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Flawed Usage of a OTP Cipher by the BND Level 2

by Jörg Drobick, published on 8/23/2015

During the cold war the foreign intelligence agency of Germany established so-called stay-behind units. Their radio messages were encrypted by a OTP method, but the keys were used multiple times. This challenge is about the effect of this multiple usage on the security of the method. You are given 5 messages, all encrypted with the same key.