A chaos-based cryptosystem for fractal image coding is proposed.The R’enyi chaotic map is employed to determine the order of processing the range blocks and to generate the keystream for masking the encoded sequence.Compared with the standard approach of fractal image coding followed by the Advanced Encryption Standard,our scheme offers a higher sensitivity to both plaintext and ciphertext at a comparable operating efficiency.The keystream generated by the R’enyi chaotic map passes the randomness tests set by the United States National Institute of Standards and Technology,and so the proposed scheme is sensitive to the key. A chaos-based cryptosystem for fractal image coding is proposed. The R’enyi chaotic map is employed to determine the order of processing the range blocks and to generate the keystream for masking the encoded sequence. Compared with the standard approach of fractal image coding followed by the Advanced Encryption Standard, our scheme offers a higher sensitivity to both plaintext and ciphertext at a comparable operating efficiency. The keystream generated by the R’enyi chaotic map passes the randomness tests set by the United States National Institute of Standards and Technology, and so the proposed scheme is sensitive to the key.