I'm a little rusty on cryptography, but I have successfully acquired a 256 bit key that is used for encryption and I want to know if it is possible to reverse it into its corresponding plain text password. If yes, how do I do that?

closed as unclear what you're asking by TildalWave, Xander, Jens Erat, schroeder, RoraΖ Feb 9 '15 at 13:37

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  • You mean a 256-bit hash? AES keys are used to encrypt data. So you would need to use the key to decrypt the password blob; if it is in fact an AES key. – RoraΖ Feb 3 '15 at 14:35
  • Yes, I guess it's a 256 bit hash corresponding to the AES key that I located in memory. If it's a hash, it cannot be reversed right? – whoami Feb 3 '15 at 14:38
  • Fairly unlikely – RoraΖ Feb 3 '15 at 14:42

This isn't a meaningful question.

An AES key is simply a sequence of 256 bits. Some uses of AES (eg. file encryption) compute their key from a password through the use of a key derivation function (KDF), but most (such as SSL and most disk encryption) simply generate a block of random data and use that as the key.

Even if the implementation you're working with is one that runs a password through a KDF, reversing it is not practical: virtually every KDF uses a cryptographic hash function, and reversing it means performing a preimage attack -- something every cryptographic hash function is supposed to be resistant to.

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