2 Digital signature on the basis of El-Gamal cipher
Let’s suppose that addresser intends to sign the document M. He chooses a big simple number p and a number g. These numbers are transferred or stored in open view and they can be common for whole group of users. Addresser choose random number k – secret key, 1< k <p-1, and calculate
Number Y he showed as an open key.
Let’s describe the sequencing for signature constructing. At first the hash-function h(M)=m value is calculated and we choose such random number x, so x<p-1, and number that is coprime with p-1, and next numbers are calculated:
Formed sign message looks like (M, r, s) .
Recipient gets at first the hash-function h(M)=m value and only then verifies the signature authenticity using the equality
If equality executes, signature is authentic.
Example 1.1 Let p = 23; g = 5; k = 7; h(M)=3; x = 5.
Addresser calculates the open key
Proceeds to signature calculating:
Sign message is formed as (M,20,21), and is transferred to the recipient.
Recipient verifies the signature authenticity. At first he calculates hash-function value h(M)=3, and then
Recipient makes conclusion that signature authentic.
Approaches to systems creation of information protection
Вefore to create a concrete system of protection of information (SPI), it is necessary to determine what exactly information is subject of protection, what forces, methods and facilities, for this purpose will be required.
On this account a SPI are created on a method supposing following, cyclic repetitive sequence of executions during of all period of its functioning (Pict. 1).
1. Determination of information, to subject of protection.
2. An exposure of complete great number of potential possible threats and channels of information loss.
3. An estimation of vulnerability and risks of information at the present great number of threats and loss channels.
4. Determination of requirements to protection.
5. Realization of choice of protection facilities and their descriptions.
6. Introduction and employing organization of chosen measures, methods and facilities of protection.
7. Realization of control of integrity and management of protection system.
The indicated sequence of executions is carried out continuously on the exclusive cycle, with a proper analysis of the state of SPI and clarification of requirements to it after every step.
of
information, to subject of protection
Analysis of the state of integrity of information
and clarification of requirements to SPI
Basic
stages
of
creation
of
protection
systems
Picture 1 - Continuous
cycle of SPI creation
2
An exposure of complete great number potential of possible threats
and channels of information loss
6.
Introduction and employing organization of chosen measures, methods
and facilities of protection
3
An estimation of vulnerability and risks of information at the
present great number of threats and loss channels
5.
Realization of choice of protection facilities and their
descriptions
4.
Determination of system requirements to protection
1 Determination
7 Realization of control of integrity and management of protection system
The construction of SPI is always begun with determination of information volume which must be protected. Such estimation on principle is needed and must be on possibility exact, as measures are directed on its protection cost very expensive. It is enough to say that leading firms in countries with a highly developed economy are expending about 20 percents of net profit for protection of production and commercial secrets.
The system of protection must be created simultaneously with creation of enterprise or organization where it will work. It will help to take minimum economic and moral losses in the case of disturbers attack to information. To that purpose security service is created. Tasks of this service are: realization of legal, organizational and technical measures of protection.
Creation of such service must be begun with the economic ground of its creation, because not every organization is in strength to bear expenses on its maintenance.