(57) In the method, to the traffic signal an additional watermark signal is added which
is not audible at the presence of the traffic signal, and then the signal is transmitted
on a telecommunication link to a subscriber, where it is received and decoded, as
a result of which a Watermark Binary Signature and a first Hash Function are received.
The Watermark Binary Structure is compared at the receiving side of the link with
the declared by the subscriber Watermark Binary Watermark Structure. A second Hash
Function is determined from the non-decoded received signal. The two Hash Functions
are compared with each other in order to determine whether the audio message has been
edited.
To the subscriber's terminal an Electronic Subscriber Module (EMA) is connected which
comprises in its structure a transmitting line (1) and a receiving line (2) of an
additional signal (SD), in which transmitting line (1) the following main functional
blocks are provided: Hash Function generator (gFS) and a Watermark Binary Signature
generator (gBSZW), as well as an Additional Signal Generating unit (uFSD), while in
the receiving line (2) the following main functional blocks are provided: an Additional
Signal decoder (dSD), a Hash Function decoder (dFS), and a Hash Function comparator
(kFS).
The advantageous features of the invention are constituted by a function of secret
identification of a subscriber and a function of verification of integrity of a traffic
signal as a subscriber's audio message, based on the technique of marking traffic
channel in telecommunication links. These two functions: subscriber identification
and audio message integrity verification, are performed in a secret manner, at the
background of the traffic signal, and thus the subscriber with a terminal without
the described apparatus connected thereto will not be aware that he is being authorized
as a subscriber, and moreover the method and the apparatus are independent from the
telecommunication link infrastructure and they do not interfere with its internal
components.
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