constant_time.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package subtle implements functions that are often useful in cryptographic
     6  // code but require careful thought to use correctly.
     7  package subtle
     8  
     9  import (
    10  	"crypto/internal/constanttime"
    11  	"crypto/internal/fips140/subtle"
    12  )
    13  
    14  // These functions are forwarded to crypto/internal/constanttime for intrinsified
    15  // operations, and to crypto/internal/fips140/subtle for byte slice operations.
    16  
    17  // ConstantTimeCompare returns 1 if the two slices, x and y, have equal contents
    18  // and 0 otherwise. The time taken is a function of the length of the slices and
    19  // is independent of the contents. If the lengths of x and y do not match it
    20  // returns 0 immediately.
    21  func ConstantTimeCompare(x, y []byte) int {
    22  	return subtle.ConstantTimeCompare(x, y)
    23  }
    24  
    25  // ConstantTimeSelect returns x if v == 1 and y if v == 0.
    26  // Its behavior is undefined if v takes any other value.
    27  func ConstantTimeSelect(v, x, y int) int {
    28  	return constanttime.Select(v, x, y)
    29  }
    30  
    31  // ConstantTimeByteEq returns 1 if x == y and 0 otherwise.
    32  func ConstantTimeByteEq(x, y uint8) int {
    33  	return constanttime.ByteEq(x, y)
    34  }
    35  
    36  // ConstantTimeEq returns 1 if x == y and 0 otherwise.
    37  func ConstantTimeEq(x, y int32) int {
    38  	return constanttime.Eq(x, y)
    39  }
    40  
    41  // ConstantTimeCopy copies the contents of y into x (a slice of equal length)
    42  // if v == 1. If v == 0, x is left unchanged. Its behavior is undefined if v
    43  // takes any other value.
    44  func ConstantTimeCopy(v int, x, y []byte) {
    45  	subtle.ConstantTimeCopy(v, x, y)
    46  }
    47  
    48  // ConstantTimeLessOrEq returns 1 if x <= y and 0 otherwise.
    49  // Its behavior is undefined if x or y are negative or > 2**31 - 1.
    50  func ConstantTimeLessOrEq(x, y int) int {
    51  	return constanttime.LessOrEq(x, y)
    52  }
    53
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