EECC key terms

The original, readable message or data before any encryption is applied. It is the input to an encryption algorithm and the final output after successful decryption.

The scrambled, unreadable output produced when plaintext is transformed by an encryption algorithm and key. It is what an attacker intercepts and what must be decrypted to recover the original message.

The reversible process of converting plaintext into ciphertext using a cryptographic algorithm and key so that unauthorized parties cannot read the message. It provides confidentiality but not by itself integrity or authenticity.

The process of converting ciphertext back into readable plaintext using the correct cryptographic key and algorithm. Without the proper key, decryption should be computationally infeasible for a secure system.

A core design rule stating that a cryptosystem should remain secure even if everything about it except the key is public knowledge. Security must depend solely on the secrecy of the key.

A secret value, usually a string of bits, that controls how a cryptographic algorithm transforms data. The same algorithm with different keys produces different outputs, and key secrecy determines overall security.

The total set of all possible keys a cryptographic algorithm can accept, often expressed as the number of bits in the key. A larger key space makes brute-force guessing harder.

A symmetric encryption algorithm that processes fixed-size chunks (blocks) of data, such as 128 bits, applying the same key-driven transformation to each block. Examples include AES and DES.

A symmetric encryption algorithm that encrypts data one bit or byte at a time by combining it with a pseudorandom keystream generated from the key. It suits continuous data flows and requires a unique nonce per key.

A widely adopted symmetric block cipher standardized by NIST in FIPS 197, using 128-bit blocks and key sizes of 128, 192, or 256 bits. It replaced DES as the global standard for symmetric encryption.

An early symmetric block cipher with a 56-bit effective key and 64-bit blocks, now considered insecure due to its small key space. It was superseded by AES but remains historically and educationally important.

A defined method for applying a block cipher to data longer than one block, such as CBC, CTR, or GCM. The mode determines how blocks are chained and whether the scheme also provides authentication.

A non-secret value used with a mode of operation to ensure identical plaintexts encrypt to different ciphertexts. It must be unique and, for some modes, unpredictable, but it need not be secret.

A number used once in a cryptographic operation, such as with stream ciphers or authenticated encryption. Reusing a nonce with the same key can catastrophically break confidentiality or integrity.

An encryption scheme that provides both confidentiality and integrity/authenticity in one construction, such as AES-GCM or ChaCha20-Poly1305. It detects tampering and binds ciphertext to associated data.

A form of authenticated encryption that also authenticates additional plaintext data, such as packet headers, without encrypting it. It is standard in modern network protocols like TLS 1.3.

Encryption using a mathematically related key pair, where one key encrypts and the other decrypts. It solves key distribution but is slower than symmetric encryption, so it is often used to exchange symmetric keys.

The key in an asymmetric pair that may be freely distributed to anyone. It is used to encrypt messages to the owner or to verify the owner's digital signatures.

The secret half of an asymmetric key pair, known only to its owner. It is used to decrypt messages encrypted with the matching public key or to create digital signatures.

A widely used asymmetric algorithm whose security rests on the difficulty of factoring large integers. It supports encryption and digital signatures and typically uses key sizes of 2048 bits or more.

A family of asymmetric algorithms based on the algebraic structure of elliptic curves over finite fields. It offers equivalent security to RSA with much smaller keys, making it efficient for constrained devices.

A protocol allowing two parties to jointly establish a shared secret over an insecure channel without transmitting it directly. Its security relies on the difficulty of the discrete logarithm problem.

A scheme combining asymmetric and symmetric cryptography: a public-key operation protects a randomly generated symmetric key, which then encrypts the bulk data. This balances key distribution with performance.

A one-way mathematical function that maps input of any length to a fixed-size digest. A secure cryptographic hash is preimage-resistant, collision-resistant, and produces unpredictable output changes.

The fixed-length output produced by a hash function, such as 256 bits for SHA-256. It acts as a compact fingerprint of the input data and is used for integrity checks and signatures.

The property that it is computationally infeasible to find two different inputs producing the same hash output. It is essential for signatures and certificate integrity.

A short value computed from a message and a shared secret key to prove integrity and authenticity between parties holding that key. It detects tampering but does not provide non-repudiation.

A keyed message authentication code built by hashing data together with a secret key in a specific nested construction. It provides integrity and authenticity using any cryptographic hash function.

A signed electronic document binding a public key to an identity, issued by a certificate authority. It lets parties trust a public key without prior contact by relying on the issuer's signature.

A trusted entity that verifies identities and issues, signs, and revokes digital certificates. Its root keys anchor the trust chain that relying parties use to validate certificates.

The widely used standard format for public key certificates, defining fields such as subject, issuer, validity period, public key, and extensions. TLS and many enterprise systems rely on it.

An ordered sequence of certificates from an end-entity certificate through intermediate CAs up to a trusted root. Validators check signatures and policies along the chain to establish trust.

A signed list published by a certificate authority naming certificates that have been revoked before their expiry. Clients check it to reject compromised or misissued certificates.

A protocol for querying a certificate authority in real time about whether a specific certificate is revoked. It is more current than CRLs but introduces privacy and availability concerns.

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

The full lifecycle of cryptographic keys: generation, distribution, storage, rotation, backup, and destruction. Weak key management undermines even strong algorithms.

The practice of periodically replacing cryptographic keys with new ones to limit the impact of compromise and comply with policy. Old keys are retired after data is re-encrypted or no longer needed.

A key management arrangement in which a copy of a key is stored with a trusted third party so it can be recovered under defined conditions. It aids recovery but creates a high-value target.

A protocol that secures network communications by negotiating algorithms, authenticating the server (often via certificates), and establishing session keys for encrypted, integrity-protected traffic.

The process by which two parties establish a shared secret key over an untrusted channel. It may use Diffie-Hellman, RSA key transport, or a combination within a handshake.

A property where compromise of long-term keys does not expose past session keys or recorded traffic. It is achieved by using ephemeral key exchange per session.

An attack that systematically tries every possible key or password until the correct one is found. Its feasibility depends on key space size and available computing power.

An attack that tries likely passwords or keys from a prepared list rather than exhausting the entire key space. It exploits human-chosen secrets and is countered by salting and slow hashing.

A cryptanalytic attack exploiting the birthday paradox to find hash collisions faster than brute force, roughly in the square root of the output space. It motivates larger digest sizes.

An attack where an adversary secretly relays or alters communications between two parties who believe they are talking directly. Proper authentication and certificate validation prevent it.

A random value added to a password before hashing so identical passwords produce different digests. It defeats precomputed tables and makes dictionary attacks far more expensive.

The science of analyzing cryptographic systems to find weaknesses or recover plaintext or keys without authorization. It drives the design of stronger algorithms and larger key sizes.

A U.S. government standard (FIPS 140-2/140-3) specifying security requirements for cryptographic modules. Validated modules are required in many government and regulated environments.

The U.S. National Institute of Standards and Technology, which develops and publishes cryptographic standards such as AES, SHA-2, and post-quantum algorithms. Compliance often references its publications.

An international standard (ISO/IEC 15408) for evaluating and certifying the security of IT products, including cryptographic systems, against defined assurance levels.

The Payment Card Industry Data Security Standard, which mandates strong cryptography, key management, and protection of cardholder data for organizations handling payment cards.

Encryption in which the same secret key is used to both encrypt and decrypt data. It is fast and efficient but requires a secure method to share the key between parties.