74 lines
1.9 KiB
Go
74 lines
1.9 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package subtle implements functions that are often useful in cryptographic
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// code but require careful thought to use correctly.
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package subtle
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// ConstantTimeCompare returns 1 if and only if the two slices, x
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// and y, have equal contents. The time taken is a function of the length of
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// the slices and is independent of the contents.
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func ConstantTimeCompare(x, y []byte) int {
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if len(x) != len(y) {
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return 0
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}
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var v byte
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for i := 0; i < len(x); i++ {
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v |= x[i] ^ y[i]
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}
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return ConstantTimeByteEq(v, 0)
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}
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// ConstantTimeSelect returns x if v is 1 and y if v is 0.
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// Its behavior is undefined if v takes any other value.
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func ConstantTimeSelect(v, x, y int) int { return ^(v-1)&x | (v-1)&y }
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// ConstantTimeByteEq returns 1 if x == y and 0 otherwise.
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func ConstantTimeByteEq(x, y uint8) int {
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z := ^(x ^ y)
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z &= z >> 4
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z &= z >> 2
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z &= z >> 1
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return int(z)
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}
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// ConstantTimeEq returns 1 if x == y and 0 otherwise.
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func ConstantTimeEq(x, y int32) int {
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z := ^(x ^ y)
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z &= z >> 16
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z &= z >> 8
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z &= z >> 4
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z &= z >> 2
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z &= z >> 1
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return int(z & 1)
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}
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// ConstantTimeCopy copies the contents of y into x (a slice of equal length)
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// if v == 1. If v == 0, x is left unchanged. Its behavior is undefined if v
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// takes any other value.
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func ConstantTimeCopy(v int, x, y []byte) {
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if len(x) != len(y) {
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panic("subtle: slices have different lengths")
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}
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xmask := byte(v - 1)
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ymask := byte(^(v - 1))
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for i := 0; i < len(x); i++ {
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x[i] = x[i]&xmask | y[i]&ymask
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}
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}
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// ConstantTimeLessOrEq returns 1 if x <= y and 0 otherwise.
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// Its behavior is undefined if x or y are negative or > 2**31 - 1.
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func ConstantTimeLessOrEq(x, y int) int {
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x32 := int32(x)
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y32 := int32(y)
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return int(((x32 - y32 - 1) >> 31) & 1)
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}
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