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File signature

File signature

(also magic number, file header)

File signature definition

File signature is a specific sequence of bytes in a file enabling programs to identify the file type without relying on the file extension. File signatures can help programs read a file when its extension has been changed or misidentified.

The benefits of a file signature

  • Identify a file type. While file extensions are the most common way to identify a file type, a file signature can do this more accurately.
  • Verify file integrity. A file signature helps verify the file’s integrity by ensuring the file was not tampered with. Especially important for software updates and digital certificates.
  • Prevent malware. Criminals often try to disguise malicious files. An antivirus software can identify the file signature and help prevent malware.
  • Improve efficiency. Operating systems can analyze the file signature and help pick the right software to open the file.
  • Confirm compatibility. File signatures can help programs to determine whether a file is compatible with a particular device, operating system, or architecture.

Examples of file signatures

  • The JPEG file signature is FF D8 FF E0
  • The MP3 file signature is 49 44 33
  • The signature of .zip and file formats based on it (EPUB, APK, DOCX) is 50 4B 03 04.

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