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5. message authentication and hash function
1) Message authentication can be achieved through message encryption, message authentication codes (MACs), or hash functions. 2) MACs provide authentication by appending a fixed-size block that depends on the message and a secret key. Receivers can verify messages by recomputing the MAC. 3) Hash functions map variable-length data to fixed-length outputs and are easy to compute but infeasible to reverse or find collisions. Common hash functions include MD5 and SHA-512.
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Introduction to message authentication and hash functions as essential tools for ensuring data integrity.
Identification of various network attack types impacting message security, including authentication and modification threats.
Overview of three alternatives for message authentication: encryption, MACs, and hash functions.
How symmetric encryption provides message authenticity and sender authentication using shared keys.
Discussion on public-key encryption and its limitations for sender authentication, along with signing methods.
Introduction to MAC, its dependence on message and secret key, and its role as a message signature.
Details on MAC functionalities, its ability to provide authentication, and considerations for encryption.
Technical characteristics of MAC, including its many-to-one function and difficulty in finding collisions.
Essential requirements for MAC to ensure security and unpredictability for given messages.
MAC’s role in relation to overall message authentication mechanisms.
Exploration of how authentication relates to both plaintext and ciphertext in encrypted messages.
Application of symmetric ciphers for generating MACs using block chaining modes and notable algorithms.
Definition of hash functions as algorithms mapping variable data sizes to fixed lengths for data integrity.
Key features of hash functions, including their feasibility constraints and secure output characteristics.
Overview of the MD5 hashing algorithm, its block processing, and structure for generating hashes.
Explanation of MD5 operations including logical functions, bit rotations, and modular calculations.
Overview of SHA-512 cryptographic hash function specifications, including message size and digest.
Summary of processing steps in SHA-512, including padding and initialization of the hash buffer.
Description of padding techniques used in SHA-512 to ensure correct input block sizes.
Details on appending length to the hash input to secure original message integrity.
Initialization processes for SHA-512 used to hold intermediate and final hashing values.
Handling of message blocks in SHA-512, explaining its iterative rounds and updating mechanism.
Description of preparing input sequences for processing single message blocks in SHA-512.
Understanding conditional functions within SHA-512 for input processing based on majority logic.
Introduction to HMAC (Hash-based Message Authentication Code) for verifying data integrity.
Expansion on HMAC’s functionality, including its dependence on underlying hash functions like SHA and MD5.
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5. message authentication and hash function
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- 2. Authentication Requirement Disclosure TrafficAnalysis Masquerade Content Modification Sequence Modification Timing Modification Source Repudiation Destination Repudiation Attacks in the Network
- 3. Message Authentication Three AlternativeFunctions used Message Encryption Message Authentication Code (MAC) Hash Function
- 4. Message Encryption Provides MessageAuthentication Symmetric Encryption Receiver know sender must have created it, since only sender and receiver now key used Provides both: sender authentication and message authenticity.
