gpg-agent features of loopback-pinentry mode, preset_passphrase

[Aaron Haggerty]

Fuck u

A

> On May 18, 2015, at 11:03 PM, NIIBE Yutaka <gniibe at fsij.org> wrote:
> 
>> On 05/18/2015 07:12 PM, Werner Koch wrote:
>> Actually, I expected that the loopback mode would be used with
>> --command-fd and not with the one-time setting of a passphrase.  I kept
>> passphrase working because that can be used for symmteric encryption.
>> 
>> After all loopback mode is a hack to bypass the standard way of asking
>> for passphrases and to allow a simpler thing than a pinentry-wrapper
>> (e.g. for use by CGIs).  We should never advertise it as a way to query
>> an unprotect-the-secret-key-passphrase - this would defeat the split
>> between gpg and gpg-agent.
>> 
>> Your suggestion to query the availibility of feature first is good from
>> the average user perspective.  However, average users should not use the
>> loopback mode anyway (unless a tool uses it invisible).
> 
> Thank you for the explanation.  I understand the intent and
> background.
> 
> I decline adding error message to user for suggesting loopback mode.
> 
> 
> Well, let's consider how to handle the issue 1928:
>     https://bugs.gnupg.org/gnupg/issue1928
> 
> With classic and stable versions, it worked:
> 
>  (0) gpg --batch --passphrase-file pass-file --decrypt encrypted-file
> 
> Now with 2.1, what's the answer to the existing script(s)?
> 
> Using command-file, it would be:
> 
>  (1) gpg --batch --pinentry-mode=loopback --command-file input-file \
>          --decrypt encrypted-file
> 
> This requires allow-loopback-pinentry option in .gnupg/gpg-agent.conf.
> 
> I understand that using loopback mode is for expert, so, I think that
> the requirement of configuration of allow-loopback-pinentry is
> legitimate (it makes sense to have default as not allowing loopback
> mode).
> 
> Although it would not be intended, following also works with 2.1 (with
> allow-loopback-pinentry option of gpg-agent).
> 
>  (2) gpg2 --batch --pinentry-mode=loopback --passphrase-file pass-file \
>           --decrypt encrypted-file
> 
> 
> While the split between gpg and gpg-agent highly makes sense for
> interactive usages, in general, there might still be valid usages
> where it doesn't matter much and where it's OK to invoke gpg-agent for
> every invocation of gpg command.
> 
> While we lead/ask people to pinentry wrapper solution or (1) with
> GnuPG 2.1, I think that requiring change from (0) to (1) or (2) would
> be still a regression.
> 
> Just in case, following is a patch to support (0) with GnuPG 2.1.  It
> let give gpg to pass "OPTION pinentry-mode=loopback" when the function
> have_static_passphrase returns true and to offer the string of
> get_static_passphrase to gpg-agent.
> 
> 
> BTW, in the commit of 1cd6445eec4c3642ad92afb02f3563a01cc10c10 in
> January 30, 2013, I think that the comment
> 
>    /* We do not pass errors to avoid breaking other code.  */
> 
> should have been removed.
> 
> 
> diff --git a/g10/call-agent.c b/g10/call-agent.c
> index edee66e..258a48b 100644
> --- a/g10/call-agent.c
> +++ b/g10/call-agent.c
> @@ -163,18 +163,18 @@ default_inq_cb (void *opaque, const char *line)
>       if (err)
>         log_error (_("failed to proxy %s inquiry to client\n"),
>                    "PINENTRY_LAUNCHED");
> -      /* We do not pass errors to avoid breaking other code.  */
> +      return err;
>     }
> -  else if ((has_leading_keyword (line, "PASSPHRASE")
> -            || has_leading_keyword (line, "NEW_PASSPHRASE"))
> -           && opt.pinentry_mode == PINENTRY_MODE_LOOPBACK)
> +
> +  if ((has_leading_keyword (line, "PASSPHRASE")
> +       || has_leading_keyword (line, "NEW_PASSPHRASE")))
>     {
>       if (have_static_passphrase ())
>         {
>           const char *s = get_static_passphrase ();
> -          err = assuan_send_data (parm->ctx, s, strlen (s));
> +          return assuan_send_data (parm->ctx, s, strlen (s));
>         }
> -      else
> +      else if (opt.batch || opt.pinentry_mode == PINENTRY_MODE_LOOPBACK)
>         {
>           char *pw;
> 
> @@ -189,11 +189,11 @@ default_inq_cb (void *opaque, const char *line)
>           else
>             err = assuan_send_data (parm->ctx, pw, strlen (pw));
>           xfree (pw);
> +          return err;
>         }
>     }
> -  else
> -    log_debug ("ignoring gpg-agent inquiry '%s'\n", line);
> 
> +  log_debug ("ignoring gpg-agent inquiry '%s'\n", line);
>   return err;
> }
> 
> @@ -306,9 +306,10 @@ start_agent (ctrl_t ctrl, int for_card)
>           assuan_transact (agent_ctx, "OPTION agent-awareness=2.1.0",
>                            NULL, NULL, NULL, NULL, NULL, NULL);
>           /* Pass on the pinentry mode.  */
> -          if (opt.pinentry_mode)
> +          if (have_static_passphrase () || opt.pinentry_mode)
>             {
>               char *tmp = xasprintf ("OPTION pinentry-mode=%s",
> +                                     opt.batch ? "loopback" :
>                                      str_pinentry_mode (opt.pinentry_mode));
>               rc = assuan_transact (agent_ctx, tmp,
>                                NULL, NULL, NULL, NULL, NULL, NULL);
> -- 
> 
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