Summary: As a trainee, I got the task to extract encrypted passwords of our external password manager (Zoho Vault) and decrypt them. The documentation regarding how to decrpyt them is...none. I ask the support for help, but they send me only some pages of their documentation...

Research and attempts: According of my account and the documentation of Zoho Vault API, the algorithm is a "PBKDF2_AES". I used at first the PBKDF2 encryption to generate a key, by using a passphrase + a salt + an iteration of 1000, which I received with some API calls. Next, I tried to use the Zoho Vault decrypting function (which decrypts AES encryptions), but I didnt got the result I wanted. After that, I checked an Online AES Encrypter/Decrypter and tried my luck there. After filling the forms with all the required info, I received an error. Just to be sure, that it was the right encrypt/decrypt method, I encrypted some other example data and the result had the same Base64 pattern password I tried to encrypt. After I checked the "PBKDF2 generated key" and mine. The one I made was for a AES-256. But the "PBKDF2 generated key" seems to be 64 byte long/AES-512.

Which I did some research and it almost seems it doesnt exist.

I just cant figure out how to continue... If needed, I can share all required keys and encrypted data, since they are all dummies for the later used account anyway.

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    $\begingroup$ "it almost seems it doesnt exist"; AES-512 doesn't exist. Actually, there are a few proposals for "augmented AES" out there, however they aren't AES, no one takes them seriously, and (AFAIK) aren't used anywhere in practice... $\endgroup$ – poncho Aug 27 '20 at 15:25
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    $\begingroup$ Also: standard password hashing (as strongly suggested by PBKDF2) is normally not actual encryption: there is no computationally efficient way to find the password from the password hash, even with knowledge of the key/pepper (if any). If there's a better way than checking a password guess, the system is considered broken. Have you been sent on a snipe hunt? $\endgroup$ – fgrieu Aug 27 '20 at 19:25

But the "PBKDF2 generated key" seems to be 64 byte long

Sounds like the algorithm is actually PBKDF2-SHA512 or some other 512-bit has function, as PBKDF2 does NOT use AES as its PRF. Generally this is truncated down to 256 bits to use with your block cipher. I would check what you are using as the PRF, try replicating the master key by choosing different 512-bit hash functions until you get a match, then work onto decryption after.


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