I received an urgent call from a client. The client’s computer got hit by the VVV virus AKA TeslaCrypt. All of their files were renamed to .vvv and when trying to open them, a message said that the only way to get them back was to pay $500 USD before a specific date, or $1000 USD after. The payment had to be in bitcoins. First question I asked: “Do you have a backup?” Client said “No”. Having read up about ransomware like CryptoLocker, I knew this was bad news. Normally once the files are encrypted, it’s game over. Only way out is backup. Nevertheless, I dove into researching a possible solution – just in case.
There were 4 possible methods that I tried:
- Restore from windows shadow copy. This didn’t work in this version of TeslaCrypt. The criminals learned to wipe the shadow copies before encrypting the files.
- Undelete files (someone claimed that when the files are encrypted a copy is made and original deleted). This didn’t work, I could not find a single deleted file that matched it’s encrypted counterpart. All I found were files that were legitimately deleted by the user long before the infection. This kind of makes sense, because surely the encryption process will overwrite the data rather than creating a copy. But anything is worth a try when you are desperate.
- Decrypt using key.dat (where the decryption key is stored). This didn’t work either because this was newer version of TeslaCrypt. In the old version the criminals were stupid enough to leave the decryption key right on the infected system. In the new version, they hold the key on a server they control.
- Decrypt using a tool called teslacrack.py. This eventually ended up working – but more on that later.
Running out of time, and faced with the slim chance of recovery, my client felt he had no choice other than to pay the ransom. The criminals are running an organized business, and this gives it the impression that they may actually deliver the decryption key after payment in order to preserve their reputation. After all, if people have bad experience after sending a payment, the word will spread and no one will ever send them any money no matter how desperate they are. On the other hand if the payment and decryption are very quick and easy, people will see it as an easy way out. This, combined with how easy it is for the criminal to give out the decryption key (just a single click of a button) it is in the criminal’s best interest to deliver the decryption key promptly. All signs pointed to a well organized setup. The criminals even have even had a working web support and billing system where you can get answers to your questions regarding on how to submit your Bitcoin payment. The response time to a general question ended up being about 4 hours – which is not bad. Actually better than support at many large enterprises. Still, there are so many things that could go wrong. Maybe the criminals are just plain evil and see this as a onetime money grab. Maybe they could not care less about their reputation. Maybe the criminals get shut down just before having the chance to send you the key. Maybe the criminals screw up and lose the key, so even though they might have wanted to give it to you, they simply don’t have it. Maybe the criminals are stupid and don’t use business sense for deciding how to behave. You are doomed if you send payment, and you are doomed if you don’t. I was glad that it wasn’t me in this situation. I would have no idea what to do next.
My client on the other hand had to make that decision – and quickly. He decided to pay. Trouble was that the only accepted method of payment was through bit Bitcoin (BTC). Because he did not have $500 USD in BTC, he had to buy Bitcoins first. Even though it’s becoming easier and easier to buy Bitcoin, it’s still quite a process. You either have to go through 2-5 day verification process or you have to fully trust the Bitcoin vendor. Neither of those options was good because we were running out of time and we were not in the mood to blindly “trust people”. In the end we were lucky because now there is a Bitcoin ATM at Café Blanca in downtown Calgary. There you can buy and sell Bitcoins with cash instantly. You insert cash and the bitcoins appear in your Bitcoin wallet 2 seconds later. My client ended up gradually putting in about $700 CAD in cash to purchase 1.1 Bitcoins which the criminals demanded in order to cover the $500 USD fee. With 1.1 bitcoins ready, we went back to the criminal’s web payment portal. Just as we were reading the payment instructions for the 3rd time to be extra sure there is no mistake, we noticed that the criminals raised the cost to 1.25 bitcoins. We had to top up the bitcoin wallet and proceeded to make the payment. We sent the payment and included the transaction ID which proved receipt by the criminals. Then we waited. 10 minutes, nothing. 1 Hour – nothing. 5 Hours – nothing. 1 day – nothing. That was it. The criminals got the money and we’ll never the key. The files were still encrypted and useless.
