[Mono-dev] patch for StrongName to fix minor security bug

Andrew Yates andrewyates at gmail.com
Sat Nov 12 09:57:02 EST 2005

It is my understanding that the key generated by "sn -k foo.snk" is a
private key used to sign assemblies, and should not be shared with
anyone other than the key's owner.

If this is the case, there is a minor security bug in sn: when it
creates the key, it creates it according to the user's umask. The
umask for most distributions is 0022 by default, so this would create
the file with rw-r-r (644) permissions, allowing anyone with access to
that computer to read the key, assuming the key's parent directories
have rwx-rx-rx (755) permissions.

The key should be created with rw - - permissions (600). Below is a
patch which chmods the key to rw - - immediately after creating it, in
order to prevent unauthorized users from taking it and compromising


--- sn.cs.old   2005-11-10 08:31:54.000000000 -0500
+++ sn.cs       2005-11-12 09:32:45.000000000 -0500
@@ -352,7 +352,14 @@
                                        sn = new StrongName (size);
-                                       WriteToFile (args[i],
CryptoConvert.ToCapiKeyBlob (sn.RSA, true));
+                                               try {
+                                                       WriteToFile
(args[i], CryptoConvert.ToCapiKeyBlob (sn.RSA, true));
Mono.Unix.Native.Syscall.chmod (args[i],
+                                               }
+                                               catch {
Console.WriteLine("An error occurred while creating the file '{0}'.",
+                                                       break;
+                                               }
                                        if (!quiet)
                                                Console.WriteLine ("A
new {0} bits strong name keypair has been generated in file '{1}'.",
size, args [i]);

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