Wireshark-dev: Re: [Wireshark-dev] Remove our bundled crypto library (in favor of Libgcrypt)?
From: Peter Wu <[email protected]>
Date: Wed, 8 Feb 2017 14:40:27 +0100
On Mon, Feb 06, 2017 at 03:25:40PM -0800, Guy Harris wrote:
> On Feb 6, 2017, at 3:17 PM, João Valverde <[email protected]> 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.

> Which, if any, of those libraries can be prevented from wasting Wireshark's time by telling them not to bother gathering entropy unless they're doing it on behalf of some library called by Wireshark?  We only care about decryption.

I did not expect Libgcrypt to consume entropy when it is just doing
decryption. Ran `strace -k -e open,getrandom tshark -r ...` with TLS
decryption enabled and found that the only consumers of randomness
(/dev/urandom) at runtime are:

    wmem_init_hashing (g_random_int),
    init_dissection (ares_init_options),
    host_name_lookup_init (ares_init_options)

At startup we have a getrandom syscall from GnuTLS (constructor?):

    getrandom("\336", 1, GRND_NONBLOCK)
    _dsa_validate_dss_pq
    gnutls_supplemental_send
    gnutls_global_set_log_level

So it seems that Libgcrypt is not unnecessarily draining entropy.
-- 
Kind regards,
Peter Wu
https://lekensteyn.nl