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5

At least, doing the goof of reusing the OTP makes one vulnerable to disclosure of any of the key, which trivially reveals all the others. For the rest, the consequences depends heavilly on what the keys are intended for. If the keys are intended for a block cipher that is secure including under related-key attack (as AES almost is), then there is not ...

3

Note: In this answer, I stick to a definition of the One Time Pad where the random pad is used only One Time; at least, I've the name of it as support! Otherwise, it is well known that the OTP encryption scheme consisting of XOR with a repeated key is insecure by even the weakest standard (unknown plaintext with redundancy). INDistinguishability under ...

2

Let's just consider keys of bitlength 1, it works like that for any length. We have $k_1$ and $k_2$, the 2 random keys. And we have $k_3$, the OTP key. And then we give $x_1 = k_1 \oplus k_3$ and $x_2 = k_2 \oplus k_3$ to the attacker How can you attack the OTP? You can't. However, you don't need it. Because $x_1$ and $x_2$ quite obviously reveal a lot ...

2

You need to understand that any variation on the OTP would ultimately be equivalent to the OTP security-wise, since it is unconditionally "secure" (the ciphertext leaks zero information about the plaintext or the key), and so you'd just making it harder to compute for now reason. So, sure, you can use the OTP, or some variant thereof, on 128-bit messages ...

1

For example, let say that you have a message: "100 dollars should be moved." and you encrypt it with OTP. Then everybody can just take the first character "1" and change it to a 9 by XOR the 1 from the cipher-text and then XOR a "9" with the key you got. What you are describing is what happens if an attacker introduces changes in the ciphertext by a ...

1

Is CBC mode in OTP more secure? No. If your one time pad satisfies the required properties (it's truly random, the attacker has no information about it, and it's only used once), then OTP already has perfect secrecy; playing around with how it works can't make things better. If your one time pad doesn't satisfy the required properties, then all bets ...

1

XORing a key and message is called a one time pad. It is perfectly secure, providing confidentiality, when used correctly. That last part is the hard part, along with finding a situation in which you only need confidentiality.

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