Randomize the password on Heimdal principal creation

When creating new principals in a Heimdal KDC, generate a long, random
password as the temporary password of the disabled principal before
randomizing keys.  This is necessary if password quality is being
enforced on create calls.  Since the principal is always inactive
until the keys have been randomized, the password should not need to
be secure (and indeed is not cryptographically random).

Change-Id: If519a82475bb0d387a19d16ef1e024b0da64779a
Reviewed-on: https://gerrit.stanford.edu/1374
Reviewed-by: Russ Allbery <rra@stanford.edu>
Tested-by: Russ Allbery <rra@stanford.edu>

Conflicts:
	NEWS

2 files changed, 41 insertions, 7 deletions

diff --git a/NEWS b/NEWS
index a9305d7..50caa05 100644
--- a/NEWS
+++ b/NEWS
@@ -13,6 +13,13 @@ wallet 1.1 (unreleased)
     Fix the code to set enctype restrictions for keytab objects in the
     wallet server.
 
+    When creating new principals in a Heimdal KDC, generate a long, random
+    password as the temporary password of the disabled principal before
+    randomizing keys.  This is necessary if password quality is being
+    enforced on create calls.  Since the principal is always inactive
+    until the keys have been randomized, the password should not need to
+    be secure (and indeed is not cryptographically random).
+
 wallet 1.0 (2013-03-27)
 
     Owners of wallet objects are now allowed to destroy them.  In previous
diff --git a/perl/Wallet/Kadmin/Heimdal.pm b/perl/Wallet/Kadmin/Heimdal.pm
index bb07b93..a1d63ae 100644
--- a/perl/Wallet/Kadmin/Heimdal.pm
+++ b/perl/Wallet/Kadmin/Heimdal.pm
@@ -1,7 +1,7 @@
 # Wallet::Kadmin::Heimdal -- Wallet Kerberos administration API for Heimdal.
 #
 # Written by Jon Robertson <jonrober@stanford.edu>
-# Copyright 2009, 2010
+# Copyright 2009, 2010, 2014
 #     The Board of Trustees of the Leland Stanford Junior University
 #
 # See LICENSE for licensing terms.
@@ -40,6 +40,34 @@ sub canonicalize_principal {
     return $principal;
 }
 
+# Generate a long random password.
+#
+# Please note: This is not a cryptographically secure password!  It's used
+# only because the Heimdal kadmin interface requires a password on create.
+# The keys will be set before the principal is ever set active, so it will
+# never be possible to use the password.  It just needs to be random in case
+# password quality checks are applied to it.
+#
+# Make the password reasonably long and include a variety of character classes
+# so that it should pass any password strength checking.
+sub insecure_random_password {
+    my ($self) = @_;
+    my @classes = (
+        'abcdefghijklmnopqrstuvwxyz',
+        'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
+        '0123456789',
+        '~`!@#$%^&*()-_+={[}]|:;<,>.?/'
+    );
+    my $password = q{};
+    for my $i (1..20) {
+        my $class = $i % scalar (@classes);
+        my $alphabet = $classes[$class];
+        my $letter = substr ($alphabet, int (rand (length $alphabet)), 1);
+        $password .= $letter;
+    }
+    return $password;
+}
+
 ##############################################################################
 # Public interfaces
 ##############################################################################
@@ -71,18 +99,17 @@ sub create {
     return 1 if $exists;
 
     # The way Heimdal::Kadm5 works, we create a principal object, create the
-    # actual principal set inactive, then randomize it and activate it.
-    #
-    # TODO - Paranoia makes me want to set the password to something random
-    #        on creation even if it is inactive until after randomized by
-    #        module.
+    # actual principal set inactive, then randomize it and activate it.  We
+    # have to set a password, even though we're about to replace it with
+    # random keys, but since the principal is created inactive, it doesn't
+    # have to be a very good one.
     my $kadmin = $self->{client};
     eval {
         my $princdata = $kadmin->makePrincipal ($principal);
         my $attrs = $princdata->getAttributes;
         $attrs |= KRB5_KDB_DISALLOW_ALL_TIX;
         $princdata->setAttributes ($attrs);
-        my $password = 'inactive';
+        my $password = $self->insecure_random_password;
         $kadmin->createPrincipal ($princdata, $password, 0);
         $kadmin->randKeyPrincipal ($principal);
         $kadmin->enablePrincipal ($principal);