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每次Feistel轮函数内部，均经过4种运算，即：
go标准库中DES Feistel轮函数代码如下：
func feistel(right uint32, key uint64) (result uint32) { //右侧32位扩展置换为48位，并与48位子密钥做异或运算 sBoxLocations := key ^ expandBlock(right) var sBoxResult uint32 for i := uint8(0); i < 8; i++ { //sBoxLocations>>42、sBoxLocations <<= 6，按每6位分块 sBoxLocation := uint8(sBoxLocations>>42) & 0x3f sBoxLocations <<= 6 //6位中取第1位和第6位组成行号 row := (sBoxLocation & 0x1) | ((sBoxLocation & 0x20) >> 4) //剩余第2、3、4、5位组成列号 column := (sBoxLocation >> 1) & 0xf //feistelBox包括了S盒置换和P盒置换的实现 sBoxResult ^= feistelBox[i][16*row+column] } return sBoxResult}var feistelBox [8][64]uint32//P盒置换func permuteBlock(src uint64, permutation []uint8) (block uint64) { for position, n := range permutation { bit := (src >> n) & 1 block |= bit << uint((len(permutation)-1)-position) } return}//初始化feistelBoxfunc init() { for s := range sBoxes { for i := 0; i < 4; i++ { for j := 0; j < 16; j++ { f := uint64(sBoxes[s][i][j]) << (4 * (7 - uint(s))) f = permuteBlock(f, permutationFunction[:]) feistelBox[s][16*i+j] = uint32(f) } } }}//代码位置src/crypto/des/block.go 附go标准库中使用的扩展置换表和P盒置换表：
//扩展置换表var expansionFunction = [48]byte{ 0, 31, 30, 29, 28, 27, 28, 27, 26, 25, 24, 23, 24, 23, 22, 21, 20, 19, 20, 19, 18, 17, 16, 15, 16, 15, 14, 13, 12, 11, 12, 11, 10, 9, 8, 7, 8, 7, 6, 5, 4, 3, 4, 3, 2, 1, 0, 31,}//P盒置换表var permutationFunction = [32]byte{ 16, 25, 12, 11, 3, 20, 4, 15, 31, 17, 9, 6, 27, 14, 1, 22, 30, 24, 8, 18, 0, 5, 29, 23, 13, 19, 2, 26, 10, 21, 28, 7,}//代码位置src/crypto/des/const.go 附go标准库中使用的S盒置换表：
var sBoxes = [8][4][16]uint8{ // S-box 1 { {14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7}, {0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8}, {4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0}, {15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13}, }, // S-box 2 { {15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10}, {3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5}, {0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15}, {13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9}, }, // S-box 3 { {10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8}, {13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1}, {13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7}, {1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12}, }, // S-box 4 { {7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15}, {13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9}, {10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4}, {3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14}, }, // S-box 5 { {2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9}, {14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6}, {4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14}, {11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3}, }, // S-box 6 { {12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11}, {10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8}, {9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6}, {4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13}, }, // S-box 7 { {4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1}, {13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6}, {1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2}, {6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12}, }, // S-box 8 { {13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7}, {1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2}, {7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8}, {2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11}, },}//代码位置src/crypto/des/const.go DES是一个经典的对称加密算法，但也缺陷明显，即56位的密钥安全性不足，已被证实可以在短时间内破解。
为解决此问题，出现了3DES，也称Triple DES，3DES为DES向AES过渡的加密算法，它使用3条56位的密钥对数据进行三次加密。为了兼容普通的DES，3DES并没有直接使用加密->加密->加密的方式，而是采用了加密->解密->加密的方式。当三重密钥均相同时，前两步相互抵消，相当于仅实现了一次加密，因此可实现对普通DES加密算法的兼容。3DES解密过程，与加密过程相反，即逆序使用密钥。go标准中3DES加密算法的实现如下：
type tripleDESCipher struct { cipher1, cipher2, cipher3 desCipher}func NewTripleDESCipher(key []byte) (cipher.Block, error) { if len(key) != 24 { return nil, KeySizeError(len(key)) } c := new(tripleDESCipher) c.cipher1.generateSubkeys(key[:8]) c.cipher2.generateSubkeys(key[8:16]) c.cipher3.generateSubkeys(key[16:]) return c, nil}//3DES加密func (c *tripleDESCipher) Encrypt(dst, src []byte) { c.cipher1.Encrypt(dst, src) c.cipher2.Decrypt(dst, dst) c.cipher3.Encrypt(dst, dst)}//3DES解密func (c *tripleDESCipher) Decrypt(dst, src []byte) { c.cipher3.Decrypt(dst, src) c.cipher2.Encrypt(dst, dst) c.cipher1.Decrypt(dst, dst)}//代码位置src/crypto/des/cipher.go 相比DES，3DES因密钥长度变长，安全性有所提高，但其处理速度不高。
因此又出现了AES加密算法，AES较于3DES速度更快、安全性更高，后续单独总结。感谢关注兄弟连区块链教程分享！
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