摘要：The authors propose a new type of hash iterative structure-the ring-iterative structure with feedback which is subdivided into the single feedback ring iteration and the multiple feedback ring iteration, namely SFRI and MFRI. Prove that SFRI is at least equivalent to the MD structure in security, and MFRI is at least equivalent to SFRI in security (property 1 makes people incline to believe MFRI is more secure than MD). Analyze the resistance of MFRI, which results from the joint event on message modification, endless loop on message modification and incompatibility of the sufficient conditions, to the multi-block differential collision attack. Argue the ineffectiveness of the D-way second preimage attack on MFRI. Discuss the time and space expenses of MFRI, and point out the advantage of MFRI over the tree-iterative structure and the zipper-iterative structure.