Asgaard <asgaard@cor.sos.sll.se> writes:
On Sun, 12 Jan 1997, Adam Back wrote:
[...] Anyone know how modular the design is, for instance if it would be possible to give a GSM A5 based cell phone a crypto upgrade using published electrical interface standards? (I want one of those - Nokia phone with IDEA + 2048 bit RSA signatures + DH forward secrecy!)
I don't understand what you are getting at here. This would demand cooperation from the cell phone provider, with a compatible device at the other end of the airwaves.
If you super-encrypted the IDEA encrypted traffic with A5, it should not require cooperation of the cell phone provider. You always need a capable device at the other end. If the phone at the other end isn't IDEA/RSA/DH capable, you can fall back to only A5. My question about electrical interfaces was wondering if the above could be acheived by producing a plugable mini-smartcard, or desolderable IC which would allow this to be done with standard GSM phones.
Then the call would go unencrypted through much of the system until it reached the callee's current cell sender anyway. GSM is alledgedly A5 encrypted only in the air.
And if A5 is a 'decent' algorithm or not is up to discussion. It hasn't been up on the list for a long time now but from earlier discussions I remember that the latest versions of A5, if not 'strong' in a crypto anarchy sense, are susceptible to attack only from very sophisticated adversaries and certainly not from Newt's 'couple'.
Not from Newt's eavesdroppers sure, but it wouldn't cost that much for someone who wanted the traffic. 40 bits of effective key space at most, Adam -- 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`