Recommandé
Contenu connexe
Tendances
Tendances (20)
Similaire à Message authentication code_course_bouchra_echandouri
Similaire à Message authentication code_course_bouchra_echandouri (20)
Dernier
Dernier (20)
Message authentication code_course_bouchra_echandouri
- 1. **** Message Authentication Code course Bouchra ECHANDOURI b.echandouri@gmail.com January 31, 2018
- 2. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Outline 1 Introduction Security Properties/Goals Cryptographic Primitive 2 Message Authentication Codes Description Construction 3 Cipher based Message Authentication Codes Symmetric Encryption Construction 4 Hash based Message Authentication Codes Hash function Construction 5 Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Bouchra ECHANDOURI Message Authentication Code January 31, 2018 2/26
- 3. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Introduction • Private data transmission over arbitrary canal is considered very risky. • the need for designing robust cryptographic solutions ensuring both data integrity and authentication is very attempting. • Message Authentication Code (MAC) is one of the most provably secure algorithms that ensure authenticity. • Using a shared secret key, the receiver checks if an alteration have happened during transmission. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 3/26
- 4. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Properties/Goals Availability ⇒ Any authorized entity can get access to data at any time. Confidentiality ⇒ Only authorized entities to acces to the data can understand it (ensured using Secret and Public key Encryption). Integrity ⇒ Only authorized entities to acces to the data can modify it(ensured using Hash function). ⇒ Authenticity:Only authorized entities to acces to the data can modify it using a secret key (ensured using Message Authentication Codes and Digital signature). Bouchra ECHANDOURI Message Authentication Code January 31, 2018 4/26
- 5. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Properties/Goals Sometimes we are not worried so much about secrecy, but our need is to be assured that we have received exactly the data being sent from the right sender. The cryptographic primitive that we use for this is a Message Authentication Code (MAC) Bouchra ECHANDOURI Message Authentication Code January 31, 2018 5/26
- 6. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cryptographic Primitive Bouchra ECHANDOURI Message Authentication Code January 31, 2018 6/26
- 7. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Message Authentication Codes Description Definition A Message Authentication Code (MAC) is a secret key algorithm that involves the use of a secret key k and two algorithms namely a MAC generation algorithm MACGk and a MAC verification algorithm MACVk . Bouchra ECHANDOURI Message Authentication Code January 31, 2018 7/26
- 8. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Message Authentication Codes Description The MACGk algorithm takes an arbitrary message M, a secret key k and generates a unique fixed length termed Tag or checksum, the generated tag is joined to the message M to construct an authenticated message. Tag = MACGk (M) (1) Bouchra ECHANDOURI Message Authentication Code January 31, 2018 8/26
- 9. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Message Authentication Codes Description TheMACVk algorithm uses the same key k and the message M to reconstruct the valid Tag if no alteration has affected the message, otherwise it is invalid and has been altered. MACVk (M, tag) = {valid, invalid} (2) Bouchra ECHANDOURI Message Authentication Code January 31, 2018 9/26
- 10. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Message Authentication Codes Construction To conceive a MAC there are many ways, using on a keyed hash function Using a symmetric encryption algorithm, namely block cipher-based message authentication code (CMAC) and Cipher Block Chaining message authentication code (CBC-MAC). Bouchra ECHANDOURI Message Authentication Code January 31, 2018 10/26
- 11. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cipher based Message Authentication Codes Symmetric Encryption The symmetric encryption scheme has: Plaintext (Data): This is the original data that is aimed to be unintelligible, inputted to the algorithm. Encryption algorithm: This performs a number of substitutions and permutations on the plaintext. Secret Key: This is a conventional key also inputted to the encryption algorithm. The substitutions and permutations that is performed depend on the used secret key. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 11/26
- 12. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cipher based Message Authentication Codes Symmetric Encryption Ciphertext: This is the encrypted data produced as output, to make it unintelligible for authorized entities. It depends on the plaintext and the key. Decryption Algorithm: This algorithm is the encryption algorithm run in reverse. It takes the ciphertext and the secret key to produce the original plaintext. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 12/26
- 13. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cipher based Message Authentication Codes Symmetric Encryption Block cipher are Symmetric encryption schemes that split the plaintext in blocks of fixed lenght L bits and encrypt one block at one time. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 13/26
