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A new method for hiding digital data in the bitstream of an ACELP speech codec is proposed in this paper. The key element of our method is an alternative search strategy for the ACELP codebook which allows for joint data hiding and speech coding. The concept has been examplarily applied to the AMR speech codec (12.2 kbit/s mode) and it is shown that steganographic data can be reliably transmitted at a rate of up to 2 kbit/s both with a negligible effect on the subjective quality of the coded speech and with reasonable computational complexity. Apart from data hiding, it is further pointed out that our method can also be exploited to reduce the codec bit rate.