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Creating MD5 digests with Ruby

1 reply on 1 page. Most recent reply: Dec 22, 2010 7:15 AM by roger pack

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Andrew Johnson

Posts: 39
Nickname: jandrew
Registered: Mar, 2004

Simple things ...
Creating MD5 digests with Ruby Posted: Mar 26, 2004 2:41 AM
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byline: Andrew L. Johnson

MD5 is a one-way hashing algorithm for creating digest "signatures" or checksums of strings (usually entire files). Ruby’s standard library includes MD5 as part of the Digest:: set of extension classes.

Creating MD5 checksums is a simple matter of requiring the digest/md5 library and using either the Digest::MD5.digest or Digest::MD5.hexdigest class methods to return the digest of a given string — we will use hexdigests in this article as they are printable:

  #!/usr/bin/ruby -w
  require 'digest/md5'
  digest = Digest::MD5.hexdigest("Hello World\n")
  puts digest


MD5 digests are 128 bit (16 byte) signatures and are the most common method of providing checksums for files available on the net. To create a checksum of an entire file you need only pass in the file as a string. The following will print out the filename and md5 digest of all the files passed to it on the command line:

  #!/usr/bin/ruby -w
  require 'digest/md5'
  ARGV.each do |f|
    digest = Digest::MD5.hexdigest(
    puts &
amp;quot;#{f}: #{digest}"

Sometimes you want to do more than just calculate the checksum of a single string — maybe you have a large file and want to calculate the digest in small, memory friendly chunks; or maybe you are calculating a digest from a stream of input. In such cases you can create a Digest::MD5 object and use the #update (alias: #<<), digest, and #hexdigest methods.

For example purposes, we will create a digest by reading and adding one line at a time from a test file as well as calculating the digest all at once. I will use the source for this article as the test-file:

  #!/usr/bin/ruby -w
  require 'digest/md5'
  filename = 'MD5.rdoc'

  all_digest = Digest::MD5.hexdigest(

  incr_digest =
  file =, 'r')
  file.each_line do |line|
    incr_digest << line

  puts incr_digest.hexdigest
  puts all_digest

Saving this as md.rb and running it produced the following output:

  ~$ ruby md.rb

In addition to providing checksums for files you make available, or checking files and packages you’ve downloaded, another use is fingerprinting sensitive directories on your system. Creating a database of MD5 digests for sensitive files or directories means you can periodically cross-check your sensitive data against the database to see if anything has been changed without your knowledge. This can provide you with a very simple to implement addition to your intrusion detection tools.

Read: Creating MD5 digests with Ruby

roger pack

Posts: 1
Nickname: rogerdpack
Registered: Dec, 2010

Re: Creating MD5 digests with Ruby Posted: Dec 22, 2010 7:15 AM
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Sorry to resurrect, but thought I'd add that this method:


could have been useful here, at well.

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