Terms and Definitions

The following are commonly used cryptography terms and their definitions.

authentication

The process of confirming the identity of a party with whom one is communicating.

certificate

A digitally signed statement vouching for the identity and public key of an entity (person, company, and so on). Certificates can either be self-signed or issued by a Certificate Authority (CA) an entity that is trusted to issue valid certificates for other entities. Well-known CAs include Comodo, Entrust, and GoDaddy. X509 is a common certificate format that can be managed by the JDK's keytool.

cipher suite

A combination of cryptographic parameters that define the security algorithms and key sizes used for authentication, key agreement, encryption, and integrity protection.

cryptographic hash function

An algorithm that is used to produce a relatively small fixed-size string of bits (called a hash) from an arbitrary block of data. A cryptographic hash function is similar to a checksum and has three primary characteristics: it’s a one-way function, meaning that it is not possible to produce the original data from the hash; a small change in the original data produces a large change in the resulting hash; and it doesn’t require a cryptographic key.

Cryptographic Service Provider (CSP)

Sometimes referred to simply as providers for short, the Java Cryptography Architecture (JCA) defines it as a package (or set of packages) that implements one or more engine classes for specific cryptographic algorithms. An engine class defines a cryptographic service in an abstract fashion without a concrete implementation.

Datagram Transport Layer Security (DTLS) Protocol

A protocol that manages client and server authentication, data integrity, and encrypted communication between the client and server based on an unreliable transport channel such as UDP.

decryption

See encryption/decryption.

digital signature

A digital equivalent of a handwritten signature. It is used to ensure that data transmitted over a network was sent by whoever claims to have sent it and that the data has not been modified in transit. For example, an RSA-based digital signature is calculated by first computing a cryptographic hash of the data and then encrypting the hash with the sender's private key.

encryption/decryption

Encryption is the process of using a complex algorithm to convert an original message (cleartext) to an encoded message (ciphertext) that is unintelligible unless it is decrypted. Decryption is the inverse process of producing cleartext from ciphertext.

The algorithms used to encrypt and decrypt data typically come in two categories: secret key (symmetric) cryptography and public key (asymmetric) cryptography.

endpoint identification

An IPv4 or IPv6 address used to identify an endpoint on the network.

Endpoint identification procedures are handled during SSL/TLS handshake.

handshake protocol

The negotiation phase during which the two socket peers agree to use a new or existing session. The handshake protocol is a series of messages exchanged over the record protocol. At the end of the handshake, new connection-specific encryption and integrity protection keys are generated based on the key agreement secrets in the session.

java-home

Variable placeholder used throughout this document to refer to the directory where the Java Development Kit (JDK) is installed.

key agreement

A method by which two parties cooperate to establish a common key. Each side generates some data, which is exchanged. These two pieces of data are then combined to generate a key. Only those holding the proper private initialization data can obtain the final key. Diffie-Hellman (DH) is the most common example of a key agreement algorithm.

key exchange

A method by which keys are exchanged. One side generates a private key and encrypts it using the peer's public key (typically RSA). The data is transmitted to the peer, who decrypts the key using the corresponding private key.

key manager/trust manager

Key managers and trust managers use keystores for their key material. A key manager manages a keystore and supplies public keys to others as needed (for example, for use in authenticating the user to others). A trust manager decides who to trust based on information in the truststore it manages.

Keyed-Hash Message Code (HMAC)

A specific type of message authentication code that involves a cryptographic hash function and a secret cryptographic key.

Keyed-Hash Message Code (HMAC)-based Extract-and-Expand Key Derivation Function (HKDF)

A function used for key generation and validation.

keystore/truststore

A keystore is a database of key material. Key material is used for a variety of purposes, including authentication and data integrity. Various types of keystores are available, including PKCS12 and Oracle's JKS.

Generally speaking, keystore information can be grouped into two categories: key entries and trusted certificate entries. A key entry consists of an entity's identity and its private key, and can be used for a variety of cryptographic purposes. In contrast, a trusted certificate entry contains only a public key in addition to the entity's identity. Thus, a trusted certificate entry can’t be used where a private key is required, such as in a javax.net.ssl.KeyManager. In the JDK implementation of JKS, a keystore may contain both key entries and trusted certificate entries.

A truststore is a keystore that is used when making decisions about what to trust. If you receive data from an entity that you already trust, and if you can verify that the entity is the one that it claims to be, then you can assume that the data really came from that entity.

An entry should only be added to a truststore if the user trusts that entity. By either generating a key pair or by importing a certificate, the user gives trust to that entry. Any entry in the truststore is considered a trusted entry.

It may be useful to have two different keystore files: one containing just your key entries, and the other containing your trusted certificate entries, including CA certificates. The former contains private information, whereas the latter does not. Using two files instead of a single keystore file provides a cleaner separation of the logical distinction between your own certificates (and corresponding private keys) and others' certificates. To provide more protection for your private keys, store them in a keystore with restricted access, and provide the trusted certificates in a more publicly accessible keystore if needed.

message authentication code (MAC)

Provides a way to check the integrity of information transmitted over or stored in an unreliable medium, based on a secret key. Typically, MACs are used between two parties that share a secret key in order to validate information transmitted between these parties.

A MAC mechanism that is based on cryptographic hash functions is referred to as HMAC. HMAC can be used with any cryptographic hash function, such as Message Digest 5 (MD5) and the Secure Hash Algorithm (SHA-256), in combination with a secret shared key. HMAC is specified in RFC 2104.

public-key cryptography

A cryptographic system that uses an encryption algorithm in which two keys are produced. One key is made public, whereas the other is kept private. The public key and the private key are cryptographic inverses; what one key encrypts only the other key can decrypt. Public-key cryptography is also called asymmetric cryptography.

Record Protocol

A protocol that packages all data (whether application-level or as part of the handshake process) into discrete records of data much like a TCP stream socket converts an application byte stream into network packets. The individual records are then protected by the current encryption and integrity protection keys.

secret-key cryptography

A cryptographic system that uses an encryption algorithm in which the same key is used both to encrypt and decrypt the data. Secret-key cryptography is also called symmetric cryptography.

Secure Sockets Layer (SSL) Protocol

A protocol that manages client and server authentication, data integrity, and encrypted communication between the client and server. SSL has been renamed to Transport Layer Security (TLS).

session

A named collection of state information including authenticated peer identity, cipher suite, and key agreement secrets that are negotiated through a secure socket handshake and that can be shared among multiple secure socket instances.

Transport Layer Security (TLS) Protocol

A protocol that manages client and server authentication, data integrity, and encrypted communication between the client and server based on a reliable transport channel such as TCP.

trust manager

See "key manager/trust manager".

truststore

See "keystore/truststore".