crypto-refresher

# crypto-refresher - Lecture 13 Crypto-Refresher Adrian...

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1 Lecture 13 ½ Crypto-Refresher Adrian Perrig Spring 2009 Basic Cryptographic Primitives Asymmetric (public-private key) Diffie-Hellman key agreement Public-key encryption Digital signature Others (unkeyed symmetric) One-way function Cryptographic hash function Symmetric (shared-key, same-key) Block cipher (pseudo-random permutation PRP) Stream cipher (pseudo-random generators PRG) Message authentication code (MAC)

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2 Asymmetric Primitives Diffie-Hellman key agreement Public values: large prime p, generator g Alice has secret value a, Bob has secret b A B: g a (mod p) B A: g b (mod p) Bob computes (g a ) b = g ab (mod p) Alice computes (g b ) a = g ab (mod p) Eve cannot compute g ab (mod p) Asymmetric Primitives II Problem: man-in-the-middle attack Mallory can impersonate Alice to Bob, Bob to Alice A M: g a (mod p) M A: g m (mod p) M B: g m (mod p) B M: g b (mod p) Bob computes (g m ) b = g bm (mod p) Alice computes (g m ) a = g am (mod p)
3 EKE DH Protocol K = H( P ), A picks random a, B picks random b 1: A B: { g a } K K’ = H( g ab ) 2: B A: { g b } K , { N B } K’ 3: A B: { N A , N B } K’ 4: B A: { N A } K’ Dictionary attacks??? Difference between Authentication and Signature Authentication enables the receiver to verify origin, but receiver cannot convince a third party of origin Signature enables the receiver to verify origin, and receiver can convince third party of origin as well Signature provides authentication

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4 Cryptographic Hash Functions Maps arbitrary-length input into finite length output
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crypto-refresher - Lecture 13 Crypto-Refresher Adrian...

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