Comment by midas007

? What's wrong with CTR? CTR is basically an OTP. Being OTP, encryption and decryption are basically the same construction (thank you XOR).

    cipherblockdata = blockcipher(key, nonce . block #) ^ plainblockdata
    plainblockdata = blockcipher(key, nonce . block #) ^ cipherblockdata

If MAC is needed, that can happen after encrypting, before decrypting. (Needed if bytes traverse network, but maybe not for local disk or file encryption unless.)

Edit fixed my maths: