Command ip ospf authentication key 1 is implemented in which level.

A.
Interface

B.
process

C.
global

D.
enable

Explanation:
BD
Use the ip ospf authentication-key interface command to specify this password. If you enable MD5
authentication with the message-digest keyword, you must configure a password with the ip ospf messagedigest-key interface command.
interface GigabitEthernet0/1
ip address 192.168.10.1 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 CCNA
Source: Cisco Official Certification Guide, Implement Routing Update Authentication on OSPF, p.348
The OSPFv2 Cryptographic Authentication feature allows you to configure a key chain on the OSPF interface to
authenticate OSPFv2 packets by using HMAC-SHA algorithms. You can use an existing key chain that is being
used by another protocol, or you can create a key chain specifically for OSPFv2.
If OSPFv2 is configured to use a key chain, all MD5 keys that were previously configured using the ip ospf
message-digest-key command are ignored.
Device> enable
Device# configure terminal
Device(config)# interface GigabitEthernet0/0/0
Device (config-if)# ip ospf authentication key-chain sample1
Device (config-if)# end
Source: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-3s/iro-xe-3s-book/iroospfv2-crypto-authen-xe.htmlIn both cases OSPF and OSPFv1 the ip ospf authentication is inserted at interface level