Question

我正在尝试在WebAssembly中实现JWT令牌（仅编码），目标是拥有一个非常轻量级的 wasm模块。作为Web开发人员，我的C知识是有限的。现在我已经实现了以下功能（从JS移植）来编码url-safe Base64编码器，它完美地工作。

char _keyStr[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";
char ret_val[200];

char* encode (char *data){
    int len = strlen(data);
    int i = 0;
    int j = 0;

    while(i<len){
        char chr1 = data[i++];
        int chr2Out = (i > len - 1)? 1:0;
        char chr2 = data[i++];
        int chr3Out = (i > len - 1)? 1:0;;
        char chr3 = data[i++];


        char enc1 = chr1 >> 2;
        char enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
        char enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
        char enc4 = chr3 & 63;

        if (chr2Out) {
            enc3 = enc4 = 64;
        } else if (chr3Out) {
            enc4 = 64;
        }

        ret_val[j++] = _keyStr[enc1];
        ret_val[j++] = _keyStr[enc2];
        ret_val[j++] = _keyStr[enc3];
        ret_val[j++] = _keyStr[enc4];

    }
    ret_val[j] = '\0';
    return ret_val;
}

我的下一个挑战是能够使用HmacSHA256签署我的JWT有效载荷。下面的JS小提琴，描述了我想用C完成的事情。 https://jsfiddle.net/gm7boy2p/813/

我正在努力整合第三方代码并将其与emcc进行比较。我正在寻找一个轻量级的图书馆或片段。

示例代码或任何帮助将不胜感激。

更新经过额外的研究，阅读this stackoverflow问题和this文章，看起来使用openssl或任何其他带有WebAssembly的外部库远非微不足道。所以我现在正在寻找的是一个独立的C函数，我可以将它集成到我现有的代码中。

Answer 1

使用Web程序集时，确实无法使用系统库。因此，唯一的解决方案是以符合交叉编译器已提供的库（即emscripten）的方式从源代码编译它们

因此，对于您的问题，我找到了满足您用例的库cryptopp。示例here展示了如何使用此库。

现在你怎么能为你的案例编译这个库？由于它带有一个make文件，所以你需要做的就是调用

emmake make -f GNUmakefile-cross -j8

这将生成一个.a文件，该文件实际上是一个.bc文件，可以与您希望在Web上运行的现有C / C ++程序链接。只需确保适当地包含此文件的标头。如果你为你的项目制作一个makefile会更好。

P.S我在我的系统中通过在GNUmakefile-cross文件的末尾添加这些行来在本地工作

cryptest.html: libcryptopp.a $(TESTOBJS)
    $(CXX) -s DISABLE_EXCEPTION_CATCHING=0 --preload-file TestData -o $@ $(strip $(CXXFLAGS)) $(TESTOBJS) ./libcryptopp.a $(LDFLAGS) $(LDLIBS)

我更改了test.cpp文件以包含＆＃34; HMAC＆＃34;的示例代码。然后从命令行调用以下行

emmake make -f GNUmakefile-cross cryptest.html -j8

输出即cryptest.html，在firefox中打开时运行得很完美。

Answer 2

我设法在C中创建了一个小的（library-ish）代码片段。我检查了here的结果。

此处还显示：

SHA256代码取自here。用于cgminer。

我刚修改了一下（删除了引用等）以使其独立工作。这是总代码和测试软件。

sha2.h：

/*
 * FIPS 180-2 SHA-224/256/384/512 implementation
 * Last update: 02/02/2007
 * Issue date:  04/30/2005
 *
 * Copyright (C) 2013, Con Kolivas <kernel@kolivas.org>
 * Copyright (C) 2005, 2007 Olivier Gay <olivier.gay@a3.epfl.ch>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef SHA2_H
#define SHA2_H

#define SHA256_DIGEST_SIZE ( 256 / 8)
#define SHA256_BLOCK_SIZE  ( 512 / 8)

#define SHFR(x, n)    (x >> n)
#define ROTR(x, n)   ((x >> n) | (x << ((sizeof(x) << 3) - n)))
#define CH(x, y, z)  ((x & y) ^ (~x & z))
#define MAJ(x, y, z) ((x & y) ^ (x & z) ^ (y & z))

