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GirkovArpa last won the day on September 18 2018

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  1. This is threshold encryption. You say it's different but don't specify how. Threshold encryption is a very much studied field.
  2. Alice and Bob post at random intervals inside a thread on an anonymous message board The thread of posts is interpreted as a string of bits Posts by Alice represent a 1 Posts by Bob represent a 0 The security of this key in bits is the length of the thread in posts, minus 1 So 100 posts make for 99-bit security Alice and Bob are the only ones who know the key, even though the posts which comprise it are hosted publically. All Eve sees when she browses their thread is a series of blank posts made by anonymous users. She knows what Alice and Bob are doing, but can't distinguish Alice's posts from Bob's. But Alice knows which posts belong to her, as does Bob, and so they can interpret the thread as a string of bits. True, Mallory could interrupt the process by anonymously spamming the thread. That would crash the protocol. However, it would not enable Mallory to decrypt anything, so anything encrypted by Alice or Bob using that corrupted thread could not by decrypted by Mallory (or anyone except the person who encrypted it). As long as Alice and Bob are able to make themselves indistinguishable from each other from the perspective of eavesdroppers, this protocol could be modified to work with other mediums of communication. I can't actually think of a realistic use for this, given asymmetric cryptography, but maybe you will find it interesting nonetheless. 😄
  3. Here is a Javascript implementation of the NEW version of the Hutton Cipher. The original version had the problem where the password should not contain the letter Z because otherwise, the ciphertext would periodically contain plaintext letters. But if you don't have Z in the password, plaintext letters will NEVER encrypt to themselves, and you end up with the same problem ENIGMA had. The new rule in Hutton v2 is instead of just counting to the right as many spaces as dictated by the base26 value of the key letter, you sum that value with the base26 value of whatever letter happens to be first in the scrambled alphabet. With this modification, the cipher now produces ciphertext with a 1/26 chance to encrypt a plaintext letter to itself. Which is exactly what one would want to have. Also, the keyed alphabet is now created by appending the alphabet portion in REVERSE to the key. This is because most keyed alphabets were predictably ending in XYZ.
  4. Here is a video illustrating how it works.
  5. If you use multiple keys whose lengths are relatively prime, your effective Vigenere key length is the product of the lengths of all the keys. Imagine using keys with relatively prime lengths 9, 10, and 11. Your effective key length would be 1,320 characters long! Using an easily-remembered phrase that you can break up until lengths of perhaps 29, 30, and 31, you're practically using a one-time pad 26,970 letters long that you can store in your head! Is there any way to crack such a ciphertext if it's shorter than the effective key length?
  6. Someone calling themselves Hutton invented a new pen-and-paper cipher that seems to be incredibly secure. He offered a reward of over $1,000 to anyone who could crack it, although he disappeared from the internet a month ago so I'm not sure if the challenge is still ongoing. Anyway, here is how it works. You come up with a scrambled alphabet and a key. Write your key repeatedly under your plaintext just like Vigenere. To encrypt the first plaintext letter, find it in the scrambled alphabet. Count to the right (wrapping if you reach the end) as many letters as the number which your key-letter represents (treating it as a base26 number where A = 0, Z = 25). The letter you land on is your first ciphertext letter. Before you move on to encrypting the next letter though, scratch out those two letters (the plaintext and ciphertext ones) from the scrambled alphabet, and write them under each other. This effectively swaps them. For example, if you first plaintext letter is B and your first ciphertext letter is X, scratch out B and write X under it. Scratch out X and write B under it. Here is a Javascript version of the cipher. Note that it treats password letters as numbers where A = 1 and Z = 26. This is only because I was creating it precisely according to the author's instructions and only realized the problem afterwards and couldn't be bothered to update it. It would be very interesting to know if anyone can find any real weakness with this marvelously practical pen-and-paper cipher.