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Letterlocking is the act of folding and securing a written message (such as a letter) on papyrus, parchment, or paper, without requiring it to be contained in an envelope or packet. It is a traditional method of document security that utilizes folding and cutting. [ 1 ]
The encryption can also be represented using modular arithmetic by first transforming the letters into numbers, according to the scheme, A → 0, B → 1, ..., Z → 25. [2] Encryption of a letter x by a shift n can be described mathematically as, [3] = (+) Decryption is performed similarly,
With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack. [5] It is possible to create a secure pen and paper cipher based on a one-time pad, but these have other disadvantages.
The letter at the intersection of [key-row, msg-col] is the enciphered letter. For example, the first letter of the plaintext, a, is paired with L, the first letter of the key. Therefore, row L and column A of the Vigenère square are used, namely L. Similarly, for the second letter of the plaintext, the second letter of the key is used.
Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad using modular addition. [1] The resulting ciphertext will be impossible to decrypt or break if the following four conditions are met: [2] [3] The key must be at least as long as the plaintext. The key must be truly random.
To use the Vigenère square to encrypt a message, a coder first chooses a keyword to use and then repeats it until it is the same length as the message to be encoded. If LEMON is the keyword, each letter of the repeated keyword will tell what cipher (what row) to use for each letter of the message to be coded. The cipher alphabet on the second ...
The two letters of the digram are considered opposite corners of a rectangle in the key table. To perform the substitution, apply the following 4 rules, in order, to each pair of letters in the plaintext: If both letters are the same (or only one letter is left), add an "X" after the first letter. Encrypt the new pair and continue.
To encrypt, first choose the plaintext character from the top row of the tableau; call this column P. Secondly, travel down column P to the corresponding key letter K. Finally, move directly left from the key letter to the left edge of the tableau, the ciphertext encryption of plaintext P with key K will be there.