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What are the various ways in which message authentication can be done?

Marks: 10 M

Year: Dec 2013

1. Message authentication is a mechanism or service used to verify the integrity of a message.
2. Message authentication assures that data received is exactly same as sent by the transmitter ( i.e contains no modification, insertion, detection or replay )

3. The following attacks can be identifies :

   a) Disclosure :Release of message contents to any person or process not processing the appropriate cryptographic key.

   b) Traffic Analysis: Discovery of pattern of traffic between parties.

   c) Masquerede: Insertion of messages into the network from a fraudulent source. This includes the creation of messages by an opponent that are purported to come from an authorized entity.

   d) Content Modification : Changes made to the content of a message including insertion , detection etc.

   e) Sequence Modification: Any modification to the sequence of messages.

   f) Timing Modification: Delay or replay of a message.

   g) Source Reproduction: Denial of transmission of message by source.

   h) Destination Reputation: Denial of receipt of message by destination

4. Measures to deal with:

   • Disclosure, Traffic Analysis : Message confidentiality
   • Masquerade, Content Modification, Sequence Modification, Timing Modification : Message Authentication
   • Source Reproduction: Need of digital signature.
   • Destination Reputation: Protocol designed to counter the attack.

5. Authentication Function:

   A message authentication has two levels of functionality

   At lower level: Authenticator (A value to be used to authenticate the message)

   At higher level: Authentication Protocol

   (Enables receiver to verify the authenticity of a message)

6. The types of functions that may be used to produce an authentication are:

   • Message encryption: The ciphertext of the entire message serves as authentication.
   • Message Authentication Code (MAC): A secret key of fixed length value that serves as the authenticator.
   • Hash Function: A function that maps the message of any length into a fixed length hash value which serves as the authenticator.

   • Message Encryption:

     a) Symmetric Encryption: Confidentiality and authentication

$$\text{Figure 5.12.a Symmetric Encryption}$$

• Key k is shared by A and B.
• No other party knows the key

• B is assured that message has come from A -> A is the only other party that is having k.

  b) Public key encryption: Confidentiality



$$\text{Figure 5.12.bPublic Key encryption}$$

• No authentication because any opponent could also use B’s public key to encrypt a message claiming to be from A.

  c) Public Key encryption ( Authentication and Signature)



$$\text{Figure 5.12.c Public Key encryption}$$

• Does not provide confidentiality because anyone in possession of A’s public key can decrypt the ciphertext.

  d) Public key encryption : Confidentiality , authentication and signature



$$\text{Figure 5.12.d Public key encryption}$$