During all the waiting, I resumed trying my hand at decryption. To my amazement teslacrack.py method actually worked. Not only it worked, but once I figured out the right tools and the right steps, the actual computation time to crack the key was only 30 seconds. This was amazing because normally these methods take weeks if you are extremely lucky. It turns out that in addition to a mountain worth of luck on my side, the criminals made a mistake in the way they encrypted the files. If the criminals didn’t make that mistake, no amount of luck would have helped. Cracking the key would take millions of years. It is also interesting to note that the criminals encrypted different sets of files using 2 different keys meaning that even if they let you decrypt one set of files, the other set of files would still be encrypted (presumably to force you to pay an additional fee). Furthermore the key for one set of files was cracked in 30 seconds, the second key took more than 5 days with no success. Luckily, the first set contained the critical files, and the client was not too concerned about the second set, so we stopped there. By the way, eventually the link that took us to the criminal’s billing/support site went blank. We’re never going to see that key or the $700+ CAD.
- Backup, backup, backup, backup. There is not going to be a second chance like this again. A mistake like this is not going to show up again in their next version of ransomware. In fact there are other variants of ransomware that are already impossible to crack. Did I mention backup?
- When dealing with criminals never expect a favorable outcome. If you’re sending any money for ransom, consider it lost the moment you hit send. What’s more, be prepared for escalation. Once the criminals know you are willing to send money they may come back at you with asking for more. They will either just ask for more even though you already send exactly what they asked for, or you may find out that after part of your files are decrypted, the other part is still encrypted.
How to recover:
Step 1) Take backup and work from the backup
- This is important because even though your files are encrypted and apparently useless, your day will get considerably worse if you lose them somehow. What if the ransomware detects you are trying to decrypt and deletes everything right now and then?
Step 2) Install programs:
- Python 2.7 (32 bit because it must match library below)
- Pycrypto-2.6.win32-py2.7 library (I ended up using this because I had trouble compiling the library from source)
- Msieve150_win32 (I also tried optimized versions for Intel processors and CUDA, but reading about possible bugs didn’t give me confidence, so try them, and if they work then fine, but don’t forget to have version 150 as your fail safe)
Step 3) Identify the AES key that you will try to crack
- Place some vvv files in the same folder as teslacrack.py and run teslacrack.py
- You will get something like this:
Cannot decrypt ./IMG_1111.JPG.vvv, unknown key Software has encountered the following unknown AES keys, please crack them first using msieve: 346FA15D6F7106A05553587E67AD068EBF0CE65C9ECBA74BAE144661AB502CEFFEBCFA9FBB3CDFD9E4043B3402F970051E55063D96C94AB66B443A0F9D088A23 found in ./IMG_1111.JPG.vvv Alternatively, you can crack the following Bitcoin key(s) using msieve, and use them with TeslaDecoder: E82E090D9A73DC4E93201BC56394544493EFD0DD2631F588C4083F006C1CD419F096F1D6E646AA0DE8D0230CB18D009B231DEA6EF7CAFED03C6C53830E51074A found in ./IMG_1111.JPG.vvv
Step 4) Crack the AES key
Run msieve with the AES key found in step 3 (notice 0x in front):
msieve -v -e 0x346FA15D6F7106A05553587E67AD068EBF0CE65C9ECBA74BAE144661AB502CEFFEBCFA9FBB3CDFD9E4043B3402F970051E55063D96C94AB66B443A0F9D088A23
You should see something like this
