Hearts cards in a deck6/2/2023 ![]() If the joker is the bottom card of the deck, move it just below the top card.Ģ. Move it one card down, swapping it with the card beneath it. Here’s how to produce a single output character:ġ. You’re now ready to generate keystream letters. Then arrange the cards in the initial configuration that is the key. To initialize the deck, take it in your hand face up. One will be called “joker A” and the other “joker B”. We need a deck set of 52 cards and two jokers. ![]() In a 54-card deck (52 + 2 jokers) there are 54!, or about 2.31 * 10^71, possible different orderings of a deck. The keystream is generated using a deck of cards. Generating the keystream letters is the heart of Solitaire. So 1-22=? becomes 27-22=5.)Īs you can see, decryption is the same as encryption, except that you subtract the keystream from the ciphertext message. If the first number is less than or equal to the second number, add 26 to the first number before subtracting. ![]() Subtract the keystream numbers from the ciphertext numbers, modulo 26. Convert the ciphertext message from letters into numbers:ĥ. If the receiver uses the same key as the sender, the keystream letters will be the same:ģ. Use Solitaire to generate ten keystream letters. Take the ciphertext message and put it in five-character groups.Ģ. The basic idea is that the receiver generates the same keystream, and then subtracts the keystream letters from the ciphertext letters.ġ. Basically, if the sum is more than 26, subtract 26 from the result. Add the plaintext number stream to the keystream numbers, modulo 26. Convert the keystream letters similarly:ĥ. Convert the plaintext message from letters into numbers, A=1, B=2, etc:Ĥ. So if the message is “DO NOT USE PC” then the plaintext is:Ģ. Split the plaintext message into five-character groups. To decrypt, generate the same keystream and subtract, modulo 26 from the ciphertext to recover the plaintext.ġ. Then add them modulo 26 to plaintext letters, one at a time, to create the ciphertext. To encrypt, generate the same number of keystream letters as plaintext letters. The basic idea is that Solitaire generates a stream, often called a “keystream,” of numbers between 1 and 26. Solitaire is an output-feedback mode stream cipher. The following example is from Bruce Schneier himself. The average person could use a low-tech method to securely transmit information with high-tech security.Įven though the Solitaire cipher was intended to be done manually by hand, it has been converted over to digital format and is available in multiple languages including but not limited to Javascript, Python, and Perl which can be found on Bruce Schneier’s Solitaire website. The entire process is very slow and can take up an entire evening of encrypting and decrypting a message, so keep it short.īruce Schneier’s motivation for developing the Solitaire cipher was that in totalitarian environments, a deck of cards is far more affordable and less incriminating than a personal computer with an array of cryptological utilities. Utilizing a deck of cards that has been sorted in a particular order allows for two people to create and set random letters that will be used to encrypt their messages. Shuffling a deck of playing cards provides an inherent randomness to their order which supply’s the security for the Solitaire cipher. It was designed to be secure even against well-funded adversaries with the biggest computers and the smartest cryptanalysts. The Solitaire cipher allows secure communications without having to rely on computers or other tools that might indicate that covert channels are being used, or where access to a computer is not possible. The Solitaire cipher is a low-tech cryptographic algorithm that uses a deck of playing cards to encrypt and decrypt messages. Bruce Schneier, an American cryptographer and security expert, created the Solitaire cryptographic algorithm.
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