sour16

This is a toy version of the sweet32 attack: https://sweet32.info/

The attack is an example of a birthday attack which exploits crypto algorithms with small block sizes in CBC mode. The attack requires generation of a lot of encrypted blocks with known plaintext. After the generation, identical encrypted blocks can be identified and used to identify the plaintext value of the blocks with unknown plaintext.

sour16 uses rot13 as its base encryption algorithm. Though basically any hashing/encryption algorithm with customizable block size and chained in CBC mode would work here.

Similarly to sweet32, sour16 generates a lot of encrypted HTTP packets where the only unknown is a cookie value. Then uses the attack to retrieve the cookie value.

Scripts

Packet Generation:

generate_packets.py: The script allows you to generate encrypted packets and dump them to a file. It supports -N flag to change number of packets generated (in the 1000s). It also allows configuration of the cookie value or the block size.

Example command:

./generate_packets.py --count 30 --cookie "SECRET COOKIE" --block-size 4 30k-32bit.out
# creates a file called 30k-32bit.out
# creates 30,000 encrypted packets with a 4 bytes (32 bit) block size
# each packet has the cookie set to "SECRET COOKIE"

Retrieving cookie by finding identical blocks

sour16.py: This is the script that executes the actual attack and requires a file that is generated using the generate_packets.py script. Since the block size can vary, the script needs to know the block size used for the encryption as well.

Example command:

./sour16.py --block-size 4 30k-32bit.out
Retrieved the entire cookie! SECRET COOKIE

As shown above, the cookie was succesfully retrieved!

Stats

find_expected_packet_counts.py runs many cycles of encrypt-decrypt for varying block size to figure out how many packets are needed on average. The numbers below are very course but give a rought idea of packet count as a function of block size.

|Block size| Block size| Num Packets| File size| Block count| |---|---|---|---|---| |2 byte| 16 bits| 40 packets| 28KB| 28k blocks| |3 byte| 24 bits| 1000 packets| 700KB| 364k blocks| |4 byte| 32 bits| 12500 packets| 8.4MB| 2.8M blocks| |5 byte| 40 bits| 250,000 packets| 174MB| 35M blocks|