Interaction between Crypt::RSA (Perl) and java.security.Signature (Java)

Question

I'd like to sign a file by using a RSA keypair. For this purpose I have this Perl script:

#!/usr/bin/perl

use Crypt::RSA;

my $data = ... # File contents

my $rsa = new Crypt::RSA; 
my $key = new Crypt::RSA::Key::Private(Filename => "stackoverflow.priv", Password => "*****");
my $signature = $rsa->sign(Message => $data, Key => $key, Armour => 0);

# Write signature to file

On the client side, I'd like to use the following Java function to verify the file:

private static final String PUBLICKEY_MOD = "190343051422614110006523776876348493...";
private static String PUBLICKEY_EXP = "65537";

public boolean check() {
     byte[] data = ... // Data
     byte[] dataSignature = ... // Signature (as calculated in the Perl script)

     Signature signature = Signature.getInstance("SHA256withRSA");

     signature.initVerify(getPublicKey());
     signature.update(data);
     return signature.verify(dataSignature);
}

private PublicKey getPublicKey() {
    RSAPublicKeySpec spec = new RSAPublicKeySpec(new BigInteger(PUBLICKEY_MOD), new BigInteger(PUBLICKEY_EXP));
    KeyFactory factory = KeyFactory.getInstance("RSA");
    return factory.generatePublic(spec);
}

However, check() always reports false. These things I already checked:

• data and dataSignature are correctly read
• PUBLICKEY_MOD and PUBLICKEY_EXP are correct
• getPublicKey() returns a PublicKey which has the correct attributes
• the private key and the public key are part of the same pair

Does anyone know how to verify the file correctly? Is signature correctly instanced?

Answer 1

Your first clue that something might be wrong is that you never tell Perl what hash function to use, but you tell Java to use SHA256. You have a lot of work to do on the Perl side. Also, the default padding scheme for Crypt::RSA seems to be PSS, whereas for Java it is PKCSv1.5