MCA 221 Applied Cryptography Notes cover all 4 units of this GGSIPU MCA Semester 3 Core Elective II paper in 61 pages, with 19 worked examples and numericals, 53 short-answer and 35 long-answer exam-style questions, 22 figures and four quick-revision sheets. They follow the MCA syllabus effective from academic year 2025-26.
Written by Prateek Talwar, Founder, Unnati Educations · Reviewed by Ritik Rawat, B.Tech, Senior Full Stack Developer · Checked against the MCA scheme and syllabus PDF (28 July 2025) · Updated 13 October 2026 · Editorial policy
Scheme: MCA (2 years), w.e.f. academic year 2025-26 | Applies to: academic year 2025-26 onwards | Verified against: MCA Scheme of Examination and Detailed Syllabus, BoS USIC&T 28 July 2025
MCA 221 Applied Cryptography at a glance: GGSIPU MCA Sem 3 credits, units and exam pattern
| Code and title | MCA-221 Applied Cryptography |
|---|---|
| Course and semester | MCA (2 years), Semester 3 |
| Category and credits | Core Elective II (pick one of 11); 3 credits, L 3, T/P nil |
| Units and hours | 4 units: 10 + 12 + 10 + 10 = 42 hours |
| Marks | 100; internal and end-term split not printed in the official PDF |
| End-term pattern | Compulsory Q1 (short answers, whole syllabus) of 12 marks, then one of two questions from each unit at 12 marks each (12 + 4 × 12 = 60 marks) |
| Pass mark | 40 out of 100 |
| Paired lab | MCA-265 Lab based on Core Elective II (Applied Cryptography Lab), L 0, T/P 2, 1 credit |
As a Core Elective II paper, MCA 221 competes with MCA-219 Distributed Systems or MCA-223 Cloud Computing; it sits with the other GGSIPU MCA Semester 3 papers.
Re-appear and result rules follow GGSIPU Ordinance 11.
MCA 221 Applied Cryptography Notes unit-wise: 19 worked examples and 88 exam-style questions across 4 units
These MCA 221 Applied Cryptography IPU notes move from letter ciphers to TLS and PGP, each unit ending with a revision sheet and question bank (see the sample PDF above). Other MCA papers are under GGSIPU MCA notes.
MCA 221 Unit 1: Introduction to Cryptography
Also covered as "Introduction to Cryptography and Classical Ciphers". Unit 1 (pages 3 to 15) covers Kerckhoffs's principle, block vs stream ciphers and four families of attack, then arithmetic modulo 26 and the Extended Euclidean method driving Caesar, affine, Playfair and Hill ciphers and two transposition ciphers. It has 10 worked examples, 12 short-answer and 8 long-answer questions.
| Basis | Substitution | Transposition |
|---|---|---|
| What changes | Letters are replaced | Letters are rearranged |
| Letter position | Stays the same | Changes |
| Letter frequency | Changes | Same as plaintext |
| Shannon property | Confusion | Diffusion |
Quick look: substitution vs transposition ciphers (from page 14)
- Basis
- What changes
- Substitution
- Letters are replaced
- Transposition
- Letters are rearranged
- Basis
- Letter position
- Substitution
- Stays the same
- Transposition
- Changes
- Basis
- Letter frequency
- Substitution
- Changes
- Transposition
- Same as plaintext
- Basis
- Shannon property
- Substitution
- Confusion
- Transposition
- Diffusion
MCA 221 Unit 2: Modern Cryptography
Also covered as "Modern Cryptography: DES, AES, Modes, RSA and Hash Functions". Unit 2 (pages 16 to 29) moves from confusion, diffusion and Feistel rounds into DES, its key schedule and Triple DES, then AES stages and key expansion, RSA, SHA-512 and hash vs MAC. It has 3 worked examples, 13 short-answer and 8 long-answer questions.
| Basis | DES | AES |
|---|---|---|
| Structure | Feistel network | Substitution-permutation network |
| Block size | 64 bits | 128 bits |
| Key size | 56 bits | 128, 192 or 256 bits |
| Rounds | 16 | 10, 12 or 14 |
Quick look: DES vs AES (from page 22)
- Basis
- Structure
- DES
- Feistel network
- AES
- Substitution-permutation network
- Basis
- Block size
- DES
- 64 bits
- AES
- 128 bits
- Basis
- Key size
- DES
- 56 bits
- AES
- 128, 192 or 256 bits
- Basis
- Rounds
- DES
- 16
- AES
- 10, 12 or 14
MCA 221 Unit 3: PKI and Digital Signature
Unit 3 (pages 30 to 44) covers PKI components and trust models; hash-then-sign, RSA signatures and DSA with toy numbers; the KDC flow and Diffie-Hellman; X.509 v3 fields, CRL vs OCSP, and CA attacks and defences. It has 4 worked examples, 13 short-answer and 9 long-answer questions.
Quick look: Diffie-Hellman with small numbers (from page 37)
- Public values: prime
q = 23, primitive rootα = 5. - A keeps
XA = 6secret and sendsYA = 5^6 mod 23 = 8. - B keeps
XB = 15secret and sendsYB = 5^15 mod 23 = 19. - A computes
19^6 mod 23 = 2; B computes8^15 mod 23 = 2. Shared key K = 2, never sent.
MCA 221 Unit 4: Cryptographic Protocols for Secure Communications
Unit 4 (pages 45 to 61) covers the TLS handshake and TLS 1.3; WEP to WPA3; SPINS for sensor networks and RFID hash-locks; Tor; S/Key, HOTP and TOTP; Kerberos, SAML, OAuth 2.0, PGP and S/MIME. It has 2 worked examples, 15 short-answer and 10 long-answer questions.
| Basis | HOTP (RFC 4226) | TOTP (RFC 6238) |
|---|---|---|
| Moving factor | Event counter C | 30-second time window |
| Validity | Until used | Current time step only |
| Sync problem | Counter drift | Clock drift |
| Typical use | Button hardware tokens | Authenticator apps |
Quick look: HOTP vs TOTP one-time passwords (from page 54)
- Basis
- Moving factor
- HOTP (RFC 4226)
- Event counter C
- TOTP (RFC 6238)
- 30-second time window
- Basis
- Validity
- HOTP (RFC 4226)
- Until used
- TOTP (RFC 6238)
- Current time step only
- Basis
- Sync problem
- HOTP (RFC 4226)
- Counter drift
- TOTP (RFC 6238)
- Clock drift
- Basis
- Typical use
- HOTP (RFC 4226)
- Button hardware tokens
- TOTP (RFC 6238)
- Authenticator apps
CBC and Counter mode chaining in block ciphers: excerpt from page 23 of the MCA 221 notes
Excerpt from page 23
A block cipher such as DES or AES encrypts only one fixed-size block at a time. Real messages are longer, so a mode of operation decides how the blocks are linked. The weakest mode, ECB, encrypts every block on its own, which means two identical plaintext blocks always give two identical ciphertext blocks and the pattern of the message shows through. Page 23 picks up where ECB fails.
Cipher Block Chaining (CBC)
In CBC, each plaintext block is XORed with the previous ciphertext block before it goes into the cipher. The first block has no previous ciphertext, so an Initialization Vector (IV) takes its place.
Ci = E(K, Pi ⊕ Ci−1), with C0 = IV; decryption is Pi = D(K, Ci) ⊕ Ci−1.
Because every block depends on the one before it, repeated plaintext blocks now produce different ciphertext, and the message pattern is hidden. CBC suits general bulk encryption and is also the basis of CBC-MAC.
The cost is speed and fragility. Encryption is sequential, so it cannot run in parallel. A one-bit error in a ciphertext block spoils that whole plaintext block and one bit of the next. The IV must be unpredictable and known to the receiver, and the last block needs padding.
Counter (CTR) mode
CTR never feeds plaintext into the cipher. Instead it encrypts a counter value, which goes up by one for each block, and XORs the result with the plaintext. In effect it turns a block cipher into a stream cipher.
Ci = Pi ⊕ E(K, Counter + i) and Pi = Ci ⊕ E(K, Counter + i).
