How to parse a ssh public key file. Only supports RSA keys right now.

SshKeyReader.java

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.file.Files;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPublicKeySpec;
import java.util.Base64;
import java.util.HashMap;
import java.util.Map;

public class SshKeyReader {

    public static Map<String, PublicKey> read(File publicKeyFile)
            throws IOException, InvalidKeySpecException, NoSuchAlgorithmException {
        HashMap<String, PublicKey> out = new HashMap<>();
        for (String line : Files.readAllLines(publicKeyFile.toPath())) {
            String[] fields = line.split(" +");
            if (fields.length != 3)
                continue;

            byte[] decoded = Base64.getDecoder().decode(fields[1]);
            DataInputStream keyParser = new DataInputStream(new ByteArrayInputStream(decoded));

            byte[] typeStringBytes = new byte[keyParser.readInt()];
            keyParser.read(typeStringBytes);
            String typeString = new String(typeStringBytes);

            if (typeString.equals("ssh-rsa")) {
                byte[] exponentBytes = new byte[keyParser.readInt()];
                keyParser.read(exponentBytes);
                byte[] modulusBytes = new byte[keyParser.readInt()];
                keyParser.read(modulusBytes);
                RSAPublicKeySpec spec = new RSAPublicKeySpec(new BigInteger(modulusBytes),
                        new BigInteger(exponentBytes));
                out.put(fields[2], KeyFactory.getInstance("RSA").generatePublic(spec));
            }
        }

        return out;
    }

    public static void main(String[] args)
            throws IOException, InvalidKeySpecException, NoSuchAlgorithmException {
        System.out.println(read(new File("test-rsa.pub")));
    }
}