#define SHA256_F1(x) (ROTR(x,  2) ^ ROTR(x, 13) ^ ROTR(x, 22))
#define SHA256_F2(x) (ROTR(x,  6) ^ ROTR(x, 11) ^ ROTR(x, 25))
#define SHA256_F3(x) (ROTR(x,  7) ^ ROTR(x, 18) ^ SHFR(x,  3))
#define SHA256_F4(x) (ROTR(x, 17) ^ ROTR(x, 19) ^ SHFR(x, 10))

typedef struct {
    unsigned int tot_len;
    unsigned int len;
    unsigned char block[2 * SHA256_BLOCK_SIZE];
    unsigned int h[8];
} sha256_ctx;

extern unsigned int sha256_k[64];

void sha256_init(sha256_ctx * ctx);
void sha256_update(sha256_ctx *ctx, const unsigned char *message,
                   unsigned int len);
void sha256_final(sha256_ctx *ctx, unsigned char *digest);
void sha256(const unsigned char *message, unsigned int len,
            unsigned char *digest);

#endif /* !SHA2_H */

main.c中：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "sha2.h"

#define UNPACK32(x, str)                      \
{                                             \
*((str) + 3) = (unsigned char) ((x)      );       \
*((str) + 2) = (unsigned char) ((x) >>  8);       \
*((str) + 1) = (unsigned char) ((x) >> 16);       \
*((str) + 0) = (unsigned char) ((x) >> 24);       \
}

#define PACK32(str, x)                        \
{                                             \
*(x) =   ((unsigned int) *((str) + 3)      )    \
| ((unsigned int) *((str) + 2) <<  8)    \
| ((unsigned int) *((str) + 1) << 16)    \
| ((unsigned int) *((str) + 0) << 24);   \
}

#define SHA256_SCR(i)                         \
{                                             \
w[i] =  SHA256_F4(w[i -  2]) + w[i -  7]  \
+ SHA256_F3(w[i - 15]) + w[i - 16]; \
}

unsigned int sha256_h0[8] =
{ 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
    0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 };

unsigned int sha256_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 };

/* SHA-256 functions */

void sha256_transf(sha256_ctx *ctx, const unsigned char *message,
                   unsigned int block_nb)
{
    unsigned int w[64];
    unsigned int wv[8];
    unsigned int t1, t2;
    const unsigned char *sub_block;
    int i;

    int j;

    for (i = 0; i < (int)block_nb; i++) {
        sub_block = message + (i << 6);

        for (j = 0; j < 16; j++) {
            PACK32(&sub_block[j << 2], &w[j]);
        }

        for (j = 16; j < 64; j++) {
            SHA256_SCR(j);
        }

        for (j = 0; j < 8; j++) {
            wv[j] = ctx->h[j];
        }

        for (j = 0; j < 64; j++) {
            t1 = wv[7] + SHA256_F2(wv[4]) + CH(wv[4], wv[5], wv[6])
            + sha256_k[j] + w[j];
            t2 = SHA256_F1(wv[0]) + MAJ(wv[0], wv[1], wv[2]);
            wv[7] = wv[6];
            wv[6] = wv[5];
            wv[5] = wv[4];
            wv[4] = wv[3] + t1;
            wv[3] = wv[2];
            wv[2] = wv[1];
            wv[1] = wv[0];
            wv[0] = t1 + t2;
        }

        for (j = 0; j < 8; j++) {
            ctx->h[j] += wv[j];
        }
    }
}

void sha256(const unsigned char *message, unsigned int len, unsigned char *digest)
{
    sha256_ctx ctx;

    sha256_init(&ctx);
    sha256_update(&ctx, message, len);
    sha256_final(&ctx, digest);
}

void sha256_init(sha256_ctx *ctx)
{
    int i;
    for (i = 0; i < 8; i++) {
        ctx->h[i] = sha256_h0[i];
    }

