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The ciphertext message contains all the information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it. The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable). The encrypting procedure ...
In an asymmetric key encryption scheme, anyone can encrypt messages using a public key, but only the holder of the paired private key can decrypt such a message. The security of the system depends on the secrecy of the private key, which must not become known to any other.
The message to be encrypted was written on the coiled ribbon. The letters of the original message would be rearranged when the ribbon was uncoiled from the cylinder. However, the message was easily decrypted when the ribbon recoiled on a cylinder of the same diameter as the encrypting cylinder. [2]
These can be any characters that decrypt to obvious nonsense, so that the receiver can easily spot them and discard them. The ciphertext alphabet is sometimes different from the plaintext alphabet; for example, in the pigpen cipher, the ciphertext consists of a set of symbols derived from a grid. For example: An example pigpen message
The cipher's key is , the number of rails.If is known, the ciphertext can be decrypted by using the above algorithm. Values of equal to or greater than , the length of the ciphertext, are not usable, since then the ciphertext is the same as the plaintext.
To decrypt the message, each block is multiplied by the inverse of the matrix used for encryption. The matrix used for encryption is the cipher key, and it should be chosen randomly from the set of invertible n × n matrices (modulo 26). The cipher can, of course, be adapted to an alphabet with any number of letters; all arithmetic just needs ...
Secure generation and exchange of the one-time pad values, which must be at least as long as the message. This is important because the security of the one-time pad depends on the security of the one-time pad exchange. If an attacker is able to intercept the one-time pad value, they can decrypt messages sent using the one-time pad. [18]
The final step in encrypting the message is to look up each numeric value in the table for the corresponding letters. In this example, the encrypted text would be IHHWVCSWFRCP. The table below shows the completed table for encrypting a message in the Affine cipher.