As past works have shown, information‐theoretically secure implementations transmitters of Y00 quantum noise randomised cypher are possible. An advance to the provably secure Y00 protocol by bridging gaps between experimental results and theoretical analyses under so‐called quantum collective measurement attacks with known plaintexts is aimed. It would be the strongest attack on the Y00 protocol in the context of quantum key distribution protocols. However, recently proposed security evaluations under the attacks were too abstract to apply to experiments. Therefore, security analyses directly evaluable with the equipped Y00 transmitters under attack are offered. Thus, new security indices are proposed instead of ordinary security measures, such as the bit‐error‐rate guarantee between optical signals or a masking size. Contrarily, unsolved problems are also listed.