Whirpool page 15.pdf - Chapter 6 New HASH Function 6.1 Message Authentication Message authentication is a mechanism or service used for verifying the

Whirpool page 15.pdf - Chapter 6 New HASH Function 6.1...

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Chapter 6 New HASH Function 6.1 Message Authentication Message authentication is a mechanism or service used for verifying the integrity of a message. Message authentication assures that the data received are exactly as sent by i.e., contain no modification, insertion, deletion, or replay and that the purported identity of the sender is valid. Symmetric encryption provides authentication among those who share the secret key. Encryption of a message by a sender’s private key also provides a form of authentication. The two most common cryptographic techniques for message au- thentication are a message authentication code (MAC) and secure hash function. A MAC is an algorithm that requires the use of a secret key. A MAC takes a variable length message and a secret key as input and produces an authentication code . A recipient in possession of the secret key can generate an authentication code to verify the integrity of the message. A hash function maps a 110
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variable length message into a fixed length hash value, or message digest. For message authentication, a secure hash function must be combined in some fashion with a secret key. 6.1.1 Authentication Requirements In the context of communication across a network, the following attacks can be identified: Disclosure: Release of message contents to any person or pro- cess not processing the appropriate cryptographic key. Traffic analysis: Discovery of the pattern of traffic between parties. In a connection-oriented application, the frequency and duration of connections could be determined. In either a connected-oriented or connectionless environment, the num- ber and length of the messages between the parties could be determined. Masquerade: 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. Also included are fraudulent acknowledgments of mes- sage receipt or non receipt by someone other than the message recipient. Content modification: changes to the contents of a message, 111
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including insertion, deletion, transposition, and modification. Sequence modification: Any modification to a sequence of messages between parties, including insertion, deletion, and recording. Timing modification: Delay or replay of messages. In a connection- oriented application, an entire session or sequence of messages could be a replay of some previous valid session, or individual messages in the sequence could be delayed or replayed. In a connectionless application, an individual message could be delayed or replayed. Source repudiation: Denial of transmission of message by source. Destination repudiation: Denial of receipt of message by des- tination.
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