These are the terms introduced across the four parts of the lecture.

Integrity and Hash Functions

Integrity

Ensuring that data has not been modified.

Authenticity

Ensuring that data came from the source it claims.

Commitment scheme

Publishing a value that fixes a message without revealing it.

Hiding

The property that a commitment reveals nothing about the message.

Binding

The property that a commitment cannot later match a different message.

Check digit

An extra digit computed from a number to catch transcription errors.

Parity bit

A bit recording whether a byte holds an even or odd count of ones.

Cyclic redundancy check (CRC)

A remainder computed over a message to detect accidental corruption.

Cryptographic hash function

A public function mapping any message to a fixed-size value.

Digest

The fixed-size output of a hash function. Also called a hash.

Determinism

The property that the same input always produces the same digest.

Preimage resistance

Infeasibility of finding a message that produces a given digest.

Second preimage resistance

Infeasibility of finding a second message matching a given message’s digest.

Collision

Two different messages that produce the same digest.

Collision resistance

Infeasibility of finding any two messages with the same digest.

Avalanche

A one-bit input change altering about half the digest bits unpredictably.

Pigeonhole principle

More items than containers guarantees some container holds more than one.

Birthday problem

Matching pairs appear far sooner than matching a chosen value does.

SHA-2

A family of current hash functions with several digest lengths.

SHA-256

The 256-bit member of the SHA-2 family, and the common default choice.

SHA-3

A separately designed family of current hash functions, standardized in 2015.

Message Authentication

Message authentication code (MAC)

A value computed from a message and a secret key.

Authentication tag

Another name for a MAC, and the output of an AEAD mode.

Length extension attack

Continuing a hash calculation from a tag to authenticate appended data.

HMAC

A MAC built by nesting two hashes under two key-derived values.

Manifest

An authenticated record naming a release and the digest of its files.

Encrypt-then-MAC

Encrypting first, then computing the tag over the resulting ciphertext.

Authenticated encryption with associated data (AEAD)

Encryption and an authentication tag produced in one operation.

Associated data

Readable information an AEAD mode authenticates but does not encrypt.

Non-repudiation

Evidence against a later denial that a key holder signed something.

Public Key Cryptography

Public-key cryptography

Cryptography using a related key pair instead of one shared secret. Also called asymmetric cryptography.

Public key

The half of a key pair that is published and used to verify or encrypt.

Private key

The half of a key pair kept secret and used to sign or decrypt.

One-way function

A calculation that is efficient forward and infeasible to reverse.

Discrete logarithm problem

Recovering an exponent from the result of a modular exponentiation.

Trapdoor

Secret information that makes an infeasible calculation easy.

Trapdoor function

A one-way function that can be reversed by whoever holds its trapdoor.

RSA

A public-key system whose trapdoor is the factoring of a modulus.

Elliptic-curve cryptography (ECC)

Public-key cryptography using arithmetic on the points of a curve.

Diffie-Hellman key exchange

Two parties deriving a shared secret by exchanging public values.

Key agreement

Establishing a shared secret from each party’s private contribution.

Digital Signatures

Digital signature

A value produced from a message and a private signing key.

Verification

Checking a signature against a message using the signer’s public key.

RSA-PSS

RSA’s signature scheme, combining hashing with a randomized encoding.

ECDSA

The elliptic curve digital signature algorithm, widely used in certificates.

Ed25519

A deterministic elliptic-curve signature scheme with no per-signature random value.

Lamport signature

A one-time signature scheme built from a hash function alone.

Certificates and Trust

Key fingerprint

A hash of a public key, short enough to compare by hand.

Certificate authority (CA)

A party that vouches for the binding between a key and an identity.

Digital certificate

A signed statement binding a public key to an identity.

X.509

The standard certificate format used on the web.

Certificate chain

A sequence of certificates, each vouching for the key below it.

Trust anchor

A key accepted in advance, from which a chain is verified.

Trust store

The collection of trust anchors a system is configured to accept.

Domain validation

Certificate issuance that checks only control of the name being certified.

Certificate revocation list (CRL)

A published list of certificates withdrawn before their expiration.

Online Certificate Status Protocol (OCSP)

A live query asking an issuer whether one certificate is still valid.

Certificate Transparency

Public append-only logs recording every certificate an authority issues.

Signed Software and the Supply Chain

Code signing

Signing executable code so a system can verify its origin before running it.

Per-page hashes

Digests covering each page of a file, checked as it loads into memory.

Secure boot

Each stage of startup verifying the signature on the stage it launches.

Software supply chain attack

Compromising software before it reaches the people who run it.

Reproducible build

A build that produces an identical binary from identical source.

Provenance record

A signed statement describing how a binary was produced.

Software bill of materials (SBOM)

A list of the components a software product contains.

Transparency log

A public append-only record that makes issued artifacts impossible to hide.

Post-Quantum Cryptography

Harvest now, decrypt later

Recording encrypted traffic today to decrypt it once hardware allows.

Post-quantum cryptography

Algorithms designed to resist attack by a quantum computer.

Hybrid key exchange

Combining a classical and a post-quantum exchange in one connection.