Glossary

Algorithm
90. This is a sequence of instructions for carrying out some process step by step. For example to make and consume a cup of tea the algorithm would be “boil kettle, pour boiling water over tea bag in cup, leave for five minutes, remove tea bag and drink”. In the context of digital signatures algorithms are used at various stages. The first stage employed by the sender in signing an electronic document is to create a summary of the document. The “mathematical process” used to create the summary is an algorithm known as a “hashing algorithm”. See hash.

91. The process of creating public and private keys, encrypting the document summary using the private key and decrypting the document summary using the public key are all examples of algorithms. See RSA algorithm.

Binary Numbers
92. Conventional numbering which uses the digits 0-9 is called “base 10” because the figures are organised by units, tens, hundreds and thousands etc. Computers operate using binary numbers. In binary numbers only the digits 0 and 1 are used. Each place is then equivalent to a power of 2. You have the 1’s place, 2’s place, 4’s place, etc. For example the number 5 in binary would be 101.

Biometrics
93. Biometrics is the practice of measuring durable physical characteristics to identify people. Recognition of the iris, retina, fingerprint and even the face could all feature. There is also a system in which a user signs an electronic document by using a stylus on an electronic tablet. The tablet converts the characteristics of the formation of the signature (pressure, speed, angle etc) into digital information which is then encrypted with the electronic document.

Browser
94. See paragraphs 106 and 138.

CA
95. A certification or certificate authority that, typically, issues digital certificates to other entities to allow them to prove their identity or other attributes to others.

Certificate
96. See paragraphs 24 and 50 and Article 2.9 of the Electronic Signature Directive in Appendix 2. An international standard for the form of a certificate is the X509.

Checksum
97. This is another word for the summary or hash of the electronic document.

Common criteria
98. These are criteria that are used to decide whether a particular IT product meets a particular level of security in particular circumstances. The CC are the product of international efforts to reach an agreed set of criteria and are applied in schemes run by the governments of France, Germany, the Netherlands, the UK, Canada and the United States of America. The domestic scheme is known as ITSEC. The CC have seven predefined assurance levels from EAL1 to EAL7. Level 1 is applicable where threats to security are not viewed as serious and 7 is used for assessing a system which is going to be used in extremely high risk situations and/or where high value assets justify higher costs.

Computationally infeasible
99. A phrase used to describe an outcome such as the answer to a mathematical problem that in the current state of mathematical knowledge and with available computer capacity it would take an unreasonable amount of time to calculate.

Computerised communications
100. Computers operate and communicate by a series of on and off signals. They use numbers not letters and words. The numbers used are binary and they represent on and off. “1” is “on” and “0” is “off”. Computerised records and electronic documents consist of groups of 1’s and 0’s which are called binary digits or “bits”. Each letter or other character in a text is assigned a number. Currently it is usual to use numbers in an eight bit “byte” to define characters. The word “string” is also used to refer to a group of characters or to a group of bits so a byte is a string of eight bits. There are standard conventions for translating bits into language that can be understood by people. One which currently uses eight bit characters is known as “ASCII” (the American Standard Code for Information Interchange). In ASCII the letter “E” is 01000101.

101. A computer stores “data”, the word used for information held or communicated by computers. The capacity of that storage device is measured in bytes, megabytes, gigabytes etc. There are several types of memory storage of which hard and floppy discs are examples.

102. A program is a set of instructions given to a computer. It consists of sets of rules or steps to be followed by the computer in performing its functions. Computers have three layers of programs. The lowest layer is known as the “boot strap” program which gets the computer started when it is switched on. The next layer is the operating system which organises the programs and data stored in the computer’s memory. The third layer consists of application programs which would include, for example, a word processing program and a program used to create a digital signature.

103. Programs are called “software”. They can be stored or created anywhere in a computer’s memory. Prewritten programs can be loaded into a computer’s memory by a number of means. These include loading from a telephone line, a floppy disc, a CDROM and tape.

104. Computers can be linked with one another by telephone lines, satellites etc. and the systems that join them are called networks. Being “on-line” means using a network to get information to one computer from another. Off-line means that a computer is not linked up with another. An internet is a set of networks which are joined by devices which forward information between them (routers). The Internet is the biggest example of an internet. Individuals and organisations can link to an internet by connecting their computers, usually through a telephone line, but likely to be increasingly through digital TV and mobile phones with an outside internet service provider. An intranet is a network that provides similar services within an organisation to those provided by the Internet outside.

