Encode publicKey on Java Card

Question

How to encode an ECDSA PublicKey on Java Card so that after I can decode it on another platform (e.g. sending the encoded key in a response APDU and processing it in a standard Java application)? keyPair.getPublic().getEncoded() on Java would do the trick with PKCS#8 encoding, but as far as I know getEncoded() is not available on the Java Card platform.

Answer 1

You can implement this function like this:

Card side:

• 1 KeyPair.getPublicKey() --> publicKey;
• 2 publicKey.getW() --> W;
• 3 Send W to outside;

Standard java application side:

• 1 get W data bytes;
• 2 W data bytes --> ECPoint;
• 3 Build PublicKey with the ECPoint generated in step 2 use the class ECPublicKeySpec;
• 4 Use the public key in your application;