Creating an EC Public Key using Named Curves

[Vincent Ryan]

On 8 Oct 2013, at 17:56, Michael StJohns wrote:

> I use this construct a lot, but there are a number of cases (e.g. where I'm trying to take an EC key and turn it into a structure to send to a smart card) where what I really need is to be able to produce an EllipticCurve (actually ECParamaterSpec) from a name.  

Are you seeking to extend the collection of supported named curve parameters?
Because most of the well-known named curve parameters are already supported via the mechanism below.

Adding more (to the SunEC and SunPKCS11 providers) is quite straight forward.
Adding new classes to the JDK is more difficult and already too late for JDK 8.



> 
> I started looking at why ECGenParameterSpec isn't currently a subclass of ECParameterSpec.   I *think* this is because the curve table is currently part of the individual EC providers rather than part of the JDK side implementation.

True. The database of curve parameters is part of the SunEC provider.


> 
> I'm wondering if perhaps its time to change the above and move the curve database over to the JDK side?
> 
> Mike
> 
> 
> 
> 
> 
> At 11:41 AM 10/8/2013, Vincent Ryan wrote:
>> Currently, there is no public API for named curves.
>> 
>> However you can generate named curves using the SunEC provider and the ECParameterSpec class.
>> For example,
>> 
>>       AlgorithmParameters parameters = AlgorithmParameters.getInstance("EC", "SunEC");
>>       parameters.init(new ECGenParameterSpec("secp256r1"));
>>       ECParameterSpec ecParameters = parameters.getParameterSpec(ECParameterSpec.class);
>> 
>>       return KeyFactory.getInstance("EC", "SunEC").generatePublic(new ECPublicKeySpec(new ECPoint(x, y), ecParameters));
>> 
>> 
>> It's not elegant but the list of supported named curves can be extracted from the AlgorithmParameters.EC SupportedCurves
>> property. For example,
>> 
>>       String[] curves = Security.getProvider("SunEC")
>>           .getProperty("AlgorithmParameters.EC SupportedCurves")
>>           .split("\\|");
>>       for (String curve : curves) {
>>           System.out.println(curve.substring(1, curve.indexOf(",")));
>>       }
>> 
>> 
>> 
>> 
>> On 8 Oct 2013, at 13:53, Anders Rundgren wrote:
>> 
>>> If you have the X and Y points and the name of a public key you can create a ECPublicKey using BouncyCastle.
>>> I cannot find any counterpart in JDK 7.  What am I missing?
>>> 
>>> BC:
>>> 
>>> return KeyFactory.getInstance ("EC").generatePublic (new ECPublicKeySpec (new ECPoint (x, y), new ECNamedCurveSpec (name,...)));
>>> 
>>> Cheers
>>> Anders
> 
>