Quiz 6 securing IoT (AI)

Ai generated notes for lectures 13 and 14.

Purpose of a digital signature

To prove message authenticity and integrity using the sender's private key.

Key used to verify a digital signature

The sender's public key.

Non-repudiation in digital signatures

The sender cannot deny sending the signed message.

Is signing the same as encryption?

No, they are different operations, though both use keys.

What is usually signed instead of the full message?

The hash of the message.

Why is the hash of a message signed instead of the message itself?

It is more efficient and ensures integrity via the hash.

What happens if an adversary tampers with the message or signature?

The verification process will fail.

Why can't HMACs provide non-repudiation?

Because both sender and receiver share the same secret key.

Main difference between symmetric and asymmetric encryption

Symmetric uses the same key for encryption and decryption; asymmetric uses a public/private key pair.

Why are both symmetric and asymmetric keys often used together?

To combine efficiency (symmetric) with secure key exchange (asymmetric).

Purpose of key establishment

To securely generate and share a secret key between communicating parties.

Role of a Trusted Third Party (TTP) in key establishment

It helps generate and distribute a shared session key securely.

Purpose of the nonce (Na) in key establishment

To ensure freshness and prevent replay attacks.

Who can decrypt {Kab, A}_Kb in the TTP protocol?

Only Bob, using his private key Kb.

How does Bob verify that Alice knows Kab?

Bob sends a challenge {Nb}_Kab and expects Alice to return {Nb-1}_Kab.

What information can an eavesdropper learn in the TTP exchange?

Only message 1 (A, B, Na); all others are encrypted.

What is exchanged in RSA-based key establishment?

Nonces encrypted with each other's public keys.

How is the shared key derived in RSA key exchange?

Using a hash of the XOR of both nonces.

Why can't an intercepted nonce be used as a key directly?

It must remain confidential and be combined securely.

What do Alice and Bob each choose in Diffie-Hellman?

Private keys (a, b) and compute public keys (ga, gb).

How is the shared key computed in Diffie-Hellman?

Alice: (gb)^a, Bob: (ga)^b.

What vulnerability does Diffie-Hellman share with RSA if keys are not verified?

Man-in-the-middle (MITM) attack.

What does a certificate do?

Binds an entity's identity to its public key.

Who issues certificates?

A trusted Certificate Authority (CA).

How does a CA ensure authenticity of certificates?

By signing them with its private key.

What must be verified before accepting a certificate?

The CA's signature, validity period, and matching identity.

How do hash functions help protect certificates?

They detect tampering with certificate contents.

What happens if a CA is compromised?

Fake certificates can be issued, undermining trust.

Are certificates foolproof security mechanisms?

No, they still require proper validation and trust management.

What is Bluetooth designed for?

Short-range, low-power wireless communication between devices.

Structure of a Bluetooth network

One master device with multiple slave devices.

Four main steps of early Bluetooth pairing

Create initialization key (Kinit), create link key (Kab), authenticate, create encryption key.

How was the initialization key (Kinit) generated in early Bluetooth?

Using the Bluetooth device address (BD_Addr), PIN, and random number (IN_Rand).

What happens if an adversary learns Kinit?

They can compute Kab and break the pairing security.

How could an attacker crack early Bluetooth pairing?

By guessing the PIN, computing Kinit', and testing possible Kab values.

Why is legacy Bluetooth pairing no longer used?

It is insecure due to weak PIN-based keys.

What system replaced legacy pairing in Bluetooth?

Secure Simple Pairing (used in Bluetooth Low Energy).