Commit 76142803 authored by Quanah Gibson-Mount's avatar Quanah Gibson-Mount
Browse files

ITS#7990 - add section on hashing cleartext passwords

parent f2481c8d
......@@ -964,8 +964,53 @@ for an object, and the password policy module was configured with the DN of a
default policy object and if that object exists, then the policy defined in
that object is applied.
Please see {{slapo-ppolicy(5)}} for complete explanations of features and discussion of
"Password Management Issues" at {{URL:http://www.symas.com/blog/?page_id=66}}
Please see {{slapo-ppolicy(5)}} for a complete explanation of its features.
A guiding philosophy for OpenLDAP and directory servers in general has been
that they always hand back exactly what they were given, without
modification. For example, if the cn attribute of an object was set to fOObaR,
the server will return that exact string during a search. Values of attributes
of a sensitive nature, such as userPassword, are often hashed to conceal their
values. Since the userPassword values are used internally by the directory
server to authenticate users, any hash algorithm that is applied to the value
must be compatible with the directory server. Historically this problem has
been solved by making the LDAP client application be able to hash the
userPassword attribute value in a way that is compatible with the directory
server, but this solution has the obvious drawback of requiring tight coupling
between the LDAP client and server, and limits the choices of usable hashing
algorithms to those that are accommodated by both. This is clearly a
sub-optimal solution.
In 2001 RFC 3062 became a standard that specified an LDAP extended operation
for cases like this. Extended operations are not bound by the
return-what-you-are-given philosophy and so are free to do things to attribute
values that the add and modify operations cannot. The change password extended
operation accepts a plaintext password and hashes it based on a specification
that is contained in the server. This allows the server to be in control of
the hashing algorithm which, in turn, ensures that any hashes applied to
userPassword attribute values will not prevent users from being authenticated.
The password policy module's ppolicy_hash_cleartext flag addresses this
problem by intercepting LDAP modify operations that include the userPassword
attribute and converting them to change password extended operations so they
can be hashed according to the specification contained in slapd's
configuration. When this flag is set, LDAP applications that modify the
userPassword attribute can send the password in cleartext form to the server
using a standard LDAP modify command and the server will hash the value
according to the password-hash directive before storing it. It goes without
saying that steps need to be taken to protect the cleartext password in
transit, such as using SSL, TLS, or some other link encryption method.
The following example shows the ppolicy module configured to hash cleartext
passwords:
> database mdb
> suffix "dc=example,dc=com"
> [...additional database configuration directives go here...]
>
> overlay ppolicy
> ppolicy_default "cn=default,ou=policies,dc=example,dc=com"
> ppolicy_hash_cleartext
H3: Further Information
......
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