Data Security and Privacy数据安全与隐私重要知识点

Part1: Internet Communication

1.1 Risk and Countermeasure

risk: eavesdropping data, manipulating data, impersonation
countermeasure: TLS protocol

1.2 TLS Protocol

1.2.1 Overview

1.2.1.1 HTTP (Hypertext Transfer Protocol)

• „Normal“ protocol for enabling Internet connection
• Provides no security of the data
• Everybody with access to the data can listen and change them

1.2.1.2 http ⇒ https = http + TLS

• TLS: Transport Layer Security
• It runs on top of http and provides a secure Internet connection

1.2.1.3 TLS Overview

Establish Communication -> Check Identity -> Agree on common secret key -> Encrypted Communication
后三个过程与Security有关

1.2.2 Encryption

1.2.2.1 Symmetric Key Encryption

最常用：AES (Advanced Encryption Standard)

1.2.2.2 Formal Definition

A secret key encryption scheme is composed of three sets: Key space , Message space , Ciphertext space , and three algorithms: Key generation Gen: Outputs a key ∈ , Encryption algorithm Enc: × → , Decryption algorithm Dec: K × C → M
Ensure the correctness: Dec(k, Enc(k,m))=m

1.2.3 Key Agreement

1.2.3.1 Key Agreement Procedure

Goal: Establish a common secret key between the two parties

• Over a public channel
• No previous secrets

Two approaches

• Public Key Encryption(not the Symmetric Encryption), e.g., RSA
• Key Agreement Protocol, e.g., Diffie-Hellman Protocol

1.2.3.1 Public Key Encryption

1.2.3.2 Formal Definition

A public key encryption scheme is composed of three sets: Key space , Message space , and Ciphertext space . Three algorithms: Key generation Gen:[Set of integers(这里的整数可改变security level)]→K that outputs a keypair (pk,sk), being a public key and a secret key, Encryption algorithm Enc: (pk, m) -> c, Decryption algorithm Dec: (sk, c) -> m
Correctness: For each message ∈ and each keypair (pk, s) ∈ , it holds that
Dec (sk, Enc(pk, m)) = m

1.2.3.3 Key Agreement using Public Key Encryption

为什么不直接使用Public Key Encryption Scheme对Message进行加密，而要用两种模式混合在一起？
因为Symmetric Key Encryption Scheme比Public Key Encryption Scheme更加高效，从长远来看可以更快加密Message。

1.2.3.4 Key Agreement Protocol

1.2.4 Digital Signatures

1.2.4.1 Authenticity

1.2.4.2 Digital Signature

1.2.4.2 Formal Definition

A digital signature scheme is composed of three sets: Key space K, Message space M, and Signature space S(replace the Ciphertext space (the reason is that the digital signatures do not produce any encrypted messages but produce the signature) ). Three algorithms: Key generation Gen:[Set of integers] → K that outputs a keypair (pk, sk), being a public key and a secret key; Signature algorithm Sign: K × M → S, (sk, m) -> s; Verification algorithm Verify: K × M × S → {True, False}, (pk, m, s) -> {True, False}(decide whether, under this public key, the signature really belongs to the message or not)
Verify(pk, m, Sign(sk, m)) = True

Part2: User Tracking

Part3: Privacy and Anonymization

Part4: Cryptographic Techniques