Privacy-Preserving Alibi Systems

Benjamin Davis, Hao Chen, and Matthew Franklin

An alibi provides evidence of a person's past location and can be
critical in proving her innocence.  An alibi must be bound to a
person's identity to prevent from being transferred to another person;
however, requiring a person to reveal her identity during alibi
creation would compromise the person's privacy.  We propose a
privacy-preserving alibi system, where a user conceals her identity
during alibi creation.  The user's identity is revealed only when she
chooses to present her alibi to a judge.  We design two
privacy-preserving alibi schemes.  In the first scheme, the alibi
corroborator is a public entity and therefore needs no privacy
protection.  Our second scheme protects the privacy of the
corroborator as well, where the identity of the corroborator is
revealed only when he chooses to help the alibi owner to present her
alibi to the judge.  We discuss the properties of our schemes and
demonstrate their advantages over current alibis.  As ubiquitous
mobile computing presents an attractive platform for deploying our
schemes, we have implemented our schemes on an Android device and
shown its satisfactory performance.