LeoGlossary: Cipher

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A cipher is an algorithm or method used to encrypt and decrypt data. It is a way of transforming plaintext (readable data) into ciphertext (unreadable data) and back again, using a specific key or set of keys. Ciphers are used to protect the confidentiality and security of data, such as sensitive information, personal data, and financial transactions.

There are two main types of ciphers: block ciphers and stream ciphers.

Block ciphers work by dividing the plaintext into fixed-length blocks and encrypting each block independently using the same key. They are commonly used for disk, database and message encryption. Examples of block ciphers include AES (Advanced Encryption Standard) and DES (Data Encryption Standard).
Stream ciphers work by encrypting the plaintext one bit or byte at a time, using a pseudorandom keystream that is combined with the plaintext. They are commonly used for real-time data encryption, such as in secure communication protocols like SSL/TLS. Examples of stream ciphers include RC4 and FISH.

Ciphers can be classified as either symmetric or asymmetric, depending on whether they use the same key for encryption and decryption, or a public key for encryption and a private key for decryption.

Symmetric ciphers are faster and more efficient, but they require that both parties have access to the same secret key, which can be a security risk.
Asymmetric ciphers are considered more secure, but they are generally slower and more computationally intensive.

Ciphers can also be classified as either hash-based or nonce-based. Hash-based ciphers use a hash function to produce a fixed-size output, while nonce-based ciphers use a random or pseudo-random number, called a nonce, to ensure that each encryption operation produces a unique output.

A cipher is a secret code or algorithm used to transform plaintext (readable text) into ciphertext (an unreadable jumble of letters or symbols) and vice versa. It's like a lock and key system for information, where only those who know the cipher can unlock the message.

Here's how ciphers work:

Encryption: The cipher takes the plaintext and applies a set of rules or mathematical operations to scramble it into ciphertext. This process often involves substituting letters for other letters, rearranging letters, or using mathematical transformations.
Decryption: To decipher the message, the recipient applies the same cipher to the ciphertext, but in reverse. This reverses the scrambling process and reveals the original plaintext.

Types of ciphers:

Substitution ciphers: Replace each letter in the plaintext with a different letter or symbol according to a predetermined rule. Examples include the Caesar cipher and the Vigenère cipher.
Transposition ciphers: Rearrange the order of letters in the plaintext without changing the letters themselves.
Polyalphabetic ciphers: Use multiple substitution alphabets to encrypt the plaintext, making them more difficult to break than simple substitution ciphers.
Block ciphers: Encrypt data in blocks of a fixed size, using complex mathematical operations to scramble the bits within each block. Examples include AES and DES.
Stream ciphers: Encrypt data one bit or byte at a time, using a keystream to generate a continuous stream of random bits.

Ciphers are essential for:

Protecting sensitive information: Ciphers safeguard confidential data such as passwords, financial transactions, and military communications.
Ensuring privacy: They protect personal data and online communications from unauthorized access.
Authenticating identities: Ciphers can verify the identity of the sender of a message, ensuring that it comes from a trusted source.
Maintaining data integrity: They can detect unauthorized modifications to data, ensuring its accuracy and reliability.

In modern cryptography, ciphers are often combined with other techniques, such as key management and authentication protocols, to provide robust security solutions for various applications.

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