Javacard applet and client application - Java

try someting like

RSAPublicKeySpec keySpec =
new RSAPublicKeySpec(new BigInteger(1, modulus), new new BigInteger(1,
exponent));

KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(keySpec);

to get a public key for signature verification using the Signature class.

byte[] encodedKey = publicKey.getEncoded();

to get the key in an (X.509) encoded form for writing it to a file.
use

X509EncodedKeySpec keySpec = new X509EncodedKeySpec(encodedKey);

KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(keySpec);

to create a public key from its encoded form again.

Karl

--

Karl Scheibelhofer, IAIK - Graz University of Technology
Inffeldgasse 16a, 8010 Graz, Austria
Fax: +43 316 873 5520
http://jce.iaik.tugraz.at/


"Nicholas" <nico282@hotmail.com> wrote in message
news:1gja0fz.hckfguqq3g5cN%nico282@hotmail.com...
> Hi.
>
> I'm developing a Javacard applet for digital signature. I also have to
> write a client to verify the signatures (RSA_SHA_PKCS1).
>
> I think I managed to code the applet, but i'm very confused about the
> standard java part of the work: from the applet I can generate a keypair
> and get the public key, in form of 2 byte[] for the modulus and the
> exponent.
>
> - How can I rebuild a PublicKey object to verify the signature ???
>
> - Is there a standard way to write the key to a file for a later use ???
>
>
> Thanks in advance,
>
> Nic :-)

Karl, thank you very much for you help. It was precious to me !!!!! You
saved me a lot of time investigating for the right classes and methods
!!! :-D

Now my application can sign data with a Javacard, and verify the
signature with the exported public key.

Again, thanks :-)

Nicholas


Karl Scheibelhofer <karl.scheibelhofer@iaik.tugraz.at> wrote:

> try someting like
>
> RSAPublicKeySpec keySpec =
> new RSAPublicKeySpec(new BigInteger(1, modulus), new new BigInteger(1,
> exponent));
>
> KeyFactory keyFactory = KeyFactory.getInstance("RSA");
> PublicKey publicKey = keyFactory.generatePublic(keySpec);
>
> to get a public key for signature verification using the Signature class.
>
> byte[] encodedKey = publicKey.getEncoded();
>
> to get the key in an (X.509) encoded form for writing it to a file.
> use
>
> X509EncodedKeySpec keySpec = new X509EncodedKeySpec(encodedKey);
>
> KeyFactory keyFactory = KeyFactory.getInstance("RSA");
> PublicKey publicKey = keyFactory.generatePublic(keySpec);
>
> to create a public key from its encoded form again.