gpg,sm: New option --with-key-screening.

* common/pkscreening.c: New.
* common/pkscreening.h: New.
* common/Makefile.am (common_sources): Add them.
* g10/gpg.c (opts): New option --with-key-screening.
* g10/options.h (struct opt): New field with_key_screening.
* g10/keylist.c: Include pkscreening.h.
(print_pk_screening): New.
(list_keyblock_print): Call it.
(print_compliance_flags): Call it.
* sm/gpgsm.c (opts): New option --with-key-screening.
* sm/gpgsm.h (scruct opt): New field with_key_screening.
* sm/keylist.c:  Include pkscreening.h.
(print_pk_screening): New.
(print_compliance_flags): Call it.  Add new arg cert.
(list_cert_colon): Pass arg cert
(list_cert_std): Call print_pk_screening.
* sm/fingerprint.c (gpgsm_get_rsa_modulus): New.
--

This new option can be used to detect ROCA affected keys.  To scan an
entire keyring and print the affected fingerprints use this:

  gpg -k --with-key-screening --with-colons | gawk -F: \
       '$1~/pub|sub|sec|ssb|crt/ && $18~/\<6001\>/ {found=1;next};
        $1=="fpr" && found {print $10}; {found=0}'

The same works for gpgsm.  Note that we need gawk due to the "\<" in
the r.e.

Signed-off-by: Werner Koch <wk@gnupg.org>

doc/DETAILS

@@ -222,12 +222,14 @@ described here.
 
 *** Field 18 - Compliance flags
 
-    Space separated list of asserted compliance modes for this key.
+    Space separated list of asserted compliance modes and
+    screening result for this key.
 
     Valid values are:
 
     - 8  :: The key is compliant with RFC4880bis
     - 23 :: The key is compliant with compliance mode "de-vs".
+    - 6001 :: Screening hit on the ROCA vulnerability.
 
 *** Field 19 - Last update