Glossary

AES

The Advanced Encryption Standard, selected by the American National Institute of Standards and Technology after a 5 year consultation process in which a number of symmetric ciphers were evaluated. The Rijndael cipher was selected to be the standard, and is now implemented in a wide range of products using encryption, including SSL servers.

Apache

Apache is a freely available Unix based web server. It is currently the most commonly used server on Internet connected sites. Its genesis was in early 1995 when developers of some high visibility web sites decided to pool their patches and enhancements to the NCSA/1.3 server to create A patchy server. The project has since gained considerable momentum.

Asymmetric Cryptography

A synonym for public key cryptography (since the encryption key is public, and the decryption key is private, the keys for encryption and decryption are different, hence the algorithm is asymmetric).

Ben Laurie

One of the Apache developers and the person responsible for the original extensions to provide https capability for Apache.

Block Cipher

An encryption scheme in which the data is divided into fixed-size blocks (often 64 bits), each of which is encrypted independently of the others. Complete independence of blocks is cryptographically undesirable, so usually a block cipher will be used in a chaining or feedback mode in which the output from one block affects the way the next is encrypted.

CAST

CAST is a symmetric key block cipher, or to be more precise, a family of block ciphers.

Certificate

A token which underpins the principle of trust in SSL-encrypted transactions. The information within a certificate includes the issuer (the Certificate Authority that issued the certificate), the organisation that owns the certificate, public key, the validity period (usually one year) of the certificate, and the hostname that the certificate was issued in respect of. It is digitally signed by the certification authority so that none of the details can be changed without invalidating the signature.

Certification Authority

A third party organisation which is used to confirm the relationship between a party to the https transaction and that party's public key. Certification authorities may be widely known and trusted institutions for Internet based transactions; where https is used on companies internal networks, an internal department within the company may fulfil this role.

Cipher

Any encryption algorithm. Ciphers can be classified according to whether they are symmetric or public key algorithms, and by whether they operate on their data as a stream or divided into blocks.

Client-side certificate

SSL has an optional feature which allows the client (for example the browser and its user) to authenticate itself to the server by means of a certificate. Some servers will disallow connections unless they are authenticated in this way.

Common Name

A field of an X.509 certificate used for matching against the domain name when validating the certificate.

C2Net

The vendor of the Stronghold server, a web server derived from Apache that provided SSL support and had a commercial license to use RSA (enabling Stronghold to be used with RSA encryption within America for business purposes). It was acquired by Red Hat Inc. in September 2000.

DES (Data Encryption Standard)

A symmetric key block cipher algorithm developed by IBM and adopted as a standard by the US National Institute of Standards and Technology in 1975. DES and its derivatives are still the most commonly used encryption algorithms.

Digital signature

A use of public key cryptography to authenticate a message. The private key is used, showing that the signature must have been made by the owner of that key. A secure hash of the entire document is signed, so that any change to the document will invalidate the signature.

Domain validated

An SSL certificate certifies that a site is owned by a particular company, organisation or possibly an individual. The certificate authority should check that the certificate request comes from the company or organisation in question. But there are different types of checking that can be applied. A distinction has emerged between organisation-validated certificates, where the certifier checks that the organisation claimed on the certificate is the one requesting it (possible by calling a company's registered phone number, or checking the supplied address against the company's official business registration or tax registration — which formal checks are relevant will vary from country to country); or whether just control of the domain is checked: these domain validated certificates are often checked by requiring confirmation from an email address in the domain being verified.

Some certificate authorities only do domain validation, while others only do organisation validation. Some authorities do both, and add a rider to domain control certs, for example by entering "Domain Control Validated" in the organisation unit field of the certificate. Most certificate authorities only put a real organisation name on the certificate if they have validated this, and conversely put the hostname or domain name in the organisation field if it is a domain-only certificate. Netcraft distinguish domain-validated certificates by looking for a list of known strings in the subject organisation unit field. Netcraft only perform this categorisation for certificate authorities with a significant number of certificates — for the smaller authorities, it is often difficult to find information about the level of validation performed.

Most browsers do not yet differentiate between the different types of assurance implied by different types of certificate checking, but a user viewing the detail of the site certificate would be able to see the difference (if they knew what to look for). In future browsers may start to make this distinction — if only by showing the organisation field of the certificate more prominently.

