15. A method comprising: building a model for a dialog system with an embedded steganographic signature, a representation of the embedded steganographic signature to be returned from the dialog system responsive to interaction, by an interaction device, corresponding to the embedded signature, the embedded signature distinguishing the dialog system, for a given behavioral test input, from an unsigned dialog system or a signed dialog system without the embedded signature.
15. A method comprising: building a model for a dialog system with an embedded steganographic signature, a representation of the embedded steganographic signature to be returned from the dialog system responsive to interaction, by an interaction device, corresponding to the embedded signature, the embedded signature distinguishing the dialog system, for a given behavioral test input, from an unsigned dialog system or a signed dialog system without the embedded signature. 16. The method of claim 15 , wherein the embedded signature is encrypted with a key to enable decryption of the embedded signature at the interaction device.