Cryptografi

Cryptografi is method of securing data that can be used to maintain data confidentilty, authenticity or integegrity of the data and authenticity (authentication) sender. This method is intended of important that is  retricted or confidential information send of public communication can no be know and used by unauthorized parties. criptografi is studi of learning the system in which confidentiality and authentiticity data can be guaranteed. 

Cryptografi is the science and art to keep the message to be safe.. The actors or practitioners are called cryptographers cryptography. A cryptographic algorithm (a cryptographic algorithm), called a chiper, a mathematical equation that is used for encryption and decryption. usually these two equations (for encryption and decryption) has a mathematical relationship is quite close.

The process undertaken to secure a message (called plaintext) into a hidden message (called Chipertext) is encrypted (encryption). Encryption is used to encrypt the data or information that can not be read by unauthorized people. by encrypting your data is encoded (encrypted) using a key (key). to open (decrypt) data were used also a key that can be the same as the key to encrypt (for the case of private key cryptography) or with a different key (for the case of public key cryptography).

Hash

they provide a mapping between an arbitrary length input, and a (usually) fixed length (or smaller length) output. it can be anything from a simple crc32, to a full blown cryptographic hash function such as MD5 or SHA1/2/256/512. the point is that  there's one-way mapping going on. it's always a many : mapping (meaning there will always be collisions) since every function produces a smaller output than it's capable of inputting (if you feed every possible 1mb file into MD5, you'll get a ton of collisions).

Encryption
they provide a 1:1 mapping between an arbitrary length input and output. and the are always reversible. the important thing to tnote is that it's reversible using some method. and it's always 1:1 for a given key. Now, there are multiple input : key pairs that might generate the same output (in fact there usually aare, depending on the encryption funciton). good encrypted data is indistinguishable from random noise. this is different from a good hash output which is always of a consistent format.


reference : http://stackoverflow.com