Re: Remove our bundled crypto library (in favor of Libgcrypt)?

[Peter Wu <peter () lekensteyn nl>]

On Fri, Feb 10, 2017 at 12:59:46AM +0000, João Valverde wrote:
> On 02/08/2017 01:40 PM, Peter Wu wrote:
> > On Mon, Feb 06, 2017 at 03:25:40PM -0800, Guy Harris wrote:
> > > On Feb 6, 2017, at 3:17 PM, João Valverde <joao.valverde () tecnico ulisboa pt> wrote:
> > >
> > > > None from me but can we use Nettle instead? Any reason not to? Word on the street is that it is more pleasant 
> > > > to work with than gcrypt.
> >
> > I am only familiar with Libgcrypt which is not that hard to use. Have
> > you tried both libraries? What were your experiences?
> >
> > License-wise they are similar.  Based on development activity (commit
> > count), it seems that Nettle is mostly developed by one person while
> > Libgcrypt has more.
> >
> > An actual look at the Nettle documentation shows that Nettle provides
> > direct access to crypto routines (aes128_encrypt, aes256_encrypt,
> > aes_decrypt, chacha_poly1305_set_key, etc.). Libgcrypt provides a more
> > generic interface (gcry_cipher_open, gcry_cipher_encrypt) which means it
> > is easier to use when multiple ciphers can be chosen (which is the case
> > for SSL/TLS, IPsec, IKE).
> >
> > Thus, I think that it is better to stick to Libgcrypt than migrate to
> > Nettle.
>
> I was not considering a migration from gcrypt to nettle, just choosing one
> of the two libraries to replace our bundled crypto. Assuming the effort
> required for that is similar (maybe an incorrect assumption).

The status quo is that Libgcrypt is already used in many places while
nettle is only an implicit dependency (needed for GnuTLS). Since
Libgcrypt and nettle are comparable in feature set, changing to nettle
would be more effort and it seems better to stick to Libgcrypt.

GnuTLS is only needed for parsing RSA private keys (in PEM and PCKS#8
format) in the SSL/TLS dissector, so if we find a smaller library then
we could drop GnuTLS and nettle too.

Looking at some other projects, I found QEMU for which you can choose
nettle or Libgcrypt at compile time. They have introduced another
abstraction layer for block ciphers (crypto/cipher-gcrypt.c at 382
lines, crypto/cipher-nettle.c at 553 lines). I see no great benefit from
the crypto library agility, so let's not do a similar abstraction.

> Nettle has an abstract interface. See for example:
>
> https://www.lysator.liu.se/~nisse/nettle/nettle.html#HMAC

Yup, also noticed further hash/cipher abstraction:
6.1.3 The struct nettle_hash abstraction
6.2.13 The struct nettle_cipher abstraction
6.4.5 The struct nettle_aead abstraction
(+separate interface for weird CCM mode)

I guess I will go for the easy way (Libgcrypt) unless there are more
convincing arguments :-)
-- 
Kind regards,
Peter Wu
https://lekensteyn.nl
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