eMAPT key terms

The original, readable form of data before any encryption or encoding is applied. In cryptography it is the input to an encryption function and the desired output of decryption.

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

A scheme where the same secret key both encrypts and decrypts data. It is fast and suited to bulk data, but both parties must already share the key securely.

A scheme using a mathematically related key pair: a public key to encrypt or verify and a private key to decrypt or sign. It solves key distribution but is slower than symmetric ciphers.

The half of a key pair that may be shared openly. It is used to encrypt data for the owner or to verify signatures the owner created with the matching private key.

The secret half of a key pair, known only to its owner. It decrypts data encrypted with the public key and creates digital signatures; its compromise breaks all related trust.

The Advanced Encryption Standard, a symmetric block cipher operating on 128-bit blocks with 128-, 192-, or 256-bit keys. It is the dominant cipher for protecting data at rest and in transit.

A defined method for applying a block cipher to data longer than one block. Modes such as CBC, CTR, and GCM differ in how they chain blocks and whether they also provide integrity.

A non-secret value combined with the key so that encrypting identical plaintext yields different ciphertext. It must be unique per encryption and unpredictable where the mode requires it.

A value used once in a cryptographic operation to prevent replay and ensure uniqueness. Unlike a secret key, a nonce need not be confidential but must never repeat under the same key.

A mode that provides both confidentiality and integrity in one operation, such as AES-GCM or ChaCha20-Poly1305. It detects tampering via an authentication tag, preventing silent modification of ciphertext.

Authenticated Encryption with Associated Data: a construction that encrypts some data while authenticating both it and additional cleartext headers. Widely used in TLS 1.3 to protect records and metadata together.

A one-way function mapping arbitrary input to a fixed-length digest. It must be collision- and preimage-resistant; it underpins integrity checks, signatures, and password storage.

A member of the SHA-2 family producing a 256-bit digest. It is the default hash for certificate signatures and TLS handshakes; SHA-1 and MD5 are deprecated for security use.

Hash-based Message Authentication Code: a keyed hash proving both data integrity and authenticity. It is used in TLS record protection and in token formats such as JWT with shared secrets.

A short value computed with a secret key that verifies a message came from someone holding that key and was not altered. It provides integrity and authenticity, not confidentiality.

A value created with a private key over a message digest, verifiable by anyone with the public key. It proves origin and integrity and provides non-repudiation.

The process by which two parties establish a shared secret over an insecure channel. Modern designs use Diffie-Hellman so the secret is never transmitted directly.

A key agreement protocol letting two parties derive a shared secret from public values. An eavesdropper who sees the exchange cannot feasibly compute the resulting key.

A property where compromise of a long-term private key does not expose past session keys. It is achieved with ephemeral key exchange such as ECDHE in TLS.

Public-key cryptography built on the algebraic structure of elliptic curves over finite fields. It offers equivalent security to RSA with much smaller keys, making it efficient on mobile devices.

Elliptic Curve Digital Signature Algorithm, used to sign certificates and TLS handshake messages. Its security depends on using a unique, unpredictable random value for each signature.

The practices and hardware used to keep private keys confidential and usable, such as secure enclaves, keystores, and passphrase-encrypted containers. Weak protection nullifies the cryptography above it.

A protected container holding private keys and certificates, often encrypted with a password. On mobile platforms it is the OS-managed store apps use to keep signing keys private.

A tamper-resistant device that generates and stores keys and performs cryptographic operations internally so keys never leave it. Used for certificate authority signing and high-value key custody.

A signed data structure binding a public key to an identity, with validity dates and issuer details. It lets a verifier trust a key only after validating the issuer's signature.

The standard format for public-key certificates, defining fields like subject, issuer, validity, extensions, and signature. It is the structure used across TLS, code signing, and S/MIME.

An entity trusted to sign certificates, vouching that a public key belongs to the named subject. Browsers and operating systems ship a root store of trusted authorities.

A self-signed certificate representing a trust anchor. It is distributed in trust stores and signs intermediate certificates, forming the top of a chain of trust.

A certificate issued by a root and used to sign end-entity certificates. Intermediates keep root keys offline and let authorities revoke or rotate sub-CAs.

The ordered sequence from an end-entity certificate through intermediates to a trusted root. Validators check each signature and the trust anchor to establish a key's authenticity.

A certificate extension listing the hostnames or IP addresses the certificate is valid for. Modern clients ignore the legacy common name and match only against this list.

The client check that the server certificate's subject alternative names include the host it connected to. Skipping it enables interception even when the chain is otherwise valid.

Hard-coding a specific certificate or public key in an app so only that identity is accepted. It defends against rogue authorities but requires careful rotation to avoid bricking clients.

Invalidating a certificate before its expiry, typically via CRL or OCSP. Clients must check revocation to reject certificates whose keys were compromised or misissued.

Online Certificate Status Protocol, which lets a client ask an authority whether a specific certificate is revoked. Stapling attaches a signed status response to the handshake to reduce latency.

The negotiation that authenticates parties, agrees on cipher suites, and derives session keys before application data flows. TLS 1.3 reduces it to one round trip.

The current TLS version, removing legacy ciphers and enabling one-round-trip handshakes with forward secrecy by default. It encrypts most of the handshake, including the certificate.

A named combination of key exchange, authentication, bulk encryption, and hashing algorithms used in a TLS session. Both peers must support a common suite for the handshake to succeed.

An attack where an adversary secretly relays or alters traffic between two parties who believe they talk directly. Proper certificate validation and pinning are the primary defenses.