    ctx->len = 0;
    ctx->tot_len = 0;
}

void sha256_update(sha256_ctx *ctx, const unsigned char *message,
                   unsigned int len)
{
    unsigned int block_nb;
    unsigned int new_len, rem_len, tmp_len;
    const unsigned char *shifted_message;

    tmp_len = SHA256_BLOCK_SIZE - ctx->len;
    rem_len = len < tmp_len ? len : tmp_len;

    memcpy(&ctx->block[ctx->len], message, rem_len);

    if (ctx->len + len < SHA256_BLOCK_SIZE) {
        ctx->len += len;
        return;
    }

    new_len = len - rem_len;
    block_nb = new_len / SHA256_BLOCK_SIZE;

    shifted_message = message + rem_len;

    sha256_transf(ctx, ctx->block, 1);
    sha256_transf(ctx, shifted_message, block_nb);

    rem_len = new_len % SHA256_BLOCK_SIZE;

    memcpy(ctx->block, &shifted_message[block_nb << 6],
           rem_len);

    ctx->len = rem_len;
    ctx->tot_len += (block_nb + 1) << 6;
}

void sha256_final(sha256_ctx *ctx, unsigned char *digest)
{
    unsigned int block_nb;
    unsigned int pm_len;
    unsigned int len_b;

    int i;

    block_nb = (1 + ((SHA256_BLOCK_SIZE - 9)
                     < (ctx->len % SHA256_BLOCK_SIZE)));

    len_b = (ctx->tot_len + ctx->len) << 3;
    pm_len = block_nb << 6;

    memset(ctx->block + ctx->len, 0, pm_len - ctx->len);
    ctx->block[ctx->len] = 0x80;
    UNPACK32(len_b, ctx->block + pm_len - 4);

    sha256_transf(ctx, ctx->block, block_nb);

    for (i = 0; i < 8; i++) {
        UNPACK32(ctx->h[i], &digest[i << 2]);
    }
}

unsigned char * HMAC_SHA256(const char * msg, const char * key)
{
    unsigned int blocksize = 64;
    unsigned char * Key0 = (unsigned char *)calloc(blocksize, sizeof(unsigned char));
    unsigned char * Key0_ipad = (unsigned char *)calloc(blocksize, sizeof(unsigned char));
    unsigned char * Key0_ipad_concat_text = (unsigned char *)calloc( (blocksize + strlen(msg)), sizeof(unsigned char));
    unsigned char * Key0_ipad_concat_text_digest = (unsigned char *)calloc( blocksize, sizeof(unsigned char));
    unsigned char * Key0_opad = (unsigned char *)calloc(blocksize, sizeof(unsigned char));
    unsigned char * Key0_opad_concat_prev = (unsigned char *)calloc(blocksize + 32, sizeof(unsigned char));

    unsigned char * HMAC_SHA256 = (unsigned char *)malloc(32 * sizeof(unsigned char));

    if (strlen(key) < blocksize) {
        for (int i = 0; i < blocksize; i++) {
            if (i < strlen(key)) Key0[i] = key[i];
            else Key0[i] = 0x00;
        }
    }
    else if (strlen(key) > blocksize) {
        sha256(key, strlen(key), Key0);
        for (unsigned char i = strlen(key); i < blocksize; i++) {
            Key0[i] = 0x00;
        }
    }

    for (int i = 0; i < blocksize; i++) {
        Key0_ipad[i] = Key0[i] ^ 0x36;
    }
    for (int i = 0; i < blocksize; i++) {
        Key0_ipad_concat_text[i] = Key0_ipad[i];
    }
    for (int i = blocksize; i < blocksize + strlen(msg); i++) {
        Key0_ipad_concat_text[i] = msg[i - blocksize];
    }

    sha256(Key0_ipad_concat_text, blocksize + (unsigned int)strlen(msg), Key0_ipad_concat_text_digest);

    for (int i = 0; i < blocksize; i++) {
        Key0_opad[i] = Key0[i] ^ 0x5C;
    }

    for (int i = 0; i < blocksize; i++) {
        Key0_opad_concat_prev[i] = Key0_opad[i];
    }
    for (int i = blocksize; i < blocksize + 32; i++) {
        Key0_opad_concat_prev[i] = Key0_ipad_concat_text_digest[i - blocksize];
    }

    sha256(Key0_opad_concat_prev, blocksize + 32, HMAC_SHA256);
    return HMAC_SHA256;
}


int main()
{
    unsigned char * result;

    result = HMAC_SHA256("Sample #1", "MyKey");

    unsigned char arr[32] = { 0 };
    memcpy(arr, result, 32);

    for(int i = 0; i < 32; i++) {
        printf("%#02x, ", arr[i]);
    }
    return 0;
}

