Suppose you want to send a file from one computer to another, and you want to make sure that the file is intact, what you could do is send the file multiple times and compare them or you could use a Hash function.
A hash code of a file is basically a code which can be considered as essentially as a sum of all elements of a file ,in such a way that if anything in the file changes the hash code has to be changed. You can also not generate the file backwards from the hash.
Example:
suppose the contents of your files are 1,4,16 and 8.simple as can be considered as the sum of all these numbers which would come out to be 29.
The reason storing these numbers is so dangerous because ,there are three principles every hash must abide by,
1.Even the slightest change in the input value must produce a drastic change in the output hash,which is not true in our case.
2.Due to great advancements in computer field in the amount of time used to produce hash should be more,in order to make the process of cracking hash more difficult for the computer.
3.No two documents should have the same hash,the phenomena where two documents have the same hash is called as hash collision.
HASH COLLISION:
Two files having same hash value naturally is next to impossible.The reason Hash collision is so important is because it is used by hackers for impairment of valuable user documents.If the hacker could generate another file with same hash value,he could send a wrong message and it would still be correctly interpreted on the other end.
HASH ALGORITHM COMPARISON:
CRC32:
This is essentially checksum so that you can verify that you have received the correct file instead of checking every bit in the file.Though is fast ,it’s security is the least.L ot of frequent Hash collisions are bound to occur.
Message- Digest(MD5) Algorithm :
This was one of the most popular hashing algorithm due to two reasons: Fast and Secure. But with time,as the processors became more and more powerful it became easy to find the input value from the hash value, so much so that now ,even if you input hash value in google search it will give you the output.Passwords and information stored by using MD5 are under a greater security threat.
This Algorithm is completely cracked and rarely used.
For Detailed Explaination: :MD5 Algorithm
Secure Hash Algorithm(SHA):
This family of hash functions is one of the most widely used hash function.SHA-1 is the most widely used of the existing SHA hash functions. It is employed in several widely used applications and protocols including Secure Socket Layer (SSL) security.SHA-1 has almost been cracked, Browsers will stop using SHA-1 hashed valued SSL by 2018.Moreover, the newer versions are more secure and won’t be cracked in the near future.
Newer Versions:SHA-2,SHA-3,SHA256.
For Detailed Explaination: SHA Algorithm
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