About
A sha1 (Secure Hash Algorithm) is an hash function that generates 40-character string (message_digest) composed of hexadecimal characters (0–9 and a–f).
In a file system, it's calculated based on the contents of a file or directory structure (ie several files)
(Secure Hash Algorithm-1) produces a 160-bit digest.
An SHA-1 hash is:
- a 40 hexadecimal character string.
- ie 160 bits. (ie 1 hexa goes from 0 to 4 bit to code 0 to 16 character)
Security
sha1 is not a secure hash algorithm. Ref
Tools
They compute and check SHA1 message digest.
You can produce it with :
sha1sum
the linux sha1sum utility.
sha1sum myFile
3fc008db425fbe2027f0002f9ae58f9ccec4b08c myFile
Fciv
the Microsoft File Checksum Integrity Verifier.
fciv -sha1 thefile.exe
//
// File Checksum Integrity Verifier version 2.05.
//
e901af858a964192cec891cdbae76ca6789d741c thefile.exe
Openssl
openssl dgst -sha1 file