Cryptography is art which deals with the data security which is the important factor which influences our day to day life.every day we are opening out gmail, facebook , youtube in all these fields the cryptography plays a prominent role. cryptography uses the discrete matthematics to some extent. normal text data is converted into some special form example: if i was chating with my friend saying "hello" hello is converted into some special form like "khoor" and tramsitted over network as "khoor" which is termed as cipher text. after reaching to my friend it converts into "hello" and visible to him as hello. converting "hello" to "khoor" is termed as encryption. In general normal text to cipher. converting "khoor" to "hello" is termed as decryption (i.e) cipher to normal form. we can use these encryption and decrytion process in daily life.
Passwords are encrypted (i.e linux uses md5,sha-1 256 bits, sha-1 512 bits).