Technical data

15
telephone networks, provided that the other end is equipped with a similar board or with
AncVoice Coder – 2400.
HotLine – a center for generation of single-use gammas for protection of phone
conversations
The most important objective is to provide crypto-stability, that is to make it
impossible to reconstruct the plain text and the key using encrypted text, even if the scheme of
encryption is known. It is not always possible to prove crypto-stability of a particular scheme
of encryption.
One of the cryptosystems with a proved crypto-stability is the scheme in
which a random, equiprobable binary sequence is used as the gamma, and the plain text is
also represented by a binary sequence. The disadvantage of this scheme is that a long gamma
(with a length that equals to the length of plain text before encryption) has to be dispatched,
and it is also necessary to ensure that this gamma is used only once. Therefore, this scheme of
encryption is used exclusively in such cases where the task is to provide maximum security
for transmission of a small amount of data.
ANCORT has developed a scheme of encryption of plain text, represented by a binary
sequence, using a binary gamma obtained from a physical noise generator.
The random sequence generation board complies with the toughest requirements to
such products and to their components, and provides sequences of gamma symbols close to
random and equiprobable.
A gamma obtained from the physical noise generator undergoes a number of tests that
ensure the randomness and equiprobability of the recorded sequence of gamma symbols.
Gamma symbols may be recorded on CD-ROM or on diskettes.
The operation of the single-use gamma generating center consists of two stages.
During the first stage, 100000 symbols of the scheme are checked and tested. If the obtained
gamma satisfies all criteria, the generation of gamma in 100000-symbol pieces begins. If the
first stage shows that the quality of the resulting sequence does not satisfy the criteria, the
system is restarted. If it happens for three times, the physical noise generator stops working,
and the physical noise generation board failure message is displayed.
If a segment of the single-use gamma fails to satisfy the criteria, it is not recorded. If it
happens three times in a row, the physical noise generator stops its work and the failure
message is displayed.
The gamma is recorded in 100000-symbol series. The number of each section is
recorded in the beginning of the section.
The gamma is used there, where it is necessary to provide an absolute confidentiality.
ANCORT has developed a scheme for the use of such gamma for the purpose of protection of
phone conversations (fig. 1). There is also a system there that makes sure that a gamma is
used only once. If a section of the gamma has not been used to the end, it is deleted
completely.
Besides, the described gamma can be used in the same way to provide encryption for
other sorts of information: data, fax messages, etc.