In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. Decryption, the inverse of encryption, is the process of turning ciphertext into readable plaintext. Ciphertext is not to be confused with codetext because the latter is a result of a code, not a cipher.
Types of ciphers(classical ciphers and Modern Ciphers)
The history of cryptography began thousands of years ago. Cryptography uses a variety of different types of encryption. Earlier algorithms were performed by hand and are substantially different from modern algorithms, which are generally executed by a machine.
Historical pen and paper ciphers used in the past are sometimes known as classical ciphers. They include:
• Substitution cipher: the units of plaintext are replaced with ciphertext (Caesar cipher and One-time pad)
• Transposition cipher: the ciphertext is a permutation of the plaintext (Rail fence cipher)
• Polyalphabetic substitution cipher: a substitution cipher using multiple substitution alphabets (Vigenère cipher and Enigma machine)
• Permutation cipher: a transposition cipher in which the key is a permutation
Historical ciphers are not generally used as a standalone encryption solution because they are quite easy to crack. Many of the classical ciphers can be cracked using brute force or by analyzing only ciphertext with the exception of the one-time pad.
Modern ciphers
Modern ciphers are more secure than classical ciphers and are designed to withstand a wide range of attacks. An attacker should not be able to find the key used in a modern cipher, even if he knows any amount of plaintext and corresponding ciphertext. Modern encryption methods can be divided into the following categories:
• Private-key cryptography (symmetric key algorithm): the same key is used for encryption and decryption
• Public-key cryptography (asymmetric key algorithm): two different keys are used for encryption and decryption
NOTE:-
In a symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same key for decryption. In an asymmetric key algorithm (e.g., RSA), there are two separate keys: a public key is published and enables any sender to perform encryption, while a private key is kept secret by the receiver and enables only him to perform correct decryption.
Symmetric key ciphers can be divided into block ciphers and stream ciphers. Block ciphers operate on fixed-length groups of bits, called blocks, with an unvarying transformation. Stream ciphers encrypt plaintext digits one at a time on a continuous stream of data and the transformation of successive digits varies during the encryption process.
Types of ciphers(classical ciphers and Modern Ciphers)
The history of cryptography began thousands of years ago. Cryptography uses a variety of different types of encryption. Earlier algorithms were performed by hand and are substantially different from modern algorithms, which are generally executed by a machine.
Historical pen and paper ciphers used in the past are sometimes known as classical ciphers. They include:
• Substitution cipher: the units of plaintext are replaced with ciphertext (Caesar cipher and One-time pad)
• Transposition cipher: the ciphertext is a permutation of the plaintext (Rail fence cipher)
• Polyalphabetic substitution cipher: a substitution cipher using multiple substitution alphabets (Vigenère cipher and Enigma machine)
• Permutation cipher: a transposition cipher in which the key is a permutation
Historical ciphers are not generally used as a standalone encryption solution because they are quite easy to crack. Many of the classical ciphers can be cracked using brute force or by analyzing only ciphertext with the exception of the one-time pad.
Modern ciphers
Modern ciphers are more secure than classical ciphers and are designed to withstand a wide range of attacks. An attacker should not be able to find the key used in a modern cipher, even if he knows any amount of plaintext and corresponding ciphertext. Modern encryption methods can be divided into the following categories:
• Private-key cryptography (symmetric key algorithm): the same key is used for encryption and decryption
• Public-key cryptography (asymmetric key algorithm): two different keys are used for encryption and decryption
NOTE:-
In a symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same key for decryption. In an asymmetric key algorithm (e.g., RSA), there are two separate keys: a public key is published and enables any sender to perform encryption, while a private key is kept secret by the receiver and enables only him to perform correct decryption.
Symmetric key ciphers can be divided into block ciphers and stream ciphers. Block ciphers operate on fixed-length groups of bits, called blocks, with an unvarying transformation. Stream ciphers encrypt plaintext digits one at a time on a continuous stream of data and the transformation of successive digits varies during the encryption process.
