What are the differences between symmetric and asymmetric key systems?

Symmetric Key Systems

Symmetric key systems, also known as secret key cryptography, use a single, shared secret key for both encryption and decryption. This means the sender and receiver must both possess the identical key. The security of this system relies on the secrecy of the key. If the key is compromised, the encrypted data can be read by unauthorized parties. Symmetric algorithms are generally faster and more efficient for encrypting large amounts of data.

An example of a symmetric algorithm is the Advanced Encryption Standard (AES).

Asymmetric Key Systems

Asymmetric key systems, often called public key cryptography, use a pair of mathematically related keys: a public key and a private key. Data encrypted with the public key can only be decrypted by the corresponding private key, and vice versa. The public key can be freely distributed, while the private key must be kept secret by its owner. This method simplifies key distribution problems inherent in symmetric systems.

Asymmetric algorithms are typically slower than symmetric ones, making them less suitable for bulk data encryption. Their primary uses include secure key exchange, digital signatures, and establishing non-repudiation, which confirms that a sender cannot deny having sent a message and a receiver cannot deny having received it (McCullagh A, Caelli W).

An example of an asymmetric algorithm is RSA.

Key Differences

The core differences between symmetric and asymmetric key systems are summarized below:

• Number of Keys: Symmetric systems use one key, while asymmetric systems use a pair of keys (public and private).
• Key Distribution: Symmetric keys must be securely exchanged between parties before communication can begin, which is a challenge. Asymmetric public keys can be openly distributed, simplifying key exchange.
• Speed: Symmetric encryption is significantly faster, making it suitable for encrypting large data volumes. Asymmetric encryption is much slower.
• Purpose: Symmetric systems are mainly used for efficient bulk data encryption. Asymmetric systems are used for secure key exchange, digital signatures, and ensuring non-repudiation.
• Security Basis: Symmetric security relies solely on keeping the single key secret. Asymmetric security relies on keeping the private key secret and the mathematical relationship between the public and private keys.

These concepts are covered in detail in texts on network security, such as "Guide to Computer Network Security" by Joseph Migga Kizza (Kizza, J.M. Guide to Computer Network Security).