Sims 3:0x073FAA07

Signed Assemblies - MSIL
TypeID:	0x073FAA07
Game Version:	The Sims 3

Overview

Signed assemblies, encrypted .NET assemblies. They function as the game scripts.

These are the scripts that run when a Sim interacts with an object, or another Sim, or just performs its own inner metabolic processes.

Currently no way is known to get the game to accept piecemeal overrides, so global hacks for a particular assembly as of 6 / 6 / 2009 are having to replace the entire set - meaning that you can only have global hacks for a particular assembly from one creator at a time.

It is possible to create new scripts for new custom objects, however.

For some information about how to import/export scripts in s3pi DemoFE, in a way that you can look at them in Reflector, see [this thread].

There some more in depth technical guidance on how to get your code to be run by the game in [this thread].

Where used

• gameplay.package
• scripts.package
• simcore.package

In addition, scripts can be placed in custom content packages and the game will load them when they are referenced.

Format

Provided by Rick. Modified for EP2 by Grant.

BYTE Version		// Pre-EP2: 1; EP2+: 2
--if Version >= 2
	DWORD strLen	// Number of UNICODE (2-byte) characters
	UNICODE[strLen] gameversion	// from Game/bin/code_version.txt (AD85)
DWORD checksum_typeid	// 0x2BC4F79F
BYTE[64] checksum_data
WORD block_count
QWORD[block_count]	// decryption table
BYTE[block_count*512]	// encrypted data

(I think the checksum and encryption method are MD5Cng -- PLJ.)

Decryption method

Initialise the decryption seed by scanning the decryption table:

foreach(QWORD q in decryption table) decryption seed += q

Truncate (mask off) the decryption seed to the length of decryption table:

decryption seed = decryption seed & (decryption table Length - 1)

Now process each QWORD in the decryption table. Where an entry has bit 0 set, write 512 zero bytes to the output, otherwise, read 512 bytes into a buffer from the encrypted data and process as follows:

foreach(byte b in buffer)
{
  byte value = b;
  b ^= decryption table[decryption seed];
  decryption seed = (decryption seed + value) % (decryption table Length);
}

Then write out the decrypted buffer.

Encryption Method

To encrypt, reverse the process for decryption. We cannot currently create our own signatures of data, as this requires EA's private key (the signature is created with a private / public key pair).

Prior to June 2010, there was no alternative supported by the game. To circumvent the process, you required a special hack that disables the validation of signed assemblies, d3dx9_31.dll.

• Download d3dx9_31.dll.
• Place in Game\Bin.

As of EP2 and the associated game patch (June 2010), this is no longer required (...---someone complete details, please---...).

There is no need to create a valid checksum and the decryption table table can be left full of zeros (which saves identifying empty 512 byte chunks).

Note on d3dx9_31.dll needed pre-June 2010

This DLL is a wrapper for the real DLL that resides in system32, it was chosen because The Sims 3 loads this DLL pretty early on. What the wrapper does is effectively disable a specific Windows API function used in the validation of signed assembly data.

Data content

The decrypted content is a Common Language Runtime assembly.

How the game uses Assemblies

TBC