Re: Electronic Codebook

s_4@wp.pl writes:

>I have simple task:

>Sorry about my English (I still learn it... )-:)

>Some criminal, who can modifity content of incrypted messages (banks'

How can he modify them?

>transfers), make a 17 transfers to his own bank account, allways on the
>same amount (sum). Then he searching in sending messages, such
>incrypted number of bank account, which were send exactly 17 times and
>on the same amount (sum). He recognize incrypted version of his no.
>bank account, despite he doesn't know the key. Why he have to make 17

The block size is typically 8 bytes, and his account and the amounts would
have to fit in the 8 bytes with the right phase.
Also, if he knows how to encrypt the message he HAS the key.

This also assumes that the same key is used each time. If some public key
system is used, then that is not true.

>transfers?

No idea what the last sentence means. YOu said he did 17 of them. Why not
ask him why?

>Thanks for help!

>Marcin
Received on Thu Jan 19 03:44:35 2006