sha256.go

Documentation: cmd/internal/notsha256

     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 notsha256 implements the NOTSHA256 algorithm,
     6  // a hash defined as bitwise NOT of SHA256.
     7  // It is used in situations where exact fidelity to SHA256 is unnecessary.
     8  // In particular, it is used in the compiler toolchain,
     9  // which cannot depend directly on cgo when GOEXPERIMENT=boringcrypto
    10  // (and in that mode the real sha256 uses cgo).
    11  package notsha256
    12  
    13  import (
    14  	"encoding/binary"
    15  	"hash"
    16  )
    17  
    18  // The size of a checksum in bytes.
    19  const Size = 32
    20  
    21  // The blocksize in bytes.
    22  const BlockSize = 64
    23  
    24  const (
    25  	chunk = 64
    26  	init0 = 0x6A09E667
    27  	init1 = 0xBB67AE85
    28  	init2 = 0x3C6EF372
    29  	init3 = 0xA54FF53A
    30  	init4 = 0x510E527F
    31  	init5 = 0x9B05688C
    32  	init6 = 0x1F83D9AB
    33  	init7 = 0x5BE0CD19
    34  )
    35  
    36  // digest represents the partial evaluation of a checksum.
    37  type digest struct {
    38  	h   [8]uint32
    39  	x   [chunk]byte
    40  	nx  int
    41  	len uint64
    42  }
    43  
    44  func (d *digest) Reset() {
    45  	d.h[0] = init0
    46  	d.h[1] = init1
    47  	d.h[2] = init2
    48  	d.h[3] = init3
    49  	d.h[4] = init4
    50  	d.h[5] = init5
    51  	d.h[6] = init6
    52  	d.h[7] = init7
    53  	d.nx = 0
    54  	d.len = 0
    55  }
    56  
    57  // New returns a new hash.Hash computing the NOTSHA256 checksum.
    58  // state of the hash.
    59  func New() hash.Hash {
    60  	d := new(digest)
    61  	d.Reset()
    62  	return d
    63  }
    64  
    65  func (d *digest) Size() int {
    66  	return Size
    67  }
    68  
    69  func (d *digest) BlockSize() int { return BlockSize }
    70  
    71  func (d *digest) Write(p []byte) (nn int, err error) {
    72  	nn = len(p)
    73  	d.len += uint64(nn)
    74  	if d.nx > 0 {
    75  		n := copy(d.x[d.nx:], p)
    76  		d.nx += n
    77  		if d.nx == chunk {
    78  			block(d, d.x[:])
    79  			d.nx = 0
    80  		}
    81  		p = p[n:]
    82  	}
    83  	if len(p) >= chunk {
    84  		n := len(p) &^ (chunk - 1)
    85  		block(d, p[:n])
    86  		p = p[n:]
    87  	}
    88  	if len(p) > 0 {
    89  		d.nx = copy(d.x[:], p)
    90  	}
    91  	return
    92  }
    93  
    94  func (d *digest) Sum(in []byte) []byte {
    95  	// Make a copy of d so that caller can keep writing and summing.
    96  	d0 := *d
    97  	hash := d0.checkSum()
    98  	return append(in, hash[:]...)
    99  }
   100  
   101  func (d *digest) checkSum() [Size]byte {
   102  	len := d.len
   103  	// Padding. Add a 1 bit and 0 bits until 56 bytes mod 64.
   104  	var tmp [64]byte
   105  	tmp[0] = 0x80
   106  	if len%64 < 56 {
   107  		d.Write(tmp[0 : 56-len%64])
   108  	} else {
   109  		d.Write(tmp[0 : 64+56-len%64])
   110  	}
   111  
   112  	// Length in bits.
   113  	len <<= 3
   114  	binary.BigEndian.PutUint64(tmp[:], len)
   115  	d.Write(tmp[0:8])
   116  
   117  	if d.nx != 0 {
   118  		panic("d.nx != 0")
   119  	}
   120  
   121  	var digest [Size]byte
   122  
   123  	binary.BigEndian.PutUint32(digest[0:], d.h[0]^0xFFFFFFFF)
   124  	binary.BigEndian.PutUint32(digest[4:], d.h[1]^0xFFFFFFFF)
   125  	binary.BigEndian.PutUint32(digest[8:], d.h[2]^0xFFFFFFFF)
   126  	binary.BigEndian.PutUint32(digest[12:], d.h[3]^0xFFFFFFFF)
   127  	binary.BigEndian.PutUint32(digest[16:], d.h[4]^0xFFFFFFFF)
   128  	binary.BigEndian.PutUint32(digest[20:], d.h[5]^0xFFFFFFFF)
   129  	binary.BigEndian.PutUint32(digest[24:], d.h[6]^0xFFFFFFFF)
   130  	binary.BigEndian.PutUint32(digest[28:], d.h[7]^0xFFFFFFFF)
   131  
   132  	return digest
   133  }
   134  
   135  // Sum256 returns the SHA256 checksum of the data.
   136  func Sum256(data []byte) [Size]byte {
   137  	var d digest
   138  	d.Reset()
   139  	d.Write(data)
   140  	return d.checkSum()
   141  }
   142
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