Privacy-preserving location corroborations

A computer-readable storage medium comprising computer-executable instructions that, when executed by a processor, cause the processor to perform operations comprising:

• receiving a proof initiation message from a user device, wherein the proof initiation message requests a location proof to be created for use by the user device to prove that a user associated with the user device was located at a location at a time;
• in response to receiving the proof initiation message from the user device,
• recording the time,
• generating a session identifier that uniquely identifies a communications session between the user device and a localized corroborator system, and
• sending the session identifier to the user device;
• receiving the session identifier and a message digest from the user device, wherein the message digest comprises a bitwise XOR of a user identifier and a location proof identifier generated by the user device using a cryptographic hash function, wherein the user identifier uniquely identifies the user associated with the user device, and the location proof identifier uniquely identifies the location proof to be created by the localized corroborator system;
• concatenating a corroborator identifier, the location, a time difference between the time and a current time, the session identifier, and the message digest to create a concatenated message, wherein the corroborator identifier uniquely identifies the localized corroborator system;
• signing the concatenated message using a private key to create the location proof;
• and
• sending the corroborator identifier and the location proof to the user device for use by the user device to prove that the user was located at the location at the time.

A method comprising:

• receiving, by a localized corroborator system comprising a processor, a proof initiation message from a user device, wherein the proof initiation message requests a location proof to be created for use by the user device to prove that a user associated with the user device was located at a location at a time;
• in response to receiving the proof initiation message from the user device,
• recording, by the localized corroborator system, the time,
• generating, by the localized corroborator system, a session identifier that uniquely identifies a communications session between the user device and the localized corroborator system, and
• sending, by the localized corroborator system, the session identifier to the user device;
• receiving, by the localized corroborator system, the session identifier and a message digest from the user device, wherein the message digest comprises a bitwise XOR of a user identifier and a location proof identifier generated by the user device using a cryptographic hash function, wherein the user identifier uniquely identifies the user associated with the user device, and the location proof identifier uniquely identifies the location proof to be created by the localized corroborator system;
• concatenating, by the localized corroborator system, a corroborator identifier, the location, a time difference between the time and a current time, and the message digest to create a concatenated message, wherein the corroborator identifier uniquely identifies the localized corroborator system;
• signing, by the localized corroborator system, the concatenated message using a private key to create the location proof;
• and
• sending, by the localized corroborator system, the corroborator identifier and the location proof to the user device for use by the user device to prove that the user was located at the location at the time.