What is an MD5 Hash?

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MD5 (Message-Digest algorithm 5) is an algorithm that is used to verify data integrity through the creation of a 128-bit message digest from data input (which may be a message of any length) that is claimed to be as unique to that specific data as a fingerprint is to the specific individual.

MD5, which was developed by Professor Ronald L. Rivest of MIT, is intended for use with digital signature applications, which require that large files must be compressed by a secure method before being encrypted with a secret key, under a public key cryptosystem.

MD5 is currently a standard, Internet Engineering Task Force (IETF) Request for Comments (RFC) 1321. According to the standard, it is "computationally infeasible" that any two messages that have been input to the MD5 algorithm could have as the output the same message digest, or that a false message could be created through apprehension of the message digest.

MD5 is the third message digest algorithm created by Rivest. All three (the others are MD2 and MD4) have similar structures, but MD2 was optimized for 8-bit machines, in comparison with the two later formulas, which are optimized for 32-bit machines. The MD5 algorithm is an extension of MD4, which the critical review found to be fast, but possibly not absolutely secure. In comparison, MD5 is not quite as fast as the MD4 algorithm, but offers much more assurance of data security.

How is MD5 Useful?

If you've ever downloaded a large file, you probably want to be sure that the file wasn't corrupted in the process. This is particularly true with things like disk images, where using a corrupt ISO to install software can lead to disaster. Using the MD5 Hash, you can be sure that the file you have on your machine is digitally identical to the original file from the source.The file can be corrupted due to any of the following reasons.

      - Data loss during the download process, due to instability in the Internet connection/server
      - The file can be tampered due to virus infections or
      - Due to Hacker attacks
Many sources of large files will offer an MD5 Hash to compare your file to so that you can be sure the file has transferred completely and without any molestation.