3.1. Generating a Message

This section describes the behavior of a SNMPv2 entity when it acts as a SNMPv2 party for which the authentication protocol is administratively specified as the Digest Authentication Protocol. Insofar as the behavior of a SNMPv2 entity when transmitting protocol messages is defined generically in [1], only those aspects of that behavior that are specific to the Digest Authentication Protocol are described below. In particular, this section describes the encapsulation of a SNMPv2 management communication into a SNMPv2 authenticated management communication.

According to Section 3.1 of [1], a SnmpAuthMsg value is constructed during Step 3 of generic processing. In particular, it states the authInfo component is constructed according to the authentication protocol identified for the SNMPv2 party originating the message. When the relevant authentication protocol is the Digest Authentication Protocol, the procedure performed by a SNMPv2 entity whenever a management communication is to be transmitted by a SNMPv2 party is as follows.

1. The local database is consulted to determine the authentication clock and private authentication key (extracted, for example, according to the conventions defined in Section 1.5.1) of the SNMPv2 party originating the message. The local database is also consulted to determine the authentication clock of the receiving SNMPv2 party.

2. The authSrcTimestamp component is set to the retrieved authentication clock value of the message's source. The authDstTimestamp component is set to the retrieved authentication clock value of the message's intended recipient.

3. The authentication digest is temporarily set to the private authentication key of the SNMPv2 party originating the message. The SnmpAuthMsg value is serialized according to the conventions of [13] and [12]. A digest is computed over the octet sequence representing that serialized value using, for example, the algorithm specified in Section 1.5.1. The authDigest component is set to the computed digest value.

As set forth in [1], the SnmpAuthMsg value is then encapsulated according to the appropriate privacy protocol into a SnmpPrivMsg value. This latter value is then serialized and transmitted to the receiving SNMPv2 party.