CTR encrypts and decrypts fully in parallel, allows random access to any block, lets the key stream be prepared in advance, needs only the encryption function and needs no padding. A bit error affects only that bit. The one rule that must never break: the same counter value must not be used twice with the same key, because that repeats the key stream. CTR is used in high-speed networks and disk encryption, and it is the base of the GCM mode inside TLS.
Do the MCA 221 notes cover the full GGSIPU syllabus?
Yes. Every MCA-221 topic in the 2025-26 syllabus has its own section, from the Caesar cipher to S/MIME. Unit titles are the lead topic the PDF prints for each unit.
| Official unit | Official topics | Where in the notes | Status |
|---|---|---|---|
| Unit 1: Introduction to Cryptography | Introduction, block and stream ciphers, types of attacks, modular arithmetic, Caesar, additive, multiplicative, affine, Playfair and Hill ciphers, traditional transposition | Sections 1 to 6, pp. 4 to 14 | Covered |
| Unit 2: Modern Cryptography | Confusion and diffusion, DES and AES, ECB, CBC and Counter modes, RSA, hash function and message digest | Sections 1 to 6, pp. 17 to 27 | Covered |
| Unit 3: PKI and Digital Signature | Introduction to PKI, signature generation and verification, key management and distribution, digital certificates, security of certification authorities | Sections 1 to 5, pp. 31 to 42 | Covered |
| Unit 4: Cryptographic Protocols for Secure Communications | SSL/TLS, WiFi security, sensor networks and RFID, anonymous communication, 2-factor authentication, one-time passwords, Kerberos, SAML, OAuth, PGP and S/MIME | Sections 1 to 7, pp. 46 to 59 | Covered |
MCA 221 syllabus mapped to the notes
- Official unit
- Unit 1: Introduction to Cryptography
- Official topics
- Introduction, block and stream ciphers, types of attacks, modular arithmetic, Caesar, additive, multiplicative, affine, Playfair and Hill ciphers, traditional transposition
- Where in the notes
- Sections 1 to 6, pp. 4 to 14
- Status
- Covered
- Official unit
- Unit 2: Modern Cryptography
- Official topics
- Confusion and diffusion, DES and AES, ECB, CBC and Counter modes, RSA, hash function and message digest
- Where in the notes
- Sections 1 to 6, pp. 17 to 27
- Status
- Covered
- Official unit
- Unit 3: PKI and Digital Signature
- Official topics
- Introduction to PKI, signature generation and verification, key management and distribution, digital certificates, security of certification authorities
- Where in the notes
- Sections 1 to 5, pp. 31 to 42
- Status
- Covered
- Official unit
- Unit 4: Cryptographic Protocols for Secure Communications
- Official topics
- SSL/TLS, WiFi security, sensor networks and RFID, anonymous communication, 2-factor authentication, one-time passwords, Kerberos, SAML, OAuth, PGP and S/MIME
- Where in the notes
- Sections 1 to 7, pp. 46 to 59
- Status
- Covered
Official source: MCA (2 years) Scheme of Examination and Detailed Syllabus, 2025-26 onwards.
Extras like Triple DES and TLS 1.3 support long answers. Every course in GGSIPU notes is mapped to its official PDF the same way.
How to write MCA 221 answers: step-wise cipher and RSA numericals, and twelve-mark protocol answers
The paper has a compulsory 12-mark Q1 of short answers plus one 12-mark question per unit. The notes label questions 2.5 and 12.5 marks, so read them as "short" and "long" and plan long answers for 12 marks.
Numericals
For affine and Hill ciphers, find the inverse with the Extended Euclidean table and add a check line such as 7 × 15 = 105 ≡ 1 (mod 26). For Hill, show K · K⁻¹ = I and call the key invalid if its determinant is even or 13. For RSA, write n, φ(n), the gcd check, the table for d, the verification, then the exponentiation.
Theory answers
Start with the diagram the notes name (the DES round, the TLS stack and handshake, the Kerberos overview, PGP sender processing), explain each stage in two or three lines, and finish with a comparison table such as DES vs AES or PGP vs S/MIME.
Slips the notes flag
- Calling AES a Feistel cipher.
- Forgetting that the last AES round drops MixColumns.
