# Tag Info

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Ciphers with Arbitrary Finite Domains by Black and Rogaway have some options like Prefix Ciphers, Generalized Feistel networks , Cycle walking etc. Also Format preserving encryption has traits that you are looking for , but NIST standardized ones are patented by Voltage Inc. In general Feistel networks + Cycle walking would give a good option for any ...

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The Playfair cipher has a key consisting of a square of $5 \times 5$ letters (usually the J is not used, or I/J are considered one letter). Filling the square can be done in $25!$ ways (pick a letter for left upper corner, a new one for the place next to it, and so on), but then every square has equivalent forms, formed by rotating the columns and/or ...

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If a weak cipher is being used, it could be a possibility that an attacker could gather information about k(R1) and k(R2) and derive the k value. Following which, S could be decrypted with the derived k value. Eavesdropping could take place too. Similarly, a MITM would be possible too.

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Obvious, but not serious weakness that numbers R1 and R2 will be sent in plain text. This means that MITM is able to modify R1 or R2 so that Alice or Bob will always be failed at authentication, although they have legal key K. I have one suggestion how you can improve this protocol. Just because in the last step of protocol, Bob send only encrypted S, MITM ...

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IV (initial value or initialization vector) is a vague term that describes some kind of starting value for a mode of operation that is known to both parties, and generally sent in the clear with the encrypted data (and known to the attacker) IVs in many modes of operation have specific requirements to that mode. In some modes the requirement is that is ...

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