Authentication Function:
These can be classified in three
major categories –
i.
Message Encryption –
The
Cipher text of the entire message serves as its authenticator.
ii.
Message authentication code (MAC) –
A
public function of a message and a secret key that produces a fixed length
value which serves as its authenticator.
iii.
Hash Function –
A
public function that maps a message of any length into a fixed length hash
value which serve as the authenticator.
Message
authentication codes (MAC):
A MAC, which is also known as cryptographic checksum,
is generated by a function C of the form MAC = Ck
(M)
Where M is a variable length message
K is a secret key which is shared only by the sender
and receiver.
Ck (M) is the fixed length authenticator.
The MAC is appended to the message at the source at
the time when the message is assumed or known to be correct.
The receiver authenticates that message re computing
the MAC.
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