Stronger password hashes for OpenACS
This change introduces the possibility to use either the classical
OpenACS password hash algorithm "salted-sha1" or the SCRAM passord
function "scram-sha-256". The latter can be used by (a) using the
most recent version of NaviServer (from Sept 28, 2021 or newer) and
(b) by configuring the password hash preferences via Kernel package
parameter "PasswordHashAlgorithm". The package parameter can contain a
list of multiple hash algorithms in preference order. The most
preferred available algorithm is chosen.
By default, the "PasswordHashAlgorithm" is "salted-sha1", and the
behavior is as before. After upgrading to the new version of acs-tcl
and acs-kernel, the preference list can be configured. When a user
logs in and the preferred available algorithm is different from the
previously used algorithm, the upgrade is performed for the user
automatically.
The usage of SHA1 in OpenACS is easily target of security audits (see
[1]). The biggest danger is that if somebody gets full access to the
"users" table (e.g. when decommissioning a hard disk). In this case
the hashes can be attacked with dictionaries by using some crypto
hardware (when someone gets raw access to the DB, one has usually some
other big problems). However, by using the "scram-sha-256" hash
function this danger is substantially reduced. This function computes
a password hash using PBKDF2 (Password-Based Key Derivation Function
2). This function is used to reduce vulnerabilities of brute-force
attacks against password hashes. The hash function of SCRAM is PBKDF2
[RFC2898] with HMAC as the pseudorandom function (PRF) and with dkLen
== output length of HMAC == output length of the digest function. So,
it uses a better hash algorithm (sha-256 vs. sha1) and applies this a
high number of times (15K times for a password hash computation).
NaviServer supports as well the even better SCRYPT algorithm, but this
is only available when NaviServer is compiled with OpenSSL 3.0 or
newer. On the contrary, scram-sha-256 (actually PKCS5_PBKDF2_HMAC) is
available since OpenSSL 1.0.0 (2015).
All the improved hash functions require NaviServer with its tight
integration to the crypto functions of OpenSSL.
[1]
https://openacs.org/forums/message-view?message_id=5522562
