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

[Tomas G. <to...@pr...>]

Good hunting of the originating committ!

I see it originates from this issue:
https://jira.primekey.se/browse/ECA-2801

There is no reference to the size 224 being a limit there, so we don't
know. Being since 2013, it's interesting that this is the first time
anyone asks for curves shorter than 224. Since EC is being used
extensively, I guess there is no real wide spread use of the sorter curves.

I made a note of this in the documentation for the next release. Unless
there is a substantial argument why you want to use shorter curves, I'll
leave it as it is.

Regards,
Tomas

On 2018-12-29 23:28, Andreas Kuehne wrote:
> Hi Jaime,
>
> an unclear reasoning and origin is a good starting point for conspiracy
> theories!
>
> The code snippet seems to implement a DIY approach to decide on
> algorithm suitability. A more standardized approach is given in
>
> Data Structure for the Security Suitability of Cryptographic Algorithms
> (DSSC)
> https://tools.ietf.org/html/rfc5698
>
> This could be a good base for a catalog  of supported algorithm.  A
> quick search did not reveal any ready-made implementations but I would
> guess a given standard is better than re-inventing a wheel.
>
> Greetings,
>
> Andreas
>> 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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>>>
>>> --
>>> Andreas Kühne
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>>> mailto: ku...@tr...
>>>
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>>>
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>>>
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>>
>>
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>
> --
> Andreas Kühne
> phone: +49 177 293 24 97
> mailto: ku...@tr...
>
> Trustable Ltd. Niederlassung Deutschland Gartenheimstr. 39C - 30659
Hannover Amtsgericht Hannover HRB 212612
>
> Director Andreas Kühne
>
> Company UK Company No: 5218868 Registered in England and Wales
>
>
>
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