HMAC implementation using EVP_MAC

[rdiwan2023]

Hi,
Can anyone please provide me a simple example of HMAC using EVP_MAC Api?

Thanks
Rohith

[t8m]

We have such demo in our code base. https://github.com/openssl/openssl/blob/master/demos/mac/hmac-sha512.c

[rdiwan2023]

@levitte
Please find the example below:

#include <string.h>
#include <stdio.h>
#include <openssl/crypto.h>
#include <openssl/core_names.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <openssl/params.h>

static unsigned char key[] ={0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F};

static const unsigned char data[] = "Sample message for keylen<blocklen";
static const unsigned char expected_output[] = {0xFD, 0x44, 0xC1, 0x8B, 0xDA, 0x0B, 0xB0, 0xA6, 0xCE, 0x0E, 0x82, 0xB0, 0x31, 0xBF, 0x28, 0x18, 0xF6, 0x53, 0x9B, 0xD5, 0x6E, 0xC0, 0x0B, 0xDC, 0x10, 0xA8, 0xA2, 0xD7, 0x30, 0xB3, 0x63, 0x4D, 0xE2, 0x54, 0x5D, 0x63, 0x9B, 0x0F, 0x2C, 0xF7, 0x10, 0xD0, 0x69, 0x2C, 0x72, 0xA1, 0x89, 0x6F, 0x1F, 0x21, 0x1C, 0x2B, 0x92, 0x2D, 0x1A, 0x96, 0xC3, 0x92, 0xE0, 0x7E, 0x7E, 0xA9, 0xFE, 0xDC};

/*
 * A property query used for selecting the MAC implementation.
 */
static const char *propq = NULL;

int main(void)
{
    int ret = EXIT_FAILURE;
    OSSL_LIB_CTX *library_context = NULL;
    EVP_MAC *mac = NULL;
    EVP_MAC_CTX *mctx = NULL;
    EVP_MD_CTX *digest_context = NULL;
    unsigned char *out = NULL;
    size_t out_len = 0;
    OSSL_PARAM params[4], *p = params;
    char digest_name[] = "SHA3-512";

    library_context = OSSL_LIB_CTX_new();
    if (library_context == NULL) {
        fprintf(stderr, "OSSL_LIB_CTX_new() returned NULL\n");
        goto end;
    }

    /* Fetch the HMAC implementation */
    mac = EVP_MAC_fetch(library_context, "HMAC", propq);
    if (mac == NULL) {
        fprintf(stderr, "EVP_MAC_fetch() returned NULL\n");
        goto end;
    }

    /* Create a context for the HMAC operation */
    mctx = EVP_MAC_CTX_new(mac);
    if (mctx == NULL) {
        fprintf(stderr, "EVP_MAC_CTX_new() returned NULL\n");
        goto end;
    }

    /* The underlying digest to be used */
    *p++ = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_DIGEST, digest_name,
                                            sizeof(digest_name));
    *p = OSSL_PARAM_construct_end();

    /* Initialise the HMAC operation */
    if (!EVP_MAC_init(mctx, key, sizeof(key), params)) {
        fprintf(stderr, "EVP_MAC_init() failed\n");
        goto end;
    }

    /* Make one or more calls to process the data to be authenticated */
    if (!EVP_MAC_update(mctx, data, sizeof(data))) {
        fprintf(stderr, "EVP_MAC_update() failed\n");
        goto end;
    }

    /* Make a call to the final with a NULL buffer to get the length of the MAC */
    if (!EVP_MAC_final(mctx, NULL, &out_len, 0)) {
        fprintf(stderr, "EVP_MAC_final() failed\n");
        goto end;
    }
    out = OPENSSL_malloc(out_len);
    if (out == NULL) {
        fprintf(stderr, "malloc failed\n");
        goto end;
    }
    /* Make one call to the final to get the MAC */
    if (!EVP_MAC_final(mctx, out, &out_len, out_len)) {
        fprintf(stderr, "EVP_MAC_final() failed\n");
        goto end;
    }

    printf("Generated MAC:\n");
    BIO_dump_indent_fp(stdout, out, out_len, 2);
    putchar('\n');

