This package emulate the well know function sha1sum of Node.js in pure javascript allowing one to use this function in browser context.

In cryptography field, SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function designed by the United States National Security Agency and is a U.S. Federal Information Processing Standard published by the United States NIST, SHA-1 produces a 160-bit (20-byte) hash value known as a message digest. A SHA-1 hash value is typically rendered as a hexadecimal number, 40 digits long.

This a dependency of browserify

Node.js is an event-based server-side JavaScript engine.