加密解密算法|使用C语言实现加密解密算法XTEA

一、前言

数据通信时我们经常用到加密，尤其在单片机开发中计算能力有限，因此找到一个适合单片机加密的方式格外的重要，今天介绍一下XTEA加密算法。

在数据的加解密领域，算法分为对称密钥与非对称密钥两种。对称密钥与非对称密钥由于各自的特点，所应用的领域是不尽相同的。对称密钥加密算法由于其速度快，一般用于整体数据的加密，而非对称密钥加密算法的安全性能佳，在数字签名领域得到广泛的应用。

TEA算法是由剑桥大学计算机实验室的David Wheeler和Roger Needham于1994年发明，TEA是TIny EncrypTIon Algorithm的缩写，以加密解密速度快，实现简单著称。TEA算法每一次可以操作64bit(8byte)，采用128bit(16byte)作为key，算法采用迭代的形式，推荐的迭代轮数是64轮，最少32轮。为解决TEA算法密钥表攻击的问题，TEA算法先后经历了几次改进，从XTEA到BLOCK TEA，直至最新的XXTEA。XTEA也称做TEAN，它使用与TEA相同的简单运算，但四个子密钥采取不正规的方式进行混合以阻止密钥表攻击。Block TEA算法可以对32位的任意整数倍长度的变量块进行加解密的操作，该算法将XTEA轮循函数依次应用于块中的每个字，并且将它附加于被应用字的邻字。

二、XTEA加密中的ECB和CBC

CBC模式的全称是Cipher Block Chaining模式（密文分组链接模式），之所以叫这个名字，是因为密文分组像链条一样相互连接在一起。在CBC模式中，首先将明文分组与前一个密文分组进行XOR运算，然后再进行加密。

CBC模式加解密过程如下：

三、XTEA C语言实现

代码来自mbed TLS

/* Implementation that should never be optimized out by the compiler */static void mbedtls_zeroize( void *v, size_t n ) {volatile unsigned char *p = v; while( n-- ) *p++ = 0;}/** 32-bit integer manipulation macros (big endian)*/#ifndef GET_UINT32_BE#define GET_UINT32_BE(n,b,i) \{\(n) = ( (uint32_t) (b)[(i) ] << 24 ) \| ( (uint32_t) (b)[(i) + 1] << 16 ) \| ( (uint32_t) (b)[(i) + 2] << 8 ) \| ( (uint32_t) (b)[(i) + 3] ); \}#endif#ifndef PUT_UINT32_BE#define PUT_UINT32_BE(n,b,i) \{\(b)[(i) ] = (unsigned char) ( (n) >> 24 ); \(b)[(i) + 1] = (unsigned char) ( (n) >> 16 ); \(b)[(i) + 2] = (unsigned char) ( (n) >> 8 ); \(b)[(i) + 3] = (unsigned char) ( (n) ); \}#endifvoid mbedtls_xtea_init( mbedtls_xtea_context *ctx ){memset( ctx, 0, sizeof( mbedtls_xtea_context ) );}void mbedtls_xtea_free( mbedtls_xtea_context *ctx ){if( ctx == NULL )return;mbedtls_zeroize( ctx, sizeof( mbedtls_xtea_context ) );}/** XTEA key schedule*/void mbedtls_xtea_setup( mbedtls_xtea_context *ctx, const unsigned char key[16] ){int i;memset( ctx, 0, sizeof(mbedtls_xtea_context) );for( i = 0; i < 4; i++ ){GET_UINT32_BE( ctx->k[i], key, i << 2 );}}

