Mode 33400: mega.nz password-protected link (PBKDF2-HMAC-SHA512)

[DCNick3]

mega.nz is a centralized file-sharing service with some nice security features, like client-side file decryption. Apparently it is not widely known, but mega password-protected links are implemented fully on the client side using PBKDF2-HMAC-SHA512 to derive a key and an HMAC-SHA256 to verify the derived key.

This PR adds support for cracking passwords for such links.

Relevant documentation

• mega.nz whitepaper
• format description in source code
• password decryption function.

Example hash

P!AgD________U2XVjJi1vxkJgMPf5rkQYUn1H_6WI_sKtiic69mqBKP_____________________O_PDG0Om7BSapL1QoRAgUrz9vzaZmrYnU8t-Au6hteg

It corresponds to the following link:

https://mega.nz/#P!AgD________U2XVjJi1vxkJgMPf5rkQYUn1H_6WI_sKtiic69mqBKP_____________________O_PDG0Om7BSapL1QoRAgUrz9vzaZmrYnU8t-Au6hteg

This hash follows the algorithm, but does not correspond to a real file.

Notes

I did not test this on file links (they have 01 at the second byte and a different key length), but I did try to support it.

I am unsure of some of the choices I made in the PR and would like some input from the maintainers:

1. What should the category for such a hash should be? I've used HASH_CATEGORY_APPLICATION_DATABASE, but it's not really an application and more like a centralized service..
2. I am not sure if the use of COMPARE_M in the kernel makes sense. Intuitively, we already know the digest we want to compare with so, probably COMPARE_S should be used instead? I was not able to figure out how to use it here though

[WhiteyCookie]

Why isn't this already implemented? Can't wait. Plz hashcat people, do it before Christmas :)