DSA

The Digital Signature Algorithm mandated by the Federal Information Processing Standard FIPS 186. This is a public key system, but unlike RSA it can only be used for making signatures.

Eric Young

The original developer of SSLeay. Eric is Australian, so his work was not encumbered by US export regulations.

HTTP

The Hyper Text Transfer Protocol is the protocol used between a Web browser and a server to request a document and transfer its contents. The specification is maintained and developed by the World Wide Web Consortium.

HTTPS

HTTPS is ordinary HTTP exchanged over an SSL encrypted session.

IDEA

The International Data Encryption Algorithm is a symmetric key block cipher algorithm developed by Xuejia Lai and James Massey in 1991. It is covered by patents that will expire in 2010-2011; as a result it is not as commonly used in conjunction with open-source servers like Apache.

MD2

A secure hash, or message digest, algorithm developed by Ron Rivest.

MD5

A secure hash, or message digest, algorithm developed by Ron Rivest.

Microsoft

See www.microsoft.com

Netscape

See www.netscape.com

OpenSSL

OpenSSL is the name now used for the SSL library originally known as SSLeay.

Private Certification

The owner of a certificate can set up their own certification authority to sign it themselves, instead of having a recognised third-party certification authority do so. To do this they have to create a public key/private key pair for use in making the signature in addition to the key to be certified in the certificate. This is a valid way of setting up certification for use in a closed environment in which the users know the certifying organisation and are prepared to install its signing key in their browser. Other users, who have no relationship with the organisation concerned are unlikely to accept this type of certificate. Compare "Self-signed Certificate"

Private Key

The part of the key in a public key system which is kept secret and is used only by its owner. This is the key used for decrypting messages, and for making digital signatures.

Protocol

A protocol is an algorithm, or or step by step procedure, carried out by more than one party. Examples are network protocols, in which the steps are intended to ensure reliable transmission of information, or cryptographic protocols, in which the aim is to maintain some form of security relationship between the parties.

Public Key

The part of the key in a public key system which is distributed widely, and is not kept secure. This is the key used for encryption (as opposed to decryption) or for verifying signatures. Compare private key.

Public Key Cryptography

A public key cipher is one in which the key used for encryption is different from the one used for decryption. Although the keys are related, it is not possible to calculate the decryption key from only the encryption key in any reasonable amount of computation time. In most practical systems, the public key system is used for encoding a session key which is used with a symmetric system to encode the actual data. The same concept is used for making digital signatures, where the secret key is used to make the signature, and the public key is used to verify it. RSA and DSA are examples of a public key algorithms.

RC2

A symmetric key block cipher, developed by RSA Data Security Inc, and now widely available.

RC4

A symmetric key stream cipher, developed by RSA Data Security Inc, and now widely available.

RSA

RSA is a public key cipher which can be used both for encrypting messages and making digital signatures The letters stand for the names of the inventors: Rivest, Shamir and Adleman. The company RSA Data Security Inc. takes its name from this algorithm, and owned the patents covering the algorithm. When the patents expired (in the USA) in 2000, RSA released the RSA algorithm into the public domain.

RSAREF

RSAREF is an implementation of the RSA public key system, and associated utilities, which was produced by RSA Data Security Inc in the 1990s. It was provided free for non-commercial use, and included the rights to use the RSA algorithm non-commercially without paying patent royalties; the REF indicated this non-commercial status (reference implementation). Companies were expected to purchase a full commercial version of RSA. When the patent on the RSA algorithm expired, RSA released RSAREF into the public domain. However, due to some high profile security vulnerabilities in RSAREF around this time, it dropped rapidly out of use once the patent expired and companies were free to write their own implementations.

Safe Passage

A solution to the problem that "export" versions of the Microsoft & Netscape browsers were only capable of using 40-bit keys (before the USA's ITAR regulations were lifted). Some companies, including C2net, produced software using this to work around the export problem. Such workarounds have ceased to be common since the regulations were relaxed.

