PBKDF2 password hashing as in ASP.NET Core

Yves Goergen nospam.list at unclassified.de
Sun Aug 30 19:54:50 EEST 2020

Thank you for your reply.

It's not that simple, though. Just because some core algorithms are 
standardised and should be compatible doesn't mean their use in 
different implementations leads to interoperable data. The key point 
here seems to be that Dovecot just supports SHA-1 with PBKDF2, not 
SHA-256. So I'm out of luck here. The different formats are no longer 
relevant then.

CRYPT-SHA512 is not anywhere near as secure as PBKDF2.

But I've read and learned a lot about secure password hashing in the 
past 24 hours. My initial point that PBKDF2 is the state of the art has 
been disproved already. This order seems to be the case [1]:

MD5/SHA1 << SHA2 << PBKDF2 < bcrypt < scrypt < Argon2

So I've changed my plans and try to go for Argon2 now. I found support 
for .NET Core [2] and Python [3].

My original question is kind of obsolete now because I also found 
another requirement: password rehashing. I'm migrating from an old 
database that has CRYPT-SHA512 hashes and want to upgrade them to 
Argon2. This affects multiple services (IMAP, SMTP, FTP, Management UI) 
so I think I'll better make a central authentication service that has 
all the passwords and crypto in one place and handles requests from 
those service daemons.

I'm currently investigating how to build such a service and integrate it 
into the services. Maybe a Unix socket is a good communication channel. 
Dovecot should be able to query it with a custom Lua script. Haven't 
looked into the other services yet. That auth service could be built 
with Python for isolation from other services, high availability and 
relatively low memory footprint. It connects to the database, reads and 
updates the hashes and does all the crypto for its clients.

Any suggestions about how to do that?


[1] https://cryptobook.nakov.com/mac-and-key-derivation/argon2
[2] https://github.com/tabrath/libsodium-core
[3] https://passlib.readthedocs.io/en/stable/lib/passlib.hash.argon2.html

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Von: Aki Tuomi <aki.tuomi at open-xchange.com>
Gesendet: Sonntag, 30. August 2020, 16:33 MESZ
Betreff: PBKDF2 password hashing as in ASP.NET Core


The PBKDF2 algorithm is standard and should be compatible with ASP.NET Core.

The salt parameter is 16 symbols from the salt character set


followed by number of rounds

hash is hex encoded 160-bit value which comes out of the PBKDF2 function 
with SHA1.

Dovecot does not currently have support for PBKDF2-SHA256, only 
PBKDF2-SHA1. You could use CRYPT-SHA512 instead which is probably just 
as good?


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