Definition(en): 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. It can be used as a checksum to verify data integrity. The SHA1 file is a text document which contains single or multiple SHA1 values.