以下是样本运行的结果：

编辑：

可以找到关于HMAC_SHA256功能的信息here。我写的那个只是为了演示目的。可以相应地修改它。

编辑2：

我添加了Base64格式的代码。我使用了维基百科上的信息。样本测试运行适用于OP的输入和输出。结果如下所示：

更新了main.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include "sha2.h"

#define HMAC_SHA256_FAIL_STRING "HMAC_SHA256 has failed." // fprintf(stderr, "%s\n", strerror(errno));

#define UNPACK32(x, str)                      \
{                                             \
*((str) + 3) = (unsigned char) ((x)      );       \
*((str) + 2) = (unsigned char) ((x) >>  8);       \
*((str) + 1) = (unsigned char) ((x) >> 16);       \
*((str) + 0) = (unsigned char) ((x) >> 24);       \
}

#define PACK32(str, x)                        \
{                                             \
*(x) =   ((unsigned int) *((str) + 3)      )    \
| ((unsigned int) *((str) + 2) <<  8)    \
| ((unsigned int) *((str) + 1) << 16)    \
| ((unsigned int) *((str) + 0) << 24);   \
}

#define SHA256_SCR(i)                         \
{                                             \
w[i] =  SHA256_F4(w[i -  2]) + w[i -  7]  \
+ SHA256_F3(w[i - 15]) + w[i - 16]; \
}

char Base64_Table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

unsigned int sha256_h0[8] =
{ 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
    0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 };

unsigned int sha256_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 };

/* SHA-256 functions */

void sha256_transf(sha256_ctx *ctx, const unsigned char *message,
                   unsigned int block_nb)
{
    unsigned int w[64];
    unsigned int wv[8];
    unsigned int t1, t2;
    const unsigned char *sub_block;
    int i;

    int j;

    for (i = 0; i < (int)block_nb; i++) {
        sub_block = message + (i << 6);

        for (j = 0; j < 16; j++) {
            PACK32(&sub_block[j << 2], &w[j]);
        }

        for (j = 16; j < 64; j++) {
            SHA256_SCR(j);
        }

        for (j = 0; j < 8; j++) {
            wv[j] = ctx->h[j];
        }

        for (j = 0; j < 64; j++) {
            t1 = wv[7] + SHA256_F2(wv[4]) + CH(wv[4], wv[5], wv[6])
            + sha256_k[j] + w[j];
            t2 = SHA256_F1(wv[0]) + MAJ(wv[0], wv[1], wv[2]);
            wv[7] = wv[6];
            wv[6] = wv[5];
            wv[5] = wv[4];
            wv[4] = wv[3] + t1;
            wv[3] = wv[2];
            wv[2] = wv[1];
            wv[1] = wv[0];
            wv[0] = t1 + t2;
        }

        for (j = 0; j < 8; j++) {
            ctx->h[j] += wv[j];
        }
    }
}

void sha256(const unsigned char *message, unsigned int len, unsigned char *digest)
{
    sha256_ctx ctx;

    sha256_init(&ctx);
    sha256_update(&ctx, message, len);
    sha256_final(&ctx, digest);
}

void sha256_init(sha256_ctx *ctx)
{
    int i;
    for (i = 0; i < 8; i++) {
        ctx->h[i] = sha256_h0[i];
    }

    ctx->len = 0;
    ctx->tot_len = 0;
}

void sha256_update(sha256_ctx *ctx, const unsigned char *message,
                   unsigned int len)
{
    unsigned int block_nb;
    unsigned int new_len, rem_len, tmp_len;
    const unsigned char *shifted_message;

