Updating to openssl v3 replacing PEM_write_bio_RSAPublicKey

[timlegge]

Hi

I have been working on converting an application to the new openssl 3+ api and I am currently replacing PEM_write_bio_RSAPublicKey.

with

PEM_write_bio_PUBKEY(stringBIO, pkey);

However one of the tests for compatability with the old version test that the output of a known private key produces the public key in both the old format and new.

PEM_write_bio_PUBKEY(stringBIO, pkey); produces the correct public key in the -----BEGIN PUBLIC KEY----- PEM format.

Is there a way in openssl3 API to produce it in -----BEGIN RSA PUBLIC KEY----- format?

Tim

[kulkarniamit]

You can use encoders to define the output format.
Example:

   ...
   OSSL_ENCODER_CTX *ctx = NULL;
   const char *pubkey_out = "rsa.pub.pkcs1";
   ...
   fp_out = fopen(pubkey_out, "w");
   if (fp_out == NULL) {
       fprintf(stderr, "Failed to open public key to write\n");
       // handle errors and exit
   }

   ctx = OSSL_ENCODER_CTX_new_for_pkey(pkey, OSSL_KEYMGMT_SELECT_PUBLIC_KEY,
            "PEM", "PKCS1", NULL);
   if (ctx == NULL || !OSSL_ENCODER_CTX_get_num_encoders(ctx)) {
       fprintf(stderr, "Failed to get an encoder context\n");
       // handle errors and exit
   }

   fprintf(stdout, "Public key PKCS1 write to %s %s\n", pubkey_out,
       OSSL_ENCODER_to_fp(ctx, fp_out) ? "success" : "failed");
   ...
   OSSL_ENCODER_CTX_free(ctx);
   ...

This should generate output in the desired format

$ grep KEY rsa.pub.pkcs1
-----BEGIN RSA PUBLIC KEY-----
-----END RSA PUBLIC KEY-----

References

• OSSL_ENCODER_CTX_new_for_pkey()
• OSSL_ENCODER_CTX_get_num_encoders()
• OSSL_ENCODER_to_fp()
• OSSL_ENCODER_CTX_free()

[timlegge]

Thanks - I thought maybe but I was not able to sort it. I will try again - thanks for the example.

[timlegge]

Thanks again I had previously found the decoder function and wondered why there was not one to do what I wanted. This worked great