Cryptography is the practice and study of techniques for secure communication in the presence of third parties. More generally, it is about constructing and analyzing protocols that overcome the influence of attackers or outside people and which are related to various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation. Applications of cryptography include ATM cards, computer passwords.

Cryptography is the science of using mathematics to encrypt and decrypt data. Cryptography enables you to store sensitive information or transmit it across insecure networks (like the Internet) so that it cannot be read by anyone except the intended recipient.

Goals of Cryptography

The Main Goals of cryptography

• Data Privacy(confidentiality)
• Data Authenticity(it came from from where it claims)
• Data integrity(it has not been modified on the way) in the digital world

Confidentiality

• Confidentiality is most commonly addressed goal
• The meaning of a message is concealed by encoding it
• The sender encrypts the message using a cryptographic key
• The recipient decrypts the message using a cryptographic key that may or may not be the same as the one used by the sender

Data Integrity

• Integrity Ensures that the message received is the same as the message that was sent
• Uses hashing to create a unique message digest from the message that is sent along with the message
• Recipient uses the same technique to create a second digest from the message to compare to the original one
• This technique only protects against unintentional alteration of the message
• A variation is used to create digital signatures to protect against malicious alteration

Authentication

• A user or system can prove their identity to another who does not have personal knowledge of their identity
• Accomplished using digital certificates
• Kerberos is a common cryptographic authentication system