101 lines
2.5 KiB
Go
101 lines
2.5 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 hmac implements the Keyed-Hash Message Authentication Code (HMAC) as
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// defined in U.S. Federal Information Processing Standards Publication 198.
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// An HMAC is a cryptographic hash that uses a key to sign a message.
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// The receiver verifies the hash by recomputing it using the same key.
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package hmac
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import (
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"crypto/md5"
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"crypto/sha1"
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"crypto/sha256"
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"hash"
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"os"
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)
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// FIPS 198:
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// http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf
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// key is zero padded to 64 bytes
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// ipad = 0x36 byte repeated to 64 bytes
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// opad = 0x5c byte repeated to 64 bytes
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// hmac = H([key ^ opad] H([key ^ ipad] text))
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const (
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// NOTE(rsc): This constant is actually the
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// underlying hash function's block size.
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// HMAC is only conventionally used with
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// MD5 and SHA1, and both use 64-byte blocks.
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// The hash.Hash interface doesn't provide a
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// way to find out the block size.
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padSize = 64
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)
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type hmac struct {
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size int
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key, tmp []byte
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outer, inner hash.Hash
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}
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func (h *hmac) tmpPad(xor byte) {
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for i, k := range h.key {
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h.tmp[i] = xor ^ k
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}
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for i := len(h.key); i < padSize; i++ {
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h.tmp[i] = xor
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}
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}
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func (h *hmac) Sum() []byte {
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sum := h.inner.Sum()
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h.tmpPad(0x5c)
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for i, b := range sum {
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h.tmp[padSize+i] = b
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}
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h.outer.Reset()
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h.outer.Write(h.tmp)
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return h.outer.Sum()
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}
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func (h *hmac) Write(p []byte) (n int, err os.Error) {
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return h.inner.Write(p)
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}
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func (h *hmac) Size() int { return h.size }
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func (h *hmac) Reset() {
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h.inner.Reset()
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h.tmpPad(0x36)
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h.inner.Write(h.tmp[0:padSize])
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}
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// New returns a new HMAC hash using the given hash generator and key.
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func New(h func() hash.Hash, key []byte) hash.Hash {
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hm := new(hmac)
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hm.outer = h()
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hm.inner = h()
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hm.size = hm.inner.Size()
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hm.tmp = make([]byte, padSize+hm.size)
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if len(key) > padSize {
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// If key is too big, hash it.
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hm.outer.Write(key)
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key = hm.outer.Sum()
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}
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hm.key = make([]byte, len(key))
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copy(hm.key, key)
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hm.Reset()
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return hm
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}
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// NewMD5 returns a new HMAC-MD5 hash using the given key.
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func NewMD5(key []byte) hash.Hash { return New(md5.New, key) }
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// NewSHA1 returns a new HMAC-SHA1 hash using the given key.
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func NewSHA1(key []byte) hash.Hash { return New(sha1.New, key) }
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// NewSHA256 returns a new HMAC-SHA256 hash using the given key.
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func NewSHA256(key []byte) hash.Hash { return New(sha256.New, key) }
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