Everything you need to know about MD5 Message Digest Algorithm
What is MD5 and what does it stand for?
MD5 stands for “Message Digest algorithm 5”.
It’s a hash function that will convert any input (number, string or file from any length) to an output containing 32 hexadecimal characters. It’s a one-way algorithm that does not have a revert method to return to the original input from the MD5 output.
That’s it, 32 hexadecimal characters, whatever the input is. It only includes letters from a to f and digits from 0 to 9. If you see anything else or if it’s longer than 32 characters, it isn’t an MD5 hash.
For example, the MD5 hash corresponding to the string “MD5Online” is “d49019c7a78cdaac54250ac56d0eda8a”.
Who invented MD5?
In 1991 Ronald Rivest announced the MD5 message hash function with official publication RFC 1321 in 1992.
What is the difference between MD4 and MD5?
- 1. A fourth round has been added.
- 2. Each step now has a unique additive constant.
- 3. The function g in round 2 was changed from (XY v XZ v YZ) to (XZ v Y not(Z)) to make g less symmetric.
- 4. Each steps now adds in the result of the previous step. This promtes after "avalanche effect", where if an input is changed slightly the output changes significantly.
- 5. The order in which input words are accesse in rounds 2 and 3 is changed, to make these patterns less like each other.
- 6. The shift amounts in each rounds have been approximately optimized to yield a faster "avalanche effect".
From Ron’s “The MD4 Message-Digest Algorithm" RFC 1186 in 1990:
The algorithm takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given prespecified target message digest. The MD4 algorithm is intended for digital signature applications, where a large file must be "compressed" in a secure manner before being encrypted with a private (secret) key under a public-key cryptosystem such as RSA."
From Ron's “The MD5 Message-Digest Algorithm" RFC 1321 in 1992:
The MD5 algorithm is an extension of the MD4 message-digest algorithm. MD5 is slightly slower than MD4, but is more conservative in design. MD5 was designed because it was felt that MD4 was perhaps being adopted for use more quickly than justified by the existing critical review; because MD4 was designed to be exceptionally fast, it is "at the edge" in terms of risking successful cryptanalytic attack. MD5 backs off a bit, giving up a little in speed for a much greater likelihood of ultimate security.
How is MD5 Used?
MD5 has many uses but the most popular is storing passwords in a database especially on Linux systems.
The most common application of the MD5 algorithm post 2008 is now as a checksum to validate that a transferred file has not been tampered with.
What are the issues with MD5?
In 2004 collisions vulnerability confirming the hash could be compromised was proven in the research paper Collisions for Hash Functions MD4, MD5, HAVAL-128 and RIPEMD by Xiaoyun Wang, Dengguo Feng, Xuejia Lai and Hongbo Yu.
By 2008 MD5 was considered "cryptographically broken and unsuitable for further use" with Vulnerability Note VU#836068 issued by the Software Engineering Institute at Carnegie Mellon University.
The Flame Malware Collision Attack is the most infamous exploitation of the issues with MD5. The attack used chosen prefix collision to generate fake Microsoft security certificates. The malware was operational for at least two years before being discovered in 2012 by Russian security firm Kaspersky Labs and targeted computers running the Microsoft Windows operating system with the intention of cyber espionage in Middle Eastern countries.
Is MD5 being used today?
Yes, large technology companies and governments still have MD5 in use. Companies such as WordPress still use MD5 hashing for password management.
A study by the University of Piraeus found that almost 50% of content management systems are still using outdated hashing schemes of which MD5 is the dominant found.
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