The document discusses the history and concepts of cryptography, especially in the context of e-commerce. It explains how cryptography evolved from ancient times to modern applications. Symmetric and asymmetric encryption methods are described, including how public/private key pairs work. Digital signatures are introduced as a way to provide authentication, integrity, and non-repudiation for electronic transactions.

1. Cryptography & E-Commerce Keeping your Secrets secret! © University of Glamorgan  SLIDE “ Some simple yet secure cipher, easily acquired and easily read, should be introduced by which messages might to all intents and purposes be ‘sealed’ to any person but the recipient” Quarterly Review 1853, [The Victorian Internet, Tom Standage]

9. The Caesar Substitution Cipher © University of Glamorgan The Caesar cipher is named after Julius Caesar, said to be the first to use it. In the Caesar cipher each character is substituted by another. This technique is called a monoalphabetic cipher. Plaintext: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Ciphertext: O P Q R S T U V W X Y Z A B C D E F G H I J K L M N Thus using a Caesar cipher, the message “Mission Impossible” would be encoded as “ AWGGWN WADCGGWPZS” So what do the following ciphertexts mean ? 1) sbwuao 2) gpkioc 3) kohqv cih tcf pfihig  SLIDE  WEB

20. Cryptography and e-commerce Examples © University of Glamorgan  WEB  SLIDE

23. Symmetric Key Digital Signatures © University of Glamorgan S sends sealed M to Arbiter SENDER K S M ARBITER Arbiter retrieves plaintext M from S M K S M K R S M Arbiter seals [ Message received from Sender E ( M , K S ), Identify of Sender S , and copy of plaintext M ] and sends all to R RECIPIENT  WEB  SLIDE 1 2 3

35. Certificates (2) © University of Glamorgan

36. Certificates (3) © University of Glamorgan

37. Certificates (4) © University of Glamorgan