Hash Function Cryptography

Cryptographic hash function
Cryptographic hash function is a hash function that has some additional security properties that can be used for data security purposes. Generally used for authentication and data integrity. Hash function is a function that efficiently convert the input string with a string of finite length with fixed length output called the hash value.
Attributes Cryptographic Hash Functions

    Hold preimej (Preimage resistant): if known hash value h is difficult (computationally not feasible) to obtain m where h = hash (m).
    Hold second preimej (Second preimage resistant): if known input is difficult to find inputs m1 m2 (not equal to m1) which causes the hash (m1) = hash (m2).
    Hold collision (Collision-resistant): difficult to find two different inputs m1 and m2 that causes hash (m1) = hash (m2)
Understanding MD5:
Understanding MD5 (Message-Digest algortihm 5) is a cryptographic hash function widely used with 128-bit hash value (source: wikipedia). MD5 Password is one of protection to the user in using the internet facilities in cyberspace, especially those associated with passwords, because a password is the key that is very valuable for us who frequently perform activities in cyberspace, we can imagine if a cracker can break through the website database such as government sites that are highly confidential and crackers are looking for a bug from the target site with a variety of methods / hacking techniques (such as: SQL Injection, Keyloggers, Social Engineering, Trojan Horse, DDOS, etc.) so that a cracker can penetrate into the database and get the password the victim in form of hash, and if successful steal password hash in the form of a total of 32bit (example hash: fdf0ef0ea5c1620f77107f3f1047fb4c) it can easily encrypt the password MD5 hash result are living in decrypted into plain text form (plain text) by using the tools / software that can be downloaded free from uncle google and website service providers to decrypt a password MD5 hash the actual password, thereby automatically the crackers were free to do all the things she wants like a steal data, modify data, alter the look of a website (deface) and even just shut it just because its main purpose is to test the security of the target site alone and to satisfy her curiosity until he could penetrate its database and does not intend to destroy, after a database impenetrable abandoned, usually it is done by a hacker group white (WhiteHat .)
A brief history of MD5 in starting in 1991 which was designed by prof. Ronald Rivest of the university in the United States of MIT, Prof.. Ronald Rivest designed the MD5 because it has found a weakness in MD4 found Hans Dobbertin. In 1996, Hans Dobbertin found a damage / crack the MD5 compression function, but this is not an attack on the MD5 hash completely, so she announced to the users of cryptography suggested that change with Whirlpool, SHA-1, or RIPEMD-160.
But gradually MD5 can no longer be relied upon because the encrypted MD5 hash result of the damage and begin to reveal a secret known to the MD5 algorithm, it was discovered the damage on August 17, 2004 by Xiaoyun Wang, Dengguo Feng, Xuejia Lay and Hongbo Yu, judging from their name comes from Chinese bamboo curtain country, just info only that the attack did they do to be able to decrypt the MD5 hash to plain text only takes one hour, using an IBM P690 cluster.
Understanding SHA
Secure hash algorithm is an algorithm slah hash function in use. SHA is a one-way hash function created by NIST and in use with the DSS (digital signature standard). SHA is based on MD4 which is made by Ronald L. Rivest. SHA called safe (secure) because in a way that the design sedimikian computationally impossible to find messages that correspond with the message in gest that in brikan.
The steps in the SHA-1 is as follows:  
 1. Doing so padding to the message length is 448 modulus 512. 64 bit binary representation of the rest is a long message. Doing inisialisasi5 word buffer (160 bits) A, B, C, D, and E with an A = 67452301, B = efcdab89, C = 98badcfe, D = 10,325,476, and E = c3d2e1f0.
    Process message in 16 word blocks (512 bits) with the provisions
        Expansion of 16 words to 80 words by mixing and shifting techniques.
        Using four rounds of 20 bit operations on message block and buffer.
        Adding the output with the input to buffer the new value mempeoleh
    The output hash value is the final value of the buffer.
So basically the SHA-1 is a hash algorithm that maps an arbitrary length input string to be output with the 160-bit fixed length.