aklog: require opt-in to enable single-DES in libkrb5

Since the introduction of rxkad-k5 in response to OPENAFS-SA-2013-003,
it is not strictly necessary to configure libkrb5 to allow weak crypto
in order to obtain an AFS token.  A sufficient amount of time has passed
since then that it is safe to assume that the default behavior is the
more-secure one, and require opt-in for the insecure behavior.

To indicate that the use of single-DES is quite risky, add the
"-insecure_des" argument to both klog and aklog, to gate the
preexisting calls that enable weak crypto/single-DES.
These calls, and the -insecure_des option, may be removed entirely
in a future commit.

Change-Id: If175d0f95f0ede0f252844086a2a023da5580732
Reviewed-on: https://gerrit.openafs.org/13689
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>

doc/man-pages/pod1/aklog.pod

@@ -8,11 +8,11 @@ aklog - Obtain tokens for authentication to AFS
 <div class="synopsis">
 
 B<aklog> [B<-d>] [B<-hosts>] [B<-zsubs>] [B<-noprdb>] [B<-noauth>] [B<-linked>]
-    [B<-force>] [B<-524>] [B<-setpag>]
+    [B<-force>] [B<-524>] [B<-setpag>] [B<-insecure_des>]
     S<<< [[B<-cell> | B<-c>] <I<cell>> [B<-k> <I<Kerberos realm>>]]+ >>>
 
 B<aklog> [B<-d>] [B<-hosts>] [B<-zsubs>] [B<-noprdb>] [B<-noauth>] [B<-linked>]
-    [B<-force>] [B<-524>] [B<-setpag>] [B<-path> | B<-p>] <I<path>>+
+    [B<-force>] [B<-524>] [B<-setpag>] [B<-insecure_des>] [B<-path> | B<-p>] <I<path>>+
 
 =for html
 </div>
@@ -119,6 +119,11 @@ normally won't be necessary.
 
 If the AFS cell is linked to another AFS cell, get tokens for both.
 
+-item B<-insecure_des>
+
+Configure libkrb5 to allow the use of the (insecure) single-DES encryption
+types.  When rxkad-k5 is in use, this is not needed.
+
 =item B<-noauth>
 
 Don't actually authenticate, just do everything else B<aklog> does up to

doc/man-pages/pod1/klog.krb5.pod

@@ -11,14 +11,15 @@ B<klog.krb5> [B<-x>] S<<< [B<-principal> <I<user name>>] >>>
     [-password <I<user's password>>] S<<< [B<-cell> <I<cell name>>] >>>
     S<<< [B<-k> <I<realm>>] >>> [B<-pipe>] [B<-silent>]
     S<<< [B<-lifetime> <I<ticket lifetime in hh[:mm[:ss]]>>] >>>
-    [B<-setpag>] [B<-tmp>] [B<-noprdb>] [B<-unwrap>] [B<-help>]
+    [B<-setpag>] [B<-tmp>] [B<-noprdb>] [B<-unwrap>] [B<-insecure_des>]
+    [B<-help>]
 
 B<klog.krb5> [B<-x>] S<<< [B<-pr> <I<user name>>] >>>
     S<<< [B<-pa> <I<user's password>>] >>>
     S<<< [B<-c> <I<cell name>>] >>>
     B<<< [B<-k> <I<realm>>] >>> [B<-pi>] [B<-si>]
     S<<< [B<-l> <I<ticket lifetime in hh[:mm[:ss]]>>] >>>
-    [B<-se>] [B<-t>] [B<-n>] [B<-u>] [B<-h>]
+    [B<-se>] [B<-t>] [B<-n>] [B<-u>] [B<-i>] [B<-h>]
 
 =for html
 </div>
@@ -221,6 +222,11 @@ sizes in conjunction with Active Directory as the Kerberos server, using
 B<-unwrap> can shrink the AFS token size so that older software can handle
 it more easily.
 
+=item B<-insecure_des>
+
+Configures libkrb5 to allow the use of the (insecure) single-DES encryption
+types.  When rxkad-k5 is in use, this is not needed.
+
 =item B<-help>
 
 Prints the online help for this command. All other valid options are

src/aklog/aklog.c

@@ -1428,7 +1428,7 @@ usage(void)
 	    "[-d] [[-cell | -c] cell [-k krb_realm]] ",
 	    "[[-p | -path] pathname]\n",
 	    "    [-zsubs] [-hosts] [-noauth] [-noprdb] [-force] [-setpag] \n"
-		"    [-linked]"
+		"    [-linked] [-insecure_des]"
 #ifndef HAVE_NO_KRB5_524
 		" [-524]"
 #endif
@@ -1447,6 +1447,7 @@ usage(void)
 #ifndef HAVE_NO_KRB5_524
     fprintf(stderr, "    -524 means use the 524 converter instead of V5 directly\n");
 #endif
+    fprintf(stderr, "    -insecure_des enables insecure single-DES for krb5.\n");
     fprintf(stderr, "    No commandline arguments means ");
     fprintf(stderr, "authenticate to the local cell.\n");
     fprintf(stderr, "\n");
@@ -1460,6 +1461,7 @@ main(int argc, char *argv[])
     int status = AKLOG_SUCCESS;
     int i;
     int somethingswrong = FALSE;
+    int insecure_des = 0;
 
     cellinfo_t cellinfo;
 
