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59 lines
2 KiB
Go
59 lines
2 KiB
Go
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// Copyright 2017 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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/*
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Package auth authenticates a message using a secret key.
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The Sum function, viewed as a function of the message for a uniform random
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key, is designed to meet the standard notion of unforgeability. This means
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that an attacker cannot find authenticators for any messages not authenticated
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by the sender, even if the attacker has adaptively influenced the messages
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authenticated by the sender. For a formal definition see, e.g., Section 2.4
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of Bellare, Kilian, and Rogaway, "The security of the cipher block chaining
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message authentication code," Journal of Computer and System Sciences 61 (2000),
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362–399; http://www-cse.ucsd.edu/~mihir/papers/cbc.html.
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auth does not make any promises regarding "strong" unforgeability; perhaps
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one valid authenticator can be converted into another valid authenticator for
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the same message. NaCl also does not make any promises regarding "truncated
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unforgeability."
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This package is interoperable with NaCl: https://nacl.cr.yp.to/auth.html.
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*/
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package auth
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import (
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"crypto/hmac"
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"crypto/sha512"
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)
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const (
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// Size is the size, in bytes, of an authenticated digest.
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Size = 32
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// KeySize is the size, in bytes, of an authentication key.
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KeySize = 32
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)
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// Sum generates an authenticator for m using a secret key and returns the
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// 32-byte digest.
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func Sum(m []byte, key *[KeySize]byte) *[Size]byte {
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mac := hmac.New(sha512.New, key[:])
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mac.Write(m)
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out := new([KeySize]byte)
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copy(out[:], mac.Sum(nil)[:Size])
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return out
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}
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// Verify checks that digest is a valid authenticator of message m under the
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// given secret key. Verify does not leak timing information.
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func Verify(digest []byte, m []byte, key *[KeySize]byte) bool {
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if len(digest) != Size {
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return false
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}
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mac := hmac.New(sha512.New, key[:])
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mac.Write(m)
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expectedMAC := mac.Sum(nil) // first 256 bits of 512-bit sum
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return hmac.Equal(digest, expectedMAC[:Size])
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}
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