PSTN/1i QSG V0.1E Page
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2.
TO RECEIVE A SECURE CALL:
2.1. If your CryptoPhone PSTN/1 is in secure mode (key in vertical position):
2.1.1.
Lift up the telephone receiver.
You will hear the “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.
2.1.2.
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.
2.1.3.
Hang up the telephone receiver when you wish to finish the call.
2.2. If your CryptoPhone PSTN/1 is in clear mode (key in horizontal position):
2.2.1.
Lift up the telephone receiver.
Note that when you lift up the
telephone receiver in clear mode while the calling party has activated
the secure mode on the other side, you will hear nothing, because
the other side is waiting for your device to identify itself and start the
key setup procedure.
2.2.2.
Switch the device from clear mode to secure mode
by turning the
key from the horizontal position to the vertical position. You will then
hear the “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.
2.2.3.
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:” as detailed above in
section 2.1.2 to protect yourself against “man-in-the-middle attacks”.
2.2.4.
Hang up the telephone receiver when you wish to finish the call.