- 14. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cipher based Message Authentication Codes Symmetric Encryption in Block cipher there exist : Cipher Block Chaining (CBC): In 1976, Ehrsam, Meyer, Smith and Tuchman introduced the Cipher Block Chaining (CBC) mode of operation. In this mode,an initialization vector must be used in the first block. Then, each block of plaintext is XORed with the previous ciphertext block before being encrypted. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 14/26
- 15. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cipher based Message Authentication Codes Symmetric Encryption Stream cipher are Symmetric encryption schemes that encrypt bits individually. This is achieved by adding a bit from a key stream to a plaintext bit. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 15/26
- 16. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Cipher based Message Authentication Codes Construction Bouchra ECHANDOURI Message Authentication Code January 31, 2018 16/26
- 17. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Hash based Message Authentication Codes Hash function Definition Hash function is one way transformation of any input, with arbitrary length, to a fixed size length output, called digest or checksum. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 17/26
- 18. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Hash based Message Authentication Codes Hash function A Hash function with inputs m, m’ and outputs h, h’ , follows these properties: Pre-image resistance: It is computationally unfeasible to find any input m from any fixed output h. 2nd-preimage resistance: It is computationally unfeasible to find any second input m’ that has the same output h=h’ as any fixed m. Collision resistance: It is computationally unfeasible to find two distinct inputs m and m’ with the same output h=h’. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 18/26
- 19. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Hash based Message Authentication Codes Construction Bouchra ECHANDOURI Message Authentication Code January 31, 2018 19/26
- 20. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Hash based Message Authentication Codes HMAC K is the key padded (with 0) to B bytes, the input block size of the hash function ipad = the byte 0x36 repeated B times opad = the byte 0x5C repeated B times. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 20/26
- 21. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Requirements on a MAC A Secure Message Authentication Codes, termed MAC(.,.), that maps a key k and a message m is secure if it fulfills these required properties. Given k and m, it is easy to generate MAC(k, m); Given k and MAC( k,m), it is computationally unfeasible to find m; Given k it is computationally unfeasible to find two different values m and m’ such that MAC(k,m) =MAC(k,m’); Given (possibly many) pairs of m and MAC( k, m), it is computationally unfeasible to compute k; Without a prior knowledge of k, it is computationally unfeasible to compute MAC(k, m) for any m. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 21/26
- 22. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Requirements on a MAC Robustness to Key Recovery Attack MAC algorithm can be attacked given knowledge of one known (Data/Tag) pair (assuming that the length of data is upper than the key length). The attacker simply recomputes the Tag on the Data with every possible key, until the key is found giving the correct MAC. ⇒ This attack has complexity 2k (k is the key length), which is feasible if k is sufficiently small. Bouchra ECHANDOURI Message Authentication Code January 31, 2018 22/26
- 23. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Requirements on a MAC Robustness to Key Recovery Attack Examples of key recovery attack : Brute force on the key space. Exhaustive key research Bouchra ECHANDOURI Message Authentication Code January 31, 2018 23/26
- 24. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Requirements on a MAC Robustness to MAC Forgery Attack Forgery attack is the most known attack on MACs function, where the malicious entity can provide at least a valid (Data/Tag) pair without holding the secret key Existential Forgery Attack: compute a valid Tag for a random Data Universal Forgery Attack: compute a valid Tag for any given Data Bouchra ECHANDOURI Message Authentication Code January 31, 2018 24/26
- 25. Introduction Security Properties/Goals Cryptographic Primitive Message Authentication Codes Description Construction Cipher based Message Authentication Codes Symmetric Encryption Construction Hash based Message Authentication Codes Hash function Construction Security Requirements on a MAC Key Recovery Attack MAC Forgery Attack Security Requirements on a MAC Robustness to MAC Forgery Attack Example of MAC Forgery Attack : Birthday attack : based on the frequency of collisions.It is a type of forgery attack on MACs that proves the maximum limit on their security, especially to those based on iterative hash functions. This attack requires using about 2n/2 Data/Tag known pairs (i.e. n as the Tag length) Bouchra ECHANDOURI Message Authentication Code January 31, 2018 25/26
- 26. Thank You