Assignment 2: Task 1

In this assignment, you have to mount a key recovery attack on a symmetric key encryption scheme in the KPA (Known Plaintext Attack) model. Mr. Cryptix has designed a new block cipher and implemented it in Java. Here is the java code for his block cipher. This block cipher uses 56 bit key and encrypts blocks of size 64 bits. The message to be encoded is assumed to be a string of ascii characters. The message is first converted into binary by converting each ascii character to 8 bit binary number. Mr. Cryptix uses the following code for this conversion. Then this binary string is encrypted with the block cipher using the ECB mode. Here is the code that encrypts using the ECB mode.

In order to know if this encryption scheme is secure, I have used this encryption scheme to encrypt a file. I have used different keys for each student. To be able to mount an attack I would let you know that the first line of the file is the following:

Here is this line converted to binary format. In the table below I have given the encryption of this line with your key. You have to use this information to mount a key recovery attack and let me know your secret key.