Cryptography and Network Security Handwritten Notes PDF

Key takeaways

• RSA, Diffie-Hellman and classical cipher numericals are reliable marks if you show each step.
• Compare DES and AES in a table: block size, key size, rounds and structure.
• Each section has exam tips and formula boxes, and the last page lists the most asked practice questions.
• These are original Uncodemy revision notes, not official university notes; check your own syllabus.

About these Cryptography handwritten notes

This page offers Uncodemy's Cryptography and Network Security notes as a free handwritten-style PDF. Cryptography and Network Security covers how data is kept confidential, intact and authentic using ciphers, keys, hashes and secure network protocols. The notes are written in short points with neat tables, labelled diagrams, boxed formulas and exam tips, so you can revise a full unit in one sitting instead of reading a long textbook chapter.

Please note: these are original Uncodemy revision notes. They follow the common syllabus that most Indian universities share for this subject, but they are not official university notes. Check your own university syllabus and add anything it lists that is missing here.

What's inside the Cryptography notes

The PDF is arranged in 9 sections plus a final page of most asked practice questions. The sections follow the usual unit order of a Cryptography and Network Security syllabus, so you can map them to your own units quickly. Here is what each section covers.

Introduction to security

The CIA triad and other goals, passive and active attacks from the X.800 view, security services and mechanisms, and cryptanalysis attack types.

Classical ciphers

Substitution ciphers such as Caesar, Playfair, Hill and Vigenère, and transposition ciphers such as rail fence and columnar.

Symmetric key cryptography

Feistel structure, DES and one DES round, AES rounds, DES vs AES, and the block cipher modes ECB, CBC, CFB, OFB and CTR.

Number theory basics

Modular arithmetic, GCD and the Euclidean algorithm, modular inverse, Fermat's and Euler's theorems.

Public key cryptography

RSA key generation, encryption and decryption with a numeric example, and Diffie-Hellman key exchange with the man-in-the-middle attack.

Hash functions, MAC and digital signatures

Properties of hash functions, SHA family, MAC and HMAC, and how digital signatures give authentication and non-repudiation.

Key management and authentication

Key distribution, X.509 certificates and PKI, and Kerberos authentication.

Network and internet security

IPSec with AH and ESP, SSL/TLS, and email security.

System security

Malware types, intrusion detection systems and firewalls.

Most asked questions (practice)

Ten exam-style questions, from the CIA triad to IPSec and SSL/TLS.

How to use handwritten notes to revise Cryptography

This subject has a few numericals that are almost guaranteed and a lot of protocol theory, so split your revision time between the two.

• Solve one RSA problem with small primes daily and check that decryption gives back the message.
• Encrypt the same word with Caesar, Playfair and Vigenère to fix each method in memory.
• Draw one DES round and the AES round steps side by side.
• Make a flow diagram of Kerberos tickets; it is easier to remember as a picture than as text.

A simple three-pass method works well with handwritten notes. In the first pass, read one section and underline only what you do not already know. In the second pass, close the notes and write the definitions, diagrams and steps for that section on a blank sheet, then compare and correct in a different colour. In the third pass, a day or two later, answer two or three exam-style Cryptography questions in timed conditions using only memory. Add your own examples and doubts in the margins so the PDF becomes your personal revision copy.

Formulas, diagrams and definitions to memorise

• RSA steps: n = p q, phi(n) = (p - 1)(q - 1), choose e, find d as the inverse of e mod phi(n), C = M^e mod n, M = C^d mod n.
• Diffie-Hellman: public values q and alpha, keys Y = alpha^X mod q, shared key K = Y^X mod q.
• DES facts: 64-bit block, 56-bit effective key, 16 rounds. AES facts: 128-bit block, 128, 192 or 256-bit keys, 10, 12 or 14 rounds.
• Properties of a hash function: pre-image resistance, second pre-image resistance and collision resistance.
• Diagrams of the Feistel round, CBC mode and the Kerberos ticket flow.

Common mistakes that cost marks

• Not checking that e and phi(n) are co-prime before finding d.
• Doing modular exponentiation in one step and getting huge numbers; reduce mod n at each step.
• Mixing up the Playfair rules for letters in the same row and the same column.
• Writing that hashing gives confidentiality; it gives integrity.

Exam focus: Cryptography topics that carry the most marks

Cryptography papers reward clean step-by-step numericals and labelled protocol diagrams.

• RSA and Diffie-Hellman numericals.
• Classical ciphers: Playfair, Hill and Vigenère.
• DES structure, AES rounds and block cipher modes.
• Hash functions, HMAC, digital signatures, Kerberos and IPSec.

Typical long questions

1. Explain the CIA triad and compare passive and active attacks.
2. Encrypt a message using Playfair and Vigenère ciphers.
3. Explain the structure of DES and one round in detail.
4. Explain block cipher modes of operation.
5. Solve RSA for given p, q, e and message.
6. Explain Diffie-Hellman key exchange and the man-in-the-middle attack.
7. Explain Kerberos and IPSec.

Marks per question change between universities and years, so confirm the pattern on a recent official paper. In long answers, start with a definition, add a labelled diagram or table, explain the steps and finish with an example or comparison. Underline the key term in each answer and leave a line between steps, because examiners mark faster when the structure is easy to see.

A 7-day revision plan for Cryptography

1. Day 1: Introduction to security, Classical ciphers.
2. Day 2: Symmetric key cryptography, Number theory basics.
3. Day 3: Public key cryptography, Hash functions, MAC and digital signatures.
4. Day 4: Key management and authentication, Network and internet security.
5. Day 5: System security.
6. Day 6: redo the numericals: one RSA problem, one Diffie-Hellman exchange, a Playfair and a Vigenère cipher, and one modular inverse.
7. Day 7: answer the most asked practice questions at the end of the notes from memory, then solve one official previous year paper in three hours and mark the units that cost you time.

Keep a single sheet of formulas, definitions and diagrams from the notes for the last hour before the exam, and do not start new topics on the final day.

Who these notes are for

• B.Tech CSE and IT students preparing for the semester Cryptography and Network Security exam.
• BCA and MCA students with an information or network security paper.
• Students preparing for entry-level security certifications who need the theory base.
• Freshers revising security basics before cybersecurity or cloud interviews.

The notes are a revision aid, not a first textbook. If a Cryptography topic is new to you, learn it from your prescribed book or class lectures first, then come back to the notes to compress and revise it. For practice, pair them with your university's official previous year papers. If your syllabus has a topic that is not covered here, you can ask for it through the handwritten notes request page linked below.

Download Cryptography and Network Security Handwritten Notes PDF

Sources and further reading

• NIST FIPS 197: Advanced Encryption Standard (AES)
• NPTEL: online courses from IITs (search for Cryptography)
• AKTU: old question papers (official archive)