Method for securing a private key on a mobile device

Abstract

Systems and methods are provided for securing a private key on a mobile device for use with public key cryptography. Specifically, a private key is reduced to two partial keys where the partial keys are stored on separate electronic devices. The partial keys combine to temporarily regenerate the private key for the purposes of notarizing (digitally signing) messages or documents, and decrypting a message or document that was encrypted using the corresponding public key. The partial keys in some embodiments may be a secret key, which can be derived from an account identifier and a password, and an exclusive key, which can be derived from the secret key and the private key. The private key can be regenerated from the secret key and the exclusive key. With the partial keys stored on separate devices, another layer of practical security is provided to public key cryptography.

What is claimed is: 
     
         1 . A method for securing a private key k, comprising:
 providing a first electronic device and a second electronic device;   pairing the first electronic device and the second electronic device via a wireless communication protocol;   generating a private key k on the second electronic device, wherein the private key k is associated with a public key K; and   splitting the private key k into a first partial key and a second partial key, wherein the first partial key is stored on the first electronic device, and the second partial key is stored only on the second electronic device such that the private key k can only be reconstructed on the second electronic device using both partial keys.   
     
     
         2 . The method of  claim 1 , further comprising:
 activating an input feature of the first electronic device to generate the first partial key;   transmitting the first partial key from the first electronic device to the second electronic device; and   activating an input feature of the second electronic device to generate the private key k associated with the public key K and to derive a second partial key from the first partial key and the private key k to split the private key k.   
     
     
         3 . The method of  claim 2 , wherein the input feature of the first electronic device is at least one of a button, an accelerometer, a voice recognition system, a biometric scanner, a key pad, a touch screen, or a microphone, and wherein the input feature of the second electronic device is at least one of a button, an accelerometer, a voice recognition system, a biometric scanner, a key pad, a touch screen, or a microphone. 
     
     
         4 . The method of  claim 2 , further comprising:
 activating, after transmitting the first partial key, an output feature of the second electronic device to prompt a user to activate the input feature of the second electronic device.   
     
     
         5 . The method of  claim 4 , wherein the output feature of the second electronic device is at least one of a light, an LED, a sound device, or haptic feedback device. 
     
     
         6 . The method of  claim 1 , wherein the first electronic device is a mobile device, and the second electronic device is a wearable device. 
     
     
         7 . The method of  claim 1 , further comprising:
 ceasing the pairing between the first electronic device and the second electronic device via the wireless communication protocol when the first electronic device and the second electronic device are separated by a distance greater than a maximum operational distance.   
     
     
         8 . The method of  claim 1 , further comprising:
 deleting the private key k from the second electronic device.   
     
     
         9 . A method for reconstructing a private key k, comprising:
 providing a mobile device and a wearable device;   pairing the mobile device and the wearable device via a wireless communication protocol;   transmitting a first partial key from the mobile device to the wearable device;   reconstructing a private key k from the first partial key and a second partial key;   performing, by the wearable device, a cryptographic operation using the reconstructed private key k; and   deleting the private key k and the first partial key from the wearable device.   
     
     
         10 . The method of  claim 9 , wherein the wearable device has an input feature, and activation of the input feature causes the wearable device to reconstruct the private key k. 
     
     
         11 . The method of  claim 9 , wherein an exclusive-or (XOR) operation on the partial keys reconstructs the private key k on the wearable device. 
     
     
         12 . The method of  claim 9 , wherein a secret sharing algorithm using the partial keys reconstructs the private key k on the wearable device. 
     
     
         13 . The method of  claim 9 , wherein a symmetric key decryption of one partial key using the other partial key reconstructs the private key k on the wearable device. 
     
     
         14 . The method of  claim 9 , wherein the cryptographic operation includes digitally signing a stream of bytes. 
     
     
         15 . The method of  claim 9 , wherein the cryptographic operation includes decrypting a stream of bytes that was encrypted using a public key K associated with the private key k. 
     
     
         16 . A method for initiating the use of the private key k, comprising:
 providing a mobile device and a wearable device, wherein the mobile device has an input feature and the wearable device has an output feature;   pairing the mobile device and the wearable device via a wireless communication protocol;   activating the input feature of the mobile device to initiate the use of a private key k on the wearable device, wherein the private key k is associated with a public key K; and   prompting, by the output feature of the wearable device, a user to approve the use of the private key k for a cryptographic operation.   
     
     
         17 . The method of  claim 16 , wherein the output feature prompts a user to approve the reconstruction of the private key k on the wearable device using a plurality of partial keys. 
     
     
         18 . The method of  claim 16 , wherein the wearable device has an input feature, and activation of the input feature of the wearable device approves the use of the private key k for the cryptographic operation. 
     
     
         19 . The method of  claim 16 , wherein the use of the private key k for the cryptographic operation is to digitally notarize (sign) one of a document, a message, or a legal contract. 
     
     
         20 . The method of  claim 16 , wherein the use of the private key k for the cryptographic operation is to decrypt one of a document, a message, or a file.