- 5. Message Encryption Provides MessageAuthentication Public-Key Encryption Encryption provides no confidence of sender, since anyone potentially knows public-key. however if sender signs message using his private-key then encrypts with recipients public key have both secrecy and authentication but at cost of two public-key uses on message
- 6. Message Authentication Code Asmall fixed-sized block of data Depends on both message and a secret key like encryption though need not be reversible. Appended to message as a signature Receiver performs same computation on message and checks with the MAC Provides assurance that message is unaltered and comes from sender
- 7. Message Authentication Code MACprovides Authentication Message can be encrypted for secrecy Generally use separate keys for each Can compute MAC either before or after encryption, Generally regarded as better done before why use a MAC? sometimes only authentication is needed Note that a MAC is not a Digital Signature
- 8. Message Authentication Code MACProperties A MAC is a cryptographic checksum MAC = CK(M) C is a function M is a variable-length message K is a secret key Many-to-One function potentially many messages have same MAC but finding these needs to be very difficult
- 9. Message Authentication Code Requirementsfor MAC MAC needs to satisfy the following: Knowing a message and MAC, is infeasible to find another message with same MAC MAC should depend equally on all bits of the message
- 10. Message Authentication Code MessageAuthentication
- 11. Message Authentication Code MessageAuthentication and Confidentiality Authentication tied to Plaintext
- 12. Message Authentication Code MessageAuthentication and Confidentiality Authentication tied to Ciphertext
- 13. Message Authentication Code UsingSymmetric Ciphers for MACs can use any cipher block chaining mode and use final block as a MAC Data Authentication Algorithm (DAA) is a widely used MAC based on DES-CBC using IV=0 and zero-pad of final block encrypt message using DES in CBC mode and send just the final block as the MAC or the leftmost M bits (16≤M≤64) of final block
- 14. Message Authentication Code UsingSymmetric Ciphers for MACs
- 15. Hash Function A hashfunction is any algorithm that maps variable length data to fixed length data.
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- 17. Hash Function • Canbe applied to any size message M • Produces a fixed-length output h • Easy to compute h=H(M) for any message M • Given h is infeasible to find x s.t. H(x)=h • Given x is infeasible to find y s.t. H(y)=H(x) • infeasible to find any x,y s.t. H(y)=H(x) Requirements for Hash Functions
- 18. Hash Function MD5 Algorithm Theinput message is broken up into chunks of 512-bit blocks (sixteen 32 bit words). The message is padded so that its length is divisible by 512 Grouped into four Round (each round process four 32 bit words)
- 19. Hash Function MD5 Algorithm 32bit denote the XOR, AND, OR and NOT operations Mi denotes a 32-bit block of the message input Ki denotes a 32-bit constant denotes a left bit rotation by s places denotes addition modulo 232
- 20. SECURE HASH ALGORITHM SHA512 Message size : < 2128 Message Digest Size : 512 Block Size : 1024
- 21. SECURE HASH ALGORITHM Step1: Append padding bits Step 2: Append Length Step 3: Initialize HASH buffer Step 4: Process message in 1024 bit Blocks Step 5: Output
- 22. SECURE HASH ALGORITHM Step1: Append padding bits The message is padded so that length ≡ 896 (mod 1024) padding is always added consist of single 1-bit followed by necessary number of 0-bits
- 23. SECURE HASH ALGORITHM Step2:Append Length a block of 128 bits is appended treated as unsigned 128-bit integer contains the length of original message
- 24. SECURE HASH ALGORITHM Step3:Initialize hash buffer hold intermediate values and final result size: 512 bit
- 25. SECURE HASH ALGORITHM Step4:Process message in 1024-bit block Consists 80 rounds updating a 512-bit buffer using a 64-bit value Wt derived from the current message block and a round constant based on cube root of first 80 prime numbers
- 26. SECURE HASH ALGORITHM Step4:Process message in 1024-bit block Step 5:Output
- 27. SECURE HASH ALGORITHM Creationof 80-word Input Sequence for SHA-512 Processing of Single Block
- 28. SECURE HASH ALGORITHM Ch(e,f,g)= If e then f else g Maj(a, b, c) = TRUE if majority of a, b, c is TRUE Wt = 64 bit word Kt = 64 bit additive constant
- 29. HMAC • Stands forHash-based Message Authentication Code • It used to verify data integrity and authenticity of a message • It uses current cryptographic hash functions with a secret key (SHA or MD5) The name of the function changes depending on what hash function you use MD5 would result to HMAC-MD5 SHA# would result to HMAC-SHA#
- 30. HMAC • Stands forHash-based Message Authentication Code • It used to verify data integrity and authenticity of a message • It uses current cryptographic hash functions with a secret key (SHA or MD5) The name of the function changes depending on what hash function you use MD5 would result to HMAC-MD5 SHA# would result to HMAC-SHA#