Cryptographic Hash Functions Message Authentication Digital Signatures

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Cryptographic Hash FunctionsMessage
AuthenticationDigital Signatures
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Abstract

• We will discuss
• Cryptographic hash functions
• Message authentication codes
• HMAC and CBC-MAC
• Digital signatures

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Encryption/Decryption

• Provides message confidentiality.
• Does it provide message authentication?

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• Collision-resistant hash functions can be built
  from collision-resistant compression functions
  using Merkle-Damgard construction.

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Merkle-Damgard Construction
m1 m2 m3
mk
v0 v1 v2
vk
h(m)

f
f
f
f
IV
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m m1 m2 m3
ms
X hk(m)

h(m)
f
f
k X
f
f
IV
ms1
f
hk(m) hk(mms1)
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Cipher Block Chaining (CBC)
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Message m MACk(m)
Message m Sigpr(m)
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Encryption (using RSA)
Bob
Alice
PUBob
PRBob
M
C
E
D
M
Digital signature (using RSA-1)
Bob
Alice
PUBob
PRBob
E(S) M?
M
S
E
D
Verify Sign
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