Hack-petya mission accomplished – Petya ransomware decryptor

Re:Hack-petya mission accomplished – Petya ransomware decryptor by Cpoll on Monday April 11, 2016 @04:40PM (#11474899)

I'm guessing the ransomware uses Salsa10 because it's fast?

According to https://www.cryptopp.com/benchmarks.html, Salta20 is 4x faster than AES - and if I understand it, Salsa10 is half the iterations.

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Re:Hack-petya mission accomplished – Petya ransomware decryptor by TillE on Monday April 11, 2016 @06:30PM (#11475675)

Salsa20 / ChaCha20 are quite nice when you want to do byte-for-byte file encryption. It's a good choice in a lot of situations.

The unusually reduced number of rounds is more difficult to explain, since I expect hard drive I/O would be the bottleneck in almost any situation. Maybe it's just a little more "stealthy" to not have elevated CPU usage while the ransomware is incubating.

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Re:Hack-petya mission accomplished – Petya ransomware decryptor by pbsd on Monday April 11, 2016 @06:45PM (#11475752)

It's not Salsa10; it's just that the author is counting double-rounds, which makes it looks like it's half the iterations. This has as many rounds as Salsa20, but whoever converted this to 16-bit words didn't know what they were doing---the security degradation is enormous.

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Re:Hack-petya mission accomplished – Petya ransomware decryptor by nightcracker on Monday April 11, 2016 @07:14PM (#11475907)

Even ChaCha8 (similar to Salsa8) so far is infeasible. The problem is that the randomware used a modified Salsa algorithm that uses 16-bit words instead of 32-bit words. This demolishes the algorithm, and is not a standard modification.

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