HMAC (Hash Message Authentication Code) is a message authentication code that uses a cryptographic hash function in combination with a secret key to verify both the data integrity and the authenticity of a message. It allows for two parties sharing a secret key to authenticate messages using a hash function. The security of HMAC relies on the underlying hash algorithm and is more secure than simply using MD5 against birthday attacks due to its use of a cryptographic key.

1. HMAC
Hash Message
Authentication
Code
By
V.Saranraj B.E

2. H-mac:
Introduction
Objectives for H-mac
H-mac algorithm
Example
H-mac security
Example

3. Introduction:
 The IP authentication scheme uses a called
Hash Message Authentication Codes (HMAC).
 If H-mac is an encrypted message in RFC
1024.
 HMAC uses a shared key between two parties
rather than public key methods for message
authentication.

4. Objectives for HMAC:
 To use, without modifications, available hash
function.
 To allow for easy replaceability.
 To hash function in case faster , more secure
the hash function.
 To use and handle keys in a simple way.

5. HMAC security:
1. The security of HMAC relates to that of the
underlying hash algorithm.
2. Attacking HMAC :
Brute-force attack on key used.
Birthday attack is an observe a
very large number of message. Choose hash
function used based on speed versus security
constraints.
Note that HMAC is more secure than MD5 for
birthday attack.