# What is Ciphertext?

The term nothing is sometimes used as a synonym for ciphertext. however, it refers to the method of encoding rather than the leave .

### Types of ciphers

There are versatile types of ciphers, including :

**Substitution ciphers.**Replace bits, characters, or character blocks in plaintext with alternate bits, characters or character blocks to produce ciphertext. A substitution cipher may be monoalphabetic or polyalphabetic:- A single alphabet is used to encrypt the entire plaintext message. For example, if the letter A is enciphered as the letter K, this will be the same for the entire message.
- A more complex substitution using a mixed alphabet to encrypt each bit, character or character block of a plaintext message. For instance, the letter A may be encoded as the letter K for part of the message, but later it might be encoded as the letter W.

**Transposition ciphers.**Unlike substitution ciphers that replace letters with other letters, transposition ciphers keep the letters the same, but rearrange their order according to a specific algorithm. For instance, in a simple columnar transposition cipher, a message might be read horizontally but would be written vertically to produce the ciphertext.**Polygraphic ciphers.**Substituting one letter for another letter, a polygraphic cipher performs substitutions with two or more groups of letters. This masks the frequency distribution of letters, making frequency analysis attacks much more difficult.**Permutation ciphers.**In this cipher, the positions held by plaintext are shifted to a regular system so that the ciphertext constitutes a permutation of the plaintext.**Private-key****cryptography.**In this cipher, the sender and receiver must have a pre-shared key. The shared key is kept secret from all other parties and is used for encryption, as well as decryption. This cryptography is also known as “symmetric key algorithm.”**Public-key cryptography****.**In this cipher, two different keys — public key and private key — are used for encryption and decryption. The sender uses the public key to perform the encryption, but the private key is kept secret from the receiver. This is also known as “asymmetric key algorithm.”

### Uses of ciphertext

symmetrical ciphers, which are typically used to secure on-line communications, are incorporated into many different net protocols to be used to encrypt exchanges. For exercise, Transport Layer Security uses ciphers to encrypt application layer data.

Reading: What is Ciphertext?

virtual individual networks connecting distant workers or remote branches into corporate networks use protocols with symmetrical ciphers to protect data communications. symmetrical ciphers protect data privacy in most Wi-Fi networks, on-line bank, e-commerce services and mobile telephone .

other protocols, including batten husk, OpenPGP and Secure/Multipurpose Internet Mail Extensions use asymmetrical cryptanalysis to encrypt and authenticate endpoints but besides to securely exchange the symmetrical keys to encrypt seance data. For performance reasons, protocols often rely on ciphers to encrypt session data .

### Ciphertext attacks

The known ciphertext attack, or ciphertext-only approach ( COA ), is an attack method used in cryptanalysis when the attacker has access to a particular set of ciphertext. however, in this method, the attacker does n’t have access to the equate cleartext, i.e., data that is transmitted or stored unencrypted. The COA succeeds when the corresponding plaintext can be determined from a given place of ciphertext. sometimes, the key that ‘s used to encrypt the ciphertext can be determined from this attack.

Read more: A Few Thoughts on Cryptographic Engineering

In a choose ciphertext attack ( CCA ), the attacker can make the victim ( who knows the hidden key ) decrypt any ciphertext and send back the result. By analyzing the choose ciphertext and the corresponding plaintext they receive, the attacker tries to guess the mystery key the victim used. The finish of the CCA is to gain data that diminishes the security of the encoding scheme .

Related-key attack is any shape of cryptanalysis where the attacker can observe the mathematical process of a cipher under respective different keys whose values the attacker does n’t know initially. however, there is some mathematical relationship connecting the keys that the attacker does know.

### Ciphertext example

One of the earliest and simplest ciphers is the Caesar zero, which uses a symmetrical key algorithm. The key acts as a shared clandestine between two ( or more ) parties that can be used to send secret information no matchless can read without a copy of the key .

The Caesar cipher is a substitution cipher in which each letter in the plaintext is “ careen ” a certain count of places down the alphabet. For exercise, with a chemise of 1, A would be B, B would be replaced by C, etc. The method acting is named after Julius Caesar, who is said to have used it to communicate with his generals .

here is an example of the encoding and decoding steps involved with the Caesar code. The textbook to be encrypted is “ defend the east wall of the castle, ” with a shift ( key ) of 1 .

- Plaintext: defend the east wall of the castle
- Ciphertext: efgfoe uif fbtu xbmm pg uif dbtumf