class SSHKey

def randomart(dgst_alg = "MD5")
  fieldsize_x = 17
  fieldsize_y = 9
  x = fieldsize_x / 2
  y = fieldsize_y / 2
  case dgst_alg
    when "MD5"    then raw_digest = Digest::MD5.digest(ssh_public_key_conversion)
    when "SHA256" then raw_digest = Digest::SHA2.new(256).digest(ssh_public_key_conversion)
    when "SHA384" then raw_digest = Digest::SHA2.new(384).digest(ssh_public_key_conversion)
    when "SHA512" then raw_digest = Digest::SHA2.new(512).digest(ssh_public_key_conversion)
  else
    raise "Unknown digest algorithm: #{digest}"
  end
  augmentation_string = " .o+=*BOX@%&#/^SE"
  len = augmentation_string.length - 1
  field = Array.new(fieldsize_x) { Array.new(fieldsize_y) {0} }
  raw_digest.bytes.each do |byte|
    4.times do
      x += (byte & 0x1 != 0) ? 1 : -1
      y += (byte & 0x2 != 0) ? 1 : -1
      x = [[x, 0].max, fieldsize_x - 1].min
      y = [[y, 0].max, fieldsize_y - 1].min
      field[x][y] += 1 if (field[x][y] < len - 2)
      byte >>= 2
    end
  end
  fieldsize_x_halved = fieldsize_x / 2
  fieldsize_y_halved = fieldsize_y / 2
  field[fieldsize_x_halved][fieldsize_y_halved] = len - 1
  field[x][y] = len
  type_name_length_max = 4  # Note: this will need to be extended to accomodate ed25519
  bits_number_length_max = (bits < 1000 ? 3 : 4)
  formatstr = "[%#{type_name_length_max}s %#{bits_number_length_max}u]"
  output = "+--#{sprintf(formatstr, type.upcase, bits)}----+\n"
  fieldsize_y.times do |y|
    output << "|"
    fieldsize_x.times do |x|
      output << augmentation_string[[field[x][y], len].min]
    end
    output << "|"
    output << "\n"
  end
  output << "+#{"-" * fieldsize_x}+"
  output
end