--pgp6 flag. This is not nearly as involved as --pgp2. In short, it

turns off force_mdc, turns on no_comment, escape_from, and force_v3_sigs,
and sets compression to 1.  It also restricts the user to IDEA (if
present), 3DES, CAST5, MD5, SHA1, and RIPEMD160. See the comments above
algo_available() for lots of discussion on why you would want to do this.

g10/ChangeLog

@@ -1,3 +1,13 @@
+2002-01-28  David Shaw  <dshaw@jabberwocky.com>
+
+	* g10.c (main), options.h, pkclist.c (algo_available): --pgp6
+	flag.  This is not nearly as involved as --pgp2.  In short, it
+	turns off force_mdc, turns on no_comment, escape_from, and
+	force_v3_sigs, and sets compression to 1.  It also restricts the
+	user to IDEA (if present), 3DES, CAST5, MD5, SHA1, and RIPEMD160.
+	See the comments above algo_available() for lots of discussion on
+	why you would want to do this.
+
 2002-01-27  David Shaw  <dshaw@jabberwocky.com>
 
 	* keygen.c (keygen_set_std_prefs): Comment

g10/encode.c

@@ -624,20 +624,3 @@ encode_crypt_files(int nfiles, char **files, STRLIST remusr)
         }
     }
 }
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-

g10/g10.c

@@ -158,6 +158,8 @@ enum cmd_and_opt_values { aNull = 0,
     oOpenPGP,
     oPGP2,
     oNoPGP2,
+    oPGP6,
+    oNoPGP6,
     oCipherAlgo,
     oDigestAlgo,
     oCompressAlgo,
@@ -388,6 +390,8 @@ static ARGPARSE_OPTS opts[] = {
     { oOpenPGP, "openpgp", 0, N_("set all packet, cipher and digest options to OpenPGP behavior")},
     { oPGP2, "pgp2", 0, N_("set all packet, cipher and digest options to PGP 2.x behavior")},
     { oNoPGP2, "no-pgp2", 0, "@"},
+    { oPGP6, "pgp6", 0, "@"},
+    { oNoPGP6, "no-pgp6", 0, "@"},
     { oS2KMode, "s2k-mode",  1, N_("|N|use passphrase mode N")},
     { oS2KDigest, "s2k-digest-algo",2,
 		N_("|NAME|use message digest algorithm NAME for passphrases")},
@@ -1064,6 +1068,8 @@ main( int argc, char **argv )
 	    break;
 	  case oPGP2: opt.pgp2 = 1; break;
 	  case oNoPGP2: opt.pgp2 = 0; break;
+	  case oPGP6: opt.pgp6 = 1; break;
+	  case oNoPGP6: opt.pgp6 = 0; break;
 	  case oEmuChecksumBug: opt.emulate_bugs |= EMUBUG_GPGCHKSUM; break;
 	  case oEmu3DESS2KBug:	opt.emulate_bugs |= EMUBUG_3DESS2K; break;
 	  case oEmuMDEncodeBug: opt.emulate_bugs |= EMUBUG_MDENCODE; break;
@@ -1295,7 +1301,11 @@ main( int argc, char **argv )
     set_debug();
     g10_opt_homedir = opt.homedir;
 
-    /* Do this after the switch(), so it can override settings. */
+    /* Do these after the switch(), so they can override settings. */
+    if(opt.pgp2 && opt.pgp6)
+      log_error(_("%s not allowed with %s!\n"),"--pgp2","--pgp6");
+    else
+      {
 	if(opt.pgp2)
 	  {
 	    int unusable=0;
@@ -1348,6 +1358,7 @@ main( int argc, char **argv )
 	      {
 		opt.rfc1991 = 1;
 		opt.rfc2440 = 0;
+		opt.force_mdc = 0;
 		opt.force_v4_certs = 0;
 		opt.no_comment = 1;
 		opt.escape_from = 1;
@@ -1359,6 +1370,16 @@ main( int argc, char **argv )
 	      }
 	  }
 
+	if(opt.pgp6)
+	  {
+	    opt.force_mdc=0;
+	    opt.no_comment=1;
+	    opt.escape_from=1;
+	    opt.force_v3_sigs=1;
+	    opt.def_compress_algo=1;
+	  }
+      }
+
     /* must do this after dropping setuid, because string_to...
      * may try to load an module */
     if( def_cipher_string ) {

g10/options.h

@@ -79,6 +79,7 @@ struct {
     int compress_sigs;
     int always_trust;
     int pgp2;
+    int pgp6;
     int rfc1991;
     int rfc2440;
     int pgp2_workarounds;

g10/pkclist.c

@@ -926,17 +926,40 @@ build_pk_list( STRLIST remusr, PK_LIST *ret_pk_list, unsigned use )
 }
 
 
+/* In pgp6 mode, disallow all ciphers except IDEA (1), 3DES (2), and
+   CAST5 (3), all hashes except MD5 (1), SHA1 (2), and RIPEMD160 (3),
+   and all compressions except none (0) and ZIP (1).  For a true PGP6
+   key all of this is unneeded as they are the only items present in
+   the preferences subpacket, but checking here covers the weird case
+   of encrypting to a key that had preferences from a different
+   implementation which was then used with PGP6.  I am not completely
+   comfortable with this as the right thing to do, as it slightly
+   alters the list of what the user is supposedly requesting.  It is
+   not against the RFC however, as the preference chosen will never be
+   one that the user didn't specify somewhere ("The implementation may
+   use any mechanism to pick an algorithm in the intersection"), and
+   PGP6 has no mechanism to fix such a broken preference list, so I'm
+   including it. -dms */
 
 static int
 algo_available( int preftype, int algo )
 {
     if( preftype == PREFTYPE_SYM ) {
+        if( opt.pgp6 && ( algo != 1 && algo != 2 && algo != 3) )
+	  return 0;
+
 	return algo && !check_cipher_algo( algo );
     }
     else if( preftype == PREFTYPE_HASH ) {
+        if( opt.pgp6 && ( algo != 1 && algo != 2 && algo != 3) )
+	  return 0;
+
 	return algo && !check_digest_algo( algo );
     }
     else if( preftype == PREFTYPE_ZIP ) {
+        if ( opt.pgp6 && ( algo !=0 && algo != 1) )
+	  return 0;
+
 	return !algo || algo == 1 || algo == 2;
     }
     else
@@ -1080,5 +1103,3 @@ select_mdc_from_pklist (PK_LIST pk_list)
     }
     return 1; /* can be used */
 }
-
-