Jim Paris posted this rather interesting statement:
<blockquote>As you may know, EdisonCarter has made a trainer for GTA that uses a straightforward exploit in the game to execute arbitrary code. He chose not to reveal his techniques, but with the new savedata encryption and decryption routines at http://forums.ps2dev.org/viewtopic.php?t=4335, now anyone can run homebrew on 2.0, 2.01, 2.50, and probably 2.60:
Decrypt the GTA cheat device using the savedata/decrypt sample
Find and modify the code (look at offset 0xc4 for the offset of the start of MIPS code)
Reencrypt the save using the savedata/encrypt sample
Note that the syscalls may be changed from the 2.0 VSH mode, since a different set of modules is loaded. Hopefully it shouldn't take long before someone clever like Fanjita can make a decent loader for us.</blockquote>