  Cryptography is always very important in data origin authentications, entity
authentication, data integrity and confidentiality. In recent years, a variety
of chaotic cryptographic schemes have been proposed. These schemes have typical
structure which performed the permutation and the diffusion stages,
alternatively. The random number generators are intransitive in cryptographic
schemes and be used in the diffusion functions of the image encryption for
diffused pixels of plain image. In this paper, we propose a chaotic encryption
scheme based on pseudorandom bit padding that the bits be generated by a novel
logistic pseudorandom image algorithm. To evaluate the security of the cipher
image of this scheme, the key space analysis, the correlation of two adjacent
pixels and differential attack were performed. This scheme tries to improve the
problem of failure of encryption such as small key space and level of security.
