Message Digest

Why Trust Techopedia

What Does Message Digest Mean?

A message digest is a cryptographic hash function containing a string of digits created by a one-way hashing formula.


Message digests are designed to protect the integrity of a piece of data or media to detect changes and alterations to any part of a message. They are a type of cryptography utilizing hash values that can warn the copyright owner of any modifications applied to their work.

Message digest hash numbers represent specific files containing the protected works. One message digest is assigned to particular data content. It can reference a change made deliberately or accidentally, but it prompts the owner to identify the modification as well as the individual(s) making the change. Message digests are algorithmic numbers.

This term is also known as a hash value and sometimes as a checksum.

Techopedia Explains Message Digest

The particular message digest will change if the file changes. Not only can message digests help determine file changes, but can also assist in locating duplicate files.

Message digests can be produced on UNIX systems with the MD5 command. MD5s are securely stored on systems and can reveal if an unauthorized user has accessed a file. It has been shown that MD5 is unreliable with problems relating to collision (where 2 keys for different data are the same) and it is no longer used.

File sharing programs, such as peer-to-peer (P2P), utilize message digests to warn users when downloading identical files. It can also pinpoint the origin of duplicate downloads. Besides MD5, SHA and CRC32 are other message digest algorithms.

Message digests are encrypted with private keys creating a digital signature. This results in a type of validation ensuring that the appropriate user is accessing protected information. Message digests protect one-way hash algorithms taking random data and transmitting a set length hash value.

To begin the process a message digest is initialized. Then the data is processed through the message digest by using updates. Final operations include padding, during which the message digest completes the hash computation and resets itself. However, the digest can be reset at any time during the process.


Related Terms

Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.