EVP_MAC_init - specify the hash algorithm

[Dr Paul Dale]

Please don't do it the PKEY way :)

Your code should look more like:

    OSSL_PARAMS params[2];
    EVP_MAC *mac = EVP_MAC_new(NULL, "HMAC", NULL);
    EVP_MAC_CTX *mac_ctx = EVP_MAC_CTX_new(mac);
    EVP_MAC_free(mac); /* Now or later is all good and depends on the
    app reusing it or not */

    params[0] = OSSL_PARAMS_construct_utf8_string("digest", "SHA256", 0);
    params[1] = OSSL_PARAMS_construct_end();

    EVP_MAC_init(mac_ctx, key, key_len, params);
    EVP_MAC_update(mac_ctx, data1, data1_len);
    EVP_MAC_update(mac_ctx, data2, data2_len);
    EVP_MAC_update(mac_ctx, data3, data3_len);
    EVP_MAC_final(mac_ctx, out, &out_size, out_len);
    EVP_MAC_CTX_free(mac_ctx);

There are various other calls that tweak the flow but this is the basic 
idea.


Pauli

On 14/7/21 8:48 am, Thomas Dwyer III wrote:
> This seems to work for me in 3.0, passing the EVP_MD to 
> EVP_DigestSignInit():
>
> pkey = EVP_PKEY_new_mac_key()
> EVP_DigestSignInit()
> EVP_DigestSignUpdate()
> EVP_DigestSignUpdate()
> .
> .
> .
> EVP_DigestSignFinal()
>
>
> Regards,
> Tom.III
>
>
>
> On Tue, Jul 13, 2021 at 11:02 AM Ken Goldman <kgoldman at us.ibm.com 
> <mailto:kgoldman at us.ibm.com>> wrote:
>
>     Porting to 3.0 ... HMAC_Init_ex() had a place for
>     the hash algorithm.  EVP_MAC_init() does not,
>     unless it's embedded in the 'params' parameter.
>
>     Any advice?  Or a sample for doing an
>     HMAC with 3.0?
>

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