Splicing resistant homomorphic passcode encryption

Patent metadata

Field	Value
Publication number	US-9646306-B1
Application number	US-201414209662-A
Country	US
Kind code	B1
Filing date	Mar 13, 2014
Priority date	Feb 11, 2014
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

A method for encrypting a passcode is disclosed. In one embodiment, the method includes: receiving an indication of a portion of the passcode from a user; encoding the portion of the passcode; encrypting the encoded portion into ciphertext using a homomorphic encryption system; updating a cumulative encryption string by executing a cumulative operation to aggregate the ciphertext corresponding to the encoded portion into the cumulative encryption string computed for a previous portion of the passcode, wherein the cumulative operation is dictated by a homomorphic property of the homomorphic encryption system; and generating a passcode message based at least in part on the cumulative encryption string, wherein the passcode message includes a message authentication code.

First claim

What is claimed is:

1. A method of safeguarding passcode entry on a mobile device, the method comprising:
detecting, by the mobile device, a swipe of a financial transaction card at a card reader attached to the mobile device;
initializing, by the mobile device, a financial transaction and receiving card data from the card reader attached to the mobile device;
receiving, by the mobile device, a decryption-side nonce associated with the card reader;
displaying, by the mobile device, a passcode entry interface on a touchscreen of the mobile device, wherein the passcode entry interface enables a user to enter a passcode;
receiving, by the mobile device, the passcode entered by the user;
determining, by the mobile device, a sequence of digits corresponding to the received passcode;
encoding, by the mobile device, each of the determined sequence of digits into an encoded digit;
encrypting, by the mobile device, the encoded digit into ciphertext using homomorphic cryptography;
maintaining, by the mobile device, a cumulative product based at least partly on the ciphertexts associated with the determined sequence of digits;
generating, by the mobile device, an encryption-side nonce;
generating, by the mobile device, a message authentication code based at least in part on the cumulative product, the encryption-side nonce, and the decryption-side nonce; and
transmitting, by the mobile device, an encrypted message including the message authentication code, wherein transmitting the encrypted message causes a process to authenticate the financial transaction to initiate, wherein the encrypted message represents the passcode entered by the user.

2. The method of claim 1 , wherein maintaining the cumulative product includes multiplying the ciphertext corresponding to a newly entered digit with the cumulative product calculated for all previous digits in the sequence.

3. The method of claim 1 , wherein encoding each digit and encrypting each encoded digit are performed after determining the digit entered by the user; and wherein maintaining the cumulative product includes updating the cumulative product in response to encrypting each encoded digit.

4. The method of claim 1 , wherein generating the message authentication code is based partly on a cryptographic hash function.

5. The method of claim 1 , wherein encoding the digit comprises:
calculating the encoded digit as a prime number raised to the power of the digit; and selecting the prime number from a set of prime bases based at least partly on the position of the digit in the sequence of digits.

6. The method of claim 1 , wherein generating the message authentication code includes executing a hashed message authentication code (HMAC) operation with a pre-hashed string as a secret cryptographic key.

7. The method of claim 6 , wherein generating the message authentication code includes computing the pre-hashed string by running the cryptographic hash function on at least the encryption-side nonce and the cumulative encryption string.

8. The method of claim 1 , wherein the cryptographic hash function is in accordance with SHA-256 or a variant thereof.

9. The method of claim 1 , wherein encoding the digit comprises: selecting, based on a sequential position (“i”) of the digit relative to other digits of the passcode, a prime number (“pi”) from a set of prime number bases; and computing the encoded digit as the selected prime number raised to the power of the digit.

Assignees

• Square Inc

Inventors

• Quigley Oliver S C
• Waddle Jason Douglas
• Adida Benjamin Michael
• Guise Max Joseph
• Boneh Dan

Classifications

• G06Q20/4012 Primary

  Verifying personal identification numbers [PIN] · CPC title

• H04W12/128

  Anti-malware arrangements, e.g. protection against SMS fraud or mobile malware · CPC title

• H04L9/008

  involving homomorphic encryption · CPC title

• H04L2463/062

  applying encryption of the keys · CPC title

• G06F21/83

  input devices, e.g. keyboards, mice or controllers thereof · CPC title