My next attempt is getting a little better.  Now how to base64 encode?

   const char *secretId=msg_to_sign.c_str();
   int msg_len = strlen( secretId );

   CryptoPP::SHA256 sha256hash;
   unsigned char hmac[ sha256hash.DIGESTSIZE ];
   memset( hmac, 0x00, sha256hash.DIGESTSIZE );
   CryptoPP::HMAC<CryptoPP::SHA256>((byte*)privateId,
pri_len).CalculateDigest(hmac, (byte*)secretId, msg_len);

Thanks.

Paul


On Dec 13, 7:20 pm, Paul Crown <[email protected]> wrote:
> Greetings,
>
> I would like to incorporate the equivalent of the following php code
> snippet in a c++ app.  I have been experimenting and have learned how
> to use a number of crypto++ functions.  I have yet, however, to fully
> wrap my mind around this snippet.
>
> I think that I have just figured out that the term "SHA256" is used in
> different respects, one as a hash method, and one as a message
> encoding method.    Which means that my c++ snippet is useless.
>
> In summary, I want to calculate HMAC with SHA256 and base64-encoding
> in c++, just like demonstrated in the php snippet below.  Can you
> please point me in the right direction?
>
> Thank you.
>
> Paul
>
> Php code snippet:
>
>     // calculate HMAC with SHA256 and base64-encoding
>
>     $signature = base64_encode(hash_hmac("sha256", $string_to_sign,
> $private_key, True));
>
> c++ snippet:
>
>    const char *secretId=msg_to_sign.c_str();
>    int msg_len = strlen( secretId );
>
>    // sha256
>    CryptoPP::SHA256 sha256hash;
>    unsigned char hash[ sha256hash.DIGESTSIZE ];
>    memset( hash, 0x00, sha256hash.DIGESTSIZE );
>    sha256hash.CalculateDigest(hash, (byte*)secretId, msg_len);  // use
> libcrypt0++ library
>
>    // hmac
>    unsigned char hmac[ sha256hash.DIGESTSIZE ];
>    memset( hmac, 0x00, sha256hash.DIGESTSIZE );
>    CryptoPP::HMAC<CryptoPP::SHA256>((byte*)secretId,
> msg_len).CalculateDigest(hmac, hash, sha256hash.DIGESTSIZE);

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