Abstract: According to embodiments, possession of a private key is replaced with possession of a registered personal electronic device, such as a smartphone, as proof of identity. Registration on a blockchain includes publishing a person's public key and registering the person's IMEI (Hardware ID) Hash, according to an embodiment. Registration on the blockchain gives others a way to verify that a transaction was signed by the person and sent from the person's personal electronic device by transmitting a challenge message to the person as a digital challenge, and verifying that the person possesses a corresponding private key by responding with an encrypted message that can be decrypted to display the original message.