How can I construct a java.security.PublicKey object from a base64 encoded string?

I have a bse64encoded string Public key from external source (Android Store) and I need to use it to verify signed content. How can I convert the string into an instance of the java.security.PublicKey interface. I am on Java 6 if that makes a difference.

The key is (probably) generated using standard java lib and not bouncy castle (its from a remote team so I am not sure). Their sample code says to use Security.generatePublicKey(base64EncodedPublicKey); but the Security object in standard java has no such method.

Solution 1:

Code for the above answer

public static PublicKey getKey(String key){
    try{
        byte[] byteKey = Base64.decode(key.getBytes(), Base64.DEFAULT);
        X509EncodedKeySpec X509publicKey = new X509EncodedKeySpec(byteKey);
        KeyFactory kf = KeyFactory.getInstance("RSA");

        return kf.generatePublic(X509publicKey);
    }
    catch(Exception e){
        e.printStackTrace();
    }

    return null;
}

Solution 2:

Ok for grins ... try this

• base64 decode the key data to get a byte array (byte[])
• Create a new X509EncodedKeySpec using the byte array
• Get an instance of KeyFactory using KeyFactory.getInstance("RSA") assuming RSA here
• call the method generatePublic(KeySpec) with the X509EncodedKeySpec
• Result /should/ be a public key for your usage.

Solution 3:

Try this....

PublicKey getPublicKey(byte[] encodedKey) throws NoSuchAlgorithmException, InvalidKeySpecException
{
    KeyFactory factory = KeyFactory.getInstance("RSA");
    X509EncodedKeySpec encodedKeySpec = new X509EncodedKeySpec(encodedKey);
    return factory.generatePublic(encodedKeySpec);
}