Toy version of the sweet32 attack
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lib Reorg shared code into a lib/ directory Oct 11, 2017 Update Nov 24, 2017


This is a toy version of the sweet32 attack:

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.


Packet Generation: 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:

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

Example command:

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

As shown above, the cookie was succesfully retrieved!

Stats 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