Cryptographic hash functions compute a fixed length string, the message digest. Even a small change in the input data should produce a large change in the digest, and it is 'very difficult' to create two messages with the same digest.

A cryptographic hash can be used for checking the integrity of data, but there is no secret involved in the hashing, so anyone can create the hash of a given message.

# compute the SHA-256 digest of the message.
RbNaCl::Hash.sha256(message)
#=> "..." # a string of bytes.

# compute the Blake2b digest of a message
RbNaCl::Hash.blake2b(message)
#=> "..." # a string of bytes.