(Encryption Basics) TEA

TEA algorithm

1 Introduction

The full name of TEA algorithm is Tiny Encryption Algorithm (Tiny Encryption Algorithm) is a simple and easy to implement encryption algorithm, usually only a few codes can be implemented

2. Encryption process

In the encryption process, two 32-bit unsigned integers are used, the key is 128 bits, and four 32-bit unsigned integers

Flow chart :

There are a total of five quantities involved in the operation in encryption, l (the first plaintext), r (the second plaintext), sum=0, given a fixed value for delta, each round of key:

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

A total of 32 executions, and finally put l, r into v[0], v[1] to store, get the ciphertext

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;
}

The decryption process is the opposite of encryption

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 algorithm

It is very similar to the TEA algorithm, the difference is that the result of the change of r and the result of the change of l are alternately assigned, and the number of displacements has been changed, and some operations have been mixed.

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;
}

Decrypt:

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 algorithm

#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

The only difference with the TEA algorithm is that only 16 rounds of encryption are used, and the CBC mode with magic modification is used

TXCBC mode:

#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;
}

Reference link:

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