@@ -1539,19 +1541,6 @@ main(int argc, char *argv[])
     initialize_PT_error_table();
     afs_set_com_err_hook(redirect_errors);
 
-    /*
-     * Enable DES enctypes, which are currently still required for AFS.
-     * krb5_allow_weak_crypto is MIT Kerberos 1.8.  krb5_enctype_enable is
-     * Heimdal.
-     */
-#if defined(HAVE_KRB5_ENCTYPE_ENABLE)
-    i = krb5_enctype_valid(context, ETYPE_DES_CBC_CRC);
-    if (i)
-        krb5_enctype_enable(context, ETYPE_DES_CBC_CRC);
-#elif defined(HAVE_KRB5_ALLOW_WEAK_CRYPTO)
-    krb5_allow_weak_crypto(context, 1);
-#endif
-
     /* Initialize list of cells to which we have authenticated */
     ll_init(&authedcells);
 
@@ -1611,6 +1600,8 @@ main(int argc, char *argv[])
 	    }
 	    else
 		usage();
+	else if (strcmp(argv[i], "-insecure_des") == 0)
+	    insecure_des = 1;
 	else if (argv[i][0] == '-')
 	    usage();
 	else if (!pmode && !cmode) {
@@ -1627,6 +1618,26 @@ main(int argc, char *argv[])
 	else
 	    usage();
 
+    /*
+     * Enable DES enctypes if requested.  This is not required when rxkad-k5
+     * is used, but some sites may not have updated.
+     * krb5_allow_weak_crypto is MIT Kerberos 1.8.  krb5_enctype_enable is
+     * Heimdal.
+     */
+    if (insecure_des) {
+#if defined(HAVE_KRB5_ENCTYPE_ENABLE)
+	i = krb5_enctype_valid(context, ETYPE_DES_CBC_CRC);
+	if (i)
+	    krb5_enctype_enable(context, ETYPE_DES_CBC_CRC);
+#elif defined(HAVE_KRB5_ALLOW_WEAK_CRYPTO)
+	krb5_allow_weak_crypto(context, 1);
+#else
+	fprintf(stderr,
+	    "%s: -insecure_des is not supported by this libkrb5\n", progname);
+	exit(AKLOG_MISC);
+#endif
+    }
+
 	if (cmode) {
 	    if (((i + 1) < argc) && (strcmp(argv[i + 1], "-k") == 0)) {
 		i+=2;

src/aklog/klog.c

@@ -116,6 +116,7 @@ main(int argc, char *argv[])
 #define aUNWRAP 11
 #define aK5 12
 #define aK4 13
+#define aDES 14
 
     cmd_AddParm(ts, "-x", CMD_FLAG, CMD_OPTIONAL, "obsolete, noop");
     cmd_Seek(ts, aPRINCIPAL);
@@ -142,6 +143,8 @@ main(int argc, char *argv[])
     ++ts->nParms;	/* skip -k5 */
     cmd_AddParm(ts, "-k4", CMD_FLAG, CMD_OPTIONAL|CMD_HIDDEN, 0);
 #endif
+    cmd_AddParm(ts, "-insecure_des", CMD_FLAG, CMD_OPTIONAL,
+		"enable insecure single-DES for krb5");
 
     code = cmd_Dispatch(argc, argv);
     KLOGEXIT(code);
@@ -413,13 +416,15 @@ CommandProc(struct cmd_syndesc *as, void *arock)
      * krb5_allow_weak_crypto is MIT Kerberos 1.8.  krb5_enctype_enable is
      * Heimdal.
      */
+    if (as->parms[aDES].items) {
 #if defined(HAVE_KRB5_ENCTYPE_ENABLE)
-    i = krb5_enctype_valid(k5context, ETYPE_DES_CBC_CRC);
-    if (i)
-        krb5_enctype_enable(k5context, ETYPE_DES_CBC_CRC);
+	i = krb5_enctype_valid(k5context, ETYPE_DES_CBC_CRC);
+	if (i)
+	    krb5_enctype_enable(k5context, ETYPE_DES_CBC_CRC);
 #elif defined(HAVE_KRB5_ALLOW_WEAK_CRYPTO)
-    krb5_allow_weak_crypto(k5context, 1);
+	krb5_allow_weak_crypto(k5context, 1);
 #endif
+    }
 
     /* Parse remaining arguments. */