XTEA-ECB

/** XTEA encrypt function*/int mbedtls_xtea_crypt_ecb( mbedtls_xtea_context *ctx, int mode,const unsigned char input[8], unsigned char output[8]){uint32_t *k, v0, v1, i;k = ctx->k;GET_UINT32_BE( v0, input, 0 );GET_UINT32_BE( v1, input, 4 );if( mode == MBEDTLS_XTEA_ENCRYPT ){uint32_t sum = 0, delta = 0x9E3779B9;for( i = 0; i < 32; i++ ){v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + k[sum & 3]);sum += delta;v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + k[(sum>>11) & 3]);}}else /* MBEDTLS_XTEA_DECRYPT */{uint32_t delta = 0x9E3779B9, sum = delta * 32;for( i = 0; i < 32; i++ ){v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + k[(sum>>11) & 3]);sum -= delta;v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + k[sum & 3]);}}PUT_UINT32_BE( v0, output, 0 );PUT_UINT32_BE( v1, output, 4 );return( 0 );}

XTEA-CBC

/** XTEA-CBC buffer encryption/decryption*/int mbedtls_xtea_crypt_cbc( mbedtls_xtea_context *ctx, int mode, size_t length,unsigned char iv[8], const unsigned char *input,unsigned char *output){int i;unsigned char temp[8];if( length % 8 )return( MBEDTLS_ERR_XTEA_INVALID_INPUT_LENGTH );if( mode == MBEDTLS_XTEA_DECRYPT )//decrypt{while( length > 0 ){memcpy( temp, input, 8 );mbedtls_xtea_crypt_ecb( ctx, mode, input, output );for( i = 0; i < 8; i++ )output[i] = (unsigned char)( output[i] ^ iv[i] );memcpy( iv, temp, 8 );input += 8;output += 8;length -= 8;}}else{while( length > 0 ){for( i = 0; i < 8; i++ )output[i] = (unsigned char)( input[i] ^ iv[i] );mbedtls_xtea_crypt_ecb( ctx, mode, output, output );memcpy( iv, output, 8 );input += 8;output += 8;length -= 8;}}return( 0 );}

四、测试

测试代码:

/** XTEA tests vectors (non-official)*/static const unsigned char xtea_test_key[6][16] ={{ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b,0x0c, 0x0d, 0x0e, 0x0f },{ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b,0x0c, 0x0d, 0x0e, 0x0f },{ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b,0x0c, 0x0d, 0x0e, 0x0f },{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00 },{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00 },{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00 }};static const unsigned char xtea_test_pt[6][8] ={{ 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48 },{ 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41 },{ 0x5a, 0x5b, 0x6e, 0x27, 0x89, 0x48, 0xd7, 0x7f },{ 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48 },{ 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41 },{ 0x70, 0xe1, 0x22, 0x5d, 0x6e, 0x4e, 0x76, 0x55 }};static const unsigned char xtea_test_ct[6][8] ={{ 0x49, 0x7d, 0xf3, 0xd0, 0x72, 0x61, 0x2c, 0xb5 },{ 0xe7, 0x8f, 0x2d, 0x13, 0x74, 0x43, 0x41, 0xd8 },{ 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41 },{ 0xa0, 0x39, 0x05, 0x89, 0xf8, 0xb8, 0xef, 0xa5 },{ 0xed, 0x23, 0x37, 0x5a, 0x82, 0x1a, 0x8c, 0x2d },{ 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41 }};/** Checkup routine*/int mbedtls_xtea_self_test( int verbose ){int i, ret = 0;unsigned char buf[8];mbedtls_xtea_context ctx;mbedtls_xtea_init( &ctx );for( i = 0; i < 6; i++ ){if( verbose != 0 )mbedtls_printf( " XTEA test #%d: ", i + 1 );memcpy( buf, xtea_test_pt[i], 8 );mbedtls_xtea_setup( &ctx, xtea_test_key[i] );mbedtls_xtea_crypt_ecb( &ctx, MBEDTLS_XTEA_ENCRYPT, buf, buf );if( memcmp( buf, xtea_test_ct[i], 8 ) != 0 ){if( verbose != 0 )mbedtls_printf( "failed\n" );ret = 1;goto exit;}if( verbose != 0 )mbedtls_printf( "passed\n" );}if( verbose != 0 )mbedtls_printf( "\n" );exit:mbedtls_xtea_free( &ctx );return( ret );}

运行: