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Diffstat (limited to 'libgo/go/crypto/subtle/constant_time.go')
-rw-r--r-- | libgo/go/crypto/subtle/constant_time.go | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/libgo/go/crypto/subtle/constant_time.go b/libgo/go/crypto/subtle/constant_time.go new file mode 100644 index 000000000..a3d70b9c9 --- /dev/null +++ b/libgo/go/crypto/subtle/constant_time.go @@ -0,0 +1,57 @@ +// Copyright 2009 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// This package implements functions that are often useful in cryptographic +// code but require careful thought to use correctly. +package subtle + +// ConstantTimeCompare returns 1 iff the two equal length slices, x +// and y, have equal contents. The time taken is a function of the length of +// the slices and is independent of the contents. +func ConstantTimeCompare(x, y []byte) int { + var v byte + + for i := 0; i < len(x); i++ { + v |= x[i] ^ y[i] + } + + return ConstantTimeByteEq(v, 0) +} + +// ConstantTimeSelect returns x if v is 1 and y if v is 0. +// Its behavior is undefined if v takes any other value. +func ConstantTimeSelect(v, x, y int) int { return ^(v-1)&x | (v-1)&y } + +// ConstantTimeByteEq returns 1 if x == y and 0 otherwise. +func ConstantTimeByteEq(x, y uint8) int { + z := ^(x ^ y) + z &= z >> 4 + z &= z >> 2 + z &= z >> 1 + + return int(z) +} + +// ConstantTimeEq returns 1 if x == y and 0 otherwise. +func ConstantTimeEq(x, y int32) int { + z := ^(x ^ y) + z &= z >> 16 + z &= z >> 8 + z &= z >> 4 + z &= z >> 2 + z &= z >> 1 + + return int(z & 1) +} + +// ConstantTimeCopy copies the contents of y into x iff v == 1. If v == 0, x is left unchanged. +// Its behavior is undefined if v takes any other value. +func ConstantTimeCopy(v int, x, y []byte) { + xmask := byte(v - 1) + ymask := byte(^(v - 1)) + for i := 0; i < len(x); i++ { + x[i] = x[i]&xmask | y[i]&ymask + } + return +} |