What is the difference between symmetric and asymmetric encryption?
Symmetric and asymmetric encryption techniques are modern cryptosystems mainly used to secure data. And they heavily depend on computationally complex algorithms and cryptographic keys to achieve the security requirements. In collaboration with hashing and digital signature algorithms, these cryptographic algorithms are used to achieve confidentiality, integrity, authentication and nonrepudiation security objectives. Besides, the algorithms are capable of securing data while at rest, in use and in transit. And of course, they primarily depend on long and secure cryptographic keys to achieve the objectives. However, symmetric algorithms never serve nonrepudiation requirements.
Symmetric encryption is a cryptosystem that employs shared secret key among all communicating parties. This shared key is used for both encrypting and decrypting a message. That means the sender and receiver of the message must possess a copy of same key in order to establish secure communication. For this reason, it is sometimes known as secret key cryptography / private key cryptography. As long as we use long keys, the algorithm is very difficult to break. In addition, the algorithm can be stream or block cipher based while applied to encryption and decryption processes. We use it in combination with public key cryptography to deliver key distribution services through, for instance, Diffie–Hellman algorithm.
The algorithm is more convenient to secure data while at rest. But, it will be involved in bulk encryption requirements even while the data traverses the networks as well. Furthermore, it is more efficient and faster than asymmetric encryption algorithms. However, it is less scalable than public key cryptography.
Assume, for instance, there are 100 users. We use a formula ((n*(n – 1))/2) to calculate the number of encryption keys. We would have ((100*(100-1))/2) = 4950 keys to accommodate the entities.
Examples: DES, AES, Blowfish, IDEA, Serpent, Twofish, Rivest Ciphers (RC), Skipjack, CAST, etc.
Finally yet importantly, the biggest weakest with this algorithm is secure key distribution between communicating parties. That is where public key cryptography comes into play.
Asymmetric encryption is a cryptosystem that uses public-private key pairs to establish secure communication channel between interacting entities. Depending on the type of services it provides, we use the public and private key pairs to encrypt and decrypt messages interchangeably. However, if we encrypt a message with the public key, we must decrypt it using the corresponding private key only and vice versa. Moreover, we sometimes call it public key cryptography.
Public key cryptography is much slower algorithm than secret key cryptography. We mainly apply it to secure data in transit. Furthermore, the algorithm facilitates secure key exchange among communicating parties. More often, we employ symmetric encryption to achieve bulk encryption and asymmetric algorithms to establish secure key distribution between parties. But, unlike symmetric cryptosystems, asymmetric algorithms provide nonrepudiation and digital signature services, in addition to the confidentiality, integrity, and authentication services.
We use “2n” to calculate the key requirements between communicating parties. For the previous example, we only need (2*100) which will be only 200 public-private key pairs.
Examples: RSA, ECC, Diffie–Hellman (DH), ElGamal, DSS (Digital signature standard), etc.
Above all, public key cryptography is much slower than symmetric algorithms but highly scalable algorithm than shared key cryptography.