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6. Glossary


The positive identification of a network entity such as a server, a client, or a user. In SSL context, authentication represents the server and client Certificate verification process.

Access Control

The restriction of access to network realms. In Apache context usually the restriction of access to certain URLs.


An unambiguous formula or set of rules for solving a problem in a finite number of steps. Algorithms for encryption are usually called Ciphers.


A data record used for authenticating network entities such as a server or a client. A certificate contains X.509 information pieces about its owner (called the subject) and the signing Certificate Authority (called the issuer), plus the owner's public key and the signature made by the CA. Network entities verify these signatures using CA certificates.

Certificate Authority (CA)

A trusted third party whose purpose is to sign certificates for network entities that it has authenticated using secure means. Other network entities can check the signature to verify that a CA has authenticated the bearer of a certificate.

Certificate Signing Request (CSR)

An unsigned certificate for submission to a Certification Authority, which signs it with the Private Key of their CA Certificate. Once the CSR is signed, it becomes a real certificate. Cipher An algorithm or system for data encryption. Examples are DES, IDEA, RC4, etc.


The result after a Plaintext passed a Cipher.

Configuration Directive

A configuration command that controls one or more aspects of a program's behavior. In Apache context these are all the command names in the first column of the configuration files.

Cryptography - Symmetric

The client and server use the same key to encrypt and to decrypt data.

Cryptography - Asymmetric

Consists of a key pair (public and private). PKI is Asymmetric Cryptography

Digital Signatures

A piece of data that is sent with an encrypted message that identifies the originator and verifies that it has not been altered.


The HyperText Transport Protocol (Secure), the standard encrypted communication mechanism on the World Wide Web. This is actually just HTTP over SSL.

Message Digest

A hash of a message, which can be used to verify that the contents of the message have not been altered in transit.


A service that provides proof of the integrity and origin of data, both in an non-forgeable relationship, which can be verified by any third party at any time, or, an authentication that with high assurance can be asserted to be genuine.

A property achieved through cryptographic methods which prevents an individual or entity from denying having performed a particular action related to data (such as mechanisms for non-rejection or authority (origin); for proof of obligation, intent, or commitment, or for proof of ownership).


The Open Source toolkit for SSL/TLS; see

Pass Phrase

The word or phrase that protects private key files. It prevents unauthorized users from encrypting them. Usually it's just the secret encryption/decryption key used for Ciphers.


The unencrypted text.

Private Key

The secret key in a Public Key Cryptography system, used to decrypt incoming messages and sign outgoing ones.

Public Key

The publicly available key in a Public Key Cryptography system, used to encrypt messages bound for its owner and to decrypt signatures made by its owner.

Public Key Cryptography

The study and application of asymmetric encryption systems, which use one key for encryption and another for decryption. A corresponding pair of such keys constitutes a key pair. Also called Asymmetric Cryptography.

Secure Sockets Layer (SSL)

A protocol created by Netscape Communications Corporation for general communication authentication and encryption over TCP/IP networks. The most popular usage is HTTPS, i.e. the HyperText Transfer Protocol (HTTP) over SSL.


The context information of an SSL communication.


The original SSL/TLS implementation library developed by Eric A. Young <>; see

Symmetric Cryptography

The study and application of Ciphers that use a single secret key for both encryption and decryption operations.

Transport Layer Security (TLS)

The successor protocol to SSL, created by the Internet Engineering Task Force (IETF) for general communication authentication and encryption over TCP/IP networks. TLS version 1 and is nearly identical with SSL version 3.

Uniform Resource Locator (URL)

The formal identifier to locate various resources on the World Wide Web. The most popular URL scheme is http. SSL uses the scheme https


An authentication certificate scheme recommended by the International Telecommunication Union (ITU-T) and used for SSL/TLS authentication.


Recommendation X.509 [CCI88c] specifies the authentication service for X.500 directories, as well as the X.509 certificate syntax. Directory authentication in X.509 can be carried out using either secret-key techniques or public-key techniques; the latter is based on public-key certificates. The standard does not specify a particular cryptographic algorithm, although an informative annex of the standard describes the RSA algorithm.

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