Asymmetric Cryptography
Understanding public key cryptography, digital signatures, and the foundation of secure internet communications.
What is Asymmetric Cryptography?
Asymmetric cryptography, also known as public key cryptography, uses a pair of mathematically related keys for encryption and decryption.
- Public Key: Can be shared openly and used to encrypt messages or verify signatures
- Private Key: Must be kept secret and used to decrypt messages or create signatures
- One-way Function: It's computationally infeasible to derive the private key from the public key
- Key Applications: Secure communications, digital signatures, authentication
Encryption & Decryption
How it Works:
- Alice wants to send a secure message to Bob
- Alice encrypts the message using Bob's public key
- Only Bob can decrypt it using his private key
Key Point: Anyone can encrypt a message for you, but only you can decrypt it.
Digital Signatures
How it Works:
- Bob signs a document with his private key
- Anyone can verify the signature using Bob's public key
- This proves the document came from Bob and wasn't altered
Key Point: Only you can sign, but anyone can verify your signature.
Common Asymmetric Algorithms
| Algorithm | Key Size | Use Cases | Strengths |
|---|---|---|---|
| RSA | 2048-4096 bits | Encryption, Digital Signatures | Widely supported, well-tested |
| DSA | 2048-3072 bits | Digital Signatures only | US Government standard |
| ECDSA | 256-521 bits | Digital Signatures | Smaller keys, faster operations |
| EdDSA | 256-448 bits | Digital Signatures | High performance, side-channel resistant |
| Diffie-Hellman | 2048-4096 bits | Key Exchange | Secure key agreement protocol |
HTTPS/TLS
Secure web browsing uses asymmetric cryptography for:
- Server authentication
- Key exchange
- Certificate verification
Email Security
PGP/GPG and S/MIME use asymmetric crypto for:
- Message encryption
- Digital signatures
- Sender authentication
SSH Keys
Secure Shell uses key pairs for:
- Passwordless authentication
- Server verification
- Secure remote access
Security Considerations
Best Practices:
- Use adequate key sizes (RSA: 2048+ bits, ECC: 256+ bits)
- Protect private keys with strong passphrases
- Store private keys securely (HSM, encrypted storage)
- Regularly rotate keys and certificates
- Use trusted Certificate Authorities
Common Vulnerabilities:
- Weak Random Number Generation: Predictable keys
- Side-Channel Attacks: Timing, power analysis
- Quantum Computing Threat: Future risk to current algorithms
- Key Management Issues: Poor storage, sharing practices
- Implementation Flaws: Padding oracle, timing attacks
Asymmetric vs Symmetric Cryptography
| Aspect | Asymmetric | Symmetric |
|---|---|---|
| Keys | Two keys (public/private pair) | One shared secret key |
| Speed | Slower (complex mathematics) | Faster (simple operations) |
| Key Distribution | Easy (public key can be shared openly) | Difficult (requires secure channel) |
| Use Cases | Key exchange, signatures, authentication | Bulk data encryption |
| Examples | RSA, ECDSA, DSA | AES, ChaCha20, 3DES |
Hybrid Approach: Most modern systems use both - asymmetric crypto for key exchange and symmetric crypto for actual data encryption (e.g., TLS/HTTPS).