NTLM hashes are not encrypted; they are hashed . Encryption is a two-way street (encrypt → decrypt with a key). Hashing is a one-way mathematical function. You cannot "decrypt" an NTLM hash any more than you can unbake a cake.
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Think of it like a blender: You put in a steak, you get a smoothie. You cannot "un-blend" the smoothie back into a steak. The only way is to guess what steak went in and see if the smoothie matches. ntlm-hash-decrypter