JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD MCA IV INFORMATION SECURITY Previous Question Paper (March/April - 2023 - R15)

Steganography is the practice of concealing the existence of a message, file, image, or video within another carrier file. Unlike cryptography, which protects the content of a message by making it unreadable, steganography protects the communication itself by hiding the fact that a secret message is being transmitted.

The process involves three main components: the cover object (the carrier), the secret message, and the stego-object (the result after embedding). Common techniques include:

• Least Significant Bit (LSB) Insertion: Replacing the least significant bits of pixels in an image or audio file with bits of the secret message, which is typically imperceptible to the human eye or ear.
• Transform Domain Techniques: Embedding data in the frequency domain (e.g., using Discrete Cosine Transform) to make the hidden information more robust against compression and signal processing attacks.
• Spread Spectrum: Spreading the secret data across the entire frequency spectrum of the cover object, making it difficult to detect or remove without knowing the specific key.

Steganography is widely used in digital watermarking for copyright protection, secure communication in restrictive environments, and covert data transmission. However, it is vulnerable to steganalysis, the art of detecting hidden information by analyzing statistical anomalies in the carrier file.

The Diffie-Hellman key exchange is vulnerable to a Man-in-the-Middle (MitM) attack because it lacks authentication. The protocol allows two parties to establish a shared secret over an insecure channel, but it does not verify the identity of the participants.

The attack proceeds as follows:

1. An attacker, Eve, intercepts the public values exchanged between Alice and Bob.
2. Eve performs two separate Diffie-Hellman exchanges: one with Alice (pretending to be Bob) and one with Bob (pretending to be Alice).
3. Alice establishes a shared secret with Eve, and Bob establishes a separate shared secret with Eve.
4. When Alice sends an encrypted message, Eve decrypts it using the secret shared with Alice, reads or modifies the content, re-encrypts it using the secret shared with Bob, and forwards it to Bob.

Because neither Alice nor Bob verifies the digital signature or certificate of the other party, they remain unaware that their communication is being intercepted and relayed by an intermediary.