1. Introduction to Public Key Encryption
Public Key Encryption (PKE), also known as asymmetric encryption, is a cryptographic system that uses two different keys for encryption and decryption:
- Public Key (shared openly) – Used for encryption.
- Private Key (kept secret) – Used for decryption.
This method allows secure communication over untrusted networks without requiring both parties to share a secret key beforehand.
2. How Public Key Encryption Works
Key Pair Generation
A pair of mathematically related keys is generated:
- The public key is shared with anyone.
- The private key is kept secret and used for decryption.
Encryption Process
- The sender encrypts the message using the recipient’s public key.
- The encrypted message (ciphertext) is sent to the recipient.
Decryption Process
- The recipient decrypts the ciphertext using their private key.
- The original plaintext message is recovered.
Since only the private key can decrypt the message, even if a hacker intercepts the encrypted message, they cannot decrypt it without the private key.
3. Key Features of Public Key Encryption
✅ Confidentiality: Ensures that only the intended recipient can decrypt the message.
✅ Authentication: Verifies the identity of the sender (using digital signatures).
✅ Non-repudiation: The sender cannot deny sending the message if a digital signature is used.
✅ Key Distribution Security: Unlike symmetric encryption, there is no need to exchange a secret key.
4. Public Key Encryption Algorithms
Several asymmetric encryption algorithms are widely used:
1. RSA (Rivest-Shamir-Adleman)
- The most commonly used public key encryption algorithm.
- Uses large prime numbers for key generation.
- Key sizes: 1024-bit, 2048-bit, 4096-bit (larger is more secure).
- Applications: Secure email, SSL/TLS (HTTPS), digital signatures.
2. Diffie-Hellman Key Exchange
- Used to securely exchange cryptographic keys over an untrusted network.
- Does not encrypt messages, only establishes a shared secret key.
- Applications: VPNs, TLS, and SSH.
3. Elliptic Curve Cryptography (ECC)
- Provides the same security as RSA but with much smaller key sizes.
- Efficient and fast, making it ideal for mobile and IoT devices.
- Applications: Blockchain, digital signatures, secure communications.
4. ElGamal Encryption
- Based on the Diffie-Hellman key exchange.
- Provides strong encryption but is slower than RSA.
5. Public Key Encryption vs. Symmetric Encryption (AES, DES, 3DES)
| Feature | Public Key Encryption (Asymmetric) | Symmetric Encryption |
|---|---|---|
| Keys Used | Public & Private Key | Single Shared Key |
| Security | More Secure | Less Secure |
| Speed | Slower | Faster |
| Use Case | Secure key exchange, authentication | Bulk data encryption |
| Examples | RSA, ECC, Diffie-Hellman | AES, DES, 3DES |
Public Key Encryption is often combined with symmetric encryption in real-world applications. For example, in TLS/SSL (used in HTTPS), asymmetric encryption secures the initial key exchange, and then symmetric encryption (AES) is used for fast communication.
6. Applications of Public Key Encryption
🔐 Secure Communication – Used in HTTPS, SSL/TLS for encrypting website traffic.
📧 Email Encryption – PGP (Pretty Good Privacy) encrypts emails.
🔏 Digital Signatures – Ensures message integrity and authenticity.
💳 Online Banking & Payments – Encrypts transactions and login credentials.
📡 Blockchain & Cryptocurrencies – Used for securing Bitcoin and Ethereum transactions.
7. Challenges of Public Key Encryption
⚠️ Computational Overhead – Slower than symmetric encryption.
⚠️ Key Management – Public and private keys must be securely generated and stored.
⚠️ Quantum Computing Threat – Future quantum computers may break traditional public key algorithms (research on post-quantum cryptography is ongoing).
8. Conclusion
Public Key Encryption is a fundamental technology for securing digital communications. It provides confidentiality, authentication, and non-repudiation, making it essential for modern cybersecurity. While it is computationally expensive, it is often combined with symmetric encryption for efficiency.