How to use EVP_DigestSignInit[_ex]()?

[Alessandro Vesely]

I fixed my code as follows:


On Fri 06/Oct/2023 11:04:31 +0200 Alessandro Vesely wrote:
> 
> my scarce crypto knowledge notwithstanding, I'm trying to maintain a DKIM 
> signing function.  With the previous openssl version, I added a snippet to sign 
> using ed25519, more or less like so:
> 
>      char *digest;              // digest already computed from
>      size_t diglen;             // normalized message header
> 
>      EVP_PKEY *crypto_pkey;     // given
> 
>      size_t crypto_outlen;      // expected
>      unsigned char *crypto_out;
> 
>      EVP_MD_CTX *md_ctx = EVP_MD_CTX_new();
>      if (md_ctx == NULL) goto error;

        int status;
        if (signalg != ED25519SHA256)
            status = EVP_DigestSignInit_ex(md_ctx, NULL,
                signalg == SHA1? "SHA1": "sha256", NULL, NULL,
                crypto_pkey, NULL);
        else
            status = EVP_DigestSignInit(md_ctx, NULL,
                NULL, NULL, crypto->crypto_pkey);

>      if (status == 1)
>          status = EVP_DigestSign(md_ctx,
>              crypto_out, &crypto_outlen,
>              digest, diglen);
>      EVP_MD_CTX_free(md_ctx);
>      if (status != 1) goto error;


Now, that works well with ED25519.  With RSA keys, all tests fail, delivering a 
signature different than expected.  Can that be because I still don't have set 
RSA_PKCS1_PADDING?  How could that be done?


Best
Ale