UPSC Mains 2013 GS Paper 3 Q16: model answer
(a) What is a digital signature? What does its authentication mean? Give various salient built-in features of a digital signature. (100 words) (b) How does the 3D printing technology work? List out the advantages and disadvantages of the technology. (100 words)
What the question wants
(a) Explain what a digital signature is, what authentication means, and its built-in features. (b) Explain how 3D printing works and list its advantages and disadvantages.
How to structure it
(a) What, authentication, features.
- Definition
- Authentication
- Salient features
(b) Process, pros, cons.
- How it works
- Advantages
- Disadvantages
How to think it through
(a) Based on public key cryptography (asymmetric keys). Signer hashes the document, encrypts the hash with private key; verifier decrypts with public key and compares hashes. Legal under IT Act 2000; certifying authorities under the Controller of Certifying Authorities. Features: authenticity, integrity, non-repudiation, time-stamping. (b) Additive manufacturing: CAD model sliced into layers; printer deposits material layer by layer (FDM plastic, SLA resin, SLS metal powder). Advantages: customisation, prototypes, less waste, complex shapes, medical implants, on-site printing. Disadvantages: slow for mass production, costly material, strength, IP piracy, printed weapons.
Model answer
(a)
A digital signature is an electronic code that proves who signed a document and that it was not changed. It uses public key cryptography.
What authentication means
- The signer makes a hash of the document and encrypts it with a private key.
- The receiver decrypts it with the signer's public key and compares it with a fresh hash.
- A match authenticates the signer and shows the document is unaltered.
- Under the IT Act, 2000, keys are certified by licensed Certifying Authorities.
Built-in features
- Authenticity: confirms the signer's identity.
- Integrity: any change breaks the match.
- Non-repudiation: the signer cannot deny signing.
- Time-stamping and secure, tamperevident storage.
It is the reason an income tax return can be filed without paper.
(b)
3D printing, or additive manufacturing, builds an object layer by layer from a digital design, instead of cutting it out of a block.
How it works
- A CAD model is sliced into thin layers by software.
- The printer deposits plastic, resin or metal powder, fusing each layer with heat or a laser.
Advantages
- Customisation: implants and prosthetics made for one patient.
- Rapid prototypes and complex shapes impossible by machining.
- Less waste of raw material.
- Printing on site: IIT Madras start-up Tvasta printed a house in 2021.
Disadvantages
- Slow and costly for mass production.
- Weaker parts in some materials.
- IP piracy and printed weapons.
- High energy use for metal printers.
It is best for making a few special things, not millions of ordinary ones.
Draw: (a) Two keys, a hashed document, and a match check. (b) A stack of thin layers forming an object.
Keywords, cases and data to drop in
(a) digital signature, public key cryptography, private key, hash, Certifying Authority, CCA, IT Act 2000, integrity, non-repudiation, DSC, e-Sign. (b) additive manufacturing, CAD, layer by layer, FDM, SLA, SLS, prosthetics, Tvasta, IP piracy, ghost guns.
Where most answers lose marks
- (a) Calling it a scanned signature image. (b) Listing only advantages.
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Question text as printed in the official UPSC Civil Services (Main) question paper. The model answer is original Battle IAS work; use it to learn structure, not to memorise.
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