【安全算法之SHA256】SHA256摘要运算的C语言源码实现

概述

大家都知道摘要算法在安全领域，也是一个特别重要的存在，而SHA256是其中最常见的一种摘要算法，它的特点就是计算复杂度较低，不等长的数据原文输入，可以得出等长的摘要值，这个值是固定为32字节。正是由于这种特殊性，很多重要的数据完整性校验领域，都可以看到SHA256的影子。在一些安全认证中，摘要运算的算法等级至少是大于等于SHA256的安全级别，足以证明SHA256的重要性。
今天给大家带来SHA256的C源码版本实现，欢迎大家深入学习和讨论。

头文件定义

头文件定义如下，主要定义了SHA256的上下文结构体，以及导出的三个API：

#ifndef __SHA256_H__
#define __SHA256_H__

#include 

#define SHA256_DIGEST_LEN 32         	// SHA256 outputs a 32 byte digest

typedef uint8_t 	BYTE;             	// 8-bit byte
typedef uint32_t  	WORD;             	// 32-bit word, change to "long" for 16-bit machines

typedef struct _sha256_ctx_t {
	uint8_t 			data[64];
	uint32_t 			data_len;
	unsigned long long 	bit_len;
	uint32_t 			state[8];
} sha256_ctx_t;

void crypto_sha256_init(sha256_ctx_t *ctx);
void crypto_sha256_update(sha256_ctx_t *ctx, const uint8_t *data, uint32_t len);
void crypto_sha256_final(sha256_ctx_t *ctx, uint8_t *digest);

#endif   // __SHA256_H__

C语言版本的实现源码

下面是SHA256的C语言版本实现，主要也是围绕导出的3个API：

#include 
#include 

#include "sha256.h"

#define ROTLEFT(a,b)    (((a) << (b)) | ((a) >> (32-(b))))
#define ROTRIGHT(a,b)   (((a) >> (b)) | ((a) << (32-(b))))
#define CH(x,y,z)       (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x,y,z)      (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) 	        (ROTRIGHT(x,2) ^ ROTRIGHT(x,13) ^ ROTRIGHT(x,22))
#define EP1(x)          (ROTRIGHT(x,6) ^ ROTRIGHT(x,11) ^ ROTRIGHT(x,25))
#define SIG0(x)         (ROTRIGHT(x,7) ^ ROTRIGHT(x,18) ^ ((x) >> 3))
#define SIG1(x)         (ROTRIGHT(x,17) ^ ROTRIGHT(x,19) ^ ((x) >> 10))

static const uint32_t k[64] = 
{
	0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
	0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
	0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
	0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
	0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
	0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
	0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
	0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
};

static void local_sha256_transform(sha256_ctx_t *ctx, const uint8_t *data)
{
	uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

	for (i = 0, j = 0; i < 16; ++i, j += 4) {
		m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
	}

	for ( ; i < 64; ++i) {
		m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
	}

	a = ctx->state[0];
	b = ctx->state[1];
	c = ctx->state[2];
	d = ctx->state[3];
	e = ctx->state[4];
	f = ctx->state[5];
	g = ctx->state[6];
	h = ctx->state[7];

	for (i = 0; i < 64; ++i) {
		t1 = h + EP1(e) + CH(e,f,g) + k[i] + m[i];
		t2 = EP0(a) + MAJ(a,b,c);
		h = g;
		g = f;
		f = e;
		e = d + t1;
		d = c;
		c = b;
		b = a;
		a = t1 + t2;
	}

	ctx->state[0] += a;
	ctx->state[1] += b;
	ctx->state[2] += c;
	ctx->state[3] += d;
	ctx->state[4] += e;
	ctx->state[5] += f;
	ctx->state[6] += g;
	ctx->state[7] += h;
}

void crypto_sha256_init(sha256_ctx_t *ctx)
{
	ctx->data_len = 0;
	ctx->bit_len  = 0;
	ctx->state[0] = 0x6a09e667;
	ctx->state[1] = 0xbb67ae85;
	ctx->state[2] = 0x3c6ef372;
	ctx->state[3] = 0xa54ff53a;
	ctx->state[4] = 0x510e527f;
	ctx->state[5] = 0x9b05688c;
	ctx->state[6] = 0x1f83d9ab;
	ctx->state[7] = 0x5be0cd19;
}

void crypto_sha256_update(sha256_ctx_t *ctx, const uint8_t *data, uint32_t len)
{
	uint32_t i;

	for (i = 0; i < len; ++i) {
		ctx->data[ctx->data_len] = data[i];
		ctx->data_len++;
		if (ctx->data_len == 64) {
			local_sha256_transform(ctx, ctx->data);
			ctx->bit_len += 512;
			ctx->data_len = 0;
		}
	}
}

void crypto_sha256_final(sha256_ctx_t *ctx, uint8_t *digest)
{
	uint32_t i;

	i = ctx->data_len;

	// Pad whatever data is left in the buffer.
	if (ctx->data_len < 56) {
		ctx->data[i++] = 0x80;
		while (i < 56) {
			ctx->data[i++] = 0x00;
		}
	} else {
		ctx->data[i++] = 0x80;
		while (i < 64) {
			ctx->data[i++] = 0x00;
		}
		local_sha256_transform(ctx, ctx->data);
		memset(ctx->data, 0, 56);
	}

