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I have ciphertext, plaintext and what I think is the key. What encryption algorithm was used and how

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hmph

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I have a series of text and data files, where the one file contains plaintext and the corresponding file contains ciphertext. The length of the plaintext and the ciphertext are identical.

I know that encryption algorithms like AES are not vulnerable to known plaintext attacks, but I think I have the password, initialisation vector and salt to decrypt the data as well. The problem is, I do not know what encryption scheme is being used!

I know that the application was written in C#, so I tried the various encryption algorithms provided by C#, such as AES etc. The problem is, my suspected key is 256 ASCII characters long or 2048 bits which is longer than any symmetric encryption algorithm that I could find.

I tried solving for basic ciphers like Caeser, Vigenere and XOR, but it is more complicated than that and I am a newcomer to cryptography

The data in question is here http://sdrv.ms/1epVftw