EUC-EO key terms

The original, readable form of data before any encryption or encoding is applied. It is the input to an encryption algorithm and the output of successful decryption.

The scrambled, unreadable output produced when plaintext is transformed by an encryption algorithm and key. Without the correct key it should reveal nothing about the original data.

A cipher should remain secure even if everything about the system except the key is public knowledge. Security must rest on secrecy of the key, not on obscurity of the design.

Relying on hidden design details or secret algorithms for protection rather than on a secret key. It fails once the design leaks, and is considered a weakness rather than a control.

A secret value that controls how a cryptographic algorithm transforms data. The same algorithm with different keys produces different results, so protecting the key is essential.

The number of bits in a cryptographic key, which sets the size of the keyspace an attacker must search. Longer keys resist brute force better, subject to algorithm strength.

An algorithm that encrypts data in fixed-size chunks, such as 64 or 128 bits, using a key. Larger messages are processed by a mode of operation that chains or combines blocks.

An algorithm that encrypts data one bit or byte at a time by combining it with a pseudorandom keystream generated from a key and nonce. Suited to continuous or real-time data.

A defined method for applying a block cipher to data longer than one block, specifying how blocks are linked, padded, and randomized. Examples include ECB, CBC, CTR, and GCM.

A non-secret value used with a key to randomize encryption so identical plaintexts yield different ciphertexts. It must be unique per operation and unpredictable where the mode requires it.

A number used once in a cryptographic operation. Unlike a secret key, it need not be hidden, but reusing it with the same key can catastrophically break modes like CTR or GCM.

Electronic Codebook, the simplest block cipher mode, encrypting each block independently. Identical plaintext blocks produce identical ciphertext blocks, leaking patterns, so it is unsuitable for most data.

A block cipher mode where each plaintext block is XORed with the previous ciphertext block before encryption, hiding repetition. It requires a unique IV and careful padding handling.

An authenticated encryption mode combining counter-mode encryption with a Galois-field authentication tag. It provides confidentiality and integrity in one pass and is widely used in TLS.

A scheme that provides both confidentiality and integrity, typically producing ciphertext plus a tag that detects tampering. AEAD variants also authenticate associated data left unencrypted.

A system using a mathematically related key pair: a public key for encryption or verification and a private key for decryption or signing. It solves key distribution without sharing secrets in advance.

Encryption where the same secret key both encrypts and decrypts. It is fast and efficient for bulk data but requires a secure method to share the key.

A public key algorithm whose security rests on the difficulty of factoring large composite numbers. It supports encryption and signatures and requires keys far larger than elliptic curve equivalents.

Public key cryptography built on the algebraic structure of elliptic curves over finite fields. It offers comparable security to RSA with much shorter keys, saving bandwidth and computation.

A trusted entity that verifies identities and issues digital certificates binding a public key to its owner. Browsers and systems rely on a set of trusted root CAs.

A standardized digital document containing a subject's public key, identity details, validity dates, and a CA's digital signature. It is the basis of TLS server authentication.

An ordered sequence of certificates from an end-entity certificate through intermediate CAs up to a trusted root. Validating the chain confirms each signature and trust anchor.

A signed list published by a CA naming certificates that are revoked before their expiry. Clients check it to reject credentials that are no longer trustworthy.

A protocol for querying a responder about a single certificate's revocation status in real time, avoiding the delay of downloading full revocation lists. It can be stapled to TLS handshakes.

A one-way algorithm mapping input of any length to a fixed-size digest. Good ones are deterministic, fast, and resistant to preimage, second-preimage, and collision attacks.

The fixed-length output produced by a hash function, often used as a compact fingerprint of data. It supports integrity checks and feeds into signatures and key derivation.

The property that finding two different inputs producing the same hash output should be computationally infeasible. Its loss, as with MD5 and SHA-1, undermines signature and integrity uses.

A short value computed from a message and a shared secret key to prove both integrity and authenticity. It differs from a plain hash because verification requires the secret key.

A construction that combines a cryptographic hash with a secret key to produce a keyed message authentication code. It is standardized, widely implemented, and resistant to length-extension issues.

A random value added to input before hashing, stored alongside the result, so identical inputs yield different digests. It defeats precomputed rainbow tables and is standard in password storage.

A cryptographic value created with a private key that lets anyone verify the signer's identity and the data's integrity. It provides authentication, integrity, and non-repudiation.

The assurance that a party cannot credibly deny having performed an action such as signing a message. Strong digital signatures with protected private keys support this property.

The process of securely delivering cryptographic keys to the parties that need them. Methods include manual exchange, key transport wrapped by public key encryption, and Diffie-Hellman agreement.

A protocol letting two parties derive a shared secret over an insecure channel without transmitting it. It provides no authentication on its own and is vulnerable to man-in-the-middle attacks.

Storing copies of cryptographic keys with a trusted third party so data can be recovered if keys are lost. It aids recovery but creates a high-value target and privacy concerns.

A protocol securing network connections with encryption, integrity, and authentication, most visibly for HTTPS. Modern versions negotiate ephemeral key exchange and authenticated cipher suites.

A suite of protocols securing IP traffic at the network layer, using Authentication Header and Encapsulating Security Payload in tunnel or transport mode. It is common in VPNs.

The protocol that negotiates and manages security associations for IPsec, authenticating peers and establishing session keys. It runs in phases to protect subsequent key agreement.

A protocol for encrypted remote login and file transfer, authenticating servers via host keys and users via keys or passwords. It protects interactive sessions from eavesdropping.

The practice of hiding the existence of a message inside another medium such as an image or audio file. Unlike encryption, it conceals that communication is happening at all.

The detection and analysis of hidden data in carriers such as images or audio. Techniques look for statistical anomalies, altered file structures, or mismatches between carrier and payload.

An exhaustive search of every possible key or password until the correct one is found. Its feasibility depends on keyspace size, attacker resources, and any rate limiting.

An attacker secretly relays or alters communications between two parties who believe they talk directly. Strong authentication of endpoints, such as certificates, is the main defense.

An attack exploiting differing error responses to learn whether decrypted padding is valid, letting an attacker decrypt CBC ciphertext block by block without the key.

A collision-finding method exploiting probability: collisions appear after roughly the square root of the keyspace. It explains why hash outputs need twice the bits of a target security level.

A precomputed table mapping hash outputs to likely passwords, enabling fast reversal of unsalted hashes. Salting and slow key-derivation functions defeat it.

Guessing passwords or keys from a curated list of likely candidates rather than exhaustively. It succeeds quickly against weak, common, or unthrottled credentials.