	// Append to the padding the total message's length in bits and transform.
	ctx->bit_len += ctx->data_len * 8;
	ctx->data[63] = ctx->bit_len;
	ctx->data[62] = ctx->bit_len >> 8;
	ctx->data[61] = ctx->bit_len >> 16;
	ctx->data[60] = ctx->bit_len >> 24;
	ctx->data[59] = ctx->bit_len >> 32;
	ctx->data[58] = ctx->bit_len >> 40;
	ctx->data[57] = ctx->bit_len >> 48;
	ctx->data[56] = ctx->bit_len >> 56;
	local_sha256_transform(ctx, ctx->data);

	// Since this implementation uses little endian byte ordering and SHA uses big endian,
	// reverse all the bytes when copying the final state to the output digest.
	for (i = 0; i < 4; ++i) {
		digest[i]      = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 4]  = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 8]  = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
		digest[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
	}
}

测试用例

针对SHA256导出的三个接口，我编写了以下测试用例：

#include 
#include 

#include "sha256.h"
#include "convert.h"

int log_hexdump(const char *title, const unsigned char *data, int len)
{
    char str[160], octet[10];
    int ofs, i, k, d;
    const unsigned char *buf = (const unsigned char *)data;
    const char dimm[] = "+------------------------------------------------------------------------------+";

    printf("%s (%d bytes):\r\n", title, len);
    printf("%s\r\n", dimm);
    printf("| Offset  : 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F   0123456789ABCDEF |\r\n");
    printf("%s\r\n", dimm);

    for (ofs = 0; ofs < (int)len; ofs += 16) {
        d = snprintf( str, sizeof(str), "| %08X: ", ofs );

        for (i = 0; i < 16; i++) {
            if ((i + ofs) < (int)len) {
                snprintf( octet, sizeof(octet), "%02X ", buf[ofs + i] );
            } else {
                snprintf( octet, sizeof(octet), "   " );
            }

            d += snprintf( &str[d], sizeof(str) - d, "%s", octet );
        }
        d += snprintf( &str[d], sizeof(str) - d, "  " );
        k = d;

        for (i = 0; i < 16; i++) {
            if ((i + ofs) < (int)len) {
                str[k++] = (0x20 <= (buf[ofs + i]) &&  (buf[ofs + i]) <= 0x7E) ? buf[ofs + i] : '.';
            } else {
                str[k++] = ' ';
            }
        }

        str[k] = '\0';
        printf("%s |\r\n", str);
    }

    printf("%s\r\n", dimm);

    return 0;
}

int main(int argc, const char *argv[])
{
	const char *data = "C1D0F8FB4958670DBA40AB1F3752EF0D";
    const char *digest_exp_str = "97B7437DF061F15182974B18E62B3D8AAFE333DCBDD2074CB8D4916509B4AD23";
	uint8_t digest_calc[SHA256_DIGEST_LEN];
    uint8_t digest_exp_hex[SHA256_DIGEST_LEN];
	sha256_ctx_t ctx;
	const char *p_calc = data;
	uint8_t data_bytes[128];
	uint16_t len_bytes;
	char data_str[128];

	if (argc > 1) {
		p_calc = argv[1];
	}

	utils_hex_string_2_bytes(data, data_bytes, &len_bytes);
	log_hexdump("data_bytes", data_bytes, len_bytes);
	utils_bytes_2_hex_string(data_bytes, len_bytes, data_str);
	printf("data_str: %s\n", data_str);
	if (!strcmp(data, data_str)) {
		printf("hex string - bytes convert OK\n");
	} else {
		printf("hex string - bytes convert FAIL\n");
	}

	crypto_sha256_init(&ctx);
	crypto_sha256_update(&ctx, (uint8_t *)p_calc, strlen(p_calc));
	crypto_sha256_final(&ctx, digest_calc);

    utils_hex_string_2_bytes(digest_exp_str, digest_exp_hex, &len_bytes);
	if (len_bytes == sizeof(digest_calc) && !memcmp(digest_calc, digest_exp_hex, sizeof(digest_calc))) {
		printf("SHA256 digest test OK\n");
        log_hexdump("digest_calc", digest_calc, sizeof(digest_calc));
	} else {
		log_hexdump("digest_calc", digest_calc, sizeof(digest_calc));
		log_hexdump("digest_exp", digest_exp_hex, sizeof(digest_exp_hex));
		printf("SHA256 digest test FAIL\n");
	}

	return 0;
}

测试用例比较简单，就是对字符串C1D0F8FB4958670DBA40AB1F3752EF0D进行SHA1运算，期望的摘要结果的hexstring是97B7437DF061F15182974B18E62B3D8AAFE333DCBDD2074CB8D4916509B4AD23，这个期望值是用算法工具算出来的。
先用API接口算出摘要值，再与期望值比较，这里有个hexstringtobyte的转换，如果比较一致则表示API计算OK；反之，接口计算失败。
同时，也欢迎大家设计提供更多的测试案例代码。

github仓库

以上代码和测试用例，及编译运行等，可以参考我的github仓库，有详细的流程介绍，欢迎大家交流讨论。如果有帮助到你的话，记得帮忙点亮一颗星哦。

更多参考链接

[1] 【安全算法的github仓库】
[2] 【安全算法之概述】一文带你简要了解常见常用的安全算法
[3] 【安全算法之base64】base64加解密的C语言源码实现
[4] 【安全算法之MD5】MD5摘要运算的C语言源码实现
[5] 【安全算法之SHA1】SHA1摘要运算的C语言源码实现
[6] 【安全算法之SHA224】SHA224摘要运算的C语言源码实现
[7] 【安全算法之SHA256】SHA256摘要运算的C语言源码实现
[8] 【安全算法之SHA384】SHA384摘要运算的C语言源码实现
[9] 【安全算法之SHA512】SHA512摘要运算的C语言源码实现