Hash valuesFirst select the desired hash function from the drop-down box: MD5, SHA1, SHA2/256 or SHA2/512. The selected hash funtion will be used to calculate the hash value (digest). Verify uses the hash function from the function column (which is the hash function used to calculate the hash value).
Calculate hashA hash value will be generated for all files that do not yet have a hash digest (the value column is empty). If a new hash value has been calculated, the status is changed to "Calculated" and Date and Time are updated to reflect the status change. If a file already has a hash value, the status is changed to "Skipped" and Date and Time remain unchanged.
[ ] re-calculate existing hashWith this box is checked [v] a new hash digest is computed for all files, even if a hash value already exists (status is Calculated or Passed). A new hash digest is created and the existing hash value is overwritten. Date and Time are updated to reflect the status change. When this box is NOT checked, files that already have their hash value calculates are Skipped.
[ ] re-calculate failed hashWith this box is checked [v] a new hash digest is computed for files that have status Failed. A new hash digest is created and the existing hash value is overwritten. Date and Time are updated to reflect the status change.
Verify hashExisting has values are verified: the hash value is re-calculated and compared to the existing hash value. If the two values match the status is changed from "Calculated" to "Verified" and Date and Time are updated. If the two values do not match the status is changed to "Failed", Date and Time remain unchanged.
To calculate a new has value, the hash function specified for that file is used (NOT the hash function from the drop-down box). If the function column specifies a hash function that is not supported by HashTFS, the status is changed to "Error". The hash function from the drop-down box is ONLY used to generate initial hash values for files that do not yet have a hash digest.
Hash functionsThere are several ways to compute a checksum (digest). HashTFS supports three popular hash functions to generate or validate a checksum: MD5, SHA1 and SHA2.
MD5An MD5 hash is still used a lot to verify the integrity of files, it is however considered less secure.
SHA1SHA1 is the successor of MD5 but today it is not used very often anymore because it does not meet the current cybersecurity standards.
SHA2SHA2 was developed after successful brute force attacks on SHA1. HashTFS supports two implementations of SHA2: SHA2/256 and SHA2/512. SHA2/256 uses 32-byte words and produces a 256 bit digest, where SHA2/512 uses 64-byte words which result in a 512 bit hash value. SHA2/256 is faster on 32-bit computers where SHA2/512 tends to be faster on 64-bit hardware. In terms of secuity there is not much difference between the two.
Recommended hash functionsTo calculate file hash(es) select the appropriate has function depending on your hardware: SHA2/256 for 32-bit processor, SHA2/512 for 64-bit processor. SHA1 hash values can be calculed for compatibility. Although MD5 is less secure than SHA2 it is often used to detect file changes. It is much faster than SHA2.
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