Cryptography

Cryptography

Cryptography can be defined as the conversion of data into a scrambled code that can be deciphered and sent across a public or private network. Cryptography uses two main styles or forms of encrypting data; symmetrical and asymmetrical. Symmetric encryptions, or algorithms, use the same key for encryption as they do for decryption. Other names for this type of encryption are secret-key, shared-key, and private-key. The encryption key can be loosely related to the decryption key; it does not 

necessarily need to be an exact copy.

Symmetric cryptography is susceptible to plain text attacks and linear cryptanalysis meaning that they are hackable and at times simple to decode. With careful planning of the coding and functions of the cryptographic process these threats can be greatly reduced. Asymmetric cryptography uses different encryption keys for encryption and decryption. In this case an end user on a network, public or private, has a pair of keys; one for encryption and one for decryption. These keys are labeled or known as a public and a private key; in this instance the private key cannot be derived from the public key.
The asymmetrical cryptography method has been proven to be secure against computationally limited intruders. The security is a mathematical definition based upon the application of said encryption. Essentially, asymmetric encryption is as good as its applied use; this is defined by the method in which the data is encrypted and for what use. The most common form of asymmetrical encryption is in the application of sending messages where the sender encodes and the receiving party decodes the message by using a random key generated by the public key of the sender.

reference 

https://en.wikipedia.org/wiki/Replay_attack