Chapter 7. Configuring Secure Connections

By default, clients and users connect to the Red Hat Directory Server over a standard connection. Standard connections do not use any encryption, so information is sent back and forth between the server and client in the clear.
Directory Server supports SSL/TLS connections, Start TLS connection, and SASL authentication, which provide layers of encryption and security that protect directory data from being read even if it is intercepted.

7.1. Requiring Secure Connections

The Directory Server has two different ways of encrypting data: SSL/TLS (either through an initial SSL connection or using Start TLS to establish encryption on a previously unencrypted connection) and SASL. If the server is configured to use it, any client can connect to the server using either encryption method to protect data.
For additional security, the Directory Server can be configured to require a certain level of encryption before it allows a connection. The Directory Server can define and require a specific security strength factor for any connection. The SSF sets a minimum encryption level, defined by its key strength, for any connection or operation.
To require a minimum SSF for any and all directory operations, set the nsslapd-minssf configuration attribute. When enforcing a minimum SSF, the Directory Server looks at each available encryption type for an operation — SSL/TLS or SASL — and determines which has the higher SSF value and then compares the higher value to the minimum SSF. (It is possible for both SASL authentication and SSL/TLS to be configured for some server-to-server connections, such as replication.)


Alternatively, use the nsslapd-minssf-exclude-rootdse configuration attribute. This sets a minimum SSF setting for all connections to the Directory Server except for queries against the root DSE. A client may need to obtain information about the server configuration, like its default naming context, before initiating an operation. The nsslapd-minssf-exclude-rootdse attribute allows the client to get that information without having to establish a secure connection first.
The SSF for a connection is evaluated when the first operation is initiated on a connection. This allows Start TLS and SASL binds to succeed, even though those two connections initially open a regular connection. After the TLS or SASL session is opened, then the SSF is evaluated. Any connection which does not meet the SSF requirements is closed with an LDAP unwilling to perform error.
Setting a minimum SSF can be used to effectively disable all standard or insecure connections to a directory.
The default nsslapd-minssf attribute value is 0, which means there is no minimum SSF for server connections. The value can be set to any reasonable positive integer. The value represents the required key strength for any secure connection.
  1. Add the nsslapd-minssf attribute to the cn=config entry:
    [root@server ~]# ldapmodify -D "cn=directory manager" -W -x
    dn: cn=config
    changetype: modify
    replace: nsslapd-minssf
    nsslapd-minssf: 128
  2. Restart the server.
    service dirsrv restart


An ACI can be set to require an SSF for a specific type of operation, as in Section 13.9.10, “Setting an ACI to Require a Certain Security Strength Factor for Some Operations”.
Secure connections can be required for bind operations by turning on the nsslapd-require-secure-binds attribute, as in Section 14.8.1, “Requiring Secure Binds”.