Cryptography provides a set of techniques for encrypting (scrambling) so data and messages are stored and transmitted securely. Cryptography can achieve secure communications even when the transmission medium (for example, the Internet) is not trustworthy. Cryptography can also encrypt sensitive files, so an intruder cannot understand them.
Cryptography also provides techniques for decrypting (unscrambling) encrypted data and messages to reveal the original state. Assuming the techniques are implemented properly, without knowledge of the secret cryptographic key necessary to decrypt a message, reconstruction of the original message is extremely difficult. Digital Envelope, an encryption method where only a particular recipient can decrypt a message, is an important cryptography technique.
Additionally, cryptography provides a set of techniques for verification of the origin of data and messages using Digital Signatures.
When using cryptography, the only part that must remain secret are the cryptographic keys, with the exception of keys known as public keys. Algorithms, key sizes, and file formats can be made public without compromising security.