code: func (conf *FileConfig) Check() error {
  	var sc ssh.Config
  	sc.SetDefaults()
  
  	for _, c := range conf.Ciphers {
  		if utils.SliceContainsStr(sc.Ciphers, c) == false {
  			return trace.BadParameter("cipher %q not supported", c)
  		}
  	}
  	for _, k := range conf.KEXAlgorithms {
  		if utils.SliceContainsStr(sc.KeyExchanges, k) == false {
  			return trace.BadParameter("KEX %q not supported", k)
  		}
  	}
  	for _, m := range conf.MACAlgorithms {
  		if utils.SliceContainsStr(sc.MACs, m) == false {
  			return trace.BadParameter("MAC %q not supported", m)
  		}
  	}
  
  	return nil
  }
docs: // Check ensures that the ciphers, kex algorithms, and mac algorithms set
  // are supported by golang.org/x/crypto/ssh. This ensures we don't start
  // Teleport with invalid configuration.