Yes.

*Post by f***@keemail.me*If there is a "bit offset" this means that the "distinguish end point

computing" before disk lookup will be done in fact 51 times as 64

consecutive bits can fit 51 times in 114bits ?

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*Post by Jan Hrach*https://brmlab.cz/project/gsm/deka/attack-theory

https://brmlab.cz/project/gsm/deka/attack-implementation

I tought after a quick reading that the plaintext equivalent of

the tables was the LFSRs state after 122 clocking and the output the 64

first bit of keystream (after 64 further clocking) with a simple reduction

function output = new plaintext

No, it's the last 64 bits of keystream after 99+64 clockings. The

reduction functions are XORed constants generated using A5/1 itself (does

anyone know if there is any special purpose in this, or if it is just

convenient?)

See >>

http://jenda.hrach.eu/gitweb/?p=deka;a=blob;f=genkernel32.sh;h=96ec2fc0a6b540101f6f6e8fa418c7b385b460d8;hb=HEAD>>

for the actual chain computation (which is unfortunately a bit hard to

read, as it is a hand-vectorized code).

However while testing there is a Bit position that poped up . Does

it mean that the compute function differ for each steps or is it just

different in each tables ?

By bit position, you probably mean the offset if the 64bit sample in

the 114bit burst.

Finally what is the purpose of the GPU when finding new KC ? Is it

just for the compute/reduction step ?

The chain is computed to the nearest endpoint on the GPU, then the

corresponding startpoint is looked up on disk, and then the chain is

reconstructed from that startpoint on the GPU again.

Hi

I have a few questions regarding the A5/1 tables. I tought after a

quick reading that the plaintext equivalent of the tables was the LFSRs

state after 122 clocking and the output the 64 first bit of keystream

(after 64 further clocking) with a simple reduction function output = new

plaintext

However while testing there is a Bit position that poped up . Does

it mean that the compute function differ for each steps or is it just

different in each tables ?

IS there a simple guide to understand the table structure somehow .

Finally what is the purpose of the GPU when finding new KC ? Is it

just for the compute/reduction step ?

Best Regards

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*Post by Jan Hrach*https://lists.srlabs.de/cgi-bin/mailman/listinfo/a51

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Jan Hrach | >> http://jenda.hrach.eu>> <>> http://jenda.hrach.eu>> >

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