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My easter visit to my father in law got me into this mess, excuse me. First news after the hello was:

"Someone was applying for a job, and i really, really needed to read his CV, so I entered the ADMIN-PASSWORD and now there is only this red skull ..."

oh no, oh nooo

Well, I always like a challenge ..., the hard task of analyzing and reimplementing the modified salsa algorithm is done.
So, here it is for everyone to play and experiment with. Btw. paying ransom isn't that much of a challenge.

The code reimplements the hashing used to verify the entered key.

• its salsa, yes, but it operates on 16-bit words, not 32-bit

• its not salsa20, but salsa10, e.g. it shuffles the matrix only for ten rounds

Data Locations:

• Nonce 8-bytes:
  • sector 54 [0x36] offset: 33 [0x21]
• Encrypted Verification Sector 512-bytes:
  • sector 55 [0x37] offset: 0 [0x0]

The code reads a file "src.txt" which is the 512-bytes from sector 55, pulls the interesting words, xor's them with 0x37 to give us the target output of the salsa hashing function.

It also reads "nonce.txt" which is the 8-byte nonce that was used in the attack.

Last, but not least, it fires up a genetic solver which gets us the key in a few seconds.

I recovered my key in say 10..30 seconds :), i just say Genetic Algorithms

PS: I know the code is a mess, but I was kinda in a hurry ..., i also had to hack into the genetic lib 'cause its not compatible with go1.6, concurrent map read/writes panics.

Get the nonce and the verification sector of the encrypted disk via dd or some hexeditor, save them as nonce.txt and src.txt in the directory where the program is, start the program, wait some seconds, have the key.

Best use the key on an image of the victim disk, inside a vm ... just to be on the safe side.