[143] in cryptography@c2.net mail archive
Re: FCPUNX:ecure Phones
daemon@ATHENA.MIT.EDU (C. Kuethe)
Mon Feb 3 23:56:59 1997
Date: Mon, 3 Feb 1997 21:41:14 -0700 (MST)
From: "C. Kuethe" <ckuethe@gpu.srv.ualberta.ca>
To: Eli Brandt <eli@gs160.sp.cs.cmu.edu>
cc: crypto list <cryptography@c2.net>
In-Reply-To: <199702040425.UAA08359@blacklodge.c2.net>
On Mon, 3 Feb 1997, Eli Brandt wrote:
> C. Kuethe wrote:
> > [...] and then the specs page says: [...]
> > Voice Scrambling
> > * Primary scrambling method: Key based sub-band scrambling, 24 active bands
> > * Second: Key based re-scramble once per second
> > * Third: Key based spectral inversion of
> > selected sub-bands
> > * Secure mode voice pass band:200 Hz - 3130 Hz
>
> This doesn't sound too secure. Assume that the plaintext is harmonic,
> with time-varying pitch. Key point: all of the harmonics vary in
> synchrony; they all have the same frequency change dF/dt, except that
> it's scaled by harmonic number. And we (the attacker) have nice long
> windows to work with.
I was trying to make that point... I was just quoting what their web page
said...
[snip]
> Personally, I wouldn't trust something like this with more than $1e4
> or so. If you use one, continuous loud music (or, better, voices) in
> the background should make unscrambling substantially harder. Note to
> designers: digital is better.
>
> > So maybe it's not just some funky analog signal processor, but if the system
> > only encrypts 200-3130 Hz, I'd think there's some data leaking out there...
>
> If that's the passband, anything else gets thrown away. Phone lines,
> for comparison, pass 300 to 3k.
As we were both saying (meaning to say) there's a lot of holes in there... and
you're rich if you'd trust $1e4 to this box.... I'd put maybe $100 on it. Not
that I have a problem with wealth. My point there is that I don't think this
device is secure enough to be placing a lot of trust in...
--
Chris Kuethe <ckuethe@gpu.srv.ualberta.ca> LPGV Electronics and Controls
<c100305@wolfcreek.cs.ualberta.ca> http://www.ualberta.ca/~ckuethe/
RSA in 2 lines of PERL lives at http://www.dcs.ex.ac.uk/~aba/rsa/
print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<>
)]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"|dc`
