How to Calculate a File's Checksum

A downloaded file's checksum can be sued to verify its integrity.

You can calculate a file's checksum to verify its integrity. The checksum can be created with two methods, either MD5 or SHA1. Both methods create a string of characters that is unique to the file you are checking. If even one bit of the file changes, the string will change. Checksum can be checked on Linux, Windows or Mac OS (SHA1 only).

Instructions

Windows

1. Download the FCIV file from the Microsoft website (see link in the Resources section) and save it on your computer.

2. Double-click the file to extract it. Save the file in C:\windows\system32\.

3. Go to the Start menu and type "cmd" (without quotations) in the Run or "Search for programs and files" field and press "Enter."

4. Navigate to the folder hosting the file.

5. Type "fciv filename" (without quotations, and substituting the name of the file you wish to check) and press "Enter" to create the MD5 checksum.

6. Type "fciv --sha1 filename" and press "Enter" to create the SHA1 checksum.

7. Compare the checksum with the one provided with the file.

Linux

1. Open a terminal and navigate to the folder where the file is located.

2. Type "md5sum filename" (without quotations, and substituting the name of your file) and press "Enter" to create the MD5 checksum.

3. Type "sha1sum filename" and press "Enter" to create the SHA1 checksum.

4. Compare the checksum with the one provided with the file.

Mac OS

1. Open Terminal and navigate to the folder hosting the file.

2. Type "/usr/bin/openssl sha1 filename" (without quotations, and substituting the name of your file) and press "Enter."

3. Compare the checksum with the one provided with the file.

Tips & Warnings

• Other versions of SHA exist but are not commonly used.

• A checksum done on different operating systems on the same file will return identical results.

• Do not try to open a file that failed a checksum check. At best the file is corrupted and will not work; at worst the file was intercepted en route and loaded with a virus.

References

• Apple: Mac OS X: How to Verify a SHA-1 Digest
• Vassar College: SHA1SUM
• Vassar College: MD5SUM

Resources

• Microsoft: Availability and description of the File Checksum Integrity Verifier utility