By using standard API calls without doing anything custom, a rule against this crypter would have to rely on flagging ordinary API calls which may cause a problematic amount of false positives and is someting analysts seem to attempt to avoid based on my research. They pick out byte sequences or strings in a file and make rules that combined give a good indication that a file is a specific type of malware. I choose this approach over others because one of the primary ways antiviruses detect malware is through static rules. TransformFinalBlock ( $payload, 16, $payload. IV = $payload $memstream = New-Object System. NET functions, and it so happens AES can be very easily decrypted like so: It uses AES, but the reason I chose that is not because AES is better cryptographically than the alternatives, I use it because PowerShell provides a very simple way to call. Take for instance my PowerShell crypter Xencrypt. They’re both relatively simple questions, but the devil is in the details. #FREE CRYPTER HOW TO#How to decrypt (and therefore also how to encrypt).We therefore need to decide on two things: The stub, as mentioned, is the decrypter and executer, as illustrated above. If you try to tackle them all at the same time it can get kind of confusing, so my recommendation is to start with the design of the stub. You basically need an encrypter, decrypter/executer (the stub) and some way to bundle the encrypted payload with the stub. The combiner - Takes the stub and the encrypted payload, and combines them in a manner that generates a valid executable or script. #FREE CRYPTER CODE#
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