[Mono-bugs] [Bug 77276][Wis] Changed - Encrypt/Decrypt generates 'Bad PKC padding' exceptions

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Changed by sebastien at ximian.com.

http://bugzilla.ximian.com/show_bug.cgi?id=77276

--- shadow/77276	2006-01-16 14:06:53.000000000 -0500
+++ shadow/77276.tmp.13112	2006-01-16 14:39:44.000000000 -0500
@@ -1,16 +1,16 @@
 Bug#: 77276
 Product: Mono: Class Libraries
 Version: 1.1
 OS: All
 OS Details: 
-Status: NEW   
-Resolution: 
-Severity: 
+Status: RESOLVED   
+Resolution: NOTABUG
+Severity: Unknown
 Priority: Wishlist
-Component: System.Security
+Component: CORLIB
 AssignedTo: sebastien at ximian.com                            
 ReportedBy: wdai at fnfr.com               
 QAContact: mono-bugs at ximian.com
 TargetMilestone: ---
 URL: 
 Cc: 
@@ -304,6 +304,51 @@
 encrypt multiple strings, It only works if the same object is used to 
 decrypt them. Decrypt by a new object works only when encrypt is called 
 once.
 
 Second problem, encryptTwiceError routine. If you  encrypt the same 
 string twice, decrypt no longer work.
+
+------- Additional Comments From sebastien at ximian.com  2006-01-16 14:39 -------
+Your code isn't safe because it depends on specific details of the
+implementation, i.e. ICryptoTransform.CanReuseTransform returns true.
+You shouldn't depend on this (and neither depend on
+CanTransformMultipleBlocks) because:
+
+(a) their values could change in future version of the framework;
+
+(b) other implementations could use other values - so it makes your
+code less re-usable;
+
+(c) algorithm implementation remapping, using CryptoConfig /
+machine.config, could break your application (and be hard to debug);
+
+(d) ICryptoTransform inherits from IDisposable. As you can't know
+(implementation specific) it's resource requirement you should
+manually dispose (i.e. not wait for the GC) of the transform when you
+don't need it anymore.
+
+The changes are simple:
+
+1. remove the ICryptoTransform from the .ctor
+
+2. In the Encrypt method, do
+
+   if ((mEncryptor == null) || (!mEncryptor.CanReuseTransform))
+      mEncryptor = rijndael.CreateEncryptor(mKeys, mIVs);
+
+3. Do the same in your Decrypt method
+
+4. Consider disposing the ICryptoTransform if it's not gonna (or
+can't) be re-used immediately. This will be more secure and will lower
+resource usage. E.g. in Encrypt
+
+     if (!mEncryptor.CanReuseTransform) {
+        mEncryptor.Dispose ();
+        mEncryptor = null;
+     }
+
+5. Enjoy code that will works on MS (including future versions), Mono
+and any 3rd party encryption algorithm for .NET ;-)
+
+Note: For simplicity I suggest you encode your encrypted data using
+base64 (Convert.[To|From]Base64String).