The FREE Cybersecurity Glossary by Thor Pedersen!

Cipher: An algorithm used for performing encryption or decryption—a series of well-defined steps that can be followed to transform an input (plaintext) into an output (ciphertext) or vice versa. Ciphers are fundamental to modern cryptography and operate based on a piece of auxiliary information known as a key. The key determines the particular transformation of plaintext into ciphertext, or vice versa, during encryption and decryption.

Cipher Suite: A set of algorithms that work together to secure network connections. It defines the way that a system will implement cryptographic functions such as key exchange, bulk encryption, and message authentication. When two devices communicate, they agree on a cipher suite to use for the session, ensuring that both parties have the necessary mechanisms to establish a secure communication channel.

Ciphertext-only attack: A type of attack where an attacker only has access to the ciphertext of a message or data and not the plaintext or the key used to encrypt it. This type of attack is often used to test the security of a cipher algorithm or to try to break the encryption. Examples include using statistical analysis to try to determine the key used to encrypt a message or using a brute-force attack to try all possible keys.

Ciphertext or Cipher Text: The output of the encryption process. It is the scrambled, unreadable version of an original plaintext message that has been encrypted using a cipher. Ciphertext is designed to be meaningless and confusing, so it is unreadable and incomprehensible to anyone who intercepts it without the correct decryption key.

Circuit-Level Gateway Firewall: A firewall that operates at the session layer of the OSI model. It manages connections between internal and external networks by creating virtual circuits, hiding and protecting the internal network's details and enabling secure communication.

Circuit-switched network: A type of network where a dedicated communication path is established between two devices before they start communicating. This path, or circuit, remains open for the duration of the communication session and is then terminated or "switched" once the session ends. Such networks are traditionally used for telephone communications, where a direct and constant connection helps ensure that the entire conversation arrives intact.