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 sha1 implements the SHA1 hash algorithm as defined in RFC 3174.
6package sha1
7
8import (
9	"crypto"
10	"hash"
11)
12
13func init() {
14	crypto.RegisterHash(crypto.SHA1, New)
15}
16
17// The size of a SHA1 checksum in bytes.
18const Size = 20
19
20// The blocksize of SHA1 in bytes.
21const BlockSize = 64
22
23const (
24	chunk = 64
25	init0 = 0x67452301
26	init1 = 0xEFCDAB89
27	init2 = 0x98BADCFE
28	init3 = 0x10325476
29	init4 = 0xC3D2E1F0
30)
31
32// digest represents the partial evaluation of a checksum.
33type digest struct {
34	h   [5]uint32
35	x   [chunk]byte
36	nx  int
37	len uint64
38}
39
40func (d *digest) Reset() {
41	d.h[0] = init0
42	d.h[1] = init1
43	d.h[2] = init2
44	d.h[3] = init3
45	d.h[4] = init4
46	d.nx = 0
47	d.len = 0
48}
49
50// New returns a new hash.Hash computing the SHA1 checksum.
51func New() hash.Hash {
52	d := new(digest)
53	d.Reset()
54	return d
55}
56
57func (d *digest) Size() int { return Size }
58
59func (d *digest) BlockSize() int { return BlockSize }
60
61func (d *digest) Write(p []byte) (nn int, err error) {
62	nn = len(p)
63	d.len += uint64(nn)
64	if d.nx > 0 {
65		n := len(p)
66		if n > chunk-d.nx {
67			n = chunk - d.nx
68		}
69		for i := 0; i < n; i++ {
70			d.x[d.nx+i] = p[i]
71		}
72		d.nx += n
73		if d.nx == chunk {
74			block(d, d.x[0:])
75			d.nx = 0
76		}
77		p = p[n:]
78	}
79	if len(p) >= chunk {
80		n := len(p) &^ (chunk - 1)
81		block(d, p[:n])
82		p = p[n:]
83	}
84	if len(p) > 0 {
85		d.nx = copy(d.x[:], p)
86	}
87	return
88}
89
90func (d0 *digest) Sum(in []byte) []byte {
91	// Make a copy of d0 so that caller can keep writing and summing.
92	d := *d0
93
94	// Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.
95	len := d.len
96	var tmp [64]byte
97	tmp[0] = 0x80
98	if len%64 < 56 {
99		d.Write(tmp[0 : 56-len%64])
100	} else {
101		d.Write(tmp[0 : 64+56-len%64])
102	}
103
104	// Length in bits.
105	len <<= 3
106	for i := uint(0); i < 8; i++ {
107		tmp[i] = byte(len >> (56 - 8*i))
108	}
109	d.Write(tmp[0:8])
110
111	if d.nx != 0 {
112		panic("d.nx != 0")
113	}
114
115	var digest [Size]byte
116	for i, s := range d.h {
117		digest[i*4] = byte(s >> 24)
118		digest[i*4+1] = byte(s >> 16)
119		digest[i*4+2] = byte(s >> 8)
120		digest[i*4+3] = byte(s)
121	}
122
123	return append(in, digest[:]...)
124}
125