Security Non Negotiable Facts

What are the Fundamental Security Services?

Authentication

Access Control

Confidentiality

Integrity

Non-Repudiation

Availability

Authentication

Assurance that an entity is really the one who it claims to be

Access Control / Authorization

It offers the assurance that the entity performing a given action has the rights to do so

Confidentiality

Guarantee that data are available only to intended parties

Integrity

Assurance that data have not been modified maliciously

Non-Repudiation

Ensures that an entity cannot deny having done an action (e..g, either the sender or the receiver cannot deny to have sent/received a particular message)

Services Availability

Property of a system to be always available and ready to serve requesting entities

What Cipher is this?

Vernam Cipher

Vernam Cipher

Keystream generator generates a random key for each plaintext. Theoretically unbreakable, but in practice hard to implement due to lack of psuedo randomness

What Cipher is this?

Electronic Code Block

What Cipher is this?

Cipher Block Chaining

Cipher Block Chaining Limitation

If error occurs, it propagates indefinitely

What Cipher is this?

Cipher Feedback

What Cipher is this?

Output Feedback

What Cipher is this?

Counter Mode

Counter Mode Advantages

Very fast, can be parallelizable

Errors only propagate to one block

What Cipher is this?

Galois Counter Mode

What is IPSec (Internet Protocol Security)?

Network layer protocol that establishes secure, encrypted tunnels between two peers

IPSec Services

Confidentiality, Integrity and Authentication

IPSec Consists of..

IKE - Internet Key Exchange (handles mutual authentication and key negotiation)

ESP (Encapsulating Security Payload) or AH (Authentication Header) (Protects actual user data traversing the network)

IKE (Internet Key Exchange)

Protocol part of IPSec responsible for authenticating, setting up the security association between peers and distributing the keys for the current session (which are temporary to ensure perfect forward secrecy)

IKE Security Services

Authentication

Integrity

IKE General Flow

IKE_SA_INIT → IKE_AUTH → CHILD_SA

IKE_SA_INIT

Initiator and Responder agree on a cryptographic algorithm. Responder also shares Diffie-Hellman public value and random nonce

Shared Diffie-Hellman is independently computed, which is used to derive the master secret

From master secret, SK_e (encryption), SK_a (integrity), and SK_d (keying material for child SAs) keypairs are derived + establishing the IKE_SA (the secure control channel)

IKE_AUTH

Mutual authentication occurs, peers negotiate and establish the first CHILD_SA (the IPSec data channel), which defines the algorithms and keys used to encrypt the actual user traffic

CHILD_SA

Once the CHILD_SA is established, all user data traffic is encrypted using ESP (Encapsulating Security Payload), and IKE continues to manage the lifecycle of both SAs

ESP (Encapsulating Security Payload)

core IPSec protocol responsible for protecting the actual user data traffic that travels over the VPN

ESP Modes

Tunnel Mode and Transport Mode

Tunnel Mode

ESP takes the entire original IP packet (including the original source/destination IP headers), encrypts it, and wraps it inside a new outer IP header that contains the public IPs of the VPN gateways

Transport Mode

Encrypts only the payload (used for end-to-end host communications)

SPD (Security Policy Database)

Dictates WHAT traffic needs IPsec protection; it contains the policy rules that specify which selectors (e.g., source/destination IPs, ports, protocols) must be secured, bypassed, or discarded

SAD (Security Association Database)

Stores HOW to protect the traffic; it holds the actual cryptographic parameters for each active Security Association (SA). Stores IKE_SA and CHILD_SA IKE_SA

WPA2 / Robust Security Network (RSN)

Second-generation Wi-Fi security protocol, officially mandated for all devices carrying the Wi-Fi trademark since 2006, and it replaced the severely flawed WEP protocol

WPA2 Services

Authentication, Access Control, and Data Confidentiality

WPA2 - Authentication

Defines an exchange between a user and an AS (authentication server) that provides mutual authentication and generates temporary keys to be used between the client and the AP over the wireless link

WPA2 - Access Control

Enforces the use of the authentication function, routes the messages properly, and facilitates key exchange. It can work with a variety of authentication protocols

WPA - Confidentiality with Message Integrity

MAC-level data are encrypted along with a message integrity code that ensures that the data have not been altered.

WPA Protocol for Access Control

IEEE 802.1, Port-based, Access Control

WPA Protocol for Authentication and Key Generation

Extensible Authentication Protocol (EAP)

WPA Protocol for Confidentiality, Data Origin Authentication and Integrity and Replay Protection

CCMP

WPA Algorithms - Confidentiality

AES-CCM (AES-CTR mode to encrypt plaintext), NIST Key Wrap

WPA Algorithms - Integrity and Data Origin Authentication

HMAC-SHA-1

AES-CBC-MAC

WPA Algorithms - Key Generation

HMAC-SHA-1

RFC 1750

Extensible Authentication Protocol (EAP)

Used to carry out mutual authentication in WPA2, exchange credentials and establish the MSK. RADIUS server authenticates client, and distributes MSK to AP

WPA-2 Personal and WPA-2 Enterprise differences

Personal: Pre-shared key is used

Enterprise: Master Session Key is generated between client and AP

4-Way Handshake

1. Anonce sent to STA to generate PTK

2. Snonce sent from STA to AP to generate PTK

3. AP demonstrates to STA it is alive and PTK is fresh via MIC (Message Integrity Code)

4. STA sends acknowledgement message (no function, finishes the handshake)

Protected Data Transfer - Schemes

WPA → Temporal Key Integrity Protocol (TKIP) (deprecated)