    tmp_len = SHA256_BLOCK_SIZE - ctx->len;
    rem_len = len < tmp_len ? len : tmp_len;

    memcpy(&ctx->block[ctx->len], message, rem_len);

    if (ctx->len + len < SHA256_BLOCK_SIZE) {
        ctx->len += len;
        return;
    }

    new_len = len - rem_len;
    block_nb = new_len / SHA256_BLOCK_SIZE;

    shifted_message = message + rem_len;

    sha256_transf(ctx, ctx->block, 1);
    sha256_transf(ctx, shifted_message, block_nb);

    rem_len = new_len % SHA256_BLOCK_SIZE;

    memcpy(ctx->block, &shifted_message[block_nb << 6],
           rem_len);

    ctx->len = rem_len;
    ctx->tot_len += (block_nb + 1) << 6;
}

void sha256_final(sha256_ctx *ctx, unsigned char *digest)
{
    unsigned int block_nb;
    unsigned int pm_len;
    unsigned int len_b;

    int i;

    block_nb = (1 + ((SHA256_BLOCK_SIZE - 9)
                     < (ctx->len % SHA256_BLOCK_SIZE)));

    len_b = (ctx->tot_len + ctx->len) << 3;
    pm_len = block_nb << 6;

    memset(ctx->block + ctx->len, 0, pm_len - ctx->len);
    ctx->block[ctx->len] = 0x80;
    UNPACK32(len_b, ctx->block + pm_len - 4);

    sha256_transf(ctx, ctx->block, block_nb);

    for (i = 0; i < 8; i++) {
        UNPACK32(ctx->h[i], &digest[i << 2]);
    }
}

char * HMAC_SHA256(char * msg, char * key)
{
    size_t blocksize;

    blocksize = 64;
    char * Key0 = (char *)calloc(blocksize, sizeof(char));
    if (Key0 == NULL) {
        return HMAC_SHA256_FAIL_STRING;
    }

    blocksize = 64;
    char * Key0_ipad = (char *)calloc(blocksize, sizeof(char));
    if (Key0_ipad == NULL) {
        free(Key0);
        return HMAC_SHA256_FAIL_STRING;
    }

    blocksize = 64 + strlen(msg);
    char * Key0_ipad_concat_text = (char *)calloc( blocksize, sizeof(char));
    if (Key0_ipad_concat_text == NULL) {
        free(Key0);
        free(Key0_ipad);
        return HMAC_SHA256_FAIL_STRING;
    }

    blocksize = 64;
    char * Key0_ipad_concat_text_digest = (char *)calloc( blocksize, sizeof(char));
    if (Key0_ipad_concat_text_digest == NULL) {
        free(Key0);
        free(Key0_ipad);
        free(Key0_ipad_concat_text);
        return HMAC_SHA256_FAIL_STRING;
    }

    blocksize = 64;
    char * Key0_opad = (char *)calloc(blocksize, sizeof(char));
    if (Key0_opad == NULL) {
        free(Key0);
        free(Key0_ipad);
        free(Key0_ipad_concat_text);
        free(Key0_ipad_concat_text_digest);
        return HMAC_SHA256_FAIL_STRING;
    }

    blocksize = 64 + 32;
    char * Key0_opad_concat_prev = (char *)calloc(blocksize + 32, sizeof(char));
    if (Key0_opad_concat_prev == NULL) {
        free(Key0);
        free(Key0_ipad);
        free(Key0_ipad_concat_text);
        free(Key0_ipad_concat_text_digest);
        free(Key0_opad);
        return HMAC_SHA256_FAIL_STRING;
    }

    blocksize = 64;
    char * HMAC_SHA256 = (char *)malloc(blocksize/2 * sizeof(char));
    if (HMAC_SHA256 == NULL) {
        free(Key0);
        free(Key0_ipad);
        free(Key0_ipad_concat_text);
        free(Key0_ipad_concat_text_digest);
        free(Key0_opad);
        free(Key0_opad_concat_prev);
        return HMAC_SHA256_FAIL_STRING;
    }

