EVP_MAC_init - specify the hash algorithm

[Dr Paul Dale]

My mistake, it's EVP_MAC_fetch not EVP_MAC_new.

The names are all case insensitive and are documented in the man7 pages: 
https://www.openssl.org/docs/man3.0/man7/EVP_MAC-HMAC.html and 
https://www.openssl.org/docs/man3.0/man7/EVP_MD-SHA2.html.

The HMAC parameter names and types are also there: 
https://www.openssl.org/docs/man3.0/man7/EVP_MAC-HMAC.html


Pauli


On 10/9/21 9:07 am, Ken Goldman wrote:
> Where does one get the parameter values?
>
> E.g., where would I see the value strings for the EVP_MAC_new algorithm
> and the digest parameter values.
>
> I can guess HMAC and SHA256, but are they documented?
>
> Case sensitive?  Which is preferred?
>
> You use EVP_MAC_new, which is undocumented.  The doc sample
> uses EVP_MAC_fetch.  Which is preferred?
>
> On 7/13/2021 7:06 PM, Dr Paul Dale wrote:
>>
>> 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);
>>
>
>
>