105. Electronic documents may be sent using the Internet. If this is done they pass over the network between servers which are computers which provide services to users. All the servers are owned and run by different organisations and, in the absence of the use of security measures, electronic documents could be read and altered by employees of any of those organisations or others (hackers) with the ability to obtain unauthorised access to servers. Once access to such documents has been obtained then, in the absence of security measures, such employees or other hackers could send documents that purport to come from other people and organisations. If security measures are inadequate or subverted it is easy to disguise the origin of a document sent over a computer network. Electronic documents sent on intranets are less vulnerable to hackers.

106. One of the major sources of information on the Internet is the World-Wide Web. This is a system for the retrieval of information which works by using the Internet and computers which are linked using the Internet. The system contains material that will interact with many browsers which are the computer programs used to allow readers to move easily from one document to another. The basic “webpage” is stored in a format which is known as HTML (the HyperText Markup Language). HyperText is a method of linking one computer location to another so a HyperText link can be made to another section of the same document or to other files in the same computer or to files located in other computers.

Cryptography
107. Cryptography is the art of transforming messages or documents to render their contents incomprehensible to outsiders, but easily recoverable by those authorised to do so. In symmetric cryptography this is done using a key. Those who have the key can use it to disguise, or encrypt, messages; and to remove the disguise, or decrypt. The actual process used to encrypt or decrypt is known as the cryptographic algorithm. For example, ‘London’ might transform to ‘wchlop’ using a particular key; but an outsider with no knowledge of the key would have no means of knowing whether the original text corresponding to ‘wchlop’ was ‘London’, ‘Geneva’ or even ‘apples’. Note that symmetric cryptography is only of use for protection of confidentiality, and has no application for digital signatures. The text describes an example of the use of symmetric cryptography in session keys under the heading “Confidentiality”.

Cryptography – asymmetric
108. The difficulty with symmetric cryptography is the need to manage keys securely; compromise of a key will in principle compromise all messages encrypted using it. One of the principal difficulties in key management with symmetric algorithms is the necessity that the same key be present at both ends of the transaction, without its secrecy having been compromised in arriving there. This problem gave rise to the concept of asymmetric cryptography, in which different keys are used at the sending and receiving ends to encrypt and decrypt data. One key is kept private by the owner, and the other can be known by anyone without defeating the security of the encryption. Hence the recipient of a message can ask senders to use the public key to encrypt messages sent to him while restricting the ability to decrypt to himself alone by virtue of his knowledge of the private key. Asymmetric cryptography is also insecure if users reveal keys.

109. In the context of signature services, the roles of the keys are reversed. The originator of a document uses the private key to generate his signature, and publishes the corresponding public key. Anyone wishing to confirm the authenticity and integrity of the document can now use the public key to do so.

CSP
110. Certification service provider referred to in the European Directive on Electronic Signatures. See CAabove.

Directory
111. A directory contains identifying information. It may include certificates of digital signatures and other methods of identification which may be used, for example to control access to computer systems and even to premises. Currently directories are only used within organisations such as inside a company or bank. In due course, however, it is theoretically possible that a number of organisations could share directories or that directories could be set up and run by intergovernmental organisations. Such authoritative directories could, for example, be used to authenticate the digital signatures of CAs.

FIPS
112. The Federal Information Processing Standards are standards and guidelines approved by the US Secretary of Commerce and which have been developed by the National Institute of Standards and Technology (NIST) for Federal computer systems. The approval is under section 513 of the Information Technology Management Reform Act 1996 and the Computer Security Act 1987. NIST supports the development of voluntary and industry standards both nationally and internationally and FIPS are developed only when there are no existing voluntary standards to address Federal requirements for security and privacy.

Handshaking
113. This is the process that occurs when two computers commence communications. One device sends a message to the other indicating that it wants to establish a communications channel. The two devices then send several messages back and forth that enable them to agree on a communications protocol.

Hash
114. This is a technical term for the summary of the electronic document that is created as the first stage of the digital signature process. To arrive at the hash of the electronic document the sender and receiver use hashing algorithms. There are a number of conventional hashing algorithms in use. They include MD5 and SHA-1. The receiver’s computer knows which hashing algorithm to use in the verification process because information about this is included with the electronic document as sent by the sender.

