * xstride] & y2) |
+ (table[j + 3 * xstride] & y3) )
+ & ((BN_ULONG)0 - (constant_time_eq_int(j,idx)&1));
+ }
+
+ b->d[i] = acc;
+ }
}
b->top = top;
@@ -782,9 +821,9 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
} else
#endif
{
- if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0, numPowers))
+ if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 0, window))
goto err;
- if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am, top, powerbuf, 1, numPowers))
+ if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&am, top, powerbuf, 1, window))
goto err;
/*
@@ -796,15 +835,15 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
if (window > 1) {
if (!BN_mod_mul_montgomery(&tmp, &am, &am, mont, ctx))
goto err;
- if (!MOD_EXP_CTIME_COPY_TO_PREBUF
- (&tmp, top, powerbuf, 2, numPowers))
+ if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 2,
+ window))
goto err;
for (i = 3; i < numPowers; i++) {
/* Calculate a^i = a^(i-1) * a */
if (!BN_mod_mul_montgomery(&tmp, &am, &tmp, mont, ctx))
goto err;
- if (!MOD_EXP_CTIME_COPY_TO_PREBUF
- (&tmp, top, powerbuf, i, numPowers))
+ if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, i,
+ window))
goto err;
}
}
@@ -812,8 +851,8 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
bits--;
for (wvalue = 0, i = bits % window; i >= 0; i--, bits--)
wvalue = (wvalue << 1) + BN_is_bit_set(p, bits);
- if (!MOD_EXP_CTIME_COPY_FROM_PREBUF
- (&tmp, top, powerbuf, wvalue, numPowers))
+ if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp, top, powerbuf, wvalue,
+ window))
goto err;
/*
@@ -833,8 +872,8 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
/*
* Fetch the appropriate pre-computed value from the pre-buf
*/
- if (!MOD_EXP_CTIME_COPY_FROM_PREBUF
- (&am, top, powerbuf, wvalue, numPowers))
+ if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&am, top, powerbuf, wvalue,
+ window))
goto err;
/* Multiply the result into the intermediate result */
--
2.7.2
