github.com/graybobo/golang.org-package-offline-cache@v0.0.0-20200626051047-6608995c132f/x/crypto/tea/cipher.go (about)

     1  // Copyright 2015 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 tea implements the TEA algorithm, as defined in Needham and
     6  // Wheeler's 1994 technical report, “TEA, a Tiny Encryption Algorithm”. See
     7  // http://www.cix.co.uk/~klockstone/tea.pdf for details.
     8  
     9  package tea
    10  
    11  import (
    12  	"crypto/cipher"
    13  	"encoding/binary"
    14  	"errors"
    15  )
    16  
    17  const (
    18  	// BlockSize is the size of a TEA block, in bytes.
    19  	BlockSize = 8
    20  
    21  	// KeySize is the size of a TEA key, in bytes.
    22  	KeySize = 16
    23  
    24  	// delta is the TEA key schedule constant.
    25  	delta = 0x9e3779b9
    26  
    27  	// numRounds is the standard number of rounds in TEA.
    28  	numRounds = 64
    29  )
    30  
    31  // tea is an instance of the TEA cipher with a particular key.
    32  type tea struct {
    33  	key    [16]byte
    34  	rounds int
    35  }
    36  
    37  // NewCipher returns an instance of the TEA cipher with the standard number of
    38  // rounds. The key argument must be 16 bytes long.
    39  func NewCipher(key []byte) (cipher.Block, error) {
    40  	return NewCipherWithRounds(key, numRounds)
    41  }
    42  
    43  // NewCipherWithRounds returns an instance of the TEA cipher with a given
    44  // number of rounds, which must be even. The key argument must be 16 bytes
    45  // long.
    46  func NewCipherWithRounds(key []byte, rounds int) (cipher.Block, error) {
    47  	if len(key) != 16 {
    48  		return nil, errors.New("tea: incorrect key size")
    49  	}
    50  
    51  	if rounds&1 != 0 {
    52  		return nil, errors.New("tea: odd number of rounds specified")
    53  	}
    54  
    55  	c := &tea{
    56  		rounds: rounds,
    57  	}
    58  	copy(c.key[:], key)
    59  
    60  	return c, nil
    61  }
    62  
    63  // BlockSize returns the TEA block size, which is eight bytes. It is necessary
    64  // to satisfy the Block interface in the package "crypto/cipher".
    65  func (*tea) BlockSize() int {
    66  	return BlockSize
    67  }
    68  
    69  // Encrypt encrypts the 8 byte buffer src using the key in t and stores the
    70  // result in dst. Note that for amounts of data larger than a block, it is not
    71  // safe to just call Encrypt on successive blocks; instead, use an encryption
    72  // mode like CBC (see crypto/cipher/cbc.go).
    73  func (t *tea) Encrypt(dst, src []byte) {
    74  	e := binary.BigEndian
    75  	v0, v1 := e.Uint32(src), e.Uint32(src[4:])
    76  	k0, k1, k2, k3 := e.Uint32(t.key[0:]), e.Uint32(t.key[4:]), e.Uint32(t.key[8:]), e.Uint32(t.key[12:])
    77  
    78  	sum := uint32(0)
    79  	delta := uint32(delta)
    80  
    81  	for i := 0; i < t.rounds/2; i++ {
    82  		sum += delta
    83  		v0 += ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1)
    84  		v1 += ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3)
    85  	}
    86  
    87  	e.PutUint32(dst, v0)
    88  	e.PutUint32(dst[4:], v1)
    89  }
    90  
    91  // Decrypt decrypts the 8 byte buffer src using the key in t and stores the
    92  // result in dst.
    93  func (t *tea) Decrypt(dst, src []byte) {
    94  	e := binary.BigEndian
    95  	v0, v1 := e.Uint32(src), e.Uint32(src[4:])
    96  	k0, k1, k2, k3 := e.Uint32(t.key[0:]), e.Uint32(t.key[4:]), e.Uint32(t.key[8:]), e.Uint32(t.key[12:])
    97  
    98  	delta := uint32(delta)
    99  	sum := delta * uint32(t.rounds/2) // in general, sum = delta * n
   100  
   101  	for i := 0; i < t.rounds/2; i++ {
   102  		v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3)
   103  		v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1)
   104  		sum -= delta
   105  	}
   106  
   107  	e.PutUint32(dst, v0)
   108  	e.PutUint32(dst[4:], v1)
   109  }