JPEG image encryption effectively protects image privacy while preserving the compression format, enabling efficient encryption. However, existing JPEG encryption methods typically encrypt each color channel separately, which may still leak information visually in the ciphertext. To address this issue, we propose a cross-channel encryption method that mixes different color channels to enhance image security. Additionally, traditional JPEG encryption methods suffer from slow encryption speeds, large ciphertext sizes compared to the original image, and uncontrolled ciphertext expansion. To overcome these challenges, we introduce a tunable range substitution strategy for AC coefficients, allowing users to balance between image security and ciphertext size, thus improving the practicality of the encryption scheme. By optimizing serial operations in the encryption algorithm, we accelerate the encryption process in parallel. Experimental results demonstrate that, compared to existing methods, our approach achieves a lower PSNR while maintaining high encryption efficiency and controllable ciphertext size.