对DES的Rectangle攻击和Boomerang攻击

作为加密标准，DES（data encryption standard）算法虽然已被AES（advanced encryption standard）算法所取代，但其仍有着不可忽视的重要作用．在一些领域，尤其是金融领域，DES和Triple DES仍被广泛使用着．而近年来又提出了一些新的密码分析方法，其中，Rectangle攻击和Boomerang攻击已被证明是非常强大而有效的．因此，有必要重新评估DES算法抵抗这些新分析方法的能力．研究了DES算法针对Rectangle攻击和Boomerang攻击的安全性．利用DES各轮最优差分路径及其概率，分别得到了对12轮DES的Rectangle攻击和对11轮DES的Boomerang攻击．攻击结果分别为：利用Rectangle攻击可以攻击到12轮DES，数据复杂度为2~(62)。个选择明文，时间复杂度为2~(42)次12轮加密；利用Boomerang攻击可以攻击到11轮DES，数据复杂度为2~(58)个适应性选择明密文，时间复杂度为2~(38)次11轮加密．由于使用的都是DES各轮的最优差分路径，所以可以相信，该结果是Rectangle攻击和Boomerang攻击对DES所能达到的最好结果．

Insight into growth details and characteristics of windmill-like polyethylene crystals

The crystallization detail of polyethylene (PE) has been scarcely studied via in-situ approach since it is an extremely fast process. In this work, optical microscopy is used to investigate crystallization details and characteristics of windmill-like polyethylene crystals. It has been shown that the straight edges of the petals appear firstly and grow in pairs from their central junctions, which subsequently induce the surrounding domains in between each pairs of petals to nucleate and crystallize into twisted lamellar overgrowths. The remaining terrace-stacked lamellae which form curved edges of the petals start to develop only after the straight edges of the petals together with the twisted lamellar overgrowths have completed their growth. It is confirmed that the preferential growth direction of these petals are along crystallographic [113] axis, which has an angle of 65, with the typical direction along b-axis adopted also by the twisted lamellar overgrowths.