trustedjava-support

[Trustedjava-support] Check signature with public key from remote peer

[rinberg\@libero\.it <ri...@li...>]

Hi. I have to send to a remote peer the public part of a key created loca=
lly. I managed to extract the byte array with the following code:

byte[] p_k =3D key.getPubKey().asByteArray();
try {
 System.out.println("PubAIK size: "+p_k.length);
 FileOutputStream file_pk =3D new FileOutputStream("aik_pubkey");
 file_pk.write(p_k, 0, p_k.length);
 file_pk.flush();
}

And then I'm sending th byte array via a socket to the remote peer togeth=
er with the encrypted data. Then I should decrypt the data when I have re=
ceived it on the remote peer, how could I do it?

Any help would be appreciated. Thank you.

Best Regards,

 Rinaldo Bergamini

Re: [Trustedjava-support] Check signature with public key from remote peer

[<ron...@ia...>]

Hi Rinaldo,

ri...@li... wrote:
> I have to send to a remote peer the public part of a key created locally.
> And then I'm sending th byte array via a socket to the remote peer together
 > with the encrypted data. Then I should decrypt the data when I have
 > received it on the remote peer, how could I do it?

It cannot be done.
In asymmetric cryptography in general you can only ENcrypt with the 
public key and only DEcrypt with the private key. That's what it is all 
about.

In case you want to do something else, here is a piece of code that 
creates a standard Java public key from a modulus in a TcBlobData object 
as a start. (Note that the exponent of public TPM RSA keys is a constant.)

Regards, Ronald

import java.security.PublicKey;
import java.math.BigInteger;

   protected RSAPublicKey convertEkModulusToJavaPublicKey(TcBlobData 
pubEkBlob) {

     // BigInteger requires a leading sign-byte
     pubEkBlob.prepend(TcTssStructFactory.newBlobData().initBYTE(((byte) 
0)));
     RSAPublicKeySpec pubEkSpec = new RSAPublicKeySpec(new 
BigInteger(pubEkBlob.asByteArray()), new BigInteger("65537"));
     try {
       RSAPublicKey pubEk = (RSAPublicKey) 
KeyFactory.getInstance("RSA").generatePublic(pubEkSpec);

       byte[] finger = (new 
iaik.security.rsa.RSAPublicKey(pubEk)).getFingerprint();
       System.out.println("key fingerprint: " 
+byteArrayToHexString(finger));

       return pubEk;

     } catch (InvalidKeySpecException e) {
       e.printStackTrace();
     } catch (NoSuchAlgorithmException e) {
       e.printStackTrace();
     }
     System.exit(1);
     return