Which one of the following is used to provide authentication and confidentiality for e-mail messages?
Digital signature
PGP
IPSEC AH
MD4
The correct answer is:
✅ PGP (Pretty Good Privacy)
Why:
- PGP provides both authentication (via digital signatures) and confidentiality (via encryption) for e-mail messages.
- Digital signature alone only authenticates and ensures integrity — it does not encrypt the content.
- IPSec AH (Authentication Header) provides integrity and authentication for IP packets, not specifically email, and does not encrypt the payload.
- MD4 is a cryptographic hash function — now considered insecure — and only provides a checksum, not authentication or confidentiality.
The correct answer is PGP.
Here’s a breakdown of why PGP (Pretty Good Privacy) is the best choice and the roles of the other options:
- PGP (Pretty Good Privacy): PGP is a comprehensive encryption program that provides both authentication and confidentiality for data communication, especially for e-mail.1
- Confidentiality: It encrypts the content of the email so that only the intended recipient can read it.2 It uses a combination of symmetric and public-key cryptography to achieve this.3
- Authentication: It uses digital signatures to verify the sender’s identity and ensure the message has not been altered in transit.4
- Confidentiality: It encrypts the content of the email so that only the intended recipient can read it.2 It uses a combination of symmetric and public-key cryptography to achieve this.3
- Digital Signature: A digital signature provides authentication and integrity (it verifies the sender and ensures the message hasn’t been changed), but it does not, by itself, provide confidentiality (encryption).5 You can sign an email without encrypting its content. While a digital signature is a component of PGP, it’s not the complete solution for both authentication and confidentiality.
- IPSEC AH (Authentication Header): IPsec is a suite of protocols used to secure Internet Protocol (IP) communications.6 The Authentication Header (AH) protocol specifically provides authentication and integrity for IP packets but does not provide confidentiality (encryption).7 It is a network-level protocol, not an application-level protocol like PGP, so it’s not used directly for e-mail messages in the same way.
- MD4: MD4 is a cryptographic hash function.8 It’s used to create a “fingerprint” of a message to ensure integrity (that the message hasn’t been changed), but it does not provide authentication or confidentiality on its own.9 MD4 is now considered cryptographically broken and is not used in modern security systems.10
PGP (Pretty Good Privacy) is the correct answer.
Here’s why each option relates to email security:
PGP (Pretty Good Privacy) ✓
PGP provides both authentication and confidentiality for email messages:
- Confidentiality: Encrypts the email content so only the intended recipient can read it
- Authentication: Uses digital signatures to verify the sender’s identity and ensure message integrity
- How it works: Uses a combination of symmetric and asymmetric encryption, plus digital signatures
Digital Signature
Provides authentication only – it verifies who sent the message and ensures it hasn’t been tampered with, but it doesn’t encrypt the message content. Anyone can still read the email.
IPSEC AH (Authentication Header)
Provides authentication only – it verifies the sender and ensures data integrity, but doesn’t encrypt the payload. Also, IPSEC operates at the network layer and isn’t specifically designed for email applications.
MD4
This is just a hashing algorithm – it creates message digests but doesn’t provide encryption or authentication by itself. MD4 is also considered cryptographically weak and deprecated.
Key Point: The question asks for a solution that provides both authentication and confidentiality. Only PGP delivers both security services specifically for email communications. PGP encrypts the message (confidentiality) and digitally signs it (authentication) in a single, integrated solution designed specifically for email security.