(加密基础)TEA篇

TEA算法

1.简介

TEA算法全称微型加密算法（Tiny Encryption Algorithm）是一种简单容易实现的加密算法，通常只需要很少的代码就可以实现

2.加密过程

在加密过程中，需要使用2个32位的无符号整数，**为128位，四个32位无符号整数

流程图：

加密中一共有五个量参与运算，l(第一个明文)，r(第二个明文)，sum=0，delta给定一个定值，**key每一轮：

sum+=delta;
l += ((r << 4) + key[0]) ^ (r + sum) ^ ((r >> 5) + key[1]);
r += ((l << 4) + key[2]) ^ (l + sum) ^ ((l >> 5) + key[3]);

一共执行32次，最后将l，r放入v[0],v[1]中存储，得到密文

void encrypt(unsigned int* v, unsigned int* key) {
	unsigned int l = v[0], r = v[1], sum = 0, delta = 0x9e3779b9;
	for (size_t i = 0; i < 32; i++) {
		sum += delta;
		l += ((r << 4) + key[0]) ^ (r + sum) ^ ((r >> 5) + key[1]);
		r += ((l << 4) + key[2]) ^ (l + sum) ^ ((l >> 5) + key[3]);
	}
	v[0] = l;
	v[1] = r;
}

解密流程跟加密相反

void decrypt(unsigned int* v, unsigned int* key) {
	unsigned int l = v[0], r = v[1], sum = 0, delta = 0x9e3779b9;
	sum = delta * 32;
	for (size_t i = 0; i < 32; i++) {
		r -= ((l << 4) + key[2]) ^ (l + sum) ^ ((l >> 5) + key[3]);
		l -= ((r << 4) + key[0]) ^ (r + sum) ^ ((r >> 5) + key[1]);
		sum -= delta;
	}
	v[0] = l;
	v[1] = r;
}

XTEA算法

跟TEA算法很类似，差别就是将r的变化结果和l变化结果进行了交替赋值，同时位移次数进行了一些变化，也掺杂了一些与操作

void encrypt(unsigned int* v, unsigned int* key) {
  unsigned int l = v[0], r = v[1], sum = 0, delta = 0x9e3779b9;
  for (size_t i = 0; i < 32; i++) {
    l += (((r << 4) ^ (r >> 5)) + r) ^ (sum + key[sum & 3]);
    sum += delta;
    r += (((l << 4) ^ (l >> 5)) + l) ^ (sum + key[(sum >> 11) & 3]);
  }
  v[0] = l;
  v[1] = r;
}

解密：

void decrypt(unsigned int* v, unsigned int* key) {
  unsigned int l = v[0], r = v[1], sum = 0, delta = 0x9e3779b9;
  sum = delta * 32;
  for (size_t i = 0; i < 32; i++) {
    r -= (((l << 4) ^ (l >> 5)) + l) ^ (sum + key[(sum >> 11) & 3]);
    sum -= delta;
    l -= (((r << 4) ^ (r >> 5)) + r) ^ (sum + key[sum & 3]);
  }
  v[0] = l;
  v[1] = r;
}

XXTEA算法

#include <stdbool.h>
#include <stdio.h>
#define MX \
  ((z >> 5 ^ y << 2) + (y >> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z))
bool btea(unsigned int* v, int n, unsigned int* k) {
  unsigned int z = v[n - 1], y = v[0], sum = 0, e, DELTA = 0x9e3779b9;
  unsigned int p, q;
  if (n > 1) { /* Coding Part */
    q = 6 + 52 / n;
    while (q-- > 0) {
      sum += DELTA;
      e = (sum >> 2) & 3;
      for (p = 0; p < n - 1; p++)
        y = v[p + 1], z = v[p] += MX;
      y = v[0];
      z = v[n - 1] += MX;
    }
    return 0;
  } else if (n < -1) { /* Decoding Part */
    n = -n;
    q = 6 + 52 / n;
    sum = q * DELTA;
    while (sum != 0) {
      e = (sum >> 2) & 3;
      for (p = n - 1; p > 0; p--)
        z = v[p - 1], y = v[p] -= MX;
      z = v[n - 1];
      y = v[0] -= MX;
      sum -= DELTA;
    }
    return 0;
  }
  return 1;
}
 
int main(int argc, char const* argv[]) {
  // test
  unsigned int v[2] = {1, 2}, key[4] = {1, 2, 3, 4};
  printf("%u,%u\n", v[0], v[1]);
  btea(v, 2, key);
  printf("%u,%u\n", v[0], v[1]);
  btea(v, -2, key);
  printf("%u,%u\n", v[0], v[1]);
  return 0;
}

TXTEA

和TEA算法的唯一区别就是仅使用了16轮加密，还有就是使用了魔改的CBC模式

TXCBC模式：

#include <stdint.h>

void encrypt (uint32_t* v, uint32_t* k) {
    uint32_t v0=v[0], v1=v[1], sum=0, i;           /* set up */
    uint32_t delta=0x9e3779b9;                     /* a key schedule constant */
    uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];   /* cache key */
    for (i=0; i < 16; i++) {                       /* basic cycle start */
        sum += delta;
        v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
        v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);  
    }                                              /* end cycle */
    v[0]=v0; v[1]=v1;
}

void decrypt (uint32_t* v, uint32_t* k) {
    uint32_t v0=v[0], v1=v[1], i;  /* set up */
    uint32_t delta=0x9e3779b9;                     /* a key schedule constant */
    uint32_t sum = delta << 4;
    uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];   /* cache key */
    for (i=0; i<16; i++) {                         /* basic cycle start */
        v1 -= ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);
        v0 -= ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
        sum -= delta;                                   
    }                                              /* end cycle */
    v[0]=v0; v[1]=v1;
}

参考链接：

https://bbs.pediy.com/thread-253844.htm