Abstract: Nowadays most image encryption methods are mainly confined to square image encryption.In order to overcome this limitation，it proposes a new encryption algorithm which can be applied to both square and rectangular image encryption.Apply the new map that formatted through the folding and stretching of the image to the location scrambling，and change the grey of each pixel in the image by using spread function that contains chaos map，so as to get an image encryption algorithm which combines position and gray scrambling.The results of simulation show that this algorithm can achieve good image encryption of any size，and it has a satisfactory encryption effect.What’s more this algorithm has a large key space，key sensitivity and it also has many other advantages such as withstand statistical and known expressly attack.

Key words: image encryption, scrambling, diffusion function, logistic map

摘要： 目前大多数图像加密方法都只是针对方形图像的加密，为了解决这一局限性提出了一种同时适用于方形和矩形图像的加密算法。将基于图像拉伸和折叠获得的新二维映射用于图像位置置乱，将含有混沌映射的扩散函数用来改变原图各像素点的灰度值，从而得到位置置乱和灰度置乱相结合的加密算法。实验仿真结果表明该算法能够很好地实现对任意大小和形状图像的加密，且加密效果令人满意。算法具有密钥空间大、密钥敏感性强以及能够抵御统计和已知明文攻击等优点。

关键词: 图像加密, 置乱, 扩散函数, logistic映射