random seeds: 4e305a00 6fb1837c factoring 2746299090781689070444389534863512001481868057180589068197106350690661 98749363149686207988485815608295042086154388677331498764717631003373547132362899 7155 (154 digits) searching for 15-digit factors P-1 stage 1 factor found searching for 20-digit factors P-1 stage 2 factor found searching for 25-digit factors P-1 stage 2 factor found commencing quadratic sieve (33-digit input) using multiplier of 3 using VC8 32kb sieve core sieve interval: 4 blocks of size 32768 processing polynomials in batches of 51 using a sieve bound of 4909 (341 primes) using large prime bound of 196360 (17 bits) polynomial 'A' values have 4 factors sieving in progress (press Ctrl-C to pause) 696 relations (302 full + 394 combined from 2196 partial), need 437 696 relations (302 full + 394 combined from 2196 partial), need 437 sieving complete, commencing postprocessing begin with 2498 relations reduce to 1007 relations in 2 passes attempting to read 1007 relations recovered 1007 relations recovered 24 polynomials attempting to build 696 cycles found 696 cycles in 1 passes distribution of cycle lengths: length 1 : 302 length 2 : 394 largest cycle: 2 relations matrix is 341 x 696 (0.1 MB) with weight 11065 (15.90/col) sparse part has weight 11065 (15.90/col) filtering completed in 1 passes matrix is 341 x 405 (0.0 MB) with weight 5168 (12.76/col) sparse part has weight 5168 (12.76/col) commencing Lanczos iteration memory use: 0.0 MB lanczos halted after 7 iterations (dim = 330) recovered 63 nontrivial dependencies commencing quadratic sieve (69-digit input) using multiplier of 23 using VC8 32kb sieve core sieve interval: 12 blocks of size 32768 processing polynomials in batches of 17 using a sieve bound of 209771 (9278 primes) using large prime bound of 19508703 (24 bits) using trial factoring cutoff of 24 bits polynomial 'A' values have 9 factors sieving in progress (press Ctrl-C to pause) 9427 relations (4473 full + 4954 combined from 52519 partial), need 9374 9427 relations (4473 full + 4954 combined from 52519 partial), need 9374 sieving complete, commencing postprocessing begin with 56992 relations reduce to 13757 relations in 2 passes attempting to read 13757 relations recovered 13757 relations recovered 11859 polynomials attempting to build 9427 cycles found 9427 cycles in 1 passes distribution of cycle lengths: length 1 : 4473 length 2 : 4954 largest cycle: 2 relations matrix is 9278 x 9427 (1.3 MB) with weight 274633 (29.13/col) sparse part has weight 274633 (29.13/col) filtering completed in 3 passes matrix is 8448 x 8512 (1.2 MB) with weight 244661 (28.74/col) sparse part has weight 244661 (28.74/col) commencing Lanczos iteration memory use: 1.2 MB lanczos halted after 135 iterations (dim = 8443) recovered 61 nontrivial dependencies p1 factor: 3 p1 factor: 5 p6 factor: 418819 p8 factor: 10304417 prp13 factor: 8162073202471 prp14 factor: 84794311049579 prp19 factor: 3135407003350317697 prp25 factor: 2560807722929541167424011 prp26 factor: 19683723106610479028057093 prp45 factor: 387847886921773814156469727175786645600806381 elapsed time 00:00:37
Depending how lucky you are, this process will run for anywhere from minutes to weeks.
Step 5) Unfactor based on prime factors from step 4
- take the 10 factors at the very end of the file and feed them into unfactor-ecdsa.py. If any factors are listed multiple times, repeat them also.
unfactor-ecdsa.py ./IMG_1111.JPG.vvv 3 5 418819 10304417 8162073202471 84794311049579 3135407003350317697 2560807722929541167424011 19683723106610479028057093 387847886921773814156469727175786645600806381 Found AES private key: b'\x6d\xb8\x64\x76\x72\x31\xc4\xff\xfc\x22\x48\x20\xa5\xbc\xcd\x6c\x4c\x30\x2f\xc3\x4d\xd6\xfa\x23\x4b\x4b\x9e\x0c\x1d\xaf\xec\x07' (6DB864767231C4FFFC224820A5BCCD6C4C302FC34DD6FA234B4B9E0C1DAFEC07)
Step 6) Use AES private key to decrypt all your files
- Edit teslacrack.py and add AES private key to the list of keys at the beginning of the file
- Run teslacrack.py C:\
- It will decrypt every vvv file that was encrypted by this specific key
Step 7) Backup, backup, backup. Next time this will NOT work.