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Thread: enhanced encryption question

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    Default enhanced encryption question

    Enhanced Enhanced Privacy is allowed on selected digital channels. Each privacy-enabled channel must have a securely-configured Key Value associated with it. Garbled voice is heard on receiving radios with Key Values which do not match that of the radio transmitting a privacy-enabled voice transmission. Nothing is heard on the receiving radio if the Key ID of the transmitting radio does not match with all the Key IDs in the list of receiving radios.
    So will I or will I not hear the transmission and it just be garbled if they have advanced encryption enabled and I do not, or I have the wrong key?
    Garbled voice is heard on receiving radios with Key Values which do not match that...
    Nothing is heard on the receiving radio if the Key ID of the transmitting radio does not match with all the Key IDs...


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    From what I have seen, you will always hear garbled voice if you have a missing or incorrect key. I'm confused about the 'Nothing is heard on the receiving radio if the Key ID of the transmitting radio does not match with all the Key IDs...' part. I've tried randomly guessing some keys in the past and always received garbled audio... I can't think of any times that I tried and the radio stayed mute during a transmission. This was true for both Basic and Enhanced privacy systems.

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    There is something called "proper code" and if ON, it will mute any traffic with the incorrect key. If OFF, you'll hear everything including gobbledygook when the key doesn't match. As far as randomly guessing keys, yeah, you'll have about a 16 billion to one shot at getting the right one...

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    Proper code? I don't ever recall seeing that in the TRBO CPS anywhere... And yeah... I know I'll never guess the code, was just basically playing around with it

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    Oops, didn't see this was in the Trbo section, I assumed P25 or SecureNet, but I assume the same concept applies, whether there is a switch for it - I don't know... The other thing that would affect this was not having a secure hardware module would cause muting of the secure traffic unless you hit "Monitor", but again I'm quoting from my experience with older P25 radios...

    Likewise, it's very possible they are using recycled ad copy from older radios since the statements seem in conflict
    Last edited by Alpha; Oct 07, 2012 at 08:10 PM.

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    Interestingly enough, I found out by accident the other day that at least on the XPR7550's, the radio will unmute to any valid key that is programmed into the receiving radio regardless of the key that is strapped to the channel.

    I have 4 keys programmed into my 7550. I provided one of the keys to a friend for temporary communications not realizing that I did not have the correct key loaded on the channel we were using. My radio unmuted fine when he transmitted, but his radio unmuted with garble when I transmissed with the key he did not have.

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    It's pretty hard for a radio to tell whether the key is right or not. There is no secondary checksum on the voice packets, if they decrypt wrong you just hear the wrong phonemes (gobbledygook). The way the radio tries to tell whether or not is has the right key is something called "entropy detection" - the more "random" the signal is the less likely you have the right key. When you're talking normally there are lots of pauses and dead times (no speech energy present) so looking at the bit stream after decryption you can see if it's trending toward lots of silence broken by occasional words. If the wrong key is used, then it would encode all the silence times as having some kind of (wrong) speech happening all the time, with no short pauses or silent times between words. I was told this is the basis of how "Proper Code" works.

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    Sounds like TRBO firmware needs a KID implementation

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    Enhanced Privacy has a KID:-

    "Enhanced Privacy uses multiple keys and a random number to ensure that the encryption data is
    different for each data message and each superframe of a voice message. This requires
    transporting crypto parameters (e.g. key Identifier, Initialization Vector) with the voice or data
    payload. A voice message, in the case of Enhanced Privacy, requires an additional header.."