Cryptography and System Security

Explore caesar cipher and generalized caesar cipher, covering additive shift and monoalphabetic cipher, encryption and decryption via mod 26 with index mapping a=0, hello example.

Explore a Caesar cipher example: encode cat to fdw using a shift of 3 with a=0 indexing, then decrypt fdw back to cat.

Explore the Playfair cipher, a symmetric substitution method with a 5x5 matrix, i and j merged, and encryption and decryption rules using row, column, and rectangle cases.

Learn how a transposition cipher reorders letters, not substitutes them, with keyless and key transposition methods. Use the rail fence technique and row-by-row or column-by-column writing to encipher and decipher.

Master RSA algorithm steps by selecting primes p and q, computing n and phi(n), choosing e not a factor of phi(n), and deriving d for encryption and decryption mod n.

Illustrates a man in the middle attack on the diffie-hellman key exchange, where an attacker intercepts messages and derives separate keys k1 and k2 with Alice and Bob.

Learn Euler's totient function and how to compute phi(n) using prime and prime-power rules, multiplicative factorization, and examples like phi(11)=10, phi(49)=42, phi(240)=64.

Explore how hash functions transform arbitrary-length input into fixed-size outputs, producing a message digest, with preimage resistance, second preimage resistance, and collision resistance.

Learn how nested mac strengthens integrity and authenticity by hashing the secret key with the message to produce an intermediate digest and a final mac value.

Learn how hash message authentication codes use a shared secret key with ipad and opad padding and iterative hashing to ensure message authenticity and integrity, surpassing nested mac.

Understand how digital certificates link a user to a public key, detailing subject, serial number, validity, issuer, and signature algorithm, and roles of end user, certification authority, and registration authority.

Explore x.509 digital certificates, including versions 1–3, serial numbers, signature algorithm, validity, subject and issuer names, public key info, extensions, and certificate renewal and revocation by the certification authority.

Explain authentication as validating a user's identity and returning true or false, via identification and central authentication, and show authorization granting access based on roles.

Learn how arp spoofing maps ip addresses to mac addresses and how attackers intercept, modify, or drop traffic through denial of service, session hijacking, and man in the middle attacks.

Identify open ports and running services on target machines through port scanning to reveal authentication requirements and entry points. Use nmap and TCP SYN scans to map network services.

Examine how IP spoofing uses spoofed source addresses to misroute traffic, mask identities, and enable denial of service by overwhelming the target network.

Learn SSL, TLS, and IPsec, including AH and ESP, with tunnel and transport modes, and how they secure data from the application layer through the session and transport layers.

SSL establishes secure end-to-end communication by encrypting data in transit, delivering confidentiality, authentication, and data integrity to prevent eavesdropping, tampering, and forgery in HTTPS connections.

Learn how TLS secures transport-layer communication through the handshake, certificate-based authentication, and session keys, enabling encrypted and authenticated data exchange between client and server.

Explore how IPsec secures network layer traffic with confidentiality, integrity, authentication, and replay protection, between hosts and networks, using AH and ESP in transport and tunnel modes.

Explore the two IP security modes: transport mode and tunnel mode; transport encrypts only the payload, while tunnel encrypts the entire IP packet for gateway-to-gateway transfer, AH and ESP protocols.

Explore the stateful multilayer inspection firewall, a dynamic hybrid that combines packet filtering, circuit level, and application level checks to enforce rules across network, session, and application layers.

Explore intrusion concepts, the CIA triad, and how intruders threaten confidentiality, integrity, and availability, and identify the three intruder classes: masquerader, Miss Fraser, and clandestine user.

Explore host-based intrusion detection systems that monitor a host with predefined rules to detect malicious or suspicious activity from both inside and outside threats, defending against malware, trojans, and vulnerabilities.

Learn how anomaly-based intrusion detection systems identify unknown attacks by building a machine learning model to analyze network data and traffic, distinguish normal from malicious activity, and generate alerts.