module Net; module SSH; module Transport
  module KeyExpander

  # Generate a key value in accordance with the SSH2 specification.
  # (RFC4253 7.2. "Output from Key Exchange")
  def self.expand_key(bytes, start, options={})
    if bytes == 0
      return ""
    end

    k = start[0, bytes]

    digester = options[:digester] or raise 'No digester supplied'
    shared   = options[:shared] or raise 'No shared secret supplied'
    hash     = options[:hash] or raise 'No hash supplied'

    while k.length < bytes
      step = digester.digest(shared + hash + k)
      bytes_needed = bytes - k.length
      k << step[0, bytes_needed]
    end

    return k
  end
  end
end; end; end