1. 1. Public Key Encryption (A Simple Case)
Uses two mathematically related digital keys
Public key (widely distributed)
Private key (kept secret by owner)
Both keys used to encrypt and decrypt message
Once key used to encrypt message, same key cannot be used to decrypt message
Sender uses recipient’s public key to encrypt message; recipient uses his/her private key to decrypt it
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2. Public Key Cryptography—A Simple Case
Figure 5.8, Page 290
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3. Asymmetric/Public key Encryption
In public key encryption mathematically algorithms produce the keys through one – way function.
In one – way function an input can’t be derived from output.
Example: it is easy to make scrambled eggs, but impossible to retrieve whole eggs from the scrambled eggs.
Keys used in Asymmetric key encryption are 128 bit, 256bit, 512bit.
Algorithm used in Asymmetric key encryption are RSA(Ron Rives, Adi Shamir and Len Adleman ) etc.
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4. The RSA Algorithm – Key Generation (Just Concept)
Select p,q p and q both prime
Calculate n = p x q
Calculate
Select integer e
Calculate d
Public Key KU = {e,n}
Private key KR = {d,n}
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5. The RSA Algorithm – Encryption/Decryption Just Concept
Plaintext: M<n
Ciphertext: C = Me (mod n)
Ciphertext: C
Plaintext: M = Cd (mod n)
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6. Example of RSA Algorithm (Just Concept)
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7. Problem: public key encryption (a simple case)
In public key encryption some elements of security are missing.
Although we can be quite sure the message was not understood or read by a third party (Message Confidentiality)
But No guarantee the sender really is the sender (no authentication of message)
This mean the sender could deny ever sending the message (repudiation)
And there is no assurance the message was not altered some how in transit.
Example: message change to Buy from sell
This suggests a potential lack of integrity in the system.
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