When you configure NTP you can have multiple keys configured on the device. For instance say you have three NTP servers that you want to authenticate with, however, each server has a different authentication key. In that case the key ID would be a key component because it will be referenced in the configuration for each of those server. Here is an example:
ntp authentication-key 1 md5 password-one
ntp authentication-key 2 md5 password-two
ntp authentication-key 3 md5 password-three
ntp server 1.1.1.1 key 1
ntp server 2.2.2.2 key 2
ntp server 3.3.3.3 key 3
However, if you have multiple keys configured on the device and all the NTP servers use the same key, in that case you can just configure the NTP trusted key without specifying the key ID for each server similar to this, let's say you want to use key ID 2 for all of them:
ntp trusted-key 2
ntp server 2.2.2.2
ntp server 3.3.3.3
Finally, the value you add after the "md5" keyword is text that will then be converted into an MD5 hash value, so you don't have to put the already converted hash value, the device will use the value you type as a seed attribute for MD5 hash. It is different than when you configure a password on the device and you select the encryption type, in that case you would need to insert the encrypted value rather than the clear text password.
