sign.rb

# ─$ ruby -v
# ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]

require 'json'
require 'digest/md5'

api_token = 'ololo'
json      = '{ "signature": "55b47124341b5bed8627499b0eb5de80", "marker": "%marker%", "host": "%server_host%", "user_ip": "%user_ip_address%", "locale": "ru", "trip_class": "Y", "passengers": { "z": 123, "adults": "1", "children": "0", "infants": "0" }, "segments": [ { "z": 123, "origin": "MOW", "destination": "LED", "date": "2015-05-25" }, { "origin": "LED", "destination": "MOW", "date": "2015-06-18" } ] }'
params    = JSON.parse(json).sort.to_h

res = []

params.each do |_, value|
  if value.is_a?(Array)
    value.each do |item|
      res.concat(item.sort.to_h.values)
    end
  elsif value.is_a?(Hash)
    res.concat(value.sort.to_h.values)
  else
    res.push(value)
  end
end

res.unshift(api_token)
with_colons = res.join(':')
signature = Digest::MD5.hexdigest(with_colons)

puts "values separated with colons: #{with_colons}"
puts "signature: #{signature}"