    if (out_len != sizeof(expected_output)) {
        fprintf(stderr, "Generated MAC has an unexpected length\n");
        goto end;
    }

    if (CRYPTO_memcmp(expected_output, out, sizeof(expected_output)) != 0) {
        fprintf(stderr, "Generated MAC does not match expected value\n");
        goto end;
    }

    ret = EXIT_SUCCESS;
end:
    if (ret != EXIT_SUCCESS)
        ERR_print_errors_fp(stderr);
    /* OpenSSL free functions will ignore NULL arguments */
    OPENSSL_free(out);
    EVP_MD_CTX_free(digest_context);
    EVP_MAC_CTX_free(mctx);
    EVP_MAC_free(mac);
    OSSL_LIB_CTX_free(library_context);
    return ret;
}

Below is the output:

Generated MAC:

  0000 - 33 7e 59 be c2 7b e8 c7-05 f3 1d 53 b6 8e 7b ad   3~Y..{.....S..{.
  0010 - 1d 51 77 7c 75 2f 9b 80-ef 67 22 f5 19 54 b9 29   .Qw|u/...g"..T.)
  0020 - 90 f6 e4 5f df 4e 2f 55-c6 52 02 bf eb 27 9a d4   ..._.N/U.R...'..
  0030 - 1a 05 1c 32 e6 71 5e 70-c9 2e 52 2e 1f c8 c2 e1   ...2.q^p..R.....

Generated MAC does not match expected value

Thnaks
Rohith

[kulkarniamit]

@rdiwan2023 Can you share how expected_output was calculated?
Both openssl mac and openssl dgst report the same mac as reported by the program for your sample data.

$ xxd msg.bin
00000000: 5361 6d70 6c65 206d 6573 7361 6765 2066  Sample message f
00000010: 6f72 206b 6579 6c65 6e3c 626c 6f63 6b6c  or keylen<blockl
00000020: 656e 00                                  en.

$ openssl mac -digest SHA3-512 \
-macopt hexkey:000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F202122232425262728292A2B2C2D2E2F303132333435363738393A3B3C3D3E3F \
-in msg.bin HMAC
337E59BEC27BE8C705F31D53B68E7BAD1D51777C752F9B80EF6722F51954B92990F6E45FDF4E2F55C65202BFEB279AD41A051C32E6715E70C92E522E1FC8C2E1

$ openssl dgst -sha3-512 -mac hmac \
-macopt hexkey:000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F202122232425262728292A2B2C2D2E2F303132333435363738393A3B3C3D3E3F msg.bin
HMAC-SHA3-512(msg.bin)= 337e59bec27be8c705f31d53b68e7bad1d51777c752f9b80ef6722f51954b92990f6e45fdf4e2f55c65202bfeb279ad41a051c32e6715e70c92e522e1fc8c2e1

[rdiwan2023]

@kulkarniamit,

Below is the example:
Input :
Key length = 64
Tag length = 64
Input Date:
"Sample message for keylen<blocklen"
Text is
5361 6D706C65 206D6573
73616765 20666F72 206B6579 6C656E3C 626C6F63 6B6C656E
Key is
00010203 04050607 08090A0B 0C0D0E0F
10111213 14151617 18191A1B 1C1D1E1F 20212223 24252627
28292A2B 2C2D2E2F 30313233 34353637 38393A3B 3C3D3E3F

MAC is:
FD44C18B DA0BB0A6 CE0E82B0 31BF2818
F6539BD5 6EC00BDC 10A8A2D7 30B3634D E2545D63 9B0F2CF7
10D0692C 72A1896F 1F211C2B 922D1A96 C392E07E 7EA9FEDC

I am referring to second example from the below link:
https://csrc.nist.gov/CSRC/media/Projects/Cryptographic-Standards-and-Guidelines/documents/examples/HMAC_SHA512.pdf

Thanks
Rohith

[rdiwan2023]

Can anyone pls reply?

[mattcaswell]

The msg.bin file you show above and the example code is including the NUL terminator in the string to pass through the MAC. The examples given in the link you provide do not include this trailing 0 byte. This discrepancy will cause a different MAC to be generated.

[rdiwan2023]

@mattcaswell,
Thanks, I am able to get correct output.

with regards
Rohith