0. Overview

Secure Data Transfer

Alice     Intruder      Bob

Intruder can:
1. snoop the communication
2. impersonate another entity
3. temper the packets

mechanism

1. Confidentiality (sometimes optional): only the sender and intended receiver should be able to understand the contents of the transmitted message
2. Authentication (always needed):
   1. End-point authentication: both the sender and receiver should be able to confirm the identity of the other party involved in the communication
   2. Message integrity: both parties ensure that the content of their communication is not altered, either maliciously or by accident, in transit

1. Confidentiality

1.1 Overview

terms

• cleartext (m): the original payload the sender is sending.
• ciphertext (c): same size of m, but encrypted from m using E.
• cipher (E & D): encryption and decryption algorithms that the both endpoints should know.
• key (Ks, Kr): a string of cipher, as input to cleartext/ ciphertext.

encryption flow

if Ks == Kr: symmetric encryption

1.2 Ciphers

1) Ceasar cipher

→ the most simple substitution cipher