- Saying Diffie-Hellman gives authentication.
- Confusing OAuth (authorization) with OpenID Connect (authentication).
Worked example: short RSA numerical (from page 25)
- Given
p = 3,q = 11,e = 7,M = 5. n = 33;φ(n) = 2 × 10 = 20;gcd(7, 20) = 1.d = 7⁻¹ mod 20 = 3, since7 × 3 = 21 ≡ 1.C = 5^7 mod 33 = 78125 mod 33 = 14.- Check:
14^3 mod 33 = 2744 mod 33 = 5 = M.
Practise this format on GGSIPU MCA important questions.
MCA 221 exam corner: 53 short-answer and 35 long-answer questions by unit
| Unit | Short answer ("2.5 Marks") | Long answer ("12.5 Marks") | Worked examples |
|---|---|---|---|
| Unit 1 | 12 | 8 | 10 |
| Unit 2 | 13 | 8 | 3 |
| Unit 3 | 13 | 9 | 4 |
| Unit 4 | 15 | 10 | 2 |
| Total | 53 | 35 | 19 |
MCA 221 questions and worked examples by unit
- Unit
- Unit 1
- Short answer ("2.5 Marks")
- 12
- Long answer ("12.5 Marks")
- 8
- Worked examples
- 10
- Unit
- Unit 2
- Short answer ("2.5 Marks")
- 13
- Long answer ("12.5 Marks")
- 8
- Worked examples
- 3
- Unit
- Unit 3
- Short answer ("2.5 Marks")
- 13
- Long answer ("12.5 Marks")
- 9
- Worked examples
- 4
- Unit
- Unit 4
- Short answer ("2.5 Marks")
- 15
- Long answer ("12.5 Marks")
- 10
- Worked examples
- 2
- Unit
- Total
- Short answer ("2.5 Marks")
- 53
- Long answer ("12.5 Marks")
- 35
- Worked examples
- 19
The MCA 221 notes list 53 short-answer and 35 long-answer exam-style questions across 4 units, plus 19 worked examples and numericals.
One question per unit, with answer pointers:
- Unit 1: Explain the affine cipher. Encrypt "HELLO" using keys (7, 2) and decrypt it. Pointer (pp. 10 to 11): ZEBBW; decrypt with
k1⁻¹ = 15. - Unit 2: Explain DES with the structure of a single round and the key generation process. Pointer (pp. 18 to 20): IP, 16 rounds, the four-step F function, PC-1 and PC-2.
- Unit 3: Differentiate between CRL and OCSP. Pointer (p. 40): periodic list vs online query; freshness, size, privacy.
- Unit 4: Explain Kerberos version 4 with the message exchanges. How is version 5 different? Pointer (pp. 54 to 56): AS, TGS, six messages, then the v4 vs v5 table.
More practice sits in the MCA 221 important questions.
Who writes and checks the MCA 221 cryptography notes?
- Prateek Talwar, author: Founder, Unnati Educations; Associate Company Secretary (ACS), ICSI, membership no. 58704, since 15 May 2019; B.Com, University of Delhi (School of Open Learning), 2012. Author profile
- Ritik Rawat, subject reviewer: Senior Full Stack Developer, Unnati Educations; B.Tech. Checked every numerical and the Unit 4 protocol flows.
These GGSIPU MCA Sem 3 Applied Cryptography notes, 2026-27 edition, follow the MCA scheme approved by the BoS of USIC&T on 28 July 2025. They were last updated 13 October 2026 under our editorial policy.
The same team prepares GGSIPU important questions for every course.
MCA 221 and the GGSIPU MCA Sem 3 papers it connects to
Every MCA paper and lab is listed on the GGSIPU MCA syllabus page.
Paired lab: with this elective, MCA-265 becomes the Applied Cryptography Lab (T/P 2, 1 credit). The PDF lists four course outcomes but no practicals; this book covers theory only.
- Unit links: Unit 1 modular inverses drive RSA (Unit 2) and DSA and Diffie-Hellman (Unit 3); Units 3 and 4 match the lab's CO3 on attacks and their prevention.
