Improved (conference) public-key distribution system based on matrices

In a recent letter we proposed four new public-key distribution systems; however, we have since found that the third system is not secure. In the present letter we first show two attacks which can break the third system we have already proposed, and then give an improved version of this system and its corresponding conference scheme. The new version may be secure. We encourage readers to attack the improved version here and the other three schemes proposed earlier.