github.com/maenmax/kairep@v0.0.0-20210218001208-55bf3df36788/src/golang.org/x/crypto/xtea/cipher.go (about) 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 xtea implements XTEA encryption, as defined in Needham and Wheeler's 6 // 1997 technical report, "Tea extensions." 7 package xtea // import "golang.org/x/crypto/xtea" 8 9 // For details, see http://www.cix.co.uk/~klockstone/xtea.pdf 10 11 import "strconv" 12 13 // The XTEA block size in bytes. 14 const BlockSize = 8 15 16 // A Cipher is an instance of an XTEA cipher using a particular key. 17 // table contains a series of precalculated values that are used each round. 18 type Cipher struct { 19 table [64]uint32 20 } 21 22 type KeySizeError int 23 24 func (k KeySizeError) Error() string { 25 return "crypto/xtea: invalid key size " + strconv.Itoa(int(k)) 26 } 27 28 // NewCipher creates and returns a new Cipher. 29 // The key argument should be the XTEA key. 30 // XTEA only supports 128 bit (16 byte) keys. 31 func NewCipher(key []byte) (*Cipher, error) { 32 k := len(key) 33 switch k { 34 default: 35 return nil, KeySizeError(k) 36 case 16: 37 break 38 } 39 40 c := new(Cipher) 41 initCipher(c, key) 42 43 return c, nil 44 } 45 46 // BlockSize returns the XTEA block size, 8 bytes. 47 // It is necessary to satisfy the Block interface in the 48 // package "crypto/cipher". 49 func (c *Cipher) BlockSize() int { return BlockSize } 50 51 // Encrypt encrypts the 8 byte buffer src using the key and stores the result in dst. 52 // Note that for amounts of data larger than a block, 53 // it is not safe to just call Encrypt on successive blocks; 54 // instead, use an encryption mode like CBC (see crypto/cipher/cbc.go). 55 func (c *Cipher) Encrypt(dst, src []byte) { encryptBlock(c, dst, src) } 56 57 // Decrypt decrypts the 8 byte buffer src using the key k and stores the result in dst. 58 func (c *Cipher) Decrypt(dst, src []byte) { decryptBlock(c, dst, src) } 59 60 // initCipher initializes the cipher context by creating a look up table 61 // of precalculated values that are based on the key. 62 func initCipher(c *Cipher, key []byte) { 63 // Load the key into four uint32s 64 var k [4]uint32 65 for i := 0; i < len(k); i++ { 66 j := i << 2 // Multiply by 4 67 k[i] = uint32(key[j+0])<<24 | uint32(key[j+1])<<16 | uint32(key[j+2])<<8 | uint32(key[j+3]) 68 } 69 70 // Precalculate the table 71 const delta = 0x9E3779B9 72 var sum uint32 = 0 73 74 // Two rounds of XTEA applied per loop 75 for i := 0; i < numRounds; { 76 c.table[i] = sum + k[sum&3] 77 i++ 78 sum += delta 79 c.table[i] = sum + k[(sum>>11)&3] 80 i++ 81 } 82 }