115. The electronic document summary is known by a variety of names including “hash”, “hash value”, “electronic document digest”, “cryptographic check”, “checksum”, “manipulation detection code”, “integrity check value” and even a “seal” (although without the legal effect of a seal). The hash is not an encryption of the electronic document. The hash is a number created from a string of text. It is substantially smaller than the text. Any document gives a specific hash. It is virtually impossible to reconstruct the document from its hash value or to find any pair of documents that give rise to the same hash. In particular, it is highly improbable that two different documents would give the same hash by chance. Any change in the document would result in a completely unrelated hash. The point of using a hash is that because it is of a fixed length, much smaller in general than the original document, it can be processed much faster. Because there is only an extremely remote chance that another document would have the same hash, it is also a means of checking whether one instance of a document is identical to another.

For example take the message “Mr Smith has sent Mr Jones £5000 in payment for the videos”. Its hash might be :

“SutMBsl3b=”

whereas the hash of “Mr Smith has sent Mr Jones £500 in payment for the videos” would look completely different perhaps as follows:

“qtAV2rpok”

(The above are not genuine hashes of the message texts but are merely used to show the nature of hashes.)

HTML
116. See paragraph 106.

IETF
117. The Internet Engineering Task Force is a large open international community of network designers, operators, vendors and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual.

118. The actual technical work of the IETF is done in its working groups which are organised by topic into several areas. The areas are managed by Area Directors who are members of the Internet Engineering Steering Group. Architectural oversight is provided by the Internet Architecture Board.

Internet
119. See paragraph 105.

Intranet
120. See paragraph 104.

ITSEC
121. The UK IT Security Evaluation and Certificating Scheme is a Government run scheme under which it is possible to obtain evaluations of products or schemes. ITSEC has authorised five Commercial Evaluation Facilities (CLEFs) to carry out these evaluations. They are Logica, EDS, Syntegra (a part of BT), IBM and Admiral. The CLEF is asked to evaluate the system or product under the Common Criteria, an international set of criteria, or under the European ITSEC criteria. The purpose of the evaluation is to provide an assurance factor in a particular climate. By “climate” is meant the circumstances in which the product or scheme will operate. The person submitting it to the CLEF will state the target of evaluation. This means they will explain to the CLEF the climate in which the product is to operate. For instance, with a digital signature product climate might include factors such as the volume of electronic documents sent or received, the number of times the wrong password could be used and whether it is expected that attacks would come from sophisticated hackers. The product or equipment will then be given a score. In ITSEC the score will vary from E1-E6. E1, the lowest, would mean that the product has been evaluated in a normal working environment as described in the instruction book. E-6 would mean that every single design aspect was studied and evaluated for a climate in which the highest level of mathematical or technical attacks might be expected. See also the levels under Common Criteria.

122. The person seeking the evaluation will generally say to what level the evaluation is required and this will depend on the market or projected use. An extreme example might be that there is no requirement for resistance against nuclear attack for an ordinary commercial product but there would be for a product intended for use at a high security military establishment.

123. The results of the evaluation are sent by the CLEF to ITSEC. It then issues a certificate as to the level of assurance that has been reached.

LRA
124. A “local registration authority” is a name given to a body that performs the registration process which precedes the issue of a certificate of a digital signature. This process may, however, be performed by the CA. The LRA may be independent of or associated with the CA.

MIME
125. This is short for multi-purpose internet mail extensions. It is a protocol created by the IETF for e-mail messages . The protocol sets out the structure and content of an e-mail. For example, it lays down how attachments are included in e-mail messages. It marks boundaries for parts of the electronic document so that the beginning and end of an attachment can easily be seen. It has a particular field for the hashing algorithm which states which hashing algorithm has been used.

126. S/MIME is a secure protocol that applies a digital signature to an e-mail message(including any attached documents) and that produces a package of information that can be stored.

Modular Arithmetic
127. This is calculation based on a circle of numbers like a clock. An everyday example of modular arithmetic is telling the time. The module is 12. If it is 10 a.m. and we say that we are going to have tea in six hours we would say that tea is at 4 o’clock not at 16 o’clock. We calculate 10+6 in what is known as (mod 12). Instead of using an image of a clock the calculation can be performed in the following way:

Do the calculation normally, then find the answer in (mod x):

divide the answer by x and note the remainder which is the answer in (mod x)

10+6 = 16 ÷ 12 = 4 (mod 12).

128. Modular arithmetic is a key mathematical process in all methods of generating and verifying digital signatures. See for example RSA algorithm.