Ciphertext

Hence often a message authentication code is added to a ciphertext to ensure that changes to the ciphertext will be noted by the receiver.

Synchronous stream ciphers In a synchronous stream cipher a stream of pseudo-random digits is generated independently of the plaintext and ciphertext messages, and then combined with the plaintext (to encrypt) or the ciphertext (to decrypt).

A common misconception is to use inverse order of encryption as decryption algorithm (i.e. first XORing P17 and P18 to the ciphertext block, then using the P-entries in reverse order).

After moving his rotors to EIN, the receiving operator then typed in the rest of the ciphertext, deciphering the message.

A hand-operated Red analog is also visible In operation, the enciphering machine accepted typewritten input (in the Roman alphabet) and produced ciphertext output, and vice versa when deciphering messages.

A message-to-be-transferred is enciphered to ciphertext at the encoding terminal by encoding the message as a number M in a predetermined set.

Another approach is to tag the ciphertext with markers at regular points in the output.

Another way of viewing this method is that, under each letter of the ciphertext, the entire alphabet is written out in reverse starting at that letter.

A set of reverse rounds are applied to transform ciphertext back into the original plaintext using the same encryption key.

As such, even today a Vigenère type cipher should theoretically be difficult to break if mixed alphabets are used in the tableau, if the keyword is random, and if the total length of ciphertext is less than 27.6 times the length of the keyword.

Attempt at cryptanalysis To continue the example from above, suppose Eve intercepts Alice's ciphertext: "EQNVZ".

Because of this multiplicative property a chosen-ciphertext attack is possible.

Block ciphers must be used in ciphertext stealing or residual block termination mode to avoid padding, while stream ciphers eliminate this issue by naturally operating on the smallest unit that can be transmitted (usually bytes).

By contrast, self-synchronising stream ciphers update their state based on previous ciphertext digits.

DES is the archetypal block cipher —an algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another ciphertext bitstring of the same length.

Fractionation Transposition is particularly effective when employed with fractionation - that is, a preliminary stage that divides each plaintext symbol into several ciphertext symbols.

Frequency analysis of such a cipher is therefore relatively easy, provided that the ciphertext is long enough to give a reasonably representative count of the letters of the alphabet that it contains.

Full decryption of an RSA ciphertext is thought to be infeasible on the assumption that both of these problems are hard, i.e., no efficient algorithm exists for solving them.

Here each ciphertext character was represented by a number.

If it is any smaller, more than one plaintext may encrypt to the same ciphertext.