When using SNMPv3 with NoAuthNoPriv, which string is matched for authentication?

When using SNMPv3 with NoAuthNoPriv, which string is matched for authentication?
A . username
B . password
C . community-string
D . encryption-key

Answer: A

Explanation:

The following security models exist: SNMPv1, SNMPv2, SNMPv3. The following security levels exits: “noAuthNoPriv” (no authentiation and no encryption C noauth keyword in CLI), “AuthNoPriv109thernet109ationre authenticated but not encrypted C auth keyword in CLI), “AuthPriv” (messages are authenticated and encrypted C priv keyword in CLI). SNMPv1 and SNMPv2 models only support the “noAuthNoPriv” model since they use plain community string to match the incoming packets. The SNMPv3 implementations could be configured to use either of the models on per-group basis (in case if “noAuthNoPriv” is configured, username serves as a replacement for community string).

Reference: http://blog.ine.com/2008/07/19/snmpv3-tutorial/