    if (strlen(key) < blocksize) {
        char * tmp = key;
        char * tmp2 = Key0;
        for (int i = 0; i < blocksize; i++) {
            if (i < strlen(key)) *tmp2++ = *tmp++;
            else *tmp2++ = 0x00;
        }
    }
    else if (strlen(key) > blocksize) {
        sha256((unsigned char *)key, strlen(key), (unsigned char *)Key0);
        for (unsigned char i = strlen(key); i < blocksize; i++) {
            Key0[i] = 0x00;
        }
    }

    for (int i = 0; i < blocksize; i++) {
        Key0_ipad[i] = Key0[i] ^ 0x36;
    }
    for (int i = 0; i < blocksize; i++) {
        Key0_ipad_concat_text[i] = Key0_ipad[i];
    }
    for (int i = blocksize; i < blocksize + strlen(msg); i++) {
        Key0_ipad_concat_text[i] = msg[i - blocksize];
    }

    sha256((unsigned char *)Key0_ipad_concat_text, blocksize + (unsigned int)strlen(msg), (unsigned char *)Key0_ipad_concat_text_digest);

    for (int i = 0; i < blocksize; i++) {
        Key0_opad[i] = Key0[i] ^ 0x5C;
    }

    for (int i = 0; i < blocksize; i++) {
        Key0_opad_concat_prev[i] = Key0_opad[i];
    }
    for (int i = blocksize; i < blocksize + 32; i++) {
        Key0_opad_concat_prev[i] = Key0_ipad_concat_text_digest[i - blocksize];
    }

    sha256((unsigned char *)Key0_opad_concat_prev, blocksize + 32, (unsigned char *)HMAC_SHA256);

    free(Key0);
    free(Key0_ipad);
    free(Key0_ipad_concat_text);
    free(Key0_ipad_concat_text_digest);
    free(Key0_opad);
    free(Key0_opad_concat_prev);
    return HMAC_SHA256;
}

char * Base64_Stringify(char * hash, size_t length)
{
    size_t no_op = 0;
    size_t Base64_size;
    char * Base64;
    unsigned long tmp = length;
    if (tmp % 3 == 0) {
        Base64_size = 4 * tmp / 3;
        Base64 = (char *)calloc(Base64_size + 1, sizeof(char));
    }
    else if (tmp % 3 == 1) {
        tmp += 2;
        Base64_size = 4 * tmp / 3;
        Base64 = (char *)calloc(Base64_size + 1, sizeof(char));
        Base64[Base64_size - 1] = '=';
        Base64[Base64_size - 2] = '=';
        no_op = 2;
    }
    else if (tmp % 3 == 2) {
        tmp += 1;
        Base64_size = 4 * tmp / 3;
        Base64 = (char *)calloc(Base64_size + 1, sizeof(char));
        Base64[Base64_size - 1] = '=';
        no_op = 1;
    }

    unsigned int b64_case = 0;
    size_t j = 0;
    for (int i = 0; i < Base64_size - no_op; i++) {
        switch (b64_case) {
            case 0:
            {
                Base64[i] = Base64_Table[(hash[j] & 0xFC) >> 2];
                j++;
                b64_case = 1;
            }
                break;
            case 1:
            {
                Base64[i] = Base64_Table[((hash[j-1] & 0x03) << 4) | ((hash[j] & 0xF0) >> 4)];
                b64_case = 2;
            }
                break;
            case 2:
            {
                Base64[i] = Base64_Table[((hash[j] & 0x0F) << 2) | ((hash[j+1] & 0xC0) >> 6)];
                j++;
                b64_case = 3;
            }
                break;
            case 3:
            {
                Base64[i] = Base64_Table[(hash[j] & 0x3F)];
                j++;
                b64_case = 0;
            }
                break;

            default:
                break;
        }
    }

    return Base64;
}


int main()
{
    char * HMAC_SHA256_result;
    char * Base64_Stringify_result;

    HMAC_SHA256_result = HMAC_SHA256("test", "secret");
    Base64_Stringify_result = Base64_Stringify(HMAC_SHA256_result, 32);

    unsigned char arr[32] = { 0 };
    memcpy(arr, HMAC_SHA256_result, 32);

    for(int i = 0; i < 32; i++) {
        printf("%#02x, ", arr[i]);
    }
    printf("\n\n");

    for(int i = 0; i < strlen(Base64_Stringify_result); i++) {
        printf("%c", Base64_Stringify_result[i]);
    }
    printf("\n\n");
    return 0;
}

我要离开旧的main.c以供参考。您还可以修改更新的main.c函数，例如calloc失败时的错误代码......

