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README.md

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+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|