Symmetric and Asymmetric Cryptography

Symmetric Cryptography

Symmetric cryptography uses the same secret key for both encryption and decryption.

Characteristics

• A single shared secret key.
• Faster than asymmetric cryptography because of simpler mathematical operations.
• Securely sharing the key between sender and receiver is challenging.
• Used for encrypting large data sets, like files, databases, and network communications.

Advantages

1. High speed, suitable for real-time applications.
2. Requires fewer computational resources.

Disadvantages

1. Difficulty in securely exchanging and managing keys (key distribution problem).
2. Does not support authentication or non-repudiation on its own.

Examples of Symmetric Algorithms

1. AES (Advanced Encryption Standard):

   • Highly secure and widely used.
   • Key sizes: 128, 192, or 256 bits.
   • Used in SSL/TLS, VPNs, and file encryption.

2. DES (Data Encryption Standard):

   • Key size: 56 bits (now considered insecure).
   • Deprecated in favor of AES.

3. Triple DES (3DES):

   • Enhances DES by applying encryption three times.
   • More secure than DES but slower.

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2. Asymmetric Cryptography

Asymmetric cryptography uses a pair of keys: a public key for encryption and a private key for decryption.

Characteristics

• Public key is shared openly, while the private key is kept secret.
• Slower than symmetric cryptography due to complex mathematical operations.
• Easier because only the private key must remain secret.
• Used for secure key exchange, digital signatures, and authentication.

Advantages

1. Solves the key distribution problem (public key can be shared openly).
2. Enables authentication, integrity, and non-repudiation via digital signatures.

Disadvantages

1. Computationally intensive, making it unsuitable for encrypting large data.
2. Slower than symmetric cryptography.

Examples of Asymmetric Algorithms

1. RSA (Rivest-Shamir-Adleman):

   • Based on the difficulty of factoring large prime numbers.
   • Key sizes: 2048+ bits for security.
   • Used in SSL/TLS, digital signatures, and email encryption.

2. ECC (Elliptic Curve Cryptography):

   • Provides equivalent security to RSA with smaller key sizes.
   • Used in modern applications like mobile devices and IoT.

3. Diffie-Hellman:

   • Used for secure key exchange (not encryption directly).
   • Often combined with symmetric cryptography for secure communications.

4. DSA (Digital Signature Algorithm):

   • Focused on generating and verifying digital signatures.

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Comparison: Symmetric vs. Asymmetric Cryptography

Feature	Symmetric Cryptography	Asymmetric Cryptography
Key Usage	Same key for encryption and decryption.	Public and private key pair.
Speed	Faster (better for bulk encryption).	Slower (used for smaller data or key exchange).
Security	Relies on secure key distribution.	More secure for key exchange.
Use Case	Encrypting large data.	Secure key exchange, digital signatures, authentication.
Examples	AES, DES, 3DES, RC4	RSA, ECC, Diffie-Hellman, DSA

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