[Assword] [PATCH] use ENCRYPT_NO_COMPRESS if available

[Jameson Graef Rollins]

On Thu, May 08 2014, Daniel Kahn Gillmor <dkg at fifthhorseman.net> wrote:
> The CRIME attacks on TLS showed that repeated compression of a message
> with a variant component can leak some information about the plaintext
> if an attacker knows something about the variant.
>
> While it seems unlikely that such an attack applies directly to
> assword, it's possible that some use of assword in an automated
> situation could fit this attack profile.
>
> Upcoming versions of gpgme should support a GPGME_ENCRYPT_NO_COMPRESS
> option.  python-gpgme should add support for it once gpgme exposes the
> flag.  The use of this flag should invalidate any CRIME-style attacks.
>
> See the IETF OpenPGP WG list for discussion about how CRIME might or
> might not apply to:
>
> https://www.ietf.org/mail-archive/web/openpgp/current/msg07252.html
>
> Note that this fix will only take effect once the dependent libraries
> are themselves updated to document and support the ENCRYPT_NO_COMPRESS
> flag during encrypt() and encrypt_sign() functions.
> ---
>  assword.py | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/assword.py b/assword.py
> index 28af9f5..61bf664 100644
> --- a/assword.py
> +++ b/assword.py
> @@ -120,11 +120,16 @@ class Database():
>              signer = self._gpg.get_key(keyid or self._keyid)
>          except:
>              raise DatabaseError('Could not retrieve GPG encryption key.')
> +        flags = gpgme.ENCRYPT_ALWAYS_TRUST
> +        try:
> +            flags |= gpgme.ENCRYPT_NO_COMPRESS
> +        except AttributeError:
> +            pass
>          self._gpg.signers = [signer]
>          encdata = io.BytesIO()
>          data.seek(0)
>          sigs = self._gpg.encrypt_sign([recipient],
> -                                      gpgme.ENCRYPT_ALWAYS_TRUST,
> +                                      flags,
>                                        data,
>                                        encdata)
>          encdata.seek(0)
> -- 
> 2.0.0.rc0

pushed.  thanks.

jamie.
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