11-12-2012, 06:47 PM
Public Key Cryptography and RSA
1Public Key Cryptography.pdf (Size: 376.86 KB / Downloads: 80)
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
Security of Public Key Schemes
like private key schemes brute force exhaustive
search attack is always theoretically possible
but keys used are too large (>512bits)
security relies on a large enough difference in
difficulty between easy (en/decrypt) and hard
(cryptanalyse) problems
more generally the hard problem is known, its just
made too hard to do in practise
requires the use of very large numbers
hence is slow compared to private key schemes