(a) What is a digital signature? What does its authentication mean? Give various salient built-in features of a digital signature. (b) How does the 3D printing technology work? List out the advantages and disadvantages of the technology.

(a) Digital signature

A digital signature is a cryptographic mechanism that uses public-key (asymmetric) cryptography to verify the authenticity and integrity of an electronic document or message. The sender signs data with a private key; the recipient verifies it with the corresponding public key.

Authentication means confirming that the message genuinely came from the claimed sender and was not altered in transit. In India, digital signatures issued by licensed Certifying Authorities carry legal validity under the Information Technology Act, 2000.

• Authenticity: binds the signer's identity to the document.
• Integrity: any tampering invalidates the signature via a changed hash value.
• Non-repudiation: the signer cannot later deny signing.
• Uses a hash function plus a digital certificate from a Certifying Authority.

(b) 3D printing

3D printing (additive manufacturing) builds a physical object layer by layer from a digital CAD model. The software slices the model into thin cross-sections, and the printer deposits or fuses material (plastic, resin, metal powder) successively until the object is complete.

• Advantages: rapid prototyping, complex customised geometries, low waste, on-demand and localised production, useful in medicine (prosthetics, implants), aerospace and spares.
• Disadvantages: slow for mass production, limited material strength and range, high-end machine cost, and risks of unregulated manufacture such as untraceable firearms.

Conclusion

Digital signatures secure the digital economy while 3D printing transforms manufacturing; both require sound legal and safety frameworks.