Index into the array of encryption keys. This index is 1-based. Possible values for this index are between 1 and 8, inclusive.
A 64-bit integer, in Little Endian byte order, that represents an encryption key.
The index of the encryption key is sent with every message sent from the sender to the receiver. Different encryption keys can be used for each message, as long as the keys of the sender and the receiver match.
For an example, refer to SetIsclMutualAuthenticationAlgorithm.