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How can I crack two ciphertexts that have used the same key twice? For example, plaintext1 uses the key "abcdefg", and plaintext2 uses the key "abcdefg".
I know that ciphertext2 ^ ciphertext1 is equal to plaintext1 ^ plaintext2. And the method to crack plaintext1 ^ plaintext2 is the same method to crack a "book cipher" (also sometimes called a "running key cipher", although a running key cipher isn't the same as a book cipher, right?)
I know that I'm supposed to use a dictionary attack, but I'm not sure which dictionary/wordlist I should use, and the algorithm used in cracking this. Can anyone provide me with a link, or some code that shows how to crack it?
I'm new to cryptography, and I just wanted to do this for fun. Can anyone help me out? Thanks.
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Once the one-time pad is used, it cannot be reused. If it is reused, someone who intercepts multiple messages can begin to compare them for similar coding for words that may occur in several messages. A simple example of how a one-time pad works is shown in the example below.
The security of the OTP relies on the randomness of the key. Unfortunately, the randomness of a key cannot be proved. The key must never be reused. Use of the same key to encrypt different messages, no matter how trivially small, compromises the cipher.
The general rule of cryptography says that one should never use the same keystream characters more than once. Otherwise, the cipher starts to be vulnerable to ciphertext-only attacks.
The One Time Pad encryption method is a binary additive stream cipher, where a stream of truly random keys is generated and then combined with the plain text for encryption or with the ciphertext for decryption by an 'exclusive OR' (XOR) addition.
The most common attack is to "slide" a common (but not too short) word along and XOR it against successive positions in the combined stream. Where the word was used in one stream, the XOR will (usually) produce readable text for the other stream.
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