BUGS Cryptanalysis

A full cryptanalysis of the BUGS Algorithm still remains to be done, however a first attempt to conduct a Cryptanalysis was done for my MSc Thesis in 2009 which is available from here and contains all the details of the attacks.

Below is a summary of what was done and found.

Attacks Selection
For the thesis I only focused on the encryption functions as a target and the following attacks were discussed:
– A Statistical analysis of the cipher to identify the Diffusion and Confusion characteristics of the ciphertexts and if there are any inherent weaknesses.
– Because of the XOR properties, it is likely a known plaintext attack on the shuffling function would work.
– A Chosen plaintext attack on the same function should also work for the same reasons and could be used to speed up the attack.
– How to build a Linear Cryptanalysis framework for this cipher.

Statistical and Probabilistic attack
Confusion
A script was designed to take a ciphertext input and generate the following:
– To count the number of times the same hexadecimal value was found.
– To count the average distance between repetitions.
That attack results indicated that the cipher may have a characteristic of bad confusion and further tests would be required to confirm that. (NEGATIVE)

Diffusion
Another script was designed to display a file as a picture with the following rule: to read the file as a bit stream and each time a 1 was found then a black pixel would be marked on the picture and for a value of 0 a white pixel will be used. With a parameter to add a new line in the picture every 512 bits.
No pattern was found and this was an indication of a good diffusion for the cipher indicates it is not apparently vulnerable to a bad diffusion attack. (POSITIVE)

Known and Chosen Plain text attacks
Those attacks targeted the shuffling encryption function. Although it is not used alone in the cipher default mode of operation, it is available as a standalone option mode and appears to be vulnerable to known and chosen plaintext attacks. As such, from this cryptanalysis we can recommend against using this cipher in that optional operation mode. (NEGATIVE in non standard mode)

Unrestricted XOR-SUM uniqueness Attack
The fourth attack while targeting the same encryption function attempted to use originality to identify characteristics between a plaintext and a corresponding ciphertext by considering a potentially new form of attack on XOR uniqueness properties. More work is required to confirm this new form of attack could have any value and this will be discussed in THIS SECTION

Linear Cryptanalysis Attack
The last attack, using a high order linear cryptanalysis framework, suggested it may be possible to gather some information on the keys used to generate the ciphertext, but no obvious LC related attacks were found. (POSITIVE)

Further attacks should also be considered as they may apply to this cipher:
– Stream cipher attacks such as related key and correlation attacks.
– Differential Cryptanalysis may also be adapted for this cipher. However, with conventional Differential Cryptanalysis, no differences in the input will always result in no differences in the output; this will not be the case with this Cipher as it uses a random IV for the encryption.

To conclude, although some potential weaknesses were highlighted, this light cryptanalysis did not show any obvious security issues.

For this thesis we will focus on the encryption functions as a target and the following attacks will be discussed:

- A Statistical analysis of the cipher to identify the Diffusion and Confusion characteristics of the ciphertexts and if there are any inherent weaknesses.

- Because of the XOR properties, it is likely a known plaintext attack on the shuffling function would work.

- A Chosen plaintext attack on the same function should also work for the same reasons and could be used to speed up the attack.

- How to build a Linear Cryptanalysis framework for this cipher.

IT Security News & BUGS Cryptography Project