Calculating Hashes

• published on February 26th, 2008

  The MD5 and SHA1 cryptographic hashes are commonly used to verify the integrity of files or create a fixed length digital representation of a string or file. PHP has some very easy functions to create hashes of both strings and files.

  Like most utility functions, generating these hashes is not part of the core Ruby objects. Instead, the Ruby Standard Library includes the Digest library. Let’s take a look at the equivalents to PHP’s common cryptographic hash functions in the Ruby universe.

  Comparing Functions/Methods

  PHP	Ruby
  md5	Digest::MD5
  md5_file	Digest::MD5
  sha1	Digest::SHA1
  sha1_file	Digest::SHA1
  crypt	String#crypt

  md5 vs. Digest::MD5

  In PHP, we use the md5 function to calculate an MD5 hash. In Ruby, we use Digest::MD5.

  PHP

  print md5("my string");
  // => 2ba81a47c5512d9e23c435c1f29373cb

  Ruby

  require "digest"
   
  print Digest::MD5.hexdigest("my string")
  # => 2ba81a47c5512d9e23c435c1f29373cb

  Above, we first required the Digest library using require "digest". This is similar to using require_once to include a class in PHP. To get the equivalent of the hash we’d generate using md5(), we use the hexdigest method.

  md5_file vs. Digest::MD5

  There are generally two different ways in Ruby to generate a cryptographic hash of a file. The first and easiest way is to use File.read to read the entire file contents into memory. We can then use the same MD5.hexdigest method on the contents to generate the hash.

  PHP

  print md5_file("my_file.jpg");
  // => 14b6a00b1a4eb40542cfecdc4d64940d

  Ruby

  require "digest"
   
  print Digest::MD5.hexdigest(File.read("my_file.jpg"))
  # => 14b6a00b1a4eb40542cfecdc4d64940d

  The code above works for many cases but for larger files, there’s a risk of consuming large amounts of memory. For these cases, we can initialize a new digest with Digest::MD5.new and then read the file in smaller chunks, incrementally building the digest with MD5#update.

  Ruby

  require "digest"
   
  digest = Digest::MD5.new
  File.open("my_file.jpg", "r") do |f|
    digest.update f.read(8192) until f.eof
  end
   
  print digest.hexdigest
  # => 14b6a00b1a4eb40542cfecdc4d64940d

  sha1 vs. Digest::SHA1

  We use the Digest::SHA1 class to build the equivalent cryptographic hash to PHP’s sha1 function. This works the same as the Digest::MD5 class mentioned above, and needs to require the Digest library using require "digest".

  PHP

  print sha1("my string");
  // => e19343e6c6c76f8f634a685eba7c0880648b1389

  Ruby

  require "digest"
   
  print Digest::SHA1.hexdigest("my string")
  # => e19343e6c6c76f8f634a685eba7c0880648b1389

  sha1_file vs. Digest::SHA1

  Just like with MD5, we can generate the SHA1 hash of a file in a couple different ways. We can generate the hash of the entire entire file with File.read

  PHP

  print sha1_file("my_file.jpg");
  // => 5de1a26c24b0d176c6cafd11bf1f03017bcc767b

  Ruby

  require "digest"
   
  print Digest::SHA1.hexdigest(File.read("my_file.jpg"))
  # => 5de1a26c24b0d176c6cafd11bf1f03017bcc767b

  We can take the same chunked approach we used for MD5 to generate a hash for larger files.

  Ruby

  require "digest"
   
  digest = Digest::SHA1.new
  File.open("my_file.jpg", "r") do |f|
    digest.update f.read(8192) until f.eof
  end
   
  print digest.hexdigest
  # => 5de1a26c24b0d176c6cafd11bf1f03017bcc767b

  crypt vs. String#crypt

  Finally we have PHP’s crypt function, which returns an encrypted string using a standard Unix DES-based encryption or an alternate based on the system. This operation has very similar usage in PHP and Ruby. Ruby uses the String#crypt method with a single salt parameter to get the same result.

  PHP

  print crypt("my string", "salt");
  // => saGMxKJ.nmUhU

  Ruby

  print "my string".crypt("salt")
  # => saGMxKJ.nmUhU

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