Self-signed Certificate

Self-signing is one way for the owner of a certificate to sign it themselves instead of having a recognised certification authority do so. In a self-signature the certificate is digitally signed by the very same key whose public part appears in the certificate data. In other words, the signature can be verified using the public key contained in the certificate. This is unlikely to be trusted by anyone wishing to use the certificate as proof of ownership of the corresponding public key. However, a signature by the owner is still useful, especially when the owner is a certification authority which must be trusted for independent reasons, as it restricts the possibilities for malicious or accidental changes to the details contained in the certificate. Compare "Private Certification"

Secret Key

Confusingly sometimes used to mean the private key of a public key system, and also sometimes used (in contrast to "public key") to refer to a symmetric key system.

Secure Hash

A process which reduces a message of arbitrary length to a fixed length fingerprint which is very unlikely to be the same for any other message. The word "secure" indicates that the algorithm has been chosen so that it is not possible to forge a message which to have given hash value, nor to create two similar messages with the same hash value.

Session Key

A key used for just one message or set of messages. In a typical system, a random session key is generated for use with a symmetric algorithm to encode the bulk of the data, and only the session key itself is communicated using public key encryption.

Server Signature

The string usually returned as part of servicing each HTTP request that gives the name and version of the web server software being used.

SET

SET is a secure protocol designed by MasterCard and Visa to facilitate financial transactions over the Internet. Compared with SSL, it places more emphasis on validating both parties to the transaction, and uses trusted servers so that a merchant holds only transaction identifiers, not actual credit card numbers.

SHA (Secure Hash Algorithm)

A secure hash, or message digest algorithm adopted as a Federal Information Processing Standard.

shttp

Secure Hypertext Transfer Protocol, provides security at the document level rather than the connection level as provided by SSL. This protocol is not widely used.

S/MIME

S/MIME is a standard for end-to-end encryption of email messages. The current version (version 3) is defined in RFC2632, RFC2633 and RFC2634.

SSL (Secure Socket Layer)

A protocol developed by Netscape for encrypted transmission over TCP/IP networks. It sets up a secure end-to-end link over which HTTP or any other application protocol can operate. The most common application of SSL is HTTPS for SSL-encrypted HTTP.

SSLeay

A freely available implementation of the SSL protocol and the cryptographic algorithms used by SSL, developed by Eric Young in Australia. Eric Young has now withdrawn from the project and further development is continued under the name OpenSSL by a team of developers.

SSL version 2

This is an older, obsolete version of the SSL protocol. While still quite widely offered by SSL servers, many sites and browsers have begun to discontinue support for SSL 2 now, because virtually all sites that offer SSL 2 also offer SSL version 3. SSL 2 has known security weaknesses, which were fixed by SSL version 3.

Stream Cipher

A stream cipher encrypts in small units, often a bit or a byte at a time, but unlike a basic block cipher the output corresponding to a given input will depend on where in the message it occurs. The simplest type of stream cipher uses a complicated function, which retains state, to generate a pseudo-random sequence which is then combined with the input using a simple operation such as bytewise addition.

Symmetric Cryptography

A symmetric cipher is one in which the same key is used for encryption and decryption. Therefore a secure method has to be found by which the sender and recipient can agree on the key. CAST, DES, IDEA, RC2 and RC4 are symmetric ciphers.

TLS

TLS, standing for Transport Layer Security, is the latest version of SSL. It is an enhancement of SSL version 3.0, and is a proposed Internet Standard (see RFC2246).

Thawte

Thawte is a South African company which acts as a certificate authority. On December 20, 1999, it was acquired by Verisign.

Triple DES

Each block is encrypted three times using DES, using at least two different keys. There are variants which differ in whether two or three keys are used, and whether some of the steps are in decryption mode. In SSL, three separate keys are used, and the middle step is a decryption.

Verisign

Verisign is the dominant certificate authority on the Internet at the present time, though many of its certificates are signed as RSA Data Security. Early versions of Microsoft and Netscape browsers had RSA Data Security configured as the only trusted certificate authority, and this more or less mandated that people wishing to use certificates on the Internet need to obtain them from Verisign, and use server software that had been accredited by Verisign. Current versions of the Microsoft & Netscape browsers have the facility for users to add new certificate authorities, and, as older versions of the browsers have been replaced, there has been an opportunity for new certificate authorities such as Thawte to emerge.

X.509

An International Telecommunication Union recommendation for the format of certificates.