26-07-2012, 02:45 PM
Public Key Cryptography and RSA
Chapter 9 Public Key Cryptography and RSA.pdf (Size: 376.86 KB / Downloads: 260)
Principles of Public Key cryptosystems
Private-Key Cryptography
traditional private/secret/single key cryptography
uses one key
shared by both sender and receiver
if this key is disclosed communications are
compromised
also is symmetric, parties are equal
hence does not protect sender from receiver forging
a message & claiming is sent by sender.
Why Public-Key Cryptography?
developed to address two key issues:
key distribution – how to have secure
communications in general without having to trust a
KDC with your key
digital signatures – how to verify a message comes
intact from the claimed sender
public invention due to Whitfield Diffie & Martin
Hellman at Stanford Uni in 1976
known earlier in classified community
The RSA Algorithm
by Rivest, Shamir & Adleman of MIT in 1977
best known & widely used public-key scheme
based on exponentiation in a finite (Galois) field
over integers modulo a prime
nb. exponentiation takes O((log n)3) operations
(easy)
uses large integers (eg. 1024 bits)
security due to cost of factoring large numbers
nb. factorization takes O(e log n log log n) operations
(hard) .