Source file src/pkg/crypto/sha256/sha256.go

// 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 the SHA224 and SHA256 hash algorithms as defined in FIPS 180-2.
package sha256

import (
    "hash"
    "os"
)

// The size of a SHA256 checksum in bytes.
const Size = 32

// The size of a SHA224 checksum in bytes.
const Size224 = 28

const (
    _Chunk     = 64
    _Init0     = 0x6A09E667
    _Init1     = 0xBB67AE85
    _Init2     = 0x3C6EF372
    _Init3     = 0xA54FF53A
    _Init4     = 0x510E527F
    _Init5     = 0x9B05688C
    _Init6     = 0x1F83D9AB
    _Init7     = 0x5BE0CD19
    _Init0_224 = 0xC1059ED8
    _Init1_224 = 0x367CD507
    _Init2_224 = 0x3070DD17
    _Init3_224 = 0xF70E5939
    _Init4_224 = 0xFFC00B31
    _Init5_224 = 0x68581511
    _Init6_224 = 0x64F98FA7
    _Init7_224 = 0xBEFA4FA4
)

// digest represents the partial evaluation of a checksum.
type digest struct {
    h     [8]uint32
    x     [_Chunk]byte
    nx    int
    len   uint64
    is224 bool // mark if this digest is SHA-224
}

func (d *digest) Reset() {
    if !d.is224 {
        d.h[0] = _Init0
        d.h[1] = _Init1
        d.h[2] = _Init2
        d.h[3] = _Init3
        d.h[4] = _Init4
        d.h[5] = _Init5
        d.h[6] = _Init6
        d.h[7] = _Init7
    } else {
        d.h[0] = _Init0_224
        d.h[1] = _Init1_224
        d.h[2] = _Init2_224
        d.h[3] = _Init3_224
        d.h[4] = _Init4_224
        d.h[5] = _Init5_224
        d.h[6] = _Init6_224
        d.h[7] = _Init7_224
    }
    d.nx = 0
    d.len = 0
}

// New returns a new hash.Hash computing the SHA256 checksum.
func New() hash.Hash {
    d := new(digest)
    d.Reset()
    return d
}

// New224 returns a new hash.Hash computing the SHA224 checksum.
func New224() hash.Hash {
    d := new(digest)
    d.is224 = true
    d.Reset()
    return d
}

func (d *digest) Size() int {
    if !d.is224 {
        return Size
    }
    return Size224
}

func (d *digest) Write(p []byte) (nn int, err os.Error) {
    nn = len(p)
    d.len += uint64(nn)
    if d.nx > 0 {
        n := len(p)
        if n > _Chunk-d.nx {
            n = _Chunk - d.nx
        }
        for i := 0; i < n; i++ {
            d.x[d.nx+i] = p[i]
        }
        d.nx += n
        if d.nx == _Chunk {
            _Block(d, d.x[0:])
            d.nx = 0
        }
        p = p[n:]
    }
    n := _Block(d, p)
    p = p[n:]
    if len(p) > 0 {
        for i, x := range p {
            d.x[i] = x
        }
        d.nx = len(p)
    }
    return
}

func (d0 *digest) Sum() []byte {
    // Make a copy of d0 so that caller can keep writing and summing.
    d := new(digest)
    *d = *d0

    // Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.
    len := d.len
    var tmp [64]byte
    tmp[0] = 0x80
    if len%64 < 56 {
        d.Write(tmp[0 : 56-len%64])
    } else {
        d.Write(tmp[0 : 64+56-len%64])
    }

    // Length in bits.
    len <<= 3
    for i := uint(0); i < 8; i++ {
        tmp[i] = byte(len >> (56 - 8*i))
    }
    d.Write(tmp[0:8])

    if d.nx != 0 {
        panic("d.nx != 0")
    }

    p := make([]byte, 32)
    j := 0
    for _, s := range d.h {
        p[j+0] = byte(s >> 24)
        p[j+1] = byte(s >> 16)
        p[j+2] = byte(s >> 8)
        p[j+3] = byte(s >> 0)
        j += 4
    }
    if d.is224 {
        return p[0:28]
    }
    return p
}