Elliptic keys

Question

Hi
I am trying to understand how to use ECC on a JavaCard.
I have two questions regarding keys:
1. Javadoc for ECPrivateKey.getS(...) states that:
Returns the value of the secret key in plaintext formWhat does that mean? Is not the value of the private key supposed to be secret so no one can access it (except indirectly by some class that will use it to generate signatures)?
2. Javadoc for ECPublicKey.setW(...) states that:
Sets the point of the curve comprising the public keyAren't we supposed to generate the public/private key pair once the curve has been set (A,B,P,N,G) somehow automatically (i.e. by calling KeyPair.genKeyPair) rather than setting values by ourselves?
Thank you
Thank you
Edited by: 815684 on Jun 6, 2011 7:36 AM

Answer 1

Hi,
815684 wrote:
1. Javadoc for ECPrivateKey.getS(...) states that:
Returns the value of the secret key in plaintext formWhat does that mean? Is not the value of the private key supposed to be secret so no one can access it (except indirectly by some class that will use it to generate signatures)?The S parameter is indeed the private key of the ECC. It has NOT to be send on the network. The function ECPrivateKey.getS(...) is almost never used since objects KeyAgreement and Signature have a Private key parameter. You might sometimes use the getS function to verify the value of your private key in debug mode.
815684 wrote:
2. Javadoc for ECPublicKey.setW(...) states that:
Sets the point of the curve comprising the public keyAren't we supposed to generate the public/private key pair once the curve has been set (A,B,P,N,G) somehow automatically (i.e. by calling KeyPair.genKeyPair) rather than setting values by ourselves?The W parameter is the public key for ECC. When calling a KeyPair.genKeyPair function, it automatically fills the all the parameters of both keys. When you create a new key pair, you have to set the length of keys you want to build. In fact, the keypair object will always generate the same (A,B,P,N,G) according to the key length. Only S (and so W) is generated randomly. But not all cards support the key generation, and you will have often to set all these parameters in static fields chosen by yourself. That's why it exists ECPublicKey.setW(...) and all the other set functions (setA,setB...)
Hope these information will be helpful
Cheers,
Cyril