Digest Authentication with SIP

Digest authentication for Session Initiation Protocol (SIP) is a type of security feature on the Oracle Communications Session Border Controller that provides a minimum level of security for basic Transport Control Protocol (TCP) and User Datagram Protocol (UDP) connections. Digest authentication verifies that both parties on a connection (host and endpoint client) know a shared secret (a password). This verification can be done without sending the password in the clear.

Digest authentication is disabled by default on the Oracle Communications Session Border Controller. When digest authentication is enabled, the Oracle Communications Session Border Controller (host) responds to authentication challenges from SIP trunking Service Providers (endpoint client). The Oracle Communications Session Border Controller performs authentication for each IP-PBX initiating the call. However, the authentication challenge process takes place between the host and the client only since the IP-PBX cannot handle authentication challenges. The following illustration shows the digest authentication process.

This call flow displays the SIP digest authentication process.

The digest authentication scheme is based on a simple challenge-response paradigm. A valid response contains a checksum (by default, the MD5 checksum) of the “username” and password. In this way, the password is never sent in the clear.

By default, the Oracle Communications Session Border Controller uses cached credentials for all requests within the same dialog, once the authentication session is established with a 200OK from the authenticating SIP element. If the in-dialog-methods attribute contains a value, it specifies the requests that have challenge-responses inserted within a dialog.

In digest authentication with SIP, the following can happen:

More than one authenticating SIP element (IP-PBX) may be the destination of requests.
More than one authentication challenge can occur in a SIP message. This can occur when there are additional authenticating SIP elements behind the first authenticating SIP element.
The Oracle Communications Session Border Controller distinguishes whether the IP-PBX is capable of handling the challenge. If Digest Authentication is disabled (no auth-attributes configured) on the Session Agent, the challenge is passed back to the IP-PBX.

Note:
If there are multiple challenges in the request, and if the Oracle Communications Session Border Controller has only some of the cached credentials configured, the Oracle Communications Session Border Controller adds challenge-responses for the requests it can handle, and does not pass the challenge back to the IP-PBX.

Challenge-Responses in Requests not in the Dialog

A digest authentication session starts from the client response to a  www-authenticate/proxy-authenticate challenge and lasts until the client receives another challenge in the protection space defined by the auth-realm. Credentials are not cached across dialogs; however, if a User Agent (UA) is configured with the auth-realm of its outbound proxy, when one exists, the UA may cache credentials for that auth-realm across dialogs.

Note:

Existing Oracle Communications Session Border Controller behavior with surrogate-agents is that they cache credentials from REGISTER for INVITE sessions only if the Oracle Communications Session Border Controller is considered a UA sending to its outbound proxy.

Configuring Digest Authentication

In the Oracle Communications Session Border Controller ACLI, you can access the Digest Authentication object at the path session-router, session-agent, auth-attribute. If enabled, the Digest Authentication process uses the attributes and values listed in this table.

Note:

If enabling Digest Authentication, all attributes listed below are required except for the in-dialog-methods attribute which is optional.

The following table lists the digest authentication object

ORACLE(auth-attribute)# show
        auth-attribute
                auth-realm                     realm01
                username                       user
                password                       ********
                in-dialog-methods              ACK INVITE SUBSCRIBE

To configure digest authentication on the Oracle Communications Session Border Controller:

In Superuser mode, type configure terminal and press Enter.
```
ORACLE# configure terminal
```
Type session-router and press Enter to access the session router-related objects.
```
ORACLE(configure)# session-router
ORACLE(session-router)#
```
Type session-agent and press Enter to access the session agent-related attributes.
```
ORACLE(session-router)# session-agent
ORACLE(session-agent)#
```
Type auth-attribute and press Enter to access the digest authentication-related attributes.
```
ORACLE(session-agent)# auth-attribute
ORACLE(auth-attribute)#
```
auth-realm — Enter the name (realm ID) of the host realm initiating the authentication challenge. This value defines the protected space in which the digest authentication is performed. Valid value is an alpha-numeric character string. Default is blank.
```
ORACLE(auth-attribute)# auth-realm realm01
```
username — Enter the username of the client. Valid value is an alpha-numeric character string. Default is blank.
```
ORACLE(auth-attribute)# username user
```
password — Enter the password associated with the username of the client. This is required for all LOGIN attempts. Password displays while typing but is saved in clear-text (i.e., *****). Valid value is an alpha-numeric character string. Default is blank.
```
ORACLE(auth-attribute)# password *******
```
in-dialog-methods — Enter the in-dialog request method(s) that digest authentication uses from the cached credentials. Specify request methods in a list form separated by a space enclosed in parentheses. Valid values are:

INVITE | BYE | ACK | CANCEL | OPTIONS | SUBSCRIBE | PRACK | NOTIFY | UPDATE | REFER
```
ORACLE(auth-attribute)# in-dialog-methods (ack invite subscribe)
```
Note:
The methods not in this list are still resubmitted if a 401/407 response is received by the Oracle Communications Session Border Controller.

If you do not specify any in-dialog-method value(s), digest authentication does not add challenge-responses to in-dialog requests within a dialog.

This attribute setting applies to in-dialog requests only.

Additional Notes

The following are additional notes that describe the digest authentication process:

The Oracle Communications Session Border Controller always challenges the first LOGIN request, and initial authentication begins with that request. The recalculated authorization key — the credentials — are then included in every subsequent request.
If the Oracle Communications Session Border Controller does not receive any communication from the client within the expiration period, the Oracle Communications Session Border Controller logs the client out and tears down the transport connection. Faced with interface loss, the Oracle Communications Session Border Controller default behavior is to flush all warrant information from the target database. This response necessitates that the client first login/re-register with the Oracle Communications Session Border Controller, and then repopulate the empty database using a series of ADD requests. This behavior ensures that client and Oracle Communications Session Border Controller target databases are synchronized.   Alternatively, when faced with interface loss, the Oracle Communications Session Border Controller can retain all warrant information within the target database. This response necessitates only that the client first login/re-register with the Oracle Communications Session Border Controller. After successful registration the client should, but is not required to, use a series of GET, ADD, and DELETE requests to ensure that the Oracle Communications Session Border Controller and client target databases are synchronized.
The Oracle Communications Session Border Controller ignores the Authentication-Info header that comes in the 200OK response after digest authentication is complete. The Oracle Communications Session Border Controller receives a 401/407 response from the client. However, some surrogate-agents may process the Authentication-Info header in a single challenge.

Digest Authentication and High Availability

The Oracle Communications Session Border Controller supports digest authentication in high availability (HA) environments. The session-agent configuration, which includes the digest authentication parameters on the primary Oracle Communications Session Border Controller, are replicated on the HA Oracle Communications Session Border Controller. However, cached credentials on the primary device are not replicated on the HA device.