Creating RSA keys from known parameters in Java

Question

I\'m working on implementing Bing Cashback. In order to verify an incoming request from Bing as valid they provide a signature. The signature is a 160-bit SHA-1 hash of the

Answer 1

RSAPublicKeySpec spec = new RSAPublicKeySpec(modulus, exponent);
KeyFactory factory = KeyFactory.getInstance("RSA");
PublicKey pub = factory.generatePublic(spec);
Signature verifier = Signature.getInstance("SHA1withRSA");
verifier.initVerify(pub);
verifier.update(url.getBytes("UTF-8")); // Or whatever interface specifies.
boolean okay = verifier.verify(signature);

Answer 2

Use java.security.spec.RSAPublicKeySpec. It can construct a key from exponent and modulus. Then use java.security.KeyFactory.generatePublic() with key spec as a parameter.

Answer 3

Something like this should do the trick:

  private PublicKey convertPublicKey(String publicKey) throws Exception{
    PublicKey pub = null;

    byte[] pubKey = Hex.decodeHex(publicKey.toCharArray());
    X509EncodedKeySpec pubSpec = new X509EncodedKeySpec(pubKey);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    pub = (RSAPublicKey) keyFactory.generatePublic(pubSpec);

    return pub;
  }

This assumes the Public key is given as a hex string, and you'll need the Apache Commons Codec library

If you have the key in a different format, try the KeyFactory for more information.