The first bonus task was to show how the birthday paradox works. You can select number of iterations the program will use.
cd bonus_1
make && ./paradox 10000The second bonus was about attacking on a stream cipher. It simply takes two encrypted strings moves one of them along and tries to stop when readable word is detected.
make && ./streamThe first part located in ukol1.cpp tries to find SHA256 collision in the first 2 bytes. The input clear text is systematically generated and output is matched against two hardcoded values.
The second task shown, that stream cipher applied twice with the same config has no security at all. It was easy to xor those two outputs and effiently get unencrypted output.
Basic idea:
in_1 = "......."
in_2 = "......."
cipher_stream = RC4_GetStream();
#The same stream used twice
out_1 = bytewise_xor(in_1, cipher_stream)
out_2 = bytewise_xor(in_2, cipher_stream)
#We know this, because `xor` will remove the cipher_stream
#Now there is not secrecy
bytewise_xor(in_1, in_2) == bytewise_xor(out_1, out_2)
This lab show different properties of block ciphers in different set-ups. The bmp image of Homer Simpson was disected and split into image header and data. Image data was encrypted and the results merged. Now we have different images encrypted with different setups. Given this we can easily (okometricky) compare the quality of encryption.
Encryption combinations
CBC-ENCRYPTION
CBC-DECRYPTION
ECB-ENCRYPTION
ECB-DECRYPTION
Is about assymetric cryptography. You can encrypt and decrypt file using private and public keys.
Program opens SSL connection to a hardcoded webserver and downloads it's certificate to the local pem file.
Program opens SSL connection to a hardcoded webserver and lists server capabilities concerning security suits and configs.