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This document discusses message authentication and the different methods used to authenticate messages: - Message authentication aims to protect message integrity and validate the identity of the sender. It addresses issues like masquerading, content modification, and repudiation. - Common methods for message authentication include hash functions, message encryption using a symmetric or public key, and message authentication codes (MACs). - A MAC uses a cryptographic function involving a secret key to map a message to a fixed-length authentication code. It ensures integrity and authenticates the sender.

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140 views17 pages

Yourppt

This document discusses message authentication and the different methods used to authenticate messages: - Message authentication aims to protect message integrity and validate the identity of the sender. It addresses issues like masquerading, content modification, and repudiation. - Common methods for message authentication include hash functions, message encryption using a symmetric or public key, and message authentication codes (MACs). - A MAC uses a cryptographic function involving a secret key to map a message to a fixed-length authentication code. It ensures integrity and authenticates the sender.

Uploaded by

ArpithaChaman
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPT, PDF, TXT or read online on Scribd
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Message Authentication

Also known as Data Origination authentication


Message digest guarantees the integrity of the
message

Message Authentication
Message authentication is concerned with:
protecting the integrity of a message
validating identity of originator
Will consider the security requirements
The three alternative functions used:
Hash function
Message encryption
Message authentication code (MAC)

Message Authentication Requirements


Disclosure
Traffic analysis
Masquerade
Content modification
Sequence modification
Timing modification
Source repudiation
Destination repudiation

Message Authentication Function


Functions used to produce an authenticator
Hash function: maps a message of any length into a
fixed length hash value
Message encryption:ciphertext of the entire message
serves as its authenticator
Message authentication code:A function of the
message and a secret key produces a fixed length
value

Hash Function

Maps a variable length message into fixed


length hash values or message digest

Hash function h=H(M)

used to detect any changes in the message

Data integrity is the main objective

Used in security applications

Block Diagram of Hash Function

Symmetric Message Encryption


encryption can also provides authentication
if symmetric encryption is used then:
receiver know sender must have created it
since only sender and receiver now key used
know content cannot of been altered

Internal and External Error Control

Public-Key Message Encryption


Public-key encryption is used:
encryption provides no confidence of sender
since anyone potentially knows public-key
however if
sender sends message using their private-key
then encrypts with recipients public key
have both secrecy and authentication
again need to recognize corrupted messages
but at cost of two public-key uses on message

Modification Detection code

It is a message digest that can prove the


integrity of the message.

Message authentication code

To ensure the integrity of the message and


data origin authentication

MAC Properties
MAC is a cryptographic checksum
T=MAC(K,M)
condenses a variable-length message M using a
secret key K to a fixed-sized authenticator
is a many-to-one function
potentially many messages have same MAC
but finding these needs to be very difficultt

Security of MACs
Three possible cases
If the size of keys allows a exhaustive search.
The size of the key is very large
Given some Pairs of messages and their macs.

Nested Mac

HMAC Design Objectives


Nist issued a standard (FIPS 198) for nested MAC
preserve original performance of hash function
without significant degradation
use and handle keys in a simple way.
have well understood cryptographic analysis of
authentication mechanism strength

HMAC

CMAC

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