SekChek’s Free Security Tools: File Hasher

View library of free security tools


The tool calculates and displays the sha1 hash (digest) value for a file. You can also use the tool to compare a file’s saved hash value with its hash value at a later point in time. This can be used to determine whether a file has been modified.

For example, assume file My Test File.docx contains the text: My old test data.

To display the file’s hash value

  • Select the file in SekChek’s Working Directory
  • Select Tools | Create File Hash

Click Save Hash to remember the file’s hash value.

File Hash: Example

Change the contents of file My Test File.docx to: My new test data.

To display the changed file’s hash value

  • Select the file in SekChek’s Working Directory
  • Select Tools | Create File Hash

File Hash: Example

To compare the two hash values

Click Compare Hash to compare the hash values of the original file and the changed version of the file.

The tool will indicate that the file’s contents (and its associated hash value) have changed.

File Hash Compare: Example

What is a hash value?

A hash value is a short numeric representation of a much larger amount of data. For example, a hash value can be used to uniquely represent the contents of a large data file or string as a very small integer value.

Hash values are commonly used to represent database keys, user passwords, and to quickly determine whether a particular file or data string has changed since its original hash value was calculated. Interestingly, a minor change to a data string will cause a major change to its hash value.

For example if a full stop is added to the end of the string ‘The quick brown fox jumps over the lazy dog’, its sha1 hash value changes:

  • from: 2FD4E1C67A2D28FCED849EE1BB76E7391B93EB12
  • to: 408D94384216F890FF7A0C3528E8BED1E0B01621

Note that hash values are not reversible. I.e. the original data string cannot be derived from its hash value.

Two examples of commonly used hash algorithms are SHA-1 and MD5.

For more information on hash algorithms and functions, see Wikipedia: Hash functions.

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