Symmetric and Asymmetric Ciphers
Symmetric
Symmetric Ciphers (secret key) have been used for many years. A simple example of such a cipher is ROT-13, in which the letters of the plaintext are substituted for the letter 13 places ahead in the English alphabet. The encrypted text formed from the initial plaintext is called the ciphertext. To decrypt the ciphertext back into plain text simply requires the application of the same key once again.
Symmetric Keys:
- Encryption key and the decryption key are identical
- One key is very easily derived from the other
Symmetric Key Advantages:
Symmetric Key Disadvantages:
- The success of symmetric key encryption is reliant on both parties in the exchange sharing a secret key prior to the transmission of the actual business documents.
- Therefore a prior secure communication session will be required to exchange this secret key.
- This ‘prior’ communication session causes a problem in itself if the parties are unknown to each other (i.e. have no previous experience upon which to base any trust)
- Difficulties of scale also occur when any such company or user wishes to communicate securely with multiple different companies or users.
Asymmetric
Asymmetric ciphers make use of two related yet different keys. The keys are related but sufficiently different that knowing one key does not allow the derivation or computation of the other. The key pair is made up of a private key and public key. Due to the relationship between the keys, the public key can be freely distributed.
By using two different keys, one for encryption and the other for decryption, Asymmetric cryptography overcomes the main disadvantage of Symmetric cryptography. However this comes at a cost, as the algorithms used for Asymmetric cryptography are slow and therefore unsuitable for encrypting large files.