Other versions used more common techniques, such as waiting for mouse movement and measuring the length of time the system remained idle. One version of the crypter waited until the currently active window changed three times before proceeding, otherwise it remained in a permanent sleep state. Next, in an effort to foil detection by sandbox environments, these crypters check for activities suggestive of being executed on a normal endpoint system. First, the Windows API calls they included in the code are commonly used by applications with graphical user interfaces This makes a sample more likely to appear to be benign when executed in a sandbox or scanned by endpoint anti-virus and may slow down code-based analysis. The Delphi crypters described by FireEye researchers used various techniques to attempt to remain undetectable. This is due to the fact that each Delphi command or function requires a lot of assembly code, greatly increasing the volume of code needing to be studied or debugged. It also has the added benefit, which may seem counter-intuitive, that it can be more difficult to perform code-based reverse engineering on. This fact means code development is quicker, easier and requires less skill and experience than other programming languages. Delphi is a so-called “high level” programming language, similar to the inimitable BASIC, in that it uses a syntax closer to a spoken language, rather than machine language. Delphi has been used to write numerous malware and continues to be used. Crypters are often sold with guarantees of being undetectable by anti-virus products and, increasingly, by sandboxes.ĭelphi is a programming language, initially an evolution of Turbo Pascal, first released by Borland in 1995 for Windows 3.1. Malware authors then pass the final malicious payload to the code generator which then creates the crypted executable, similar in concept to zipping a file and creating a self-extracting zip file. The stub is the component which decrypts and loads the actual malicious code. Crypters such as these will be sold with a code generator which uses a unique stub. Crypters have been used for a number of years to not only compress, but to make malware samples more difficult to detect and reverse engineer.Ĭrypters used by malware authors are generally sold on dark web forums, purchased with cryptocurrency.
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