Device, method and system for communication between devices in the absence of time synchronization

A client device comprising a processor and a memory storing programming instructions that configure the processor to:

• receive a first clock-skew value from a clock-skew server;
• embed the first clock-skew value in a first portion of a first electronic message, the first portion being distinct from a second portion of the first electronic message, wherein the second portion includes a payload;
• and
• send the electronic message to a recipient device, wherein the recipient device is configured to compute a time of generation of the electronic message based on the first clock-skew value and a second clock-skew value received from the clock-skew server.

A method of transmitting a cryptographic key securely from a first client device to a first recipient device using a first electronic message prepared by the first client device according to MIKEY-SAKKE identity based encryption scheme comprising:

• i) enabling, prior to transmitting the first electronic message, both the first client device and the first recipient device to cryptographically trust a clock skew service;
• ii) obtaining, prior to transmitting the first electronic message, a first clock skew certificate from the clock skew service by the first client device, the first clock skew certificate being cryptographically signed by the clock skew service and containing at least the identity of the first client device and a first clock-skew value representing the difference in time between the first client device and the clock-skew service;
• iii) obtaining, prior to transmitting the first electronic message, a second clock skew certificate from the clock skew service by the first recipient device, the second clock skew certificate being cryptographically signed by the clock skew service and containing at least the identity of the first recipient device, a second clock-skew value representing the difference in time between the first recipient device and the clock-skew service;
• iv) embedding, prior to transmitting the first electronic message, the first clock skew certificate into the first electronic message by the first client device along with a first timestamp representing the clock time within the first client device;
• v) receiving, by the first recipient device, the first electronic message transmitted by the first client device;
• vi) extracting the first clock-skew value from the first electronic message, by the first recipient, after cryptographically verifying the authenticity of the first clock skew certificate contained in the first electronic message;
• and
• vii) computing, by the first recipient device, the time of preparation of the first electronic message with reference to the clock time within the first recipient device, using the first clock-skew value, the second clock-skew value and the first timestamp.