class RbNaCl::HMAC::SHA512

@see nacl.cr.yp.to/auth.html<br><br>can also create them.
This is a secret key authenticator, i.e. anyone who can verify signatures
signatures and also has a constant-time implementation for checking them.
the provided authenticator. The class provides methods for generating
the message by recomputing the HMAC over the message and then comparing it to
The authenticator can be used at a later time to verify the provenance of
Computes an authenticator as HMAC-SHA-512

def compute_authenticator(authenticator, message) 

def compute_authenticator(authenticator, message)
  state = State.new
  self.class.auth_hmacsha512_init(state, key, key.bytesize)
  self.class.auth_hmacsha512_update(state, message, message.bytesize)
  self.class.auth_hmacsha512_final(state, authenticator)
end

def digest

Returns:
  • (String) - The authenticator, as raw bytes 
def digest
  @authenticator
end

def hexdigest

Returns:
  • (String) - The authenticator, as hex string 
def hexdigest
  @authenticator.unpack("H*").last
end

def initialize(key)

see https://tools.ietf.org/html/rfc2104#section-3

The key for HMAC can be of any length.
RFC 2104 HMAC

Create instance without checking key length 
def initialize(key)
  @key = Util.check_hmac_key(key, "#{self.class} key")
  @state = State.new
  @authenticator = Util.zeros(tag_bytes)
  self.class.auth_hmacsha512_init(@state, key, key.bytesize)
end

def update(message)

@params [#to_str] message message to construct an authenticator for

Compute authenticator for message 
def update(message)
  self.class.auth_hmacsha512_update(@state, message, message.bytesize)
  self.class.auth_hmacsha512_final(@state.clone, @authenticator)
  hexdigest
end

def verify_message(authenticator, message)

ref: https://github.com/jedisct1/libsodium/blob/master/src/libsodium/crypto_auth/hmacsha512/auth_hmacsha512.c#L109
libsodium crypto_auth_hmacsha512_verify works only for 32 byte keys 
def verify_message(authenticator, message)
  correct = Util.zeros(BYTES)
  compute_authenticator(correct, message)
  Util.verify64(correct, authenticator)
end