objectives of cryptography
Confidentiality:
Ensures that the information in a computer system and transmitted infrormation are accessible only for reading by authorized parties. This type of access includes printing , displaying, and other forms of disclosure, including simply revealing the existence of an object.
Data Integrity:
Ensures that only authorized parties are able to modify computer system assets and transmitted information. Modification includes writing , changing, changing status, deleting, creating and delaying or replaying of transmitted messages.
Authentication:
Ensures that the origin of a message or electotronic document is correctly identified, with an assurance that the identity is not false.
Non-Repudiation:
Requires that neither the sender nor the receiver of a message be able to deny the transmission.
Encrypt & Decrypt Transformation:
1.Each e belongs to K uniquely determines the bisection from M to C , denoted by Ee, is called an encryption function or an encryption transformation.
2.Each d belongs to K uniquely determines the bisection from C to M , denoted by Dd, is called an decryption function or an decryption transformation.