A system includes a user speech profile stored on a computer readable storage device, the speech profile containing a plurality of phonemes with user identifying characteristics for the phonemes, and a speech processor coupled to access the speech profile to generate a phrase containing user distinguishing phonemes based on a difference between the user identifying characteristics for such phonemes and average user identifying characteristics, such that the phrase has discriminability from other users. The speech processor may also or alternatively select the phrase as a function of ambient noise.