Hash or checksum calculation

What is a checksum?

  • A checksum is a small-sized block of data derived from another block of data for the purpose of detecting errors that may have been introduced during its transmission or storage.
    By themselves, checksums are often used to verify data integrity.
    Check digits and parity bits are special cases of checksums, appropriate for small blocks of data (such as Social Security numbers, bank account numbers, computer words, single bytes, etc.).
    (source: Wikipedia).

What is a hash?

  • Hash values, hash codes, digests, or simply hashes as like the case of checksums, fixed-size codes that result from a complex algorithm which processes some block of data, e.g. a computer file. If two computer files (e.g. two photos) have the same hash code, this probably means that the two files are identical.
    Frequent hashing algorithms: MD5 (Message Digest 5), SHA (Secure Hash Algorithm), Cyclic redundancy check (CRC)

How to calculate the hash of a file?

  • Under Windows 10, you can calculate a file’s hash with the PowerShell’s "Get-FileHash" command putting as parameter the path to the file that you can to hash. The default algorithm in this case will be SHA-2 256.
  • Under Windows or MacOS, our folder comparison utility, CrcCheckCopy, calculates the CRC32 codes of the files that need to be compared. It then does the comparison by comparing the CRC codes.

CrcCheckCopy - verify large data copies by the CRC of each file

Verify by CRC that your file/folder copies are identical.

CrcCheckCopy is a command line utility for Windows and MacOS that compares files by checksum in local or remote folders/disks/DVDs. The utility records the CRC checksum of each file in an external file. It does not need concurrent access to the two folders.