SHA-1
"Secure Hash Algorithm 1", a mathematical formula for uniquely representing any amount of data in just 160 bits (20 bytes). SHA-1, and other hash algorithms (such as MD5) are used in cryptography, digital security, computer forensics, and other areas.
Note: If two files have the same SHA-1 hash value, they are assured (with an astronomical degree of certainty) to have exactly the same contents, bit for bit.