MACs based on Hash Functions, MACs based on Block Ciphers
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This document discusses message authentication codes (MACs) based on hash functions and block ciphers. It describes Hash-based MACs (HMAC) which uses a cryptographic hash function combined with a secret key to authenticate messages. HMAC provides integrity and authentication using public/private keys. The document also covers MACs based on block ciphers, specifically the Data Authentication Algorithm (DAA) which is based on DES-CBC, and Cipher-based MAC (CMAC) which fixes security issues with CBC-MAC and can use existing encryption functions to resist attacks. CMAC chains the cipher and XORs the message blocks to generate the authentication tag.
![Data Authentication Algorithm
• Data Authentication Algorithm(DAA) is a widely used MAC based on DES-
CBC.
• Send final block as the MAC or the leftmost M bits (16≤M≤64) of final block.
• If necessary, the final block is padded on the right with zeroes to form a full
64-bit block.
O1 = E(K, D)
O2 = E(K, [D2 ⊕ O1])
O3 = E(K, [D3 ⊕ O2])
ON = E(K, [DN ⊕ ON-1])](https://image.slidesharecdn.com/insala1-181218162331/85/MACs-based-on-Hash-Functions-MACs-based-on-Block-Ciphers-9-320.jpg)
![CMAC
CMAC (Cipher-based Message Authentication Code) is a block cipher based
MAC algorithm. It may be used to provide assurance of the authenticity and,
hence, the integrity of binary data. This mode of operation fixes security
deficiencies of CBC-MAC .
C1 = E(K, M1) Where,
C2 = E(K, [M2 ⊕ C1] T = message authentication code, also
referred to as the tag
C3 = E(K, [M3 ⊕ C2]) Tlen = bit length of T
Cn = E(K, [Mn ⊕ Cn-1 ⊕K1])
MSBs(X) = the s leftmost bits of thebit string X
T = MSBTlen(Cn)](https://image.slidesharecdn.com/insala1-181218162331/85/MACs-based-on-Hash-Functions-MACs-based-on-Block-Ciphers-11-320.jpg)
MACs based on Hash Functions, MACs based on Block Ciphers
- 1. 1 VADODARA INSTITUTE OF ENGINEERING ACTIVE LEARNING ASSIGNMENT Presented By: Krishna Patel 150800107047 Maitree Patel 150800107048 Meet Patel 150800107049 : TOPIC :MACs based on Hash Functions, MACs based on Block Ciphers Information and Network Security (2170709)
- 2. Content: • Message Authentication • MACs based on Hash Functions • MACs based on Block Ciphers 1. Data Authentication Algorithm ( DAA ) 2. Cipher Based Message Authentication Codes ( CMAC )
- 3. • Message authentication is concerned with: Protecting the integrity of a message Validating identity of originator Non-repudiation of origin (dispute resolution) • Will consider the security requirements • Then three alternative functions used: Message encryption Message authentication code (MAC) Hash function Message Authentication
- 4. MACs based on Hash Functions • Hash-based message authentication code (HMAC) is a specific construction for calculating a message authentication code (MAC) involving a cryptographic hash function in combination with a secret cryptographic key. • As with any MAC, it may be used to simultaneously verify both the data integrity and the authentication of a message. • Any cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly. • The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output, and on the size and quality of the key.
- 5. MACs based on Hash Functions • Hash-based message authentication code (HMAC) provides the server and the client each with a public and private key. • The public key is known, but the private key is known only to that specific server and that specific client. • The client creates a unique HMAC, or hash, per request to the server by combing the request data and hashing that data, along with a private key and sending it as part of a request. • The server receives the request and regenerates its own unique HMAC. The server compares the two HMACs, and, if they're equal, the client is trusted and the request is executed. This process is often called a secret handshake.
- 7. MACs based on Hash Functions HMAC can be expressed as: where K = secret key; recommended length is ≥ n; if key length is greater than b-bit block, the key is input to the hash function to produce an n-bit key M = message input to HMAC, H = cryptographic hash function, K+ = K padded with zeros on the left so that the result is b bits in length, ∥= concatenation, opad = 01011100 (5C in hexadecimal) repeated b/8 times, ipad = 00110110 (36 in hexadecimal) repeated b/8 times
- 8. MACs based on Block Ciphers • We look at two MACs that are based on the use of a block cipher mode of operation. • Data Authentication Algorithm ( DAA ) • Cipher Based Message Authentication Codes ( CMAC )
- 9. Data Authentication Algorithm • Data Authentication Algorithm(DAA) is a widely used MAC based on DES- CBC. • Send final block as the MAC or the leftmost M bits (16≤M≤64) of final block. • If necessary, the final block is padded on the right with zeroes to form a full 64-bit block. O1 = E(K, D) O2 = E(K, [D2 ⊕ O1]) O3 = E(K, [D3 ⊕ O2]) ON = E(K, [DN ⊕ ON-1])
- 11. CMAC CMAC (Cipher-based Message Authentication Code) is a block cipher based MAC algorithm. It may be used to provide assurance of the authenticity and, hence, the integrity of binary data. This mode of operation fixes security deficiencies of CBC-MAC . C1 = E(K, M1) Where, C2 = E(K, [M2 ⊕ C1] T = message authentication code, also referred to as the tag C3 = E(K, [M3 ⊕ C2]) Tlen = bit length of T Cn = E(K, [Mn ⊕ Cn-1 ⊕K1]) MSBs(X) = the s leftmost bits of thebit string X T = MSBTlen(Cn)
- 12. CMAC
- 13. CMAC Advantages • Can use existing encryption functions. • Encryption functions have properties that resist pre image and collision attacks • Disadvantage • Encryption algorithms (particularly when chained) can be much slower than hash algorithms
- 15. Thank You
Editor's Notes
- #4: Up till now, have been concerned with protecting message content (ie secrecy) by encrypting the message. Will now consider how to protect message integrity (ie protection from modification), as well as confirming the identity of the sender. Generically this is the problem of message authentication, and in eCommerce applications is arguably more important than secrecy.