Answer 3

我已经创建了一个简单的示例，说明如何使用libgcrypt库创建hmac。您只需要在系统中安装它，然后使用-lgcrypt标志编译程序以链接库。

当您询问一个独立函数时，我创建了一个函数，您可以使用键和消息调用该函数，该函数返回带有base64编码结果的字符串，这正是您在JSFiddle中所要求的。

#include <stdio.h>
#include <string.h>
#include <gcrypt.h>
#include <stdint.h>


static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
                                'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
                                'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
                                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
                                'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                                'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                                'w', 'x', 'y', 'z', '0', '1', '2', '3',
                                '4', '5', '6', '7', '8', '9', '+', '/'};
static char *decoding_table = NULL;
static int mod_table[] = {0, 2, 1};


char *base64_encode(const unsigned char *data,
                    size_t input_length,
                    size_t *output_length) {

    *output_length = 4 * ((input_length + 2) / 3);

    char *encoded_data = calloc(1,*output_length+1);
    if (encoded_data == NULL) return NULL;

    for (int i = 0, j = 0; i < input_length;) {

        uint32_t octet_a = i < input_length ? (unsigned char)data[i++] : 0;
        uint32_t octet_b = i < input_length ? (unsigned char)data[i++] : 0;
        uint32_t octet_c = i < input_length ? (unsigned char)data[i++] : 0;

        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

        encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
    }

    for (int i = 0; i < mod_table[input_length % 3]; i++)
        encoded_data[*output_length - 1 - i] = '=';

    return encoded_data;
}

//don't forget to free the return pointer!
char* hmacSHA256(gcry_mac_hd_t hd, const char* key, size_t key_size, const char* msg, size_t msg_size) {
    unsigned char output[32];
    size_t outputSize = 32;
    gcry_mac_reset(hd);
    gcry_mac_setkey(hd,key,strlen(key));
    gcry_mac_write(hd,msg,strlen(msg));
    gcry_mac_read(hd,output,&outputSize);
    return base64_encode(output,outputSize,&outputSize);
}

int main() {
    const char* const key = "secret";
    const char* const msg = "test";
    //hmacsha256 returns 256 bits, meaning 32 bytes
    unsigned char output[32];
    size_t outputSize = 32;
    gcry_mac_hd_t hd;
    gcry_mac_open(&hd,GCRY_MAC_HMAC_SHA256,0,NULL);

    char* tmp = hmacSHA256(hd,key,strlen(key),msg,strlen(msg));
    printf("HMAC-SHA256: '%s'\n",tmp);
    free(tmp);

    tmp = hmacSHA256(hd,"secrett",7,msg,strlen(msg));
    printf("HMAC-SHA256: '%s'\n",tmp);
    free(tmp);

    gcry_mac_close(hd);
    return 0;
}

重要说明：

- 不要忘记释放hmacSHA256函数的返回值，并在完成散列后调用gcry_mac_close。

- 我在函数参数中包含了消息的大小和消息的大小，因为这样你可以做二进制数据的HMAC以及ASCII / UTF-8编码的字符串。如果您不打算使用二进制数据，请随意从参数中删除大小并使用strlen计算函数内部的大小，就像我调用函数时在main中一样。

- 我没有在函数中包装gcry_mac_hd_t的创建，因为重用相同的处理程序更有效，每次需要重新使用它时重置它，然后每次你创建一个新的需要它。如果在同一执行中多次调用此函数，则此优化更加明显！

使用Emscripten

3 个答案: