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Merge pull request #2464 from SparkiDev/rshift_neg

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Use constant time comparison in MaskMac with scanStart and macStart
This commit is contained in:
toddouska
2019-09-13 11:56:12 -07:00
committed by GitHub
parent a2d3da2831 2a1a9f36cc
commit 40fc86dfd2
3 changed files with 12 additions and 5 deletions
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4
src/internal.c
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@ -13241,8 +13241,8 @@ static byte MaskMac(const byte* data, int sz, int macSz, byte* expMac)
unsigned char started, notEnded;
unsigned char good = 0;
scanStart &= (~scanStart) >> (sizeof(int) * 8 - 1);
macStart &= (~macStart) >> (sizeof(int) * 8 - 1);
scanStart &= ctMaskIntGTE(scanStart, 0);
macStart &= ctMaskIntGTE(macStart, 0);
/* Div on Intel has different speeds depending on value.
* Use a bitwise AND or mod a specific value (converted to mul). */

12
wolfcrypt/src/misc.c
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@ -332,6 +332,12 @@ WC_STATIC WC_INLINE byte ctMaskGTE(int a, int b)
return (((word32)a - b ) >> 31) - 1;
}
/* Constant time - mask set when a >= b. */
WC_STATIC WC_INLINE int ctMaskIntGTE(int a, int b)
{
return (((word32)a - b ) >> 31) - 1;
}
/* Constant time - mask set when a < b. */
WC_STATIC WC_INLINE byte ctMaskLT(int a, int b)
{
@ -347,18 +353,18 @@ WC_STATIC WC_INLINE byte ctMaskLTE(int a, int b)
/* Constant time - mask set when a == b. */
WC_STATIC WC_INLINE byte ctMaskEq(int a, int b)
{
return 0 - (a == b);
return (~ctMaskGT(a, b)) & (~ctMaskLT(a, b));
}
WC_STATIC WC_INLINE word16 ctMask16Eq(int a, int b)
{
return 0 - (a == b);
return (~ctMaskGT(a, b)) & (~ctMaskLT(a, b));
}
/* Constant time - mask set when a != b. */
WC_STATIC WC_INLINE byte ctMaskNotEq(int a, int b)
{
return 0 - (a != b);
return ctMaskGT(a, b) | ctMaskLT(a, b);
}
/* Constant time - select a when mask is set and b otherwise. */

1
wolfssl/wolfcrypt/misc.h
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@ -94,6 +94,7 @@ word32 btoi(byte b);
WOLFSSL_LOCAL byte ctMaskGT(int a, int b);
WOLFSSL_LOCAL byte ctMaskGTE(int a, int b);
WOLFSSL_LOCAL int ctMaskIntGTE(int a, int b);
WOLFSSL_LOCAL byte ctMaskLT(int a, int b);
WOLFSSL_LOCAL byte ctMaskLTE(int a, int b);
WOLFSSL_LOCAL byte ctMaskEq(int a, int b);