PSTN/1i QSG V0.1E Page
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D. Placing and receiving secure calls
1.
TO PLACE A SECURE CALL:
1.1.
Put the device in secure mode.
The key must be in the vertical position.
1.2.
Lift up the telephone receiver.
You will hear a dial tone produced by the
device.
1.3.
Dial the desired number.
You will first hear the ringing tone. Once the called
party has accepted the call, the ringing tone will be followed by a “ditt-dutt ditt-
dutt” sound that signals to you that the “key setup” procedure for the secure
connection is in progress. Key setup may take from 10 to 20, but typically 15
seconds, depending on line quality. Once the key setup is completed you will
hear a “Ping” sound and can start talking to your partner.
1.4.
Verify the authenticity of the key.
Please take a look at the telephone
display and read the three letters after “SAY:” to your partner and check the
three letters after “CHK:”
Reading the three letters to your partner and verifying what your partner says
is meant to protect you against so-called “man-in-the-middle attacks” on the
secret session key. The letters are mathematically derived from the unique
secret key that is used for each call. By reading and verifying them with your
partner, you make sure that you are indeed communicating using the same
key. Please pay attention to the voice of your partner when he reads his three
letters. To be completely on the safe side against very sophisticated voice
impersonation during key verification, you could periodically re-verify the letter
code with your partner during the conversation.
1.5.
Hang up the telephone receiver when you wish to finish the call.
