Any other concerns? Truncation attack! MacK(m1,…, □ □−1 )= □ 1 ,…, □ □−1īuilding Block Π’=(Mac’,Vrfy’), a secure MAC for length n messages Attempt 3 Let m = m1,…,md where each mi is n bits and m has length ℓ=□□ Let □ □ = Mac □ ′ □ ∥ℓ∥□ □ MacK(m)= □ 1 ,…, □ □ Addresses truncation. Limitation: What if we want to authenticate a longer message?īuilding Block Π’=(Mac’,Vrfy’), a secure MAC for length n messages First: A few failed attempts Let m = m1,…,md where each mi is n bits and let □ □ = Mac □ ′ □ □ MacK(m)= □ 1 ,…, □ □ What is wrong? Block-reordering attack MacK(md,…, □ 1 )= □ □ ,…, □ 1īuilding Block Π’=(Mac’,Vrfy’), a secure MAC for length n messages Attempt 2 Let m = m1,…,md where each mi is n bits and let □ □ = Mac □ ′ □ ∥□ □ MacK(m)= □ 1 ,…, □ □ Addresses block-reordering attack. Mack (□) =FK(□) Vrfyk (□,□) = 1 if □=FK(□) 0 otherwise Theorem 4.6: If F is a PRF then this is a secure (fixed-length) MAC for messages of length n. Run PPT Macforge adversary A When adversary queries with message m, respond with O(m) Output 1 if attacker wins (otherwise 0) If O = f then Pr □□ 1□ =1 =Pr Macforge □, Π □ =1 ≤ 2 −□ If O=FK then Pr □□ 1□ =1 =Pr Macforge □,Π □ =1 >□(□) Proof: Start with attacker who breaks MAC security and build an attacker who breaks PRF security (contradiction!) Sufficient to start with attacker who breaks regular MAC security (why?)Ĩ Breaking MAC Security ( Macforge □,Π (□)) ![]() ![]() Simply uses a secure PRF F Mack (□) =FK(□) Canonical Verification Algorithm… Vrfyk (□,□) = 1 if □=FK(□) 0 otherwise There are dozens of plugins to discover and you can even create your own.Presentation on theme: "Topic 10: Constructing Message Authentication Codes"- Presentation transcript:ġ Topic 10: Constructing Message Authentication CodesĬryptography CS 555 Topic 10: Constructing Message Authentication CodesĢ Reminder: Homework 1 Due on Friday (next class) at the beginning of class Please typeset your solutionsģ Recap Data Integrity Message Authentication Codes Side-Channel Attacksīuild Secure MACs Today’s Goals: Build a Secure MAC Key tool in Construction of CCA-Secure Encryption Schemes Construct CCA-Secure Encryption Schemeĭefinition 4.1: A message authentication code (MAC) consists of three algorithms Π= Gen, Mac, Vrfy Gen ( 1 □ □) (Key-generation algorithm) Input: security parameter 1n (unary) and random bits R Output: Secret key k∈□ Mack (□ □) (Tag Generation algorithm) Input: Secret key k∈□ and message m∈ℳ and random bits R Output: a tag t Vrfyk (□,□) (Verification algorithm) Input: Secret key k∈□, a message m and a tag t Output: a bit b (b=1 means “valid” and b=0 means “invalid”) Vrfyk (□, Mack (□ □) ) =1ĥ Strong MAC Authentication ( Macsforge □,Π (□)) MacForge lets you discover and manage awesome plugins to enhance your macOS experience. Choose Software Update from the Apple menu to update Apple software and anything downloaded from the Mac App Store for anything else, use the app’s built-in software update feature or download. When you delete a bad preference file, the Mac creates a new plist file that contains all the app's defaults automatically. Plist files can become corrupt when a Mac shuts down or restarts unexpectedly or when an app freezes or crashes. The alerts started appearing in early April 2018. ![]() Mac users have been seeing warnings, stating that a app ‘is not optimized for your Mac’ for years now.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |