解决方法
应安装以下gem：’ruby-hmac’
$irb
>> require 'hmac-md5'
=> true
>> HMAC::MD5.new("abc").digest
=> "\324\035\214\331\217\000\262\004\351\200\t\230\354\370B~"
>> HMAC::MD5.new("abc").hexdigest
=> "d41d8cd98f00b204e9800998ecf8427e"
>>