WPA2 → Counter Mode-CBC MAC Protocol (CCMP)

WPA2 vs WPA3

Personal:

More robust authentication process via the Simultaneous Authentication of Equals (SAE) protocol, in place of the 4-ways handshake, forward secrecy + natural password selection

• Use of AES-GCM in place of AES-CCMP

Temporal Key Integrity Protocol (TKIP)

Core data encryption protocol designed to address flaws in WEP (later deprecated in 2008 after serious vulnerabilities were exposed)

TKIP Services

Message integrity and Data Confidentiality

TKIP Main Implementations

Each packet has a unique key, the RC4 key (generated from Temporal Key, MAC Address, Initialization Vectors)

Using MIC Key derived from PTK, integrity of data can be checked, AP computes same hash and compares the hash it received

Counter Mode-CBC MAC Protocol (CCMP)

WPA2 algorithm responsible for encrypting the payload and providing integrity via the MIC calculation

How does CCMP work?

CBC-MAC Mode for MIC calculation

CTR Mode for payload encryption

TLS

Transport Layer Security: the foundational protocol that secures communication over the Internet.

It is the successor to SSL (Secure Sockets Layer)

TLS Uses

General purpose protocol: the core technology behind HTTPS, securing web browsing, email, VoIP, and many other applications.

TLS Services

confidentiality, integrity, and authentication

TLS Algorithms

(They are algorithms of the TLS Record Protocol)

Confidentiality: AES CBC mode

Integrity: HMAC in RFC 2104

What data does TLS encrypt?

TCP traffic

TLS Main Protocols

Record Protocol and Handshake Protocol

TLS Record Protocol

Responsible for fragmenting, compressing (optional), encrypting, and transmitting all application data (e.g., HTTP) and handshake messages between the client and server

TLS Record Protocol Steps

Application data is fragmented into records, compressed, MAC is appended (message authentication code), encrypted and the TLS record header is appended

TLS Record Header Content

Message Type, Protocol variant, data size

TLS Handshake Protocol Objectives

Ran at the establishment of a TLS session to:

• Authenticate the parties (mutual authentication)

• Establish the Cipher Specifications (encryption and MAC)

• Establish keys

TLS Handshake Steps

Phase 1: Establish Security Capabilities

Phase 2: Server Authentication and Key Exchange

Phase 3: Client Authentication and Key Exchange (DH)

Phase 4: Finish - verification of successful authentication and key exchange

TLS Master Secret

Master Key from which keys for record protocol are derived.

Created using pre master key (from DH), client and server random number

TLSv1.3 vs TLSv1.2 changes

• Removed Compression Option

• No RSA for Key Exchange (only signature)

• Inclusion of 32-bit timestamp in ClientHello

• No RC4 for stream cipher, only block ciphers

• Use of Hashed Key Derivation Functions (HKDF) in place of PRF

• Use of AES-GCM for confidentiality and integrity

• 1-round trip handshake (re-use of security parameters from previous handshakes)

HTTP Secure (HTTPS)

Secure version of HTTP that runs over TLS/SSL. It secures communication between client and server

HTTPS Services

Authentication

Confidentiality

Integrity

HTTPS port

443

HTTP port

80

HTTPS Connection Initiation

HTTPs client connection triggers TLS Handshake protocol.

After successful completion of TLS Handshake, HTTPS client delivers HTTP data in a TLS Record packet

HTTPS Connection Closure

HTTP(s) client or server can indicate the closing of a connection by including the line Connection: close in an HTTP(s) record

TLS implementations must initiate an exchange of closure alerts before closing a connection (otherwise the closure is incomplete)

Secure Shell (SSH) Protocol

Protocol for secure network communication between two hosts

SSH Port

22

SSH Protocol Stack

SSH Transport-Layer Protocol, SSH User Authentication Protocol, SSH Connection Protocol

SSH Transport-Layer Protocol

Foundational component of SSH, providing a secure, low‑level channel over an insecure network, typically on top of TCP/IP

SSH Transport-Layer Flow

Identification Key Exchange, Algorithm Negotiation, Key Exchange (DH), Service Request (Authentication or Connection Protocol)

SSH Packet Structure

Payload compressed, MAC computed from sequence number and payload. Plaintext encrypted (without MAC), MAC is attached. Server recomputes MAC on ciphertext. If same, accept

SSH Packets Services

Integrity, Confidentiality, Message Authenticaiton (sender must have used symmetric key for this session to compute

SSH User Authentication Protocol

SSH Protocol used to Authenticate Client to Server

SSH User Authentication Protocol Message Types

SSH_MSG_USERAUTH_REQUEST (50: Username, connection protocol, authentication method)

SSH_MSG_USERAUTH_FAILURE (51: list of methods that are allowed, publickey, pass, hostbased)

SSH_MSG_USERAUTH_SUCCESS (52: single byte)

SSH Connection Protocol

Allows packet (data) exchange over secure connection, new communication opens a channel (max packet size and application specified during opening of channel)

SSH port forwarding/tunneling

Convert any (insecure) TCP session into a secure SSH connection (SSH tunneling). Packets are delivered to correct app via port number

SSH Port Forwarding Types

Local Forwarding and Remote Forwarding

Local Forwarding

Client and Server redirect traffic to/from SSH ports

Remote Forwarding

User SSH Client acts on server’s behalf (packets are directly delivered to SSH port on the server)