module Net::SSH::Authentication::PubKeyFingerprint

def self.fingerprint(blob, algorithm = 'MD5') 

def self.fingerprint(blob, algorithm = 'MD5')
  case algorithm.to_s.upcase
  when 'MD5'
    OpenSSL::Digest.hexdigest(algorithm, blob).scan(/../).join(":")
  when 'SHA256'
    "SHA256:#{[OpenSSL::Digest.digest(algorithm, blob)].pack('m').chomp.gsub(/=+\z/, '')}"
  else
    raise OpenSSL::Digest::DigestError, "unsupported ssh key digest #{algorithm}"
  end
end

def fingerprint(algorithm = 'MD5')

literal string +SHA256:+ is prepended.
trailing base64 padding '=' characters are stripped and the
returned by OpenSSH's `ssh-add -l -E SHA256`, i.e.,
or +SHA256+. For +SHA256+, fingerprints are in the same format
Return the key's fingerprint. Algorithm may be either +MD5+ (default),
:nodoc:
#=> "SHA256:u6mXnY8P1b0FODGp8mckqOB33u8+jvkSCtJbD5Q9klg"
my_pubkey.fingerprint('SHA256')
#=> "2f:7f:97:21:76:a4:0f:38:c4:fe:d8:b4:6a:39:72:30"
my_pubkey.fingerprint
#=> #my_pubkey = Net::SSH::KeyFactory.load_data_public_key(my_pubkey_text)
#=> "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDB2NBh4GJPPUN1kXPMu8b633Xcv55WoKC3OkBjFAbzJ alice@example.com"
my_pubkey_text = File.read('/path/to/id_ed25519.pub')
require 'net/ssh'

are supported.
This is included in pubkey classes and called from there. All RSA, DSA, and ECC keys
Public key fingerprinting utility module - internal not part of API. 
def fingerprint(algorithm = 'MD5')
  @fingerprint ||= {}
  @fingerprint[algorithm] ||= PubKeyFingerprint.fingerprint(to_blob, algorithm)
end