Secure data entry using a card reader with minimal display and input capabilities having a display

1. A method for processing payment transactions between a card, a card reader and a mobile device separate from the card reader, the method comprising:

receiving, at the card reader, a request for a password from the card;

determining, by the card reader, a value for each character of the password through user input at the mobile device by

displaying, on a graphical display included in the card reader, a character selected by the card reader;

receiving data representing user input from the mobile device, wherein the user input selects or modifies the character;

determining whether the user input is a modification input or a selection input;

in the event that the user input is a modification input:

modifying the character based on the modification input to produce a modified character; and

displaying, on the graphical display, the modified character;

in the event that the user input is a selection input:

receiving a selection signal from the mobile device that is separate from the card reader, wherein the mobile device is configured to display an indication of the user input upon receiving the selection input; and

storing a selected character specified by the selection input; and

repeating the determining of the value of each character of the password until the password is completed.

2. The method of claim 1 , where the selected character is stored in the card reader.

3. The method of claim 1 , further comprising:

generating the password from one or more selected characters stored by the card reader;

submitting the password to the card for authorization;

receiving an authentication from the card; and

sending the authentication to the mobile device.

4. The method of claim 1 , further comprising:

generating the password from one or more selected characters stored by the card reader;

encrypting the password using a cryptographic key; and

sending the encrypted password to the mobile device.

5. The method of claim 1 , wherein the indication of the user input is a graphical symbol.

6. The method of claim 5 , where the mobile device displays a number of empty spots equal to a preset length of the password, and where the mobile device displays the graphical symbol at an empty spot upