24-01-2012, 03:06 PM
Key Exchange Protocols
[attachment=16529]
Basic Concepts in Cryptography
Encryption scheme:
functions to encrypt, decrypt data
key generation algorithm
Secret key vs. public key
Public key: publishing key does not reveal key-1
Secret key: more efficient, generally key = key-1
Hash function, MAC
Map input to short hash; ideally, no collisions
MAC (keyed hash) used for message integrity
Signature scheme
Functions to sign data, verify signature
What is a “secure” cryptosystem?
One idea
If enemy intercepts ciphertext, cannot recover plaintext
Issues in making this precise
What else might your enemy know?
The kind of encryption function you are using
Some plaintext-ciphertext pairs from last year
Some information about how you choose keys
What do we mean by “cannot recover plaintext” ?
Ciphertext contains no information about plaintext
No efficient computation could make a reasonable guess
Cannot use ciphertext for any nontrivial purpose
[attachment=16529]
Basic Concepts in Cryptography
Encryption scheme:
functions to encrypt, decrypt data
key generation algorithm
Secret key vs. public key
Public key: publishing key does not reveal key-1
Secret key: more efficient, generally key = key-1
Hash function, MAC
Map input to short hash; ideally, no collisions
MAC (keyed hash) used for message integrity
Signature scheme
Functions to sign data, verify signature
What is a “secure” cryptosystem?
One idea
If enemy intercepts ciphertext, cannot recover plaintext
Issues in making this precise
What else might your enemy know?
The kind of encryption function you are using
Some plaintext-ciphertext pairs from last year
Some information about how you choose keys
What do we mean by “cannot recover plaintext” ?
Ciphertext contains no information about plaintext
No efficient computation could make a reasonable guess
Cannot use ciphertext for any nontrivial purpose