- MCA-253 Cyber Security and Cyber Laws pairs well: its Unit IV covers digital signatures under the Indian IT Act.
- MCA-213 Wireless Sensor Networks is a rival elective; Unit 4 still covers SPINS.
Other Sem 3 papers: MCA-201 Design and Analysis of Algorithms, MCA-203 AI and Machine Learning, one Core Elective III (MCA-227 to MCA-247), one Open Elective II (MCA-249 to MCA-255), labs MCA-261 to MCA-267, MCA-269 Minor Project III, and NUES papers MCA-271 and MCA-273.
MCA 221 cryptography notes FAQs
How do I get the full MCA 221 notes?
Send a WhatsApp message to 9899436384 using the "Get Full Notes" button. The full MCA 221 Applied Cryptography notes come only as a printed book, not as a PDF. Delivery takes 5 to 7 days at most, and the exact time depends on your location. Before ordering, open the watermarked sample PDF at the top of this page.
Is MCA 221 a compulsory paper in MCA Semester 3?
No. MCA 221 Applied Cryptography is one of eleven Core Elective II papers in MCA Semester 3, and each student takes any one. It carries 3 credits and three lecture hours a week. The scheme says an elective needs at least 20 students for classes; with fewer, it may be completed through an approved MOOC, with the institution's own evaluation.
What is the passing mark for MCA 221?
MCA 221 is marked out of 100, and its end-term paper is set for 60 marks (12 + 4 × 12); the official PDF does not print the internal share. The MCA scheme of examination states pass marks as 40%, which is 40 out of 100. For end-term minimums and re-appear rules, read Ordinance 11 on ipu.ac.in.
Which MCA 221 unit has the most numericals?
Unit 1. It holds 10 of the 19 MCA 221 worked examples: Caesar, additive, multiplicative, affine, Playfair and Hill ciphers, rail fence and columnar transposition, plus gcd and inverse workings. Unit 3 has four (an RSA signature, a DSA signature and two Diffie-Hellman exchanges) and Unit 2 has two RSA numericals and an S-box lookup.
Do the MCA 221 notes follow the 2025-26 syllabus?
Yes. The MCA 221 notes were checked unit by unit against the MCA syllabus approved by the BoS of USIC&T on 28 July 2025, effective from academic year 2025-26, and all four units are covered. One difference: the question banks print 2.5-mark and 12.5-mark labels, while the 2025-26 paper sets 12 marks for Q1 and 12 for each unit question.
How much maths do I need for MCA 221?
The MCA 221 syllabus names number theory and modular arithmetic as its pre-requisite. The notes rebuild what you need on pages 8 and 9: the modulo operation, congruence, additive and multiplicative inverses, the inverse table for Z26 and the Extended Euclidean algorithm. RSA in Unit 2 adds Euler's totient, Fermat's theorem and Euler's theorem in one or two lines each.
Get the full MCA 221 Applied Cryptography Notes on WhatsApp
MCA 221 book: pages and questions per unit
- Part
- Cover and index
- Pages
- 1 to 2 (2)
- Short + long questions
- -
- Part
- Unit 1
- Pages
- 3 to 15 (13)
- Short + long questions
- 12 + 8
- Part
- Unit 2
- Pages
- 16 to 29 (14)
- Short + long questions
- 13 + 8
- Part
- Unit 3
- Pages
- 30 to 44 (15)
- Short + long questions
- 13 + 9
- Part
- Unit 4
- Pages
- 45 to 61 (17)
- Short + long questions
- 15 + 10
The 61-page book holds 19 worked examples and 88 exam-style questions. These Applied Cryptography notes in English are sold only as a printed book, not a PDF. Delivery: within 5 to 7 days at most; the exact time may vary with your location.
Order the printed MCA 221 notes book on WhatsApp (4 units, 61 pages)
Unnati Educations is an independent education provider based in Vikaspuri, Delhi. We are not affiliated with, authorised by, or endorsed by Guru Gobind Singh Indraprastha University (GGSIPU). 'GGSIPU' and 'IPU' are used only to describe the syllabus our notes follow. For official information, visit ipu.ac.in.
Ready for the full notes?
Discuss coverage and delivery with our team.