Phobos Ransomware CUDA Brute

Because sometimes the truth CPU isn't good enough.

What is this

This is a proof of script to brute-force the encryption key used in Phobos ransomware. Please keep in mind this has never been successfully used in real life scenario so far. More information is available in the article that describes our thought process behind it.

Building

You'll need a CUDA-compatible GPU as well as the CUDA compilation tools. Turing architecture worked best for us but it's possible that using a newer/older one could have some benefits or work better for you.

nvcc bruteforce_range.cpp main.cu aes256.cu -O3 -rdc=true --gpu-architecture=compute_75 --gpu-code=sm_75 -o brute.exe

Running

To run the script you'll need to gather a bunch of information about the ransomware process from the infected host, as well as a pair of encrypted and unencrypted file.

To get the estimate on total keyspace run:

# ./brute.exe keyspace <config file>
./brute.exe keyspace sample_data/config.json

This will give you the total number of needed iterations you'll need to perform in the next step.

To run the cracking process:

# ./brute.exe crack <config file> <cleartext file> <encrypted file> <start_step> <end_step>
./brute.exe crack sample_data/config.json sample_data/tofu.jpg sample_data/tofu.enc 1 603

C:\Users\phobos\cuda-brute>brute.exe crack sample_data\config.json sample_data\tofu.jpg sample_data\tofu.enc 1 603

State: 0 (3.05916e+18%)
Starting the SHA task
Starting the AES task
Waiting for tasks
Doing the CPU task
CPU task done!
Batch has taken: 1.001s

State: 512 (84.743%)
Starting the SHA task
Starting the AES task
Waiting for tasks
Doing the CPU task
No more things to try!
CPU task done!
Batch has taken: 2.87958s

State: 603 (99.8342%)
Starting the SHA task
Starting the AES task
Waiting for tasks
Doing the CPU task
No more things to try!
CPU task done!
Batch has taken: 2.81375s

State: 604 (100%)
Starting the SHA task
Starting the AES task
Waiting for tasks
Doing the CPU task
Found... something?
ac9f6d86f7cc156a40601972c4257c548a1c885b4bc3f461c988cae68505eb55

If you really want to make a serious attempt at using this, be sure to set the CUDA_VISIBLE_DEVICES envvar, and fine-tune the STREAM_NO and BATCH_SIZE consts.

Credits

• AES256: Byte-oriented AES-256 implementation. - Ilya O. Levin, Hal Finney
• SHA256: SHA256CUDA - moffa13
• Rest: CERT Polska - Jarosław Jedynak / Michał Praszmo

Tests

The script was tested and should compile/work on:

• Cuda compilation tools, release 10.1, V10.1.243
• Cuda compilation tools, release 11.1, V11.1.105
• GeForce RTX 2080 - Driver Version: 450.66 CUDA Version: 11.0
• GeForce GTX 1050 - Driver Version: 526.47 CUDA Version: 12.0