If hours not to nullify, the counter of time summarizes time of all talk within a day and more (till 24 o'clock colloquial time). The counter of time can be also used to the analysis of frequency of use of the telephone set.
THAT is characterized by small time of contact piracy with the line in a connection point. As a rule, isolated cases of use of various telephone sets or lines with absence or insignificant masking of places of connection are observed.
The initial message representing sequence of symbols shares on blocks on 64 symbols everyone. Further in relation to each block performance of the following sequence of operations is carried out.
The easiest and widespread way of cryptographic transformation of analog telephone communications is splitting messages of X (t) into parts and delivery of these parts in a certain order in a communication channel.
It is obviously possible to refer to vychislitelno permanent cryptographic transformations also such cryptographic transformations at which use the malefactor for unauthorized access to the message of X (t) needs to use only certain algorithms of processing of the message of Y(t). These cryptographic transformations are capable to provide only temporary firmness.
It is characterized by high degree of reserve of carrying out unauthorized talk. It is almost impossible to elicit the connection fact at the time of its carrying out. If after connection conducting of the line is restored and the junction masks, it speaks about long (steady) use of your telephone line.
There are also "phones vampires" which continuously "sniff" at air and extend identification number and an electronic consecutive index of the authorized user for single conversation.
Unauthorized unpaid use of payphones also noticeably influences the size of financial losses of linear communication centers. One of possible ways: a long reuse of the first unpaid minute on some types of intercity payphones. Besides, for payphones also connection to a wire loop, as well as for usual THAT is also characteristic. Rather often also application of self-made counters, monetozamenitel, cards meets.
In the mode of a gammirovaniye cryptographic transformation of the message by addition on mod2 of symbols of the message with symbols of sequence (scale) developed according to a certain rule blocks on 64 symbols is carried out.
Really, if for transfer of telephone communication IKM is used, for its restoration on the reception party it is necessary to accept not less than 6800 instant values in a second. Further, if for transformation of instant values to a code the 8th digit analog-digital and digital-to-analog converters are used, the speed of transfer of symbols in a communication channel will make 54,4 kbps. Therefore, for ensuring transfer of telephone communication in this case it is necessary to increase a communication channel pass-band significantly. Besides, it is also necessary to create a shifrator (decoder) which would carry out cryptographic transformation of the message with a speed of 54,4 kbps.
Proceeding from temporary and frequency representations of open telephone communication of X (t) in practice the cryptographic transformations applied to the message of X (t) or to its amplitude-frequency range of S(f) can be used.
Passive devices of protection are intended for registration of the fact of connection and unauthorized use of the line. They do not interfere with communication process but only help the owner of the line to react to initial process of emergence of unauthorized use of the line quickly.
In practice for transformation of telephone communication of X (t) to a digital form on the transferring party and recovery of this message on the reception party speech codecs which realize one of two ways of coding of telephone communications are used: form and parameters.
Imitovstavka is transferred on a communication channel after the ciphered message. On the reception party from the accepted message the imitovstavka which is compared to the received is developed. In case of discrepancy of imitovstavka the accepted message is considered false.
As length of an entrance key of cryptographic transformation k makes 56 symbols, and on each iteration only 48 of 56 symbols are used, each symbol of an entrance key is reused.