HmacSHA256 in WebAssembly compiled with Emscripten

It is true that you cannot use the system libraries when using web-assembly. So the only solution is to compile them from source in a way the that is compliant with the libraries already provided by the cross-compiler (ie emscripten)

So for your question, I found the library cryptopp, satisfying your use case. The example here showcase how you can use this library.

Now how can you compile this library for your case? Since it comes with a make file, all you need to do is call

emmake make -f GNUmakefile-cross -j8

This will generate a .a file, which is actually a .bc file and can be linked with your existing C/C++ program, that you wish to run on web. Just make sure to include the headers of this file appropriately. It would even be better if you make a makefile for your project.

P.S I got this working locally in my system, by adding these line at the end of the GNUmakefile-cross file

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

I changed the test.cpp file to include sample code for "HMAC" and then called the following lines from the command line

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

The output ie cryptest.html, when opened in firefox worked flawlessly.

I managed to create a small (library-ish) code snippet in C. I checked the results from here.

Also shown here:

The SHA256 code is taken from here. Used in cgminer.

I just modified it a bit (removed references etc.) to make it work stand-alone. Here is the total code and test software.

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:

#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;}

Here are the results for the sample run:

EDIT:

Info on the HMAC_SHA256 function can be found here. The one I wrote is just for demonstration purposes. One can modify it accordingly.

EDIT 2:

I added the code for Base64 format. I used the information found on Wikipedia. Sample test run works for OP's input and output. Results are as shown:

Updated 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;}

I'm leaving the old main.c for reference. You can also modify the updated main.c functions, e.g. the error codes when calloc fails...

I've created a simple example of how you can create the hmac with the libgcrypt library. You just need to install it in your system and them compile the program with the -lgcrypt flag to link the library.

As you've asked a standalone function, I created a function which you can call with the key and message that returns a string with the base64 encoded result, which is exactly what you asked for in your JSFiddle.

#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;}

Important remarks:

-Don't forget to free the return value of the hmacSHA256 function and to call gcry_mac_close when you are done hashing.

-I've included the size of the key and size of the message in the function's arguments because this way you can do the HMAC of binary data as well as ASCII/UTF-8 encoded strings. If you're not going to use binary data, feel free to remove the sizes from the arguments and calculating the size inside of the function with strlen like I did in the main when I called the function.

-I didn't wrap the creation of the gcry_mac_hd_t in the function because it's more efficient to reuse the same handler and just reset it every time you need to reuse it then to create a new one every time you need it. This optimization is even more noticeable if you call this function many times in the same execution!