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Re: libnettle/libhogweed WIP

From: Eli Zaretskii
Subject: Re: libnettle/libhogweed WIP
Date: Sat, 15 Jul 2017 22:12:59 +0300

> From: Ted Zlatanov <address@hidden>
> Date: Sat, 15 Jul 2017 14:40:37 -0400
> The size of the output is determined by the cipher's parameters. So we
> need to know the parameters, which are in cplist.

As I wrote, the problem happens on the first iteration through the
loop in test-gnutls-005-aead-ciphers, so the cipher's parameters
should be known, as they are set up by the code.  But in case this
isn't telling the whole story, you will see the values below.

> Can you capture the full parameters and memory buffers passed into the
> GnuTLS functions?

I attach below the GDB transcript with this information.  Let me know
if you need more data.

> Here's the sequence we expect in the test, this in a let* form:
> 1. The IV may be actual data or it may be a list of 'iv-auto and ivsize
> which tells extract_data_from_object() to generate a random IV (which is
> returned as the second element by `gnutls-symmetric-encrypt').
> 2. We call (gnutls-symmetric-encrypt cplist (copy-sequence key) iv input 
> (copy-sequence auth))
> 3. We need to make sure the cplist, key, iv, input, and auth make it
> down to the GnuTLS C functions.
> 4. We need to look at the output returned from the GnuTLS C function and
> make sure it makes it to the return of `gnutls-symmetric-encrypt'
> together with the actual IV used.
> 5. We need to do the same as steps 1-4 for decryption.

That's what I did, and my observations were in the previous mail.  I
just didn't know what to expect, so I couldn't tell whether some of
the data was incorrect.

> If you can provide a recipe for testing your case, that would be
> helpful.

I'm just running test-gnutls-005-aead-ciphers in an interactive
session after loading gnutls-tests.el by hand.

Here's the GDB transcript:

  (gdb) break Fgnutls_symmetric_encrypt
  Breakpoint 3 at 0x12aa8f5: file gnutls.c, line 2142.
  (gdb) break Fgnutls_symmetric_decrypt
  Breakpoint 4 at 0x12aa98b: file gnutls.c, line 2169.
  (gdb) r -Q

  Thread 1 hit Breakpoint 3, Fgnutls_symmetric_encrypt (
      cipher=XIL(0xc000000006c4c2a0), key=XIL(0x8000000006c336f0),
      iv=XIL(0x8000000006c33700), input=XIL(0x8000000006c34990),
      aead_auth=XIL(0)) at gnutls.c:2142
  2142      return gnutls_symmetric (true, cipher, key, iv, input, aead_auth);
  (gdb) pp cipher
  (:cipher-id 16 :type gnutls-symmetric-cipher :cipher-aead-capable t 
:cipher-tagsize 16 :cipher-blocksize 16 :cipher-keysize 32 :cipher-ivsize 12)
  (gdb) pp key
  "                           mykey"
  (gdb) pp iv
  "            "
  (gdb) pp input
  "                "
  (gdb) pp aead_auth
  (gdb) c

  Thread 1 hit Breakpoint 4, Fgnutls_symmetric_decrypt (
      cipher=XIL(0xc000000006c4c2a0), key=XIL(0x8000000006c32fa0),
      iv=XIL(0x8000000006c336a0), input=XIL(0x8000000006c32fb0),
      aead_auth=XIL(0)) at gnutls.c:2169
  2169      return gnutls_symmetric (false, cipher, key, iv, input, aead_auth);
  (gdb) pp cipher
  (:cipher-id 16 :type gnutls-symmetric-cipher :cipher-aead-capable t 
:cipher-tagsize 16 :cipher-blocksize 16 :cipher-keysize 32 :cipher-ivsize 12)
  (gdb) pp key
  "                           mykey"
  (gdb) pp iv
  "            "
  (gdb) pp input
  "% F[MM   ¼  t
  E  ↑ %  >*Rº [z  "
  (gdb) p input
  $1 = XIL(0x8000000006c32fb0)
  (gdb) xstring
  $2 = (struct Lisp_String *) 0x6c32fb0
  "%\231F[MM∩\237\212¼µ≤t\212\nEπ \030\376%τµ>*Rº╬[zו\200"
  (gdb) p *$
  $3 = {
    size = 32,
    size_byte = -1,
    intervals = 0x0,
    data = 0x6ce0a40 "%\231F[MM∩\237\212¼µ≤t\212\nEπ \030\376%τµ>*Rº╬[zו\200"
  (gdb) pp aead_auth

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