Re: [RFC PATCH 4/5] keyctl.2: document the ability to provide KDF parameters in KEYCTL_DH_COMPUTE

[Stephan Mueller <smueller-T9tCv8IpfcWELgA04lAiVw@public.gmane.org>]

Am Donnerstag, 31. August 2017, 18:17:09 CEST schrieb Eugene Syromyatnikov:

Hi Eugene,

> On Thu, Aug 31, 2017 at 6:07 PM, Stephan Mueller <smueller-T9tCv8IpfcWELgA04lAiVw@public.gmane.org> 
wrote:
> > Am Donnerstag, 31. August 2017, 17:58:36 CEST schrieb Eugene
> > Syromyatnikov:
> > 
> > Hi Eugene,
> > 
> >> +field is a null-terminated string no longer than
> >> +.B CRYPTO_MAX_ALG_NAME
> >> +(128 bytes as of this writing) which specifies hash name
> > 
> > Is it necessary to specify that size? Note, up to 4.11 it was 64 bytes.
> > Also, it must be a valid cipher name as mentioned. Thus, I do not think
> > the size is relevant here considering the requirement to use a proper
> > name.
> 
> Right, it's probably more important for syscall decoding, but not for
> the documentation. However, my understanding is that cipher template
> can be specified (like "rfc4106(gcm(aes))"), and I'm not sure how deep
> this nesting can be and whether it is possible to reach algorithm name
> limit this way (by employing the usage of driver name instead of
> common name, for example—as I understood, it is also possible). It
> probably makes more sense to just mention this limit in the ERRORS
> section instead.

CRYPTO_MAX_ALG_NAME is given a size that all allowed cipher names can be 
represented.

Somehow in the 4.12 release cycle, somebody found a very obscure yet valid 
name for a symmetric cipher that exceeded the 64 byte limit causing the bump 
to 128 bytes.

Though, that obscure name is no SHASH. All SHASH keyed digest cipher names are 
below 64 bytes.
> 
> > Otherwise, the KDF documentation looks good.
> > 
> > Ciao
> > Stephan



Ciao
Stephan
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