Re: [Ejbca-develop] Why ECDSA keys require a minimum size of 224 bits for Crypto Token key pair generation?

[Jaime H. <hab...@gm...>]

On Sat, Dec 22, 2018 at 1:59 PM Andreas Kuehne <ku...@tr...> wrote:

> Hi Jaime,
>
> interesting finding! Due to https://safecurves.cr.yp.to/ there are at
> least two curves with (slightly) shorter key length. On the other hand the
> NIST-224 is considered insecure ...
>

Thanks for pointing out this resource.


>
> Are there any specific reasons for implementing this restriction?
>

I'm asking the same myself. I can trace back that change to the following
old (5 years ago) commit,
https://github.com/rgorosito/ejbca/commit/49a8e1c5ff448c3d27c132e46675ed27ef7cb65b#diff-52fc78614bcdfb702e0bf5b66a3ffbfc,
but the motivation for it is no clear to me at first glance.


>
> Greetings,
>
> Andreas
>
> In EJBCA 6.10.1.2+, if you create a Crypto Token from the Admin GUI and
> then you try to generate an EC keypair for it, you find that certain curves
> are not availabe, e.g. B-163, even when the documentation indicates support
> for them (seehttps://www.ejbca.org/docs/ECDSA_Keys_and_Signatures.html#src-16224742_id-.ECDSAKeysandSignaturesv6.12.0-Named_curves
> ).
>
> Looking at the source code I can see the cause for it is in the following
> method, org.cesecore.keys.util.KeyTools#checkValidKeyLength:
>
> public static void checkValidKeyLength(final String keyAlg, final int len)
> throws InvalidKeyException {
>   ...
>   if (*isEcdsa *|| isGost3410 || isDstu4145) {
>     ...
>     if ((len > 0) && (*len < 224)*) {
>       final String msg =
> intres.getLocalizedMessage("catoken.invalidkeylength", "ECDSA", "224",
> Integer.valueOf(len));
>       *throw new InvalidKeyException(msg);*
>     }
>   } ...
> }
>
> But, why is it so?. Are there potentials problems with EC curves with a key
> size smaller than 224 bits?.
>
> PS: I'm a total ignorant of EC cryptography.
>
>
>
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-- 
Jaime Hablutzel -  RPC 994690880