There are provided methods and systems for authenticating a user. A method includes receiving a voice signature certificate corresponding to a setup portion of a Voice over Internet Protocol (VoIP) call. The VoIP call further has a voice conversation portion. The voice signature certificate includes a voice signature segment. The method further includes reproducing the voice signature segment to enable verification of voice continuity from the setup portion to the voice conversation portion. The verification is performing by comparing the voice signature segment to a user's voice during the voice conversation portion.