Often times, user will have PEM encoded RSA private keys. Crypto++ requires that these keys be in DER format to load. I've been asking people to manually convert their PEM files to DER beforehand using openssl like this:

openssl pkcs8 -in in_file.pem -out out_file.der -topk8 -nocrypt -outform der

That works fine, but some people don't understand how to do that nor do they want to. So I would like to convert PEM files to DER files automatically within the program.

Is it as simple as striping the "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----" from the PEM or is some other transformation required as well? I've been told that between those markers that it's just b64 encoded DER. Here's some code that demonstrates the issue:

// load the private key
CryptoPP::RSA::PrivateKey PK;
CryptoPP::ByteQueue bytes;

try
{
    CryptoPP::FileSource File( rsa.c_str(), true, new CryptoPP::Base64Decoder() );
    File.TransferTo( bytes );
    bytes.MessageEnd();

    // This line Causes BERDecodeError when a PEM encoded file is used
    PK.Load( bytes );
}

catch ( CryptoPP::BERDecodeErr )
{
    // Convert PEM to DER and try to load the key again
}

I'd like to avoid making system calls to openssl and do the transformation entirely in Crypto++ so that users can provide either format and things "just work". Thanks for any advice.