connectbot/sshlib

Similar blocks of code found in 2 locations. Consider refactoring.
package com.trilead.ssh2.signature;
 
import com.trilead.ssh2.log.Logger;
import com.trilead.ssh2.packets.TypesReader;
import com.trilead.ssh2.packets.TypesWriter;
import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
import java.security.SignatureException;
 
public class RSASHA512Verify implements SSHSignature
{
    private static final Logger log = Logger.getLogger(RSASHA512Verify.class);
    public static final String ID_RSA_SHA_2_512 = "rsa-sha2-512";
 
    private static class InstanceHolder {
        private static final RSASHA512Verify sInstance = new RSASHA512Verify();
    }
 
    private RSASHA512Verify() {
    }
 
    public static RSASHA512Verify get() {
        return RSASHA512Verify.InstanceHolder.sInstance;
    }
 
    private static byte[] decodeRSASHA512Signature(byte[] sig) throws IOException
    {
        TypesReader tr = new TypesReader(sig);
 
        String sig_format = tr.readString();
 
        if (!sig_format.equals(ID_RSA_SHA_2_512))
            throw new IOException("Peer sent wrong signature format");
 
        /* S is NOT an MPINT. "The value for 'rsa_signature_blob' is encoded as a string
         * containing s (which is an integer, without lengths or padding, unsigned and in
         * network byte order)." See also below.
         */
 
        byte[] s = tr.readByteString();
 
        if (s.length == 0)
            throw new IOException("Error in RSA signature, S is empty.");
 
        if (log.isEnabled())
        {
            log.log(80, "Decoding rsa-sha2-512 signature string (length: " + s.length + ")");
        }
 
        if (tr.remain() != 0)
            throw new IOException("Padding in RSA signature!");
 
        return s;
    }
 
    private static byte[] encodeRSASHA512Signature(byte[] s)
    {
        TypesWriter tw = new TypesWriter();
 
        tw.writeString(ID_RSA_SHA_2_512);
 
        /* S is NOT an MPINT. "The value for 'rsa_signature_blob' is encoded as a string
         * containing s (which is an integer, without lengths or padding, unsigned and in
         * network byte order)."
         */
 
        /* Remove first zero sign byte, if present */
 
        if ((s.length > 1) && (s[0] == 0x00))
            tw.writeString(s, 1, s.length - 1);
        else
            tw.writeString(s, 0, s.length);
 
        return tw.getBytes();
    }
 
    @Override
    public byte[] generateSignature(byte[] message, PrivateKey privateKey, SecureRandom secureRandom) throws IOException
    {
        try {
            // Android's Signature is guaranteed to support this instance
            Signature s = Signature.getInstance("SHA512withRSA");
            s.initSign(privateKey, secureRandom);
            s.update(message);
            return encodeRSASHA512Signature(s.sign());
        } catch (NoSuchAlgorithmException | InvalidKeyException | SignatureException e) {
            throw new IOException(e);
        }
    }
 
    @Override
    public String getKeyFormat() {
        return ID_RSA_SHA_2_512;
    }
 
    @Override
    public PublicKey decodePublicKey(byte[] encoded) throws IOException {
        return RSASHA1Verify.get().decodePublicKey(encoded);
    }
 
    @Override
    public byte[] encodePublicKey(PublicKey publicKey) throws IOException {
        return RSASHA1Verify.get().encodePublicKey(publicKey);
    }
 
    @Override
    public boolean verifySignature(byte[] message, byte[] sshSig, PublicKey publicKey) throws IOException
    {
        byte[] javaSig = decodeRSASHA512Signature(sshSig);
        try {
            Signature s = Signature.getInstance("SHA512withRSA");
            s.initVerify(publicKey);
            s.update(message);
            return s.verify(javaSig);
        } catch (NoSuchAlgorithmException | InvalidKeyException | SignatureException e) {
            throw new IOException(e);
        }
    }
}