Lecture Notes: HMAC (Hash-based Message Authentication Code) What is HMAC? HMAC is a cryptographic function used to verify the integrity and authenticity of a message. It combines a cryptographic hash function (such as SHA-256) with a secret key to create a message authentication code (MAC). How HMAC Works 1. Key Generation: A shared secret key is generated and distributed to both the sender and receiver. 2. Message Preparation: The message is padded to a specific length and combined with the secret key. 3. Hash Calculation: A cryptographic hash function is applied to the combined message and key. 4. MAC Generation: The resulting hash value is the MAC. 5. Transmission: The message and the MAC are transmitted to the receiver. 6. MAC Verification: The receiver calculates a MAC value for the received message using the same key and algorithm. 7. Comparison: If the calculated MAC value matches the received MAC value, the message is considered authentic and has not been modified. Advantages of HMAC ● Security: HMAC is considered a secure MAC algorithm, providing strong protection against message modification and forgery. ● Efficiency: HMAC is relatively efficient to compute, making it suitable for various applications. ● Flexibility: HMAC can be used with different cryptographic hash functions, such as SHA-1, SHA-256, and SHA-512. ● Widely Used: HMAC is widely used in various cryptographic protocols, such as IPsec, TLS, and SSH. Disadvantages of HMAC ● Shared Secret Key: The shared secret key must be securely distributed to both the sender and receiver. ● Limited Non-Repudiation: HMAC does not provide non-repudiation, meaning that the sender can deny sending the message. Applications of HMAC ● Message Integrity: HMAC is used to verify the integrity of messages, ensuring that they have not been modified during transmission. ● Authentication: HMAC can be used to authenticate the sender of a message. ● Secure Protocols: HMAC is used in various secure protocols, such as IPsec, TLS, and SSH. Conclusion HMAC is a powerful and widely used message authentication code that provides strong security for digital communications. By understanding the principles of HMAC, organizations can protect their sensitive information and prevent unauthorized access or modifications.