Explain the purpose of Cryptography?

to encrypt data so that it can travel/transmit between various nodes/hops safely

It is related to Networking concept. Simply while transmitting data from sender to receiver through wires or wireless medium, data is encrypted such that hacker or intruder cannot see or understand the language. At present most widely, AES-128 encryption standard is used. Also there are few other types.

In Extend to Shivam answer, Cryptography ensures two things: + Message Confidentiality: By encrypting the message. + Message Integrity: By signing the message.

Technique through which encrypting and decrypting is achieved.

Only thing is Secure Data Transmission and LOG-IN's.

The purpose of cryptography is to protect data transmitted in the likely presence of an adversary a cryptography transformation of data is a procedure by which plain text data is disguised, or encrypted, resulting in an altered text, called ciphertext, that does not reveal the original input. The ciphertext can be reverse-transformed by a designated recipient so that the original plaintext can be recovered. Cryptography plays an essential role in 1)Authentication 2)Data confidentiality 3)Data integrity 4)Nonrepudiation

http://www.webopedia.com/TERM/C/cryptography.html

Cryptography provides an extra level of security especially at the messages and password level. Many times we used this to encrypt passwords from Plain text to encrypted string and then decrypt it. FYI, the best practice around cryptography is NOT to create your own cryptograpgy modules/API etc. instead use and rely on .NET provided one.