Abstract: In the process of embedding secret information into a limited large vector image,a pseudo-random sequence is generally used to select the position of the pixel to be embedded in the information.When the secret information is large enough,the pseudo-random number generated by the pseudo-random number generator would be repeated,thus resulting in collision.If we choose to skip all the duplicate locations,the amount of confidential information which had been embedded in a limited large vector image would be limited.Therefore,this paper proposed an improved algorithm.When the sequence generated by the pseudo-random number generator reoccurs,the repeated position will not be skipped and the embedded operation will be performed normally,and the operation process at the repeated position will be recorded and saved in some form.In reverse extraction,the key and this action record are used to extract the ciphertext.The improved algorithm,combined with cryptography and information hiding,greatly expands the amount of secret information hidden in a limited number of pictures and improves the security of information hiding.

Key words: Collusion, Cryptography, Image processing, Information hiding, Pseudo-random transform, Quantity of information hiding, Security, Stream cipher