Secure Web Transactions. Sridhar Iyer K R School of Information Technology IIT Bombay firstname.lastname@example.org http://www.it.iitb.ernet.in/~sri. Overview. Electronic Commerce Underlying Technologies Cryptography Network Security Protocols Electronic Payment Systems
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K R School of Information Technology
Maximize revenue per sale
k: shared key
- Sender and receiver agree on a key K
- No one else knows K
- K is used to derive encryption key EK & decryption key DK
- Sender computes and sends EK(Message)
- Receiver computes DK(EK(Message))
- Example: DES: Data Encryption Standard
sk: private secret key
pk: public key
Sign: sign(sk,m) = Dsk(m)
Verify: Epk(sign(sk,m)) = m
Sign on small hash function to reduce cost
First sign, then encrypt: order is important.
How to establish authenticity of public key?
5. Deposit token at bank.
If double spent reveal
identity and notify police
1. Withdraw money:
3. Send token after adding
4. Check validity and send goods
2. Transform so merchant can check validity but identity hidden