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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.