You must be able to understand and identify each one and the role it plays in the overall scheme.In order for something as powerful as encryption to break, there needs to be some kind of weakness to exploit.
That weakness is often a result of an error in implementation. In order for something as powerful as encryption to break, there needs to be some kind of secret flaw. Whats difficult is being able to identify and analyze the methods a programmer used for encryption and look for any weaknesses to exploit. If this is the case, it can be quite simple to identify the algorithm. When this is the case, you must be able to understand the inner workings of encryption algorithms to be able to identify code. The encryption implementation will likely be performed between these two points. A basic understanding of some of the low-level details of how these encryption algorithms work will be necessary. In general, most synchronous encryption algorithms have a similar flow to this; the differences may be the types of mathematical operations performed, but the core concepts remain the same. In the picture above, you see a loop involving a few blocks. In this case, its 16 bytes, but depending on the algorithm, it could be anything. Each byte of data from previous steps is used as the index to a lookup array. This means that when you are looking for the encryption code inside of a binary, it will likely be a long function with a lot of repetitive-looking code. This is one aspect that can help you identify it as encryption code when looking though the binary. These kinds of details are not too important to us because we are not cryptographers. The reason for going into such detail on the inner workings of AES is only to give you an understanding of how it works so that you can identify it in code when you see it in the wild. They were encrypting files using statically compiled AESno API calls. We had to do some research on the inner workings of various encryption methods to be able to properly identify what the algorithm was actually doing. This is good to keep an eye out for and not to be confused when you find multiple encryptions being used. Here, we have the flow chart showing the file encryption but also the algorithm that encrypts the previous key. Although it is not the encryption that is modifying the file itself, it will be what is used to keep the file encryption key secure.
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