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I have a cipher text, that was created using One-Time-Pad, but the idea is that it was encrypted badly. The message, a section of a book, was encrypted using a pad 256B long repeated many times over (like Vigenere).

Any ideas how to break it or what tools to use?

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If I understand correctly, you are in possession of many 256-byte strings, that when XOR-ed with the key will result in legible text.

To get started, take the first character of each string. All these have been XORed with the first character of the key. Just try XORing all these characters with all 256 possibilities, and check the output.

How do you now determine which one is the correct answer? For most results, values will be outside ASCII range, and can be discarded. For results that do look like letters, you can check whether the letter occurrence is what you expect (e.g. e is the most common letter in English).

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