Cryptography

Cryptography, from the Greek word “kryptos” (meaning concealed), involves the concealment of information from third-parties. It is concerned with the first two thirds of the CIA Triad – the confidentiality and integrity of data.

Generally speaking, the field can be split into:

• Encoding
• Hashing
• Encryption

Common Terms

• Plain text: Human-legible text. Can be transformed into cipher text via an encryption algorithm.
• Clear text: Synonym of “plain text”.
• Cipher text: Text that has been transformed into an unreadable message via some encryption algorithm.
• Encryption: The process of scrambling data or messages, making it unreadable and secret.
• Decryption: The opposite of encryption.
• Encoding: A means of transforming data from one format to another.
• Decoding: The opposite of encoding.
• Cryptographic key: A string of bits used by a cryptographic algorithm to transform plain text into cipher text or vice versa.
• Symmetric-key encryption: Model of encryption that uses the same shared key for both encryption and decryption.
• Asymmetric encryption: Model of encryption that uses the recipient’s public key to encrypt a message, and the recipient’s private key to decrypt a message.
• Block Cipher: An encryption algorithm that operates on a group of bit at once rather than only one bit at a time. Contrast with Stream Cipher.
• Stream Cipher: An encryption algorithm that operates on one bit of plaintext at a time. Contrast with Block Cipher.
• Hashing algorithm: A one-way function that takes arbitrary input and produces fixed-length output, such that every unique input produces unique output with very high probability.
• Hash: The output of a hashing algorithm. Synonym for “digest”.
• Digest: The output of a hashing algorithm. Synonym for “hash”.
• Salt: A string appended to a password to create a unique digest when run through a hashing algorithm.
• Entropy: The amount of unpredictability in a given ciphertext. Entropy colloquially refers to how close the ciphertext is to ideal randomly generated text.

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Relevant Note(s): Information Security