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.
5 // This package implements XTEA encryption, as defined in Needham and
6 // Wheeler's 1997 technical report, "Tea extensions."
9 // For details, see http://www.cix.co.uk/~klockstone/xtea.pdf
16 // The XTEA block size in bytes.
19 // A Cipher is an instance of an XTEA cipher using a particular key.
20 // table contains a series of precalculated values that are used each round.
27 func (k KeySizeError
) String() string {
28 return "crypto/xtea: invalid key size " + strconv
.Itoa(int(k
))
31 // NewCipher creates and returns a new Cipher.
32 // The key argument should be the XTEA key.
33 // XTEA only supports 128 bit (16 byte) keys.
34 func NewCipher(key
[]byte) (*Cipher
, os
.Error
) {
38 return nil, KeySizeError(k
)
49 // BlockSize returns the XTEA block size, 8 bytes.
50 // It is necessary to satisfy the Cipher interface in the
51 // package "crypto/block".
52 func (c
*Cipher
) BlockSize() int { return BlockSize
}
54 // Encrypt encrypts the 8 byte buffer src using the key and stores the result in dst.
55 // Note that for amounts of data larger than a block,
56 // it is not safe to just call Encrypt on successive blocks;
57 // instead, use an encryption mode like CBC (see crypto/block/cbc.go).
58 func (c
*Cipher
) Encrypt(dst
, src
[]byte) { encryptBlock(c
, dst
, src
) }
60 // Decrypt decrypts the 8 byte buffer src using the key k and stores the result in dst.
61 func (c
*Cipher
) Decrypt(dst
, src
[]byte) { decryptBlock(c
, dst
, src
) }
63 // Reset zeros the table, so that it will no longer appear in the process's memory.
64 func (c
*Cipher
) Reset() {
65 for i
:= 0; i
< len(c
.table
); i
++ {
70 // initCipher initializes the cipher context by creating a look up table
71 // of precalculated values that are based on the key.
72 func initCipher(c
*Cipher
, key
[]byte) {
73 // Load the key into four uint32s
75 for i
:= 0; i
< len(k
); i
++ {
76 j
:= i
<< 2 // Multiply by 4
77 k
[i
] = uint32(key
[j
+0])<<24 |
uint32(key
[j
+1])<<16 |
uint32(key
[j
+2])<<8 |
uint32(key
[j
+3])
80 // Precalculate the table
81 const delta
= 0x9E3779B9
84 // Two rounds of XTEA applied per loop
85 for i
:= 0; i
< numRounds
; {
86 c
.table
[i
] = sum
+ k
[sum
&3]
89 c
.table
[i
] = sum
+ k
[(sum
>>11)&3]