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crypto/subtle: normalize constant time ops docs

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ConstantTimeCompare is fairly useless if you can't rely on it being zero
when the slices are different, but thankfully it has that property
thanks to the final ConstantTimeByteEq.

Change-Id: Id51100ed7d8237abbbb15778a259065b162a48ad
Reviewed-on: https://go-review.googlesource.com/c/158643
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
This commit is contained in:
Filippo Valsorda 2019-01-20 16:18:04 -05:00 committed by Filippo Valsorda
parent 8d2e65d224
commit ef82ecd0f6
1 changed files with 4 additions and 4 deletions
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8
src/crypto/subtle/constant_time.go
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@ -6,9 +6,9 @@
// code but require careful thought to use correctly. // code but require careful thought to use correctly.
package subtle package subtle
// ConstantTimeCompare returns 1 if and only if the two slices, x // ConstantTimeCompare returns 1 if the two slices, x and y, have equal contents
// and y, have equal contents. The time taken is a function of the length of // and 0 otherwise. The time taken is a function of the length of the slices and
// the slices and is independent of the contents. // is independent of the contents.
func ConstantTimeCompare(x, y []byte) int { func ConstantTimeCompare(x, y []byte) int {
if len(x) != len(y) { if len(x) != len(y) {
return 0 return 0
@ -23,7 +23,7 @@ func ConstantTimeCompare(x, y []byte) int {
return ConstantTimeByteEq(v, 0) return ConstantTimeByteEq(v, 0)
} }
// ConstantTimeSelect returns x if v is 1 and y if v is 0. // ConstantTimeSelect returns x if v == 1 and y if v == 0.
// Its behavior is undefined if v takes any other value. // Its behavior is undefined if v takes any other value.
func ConstantTimeSelect(v, x, y int) int { return ^(v-1)&x | (v-1)&y } func ConstantTimeSelect(v, x, y int) int { return ^(v-1)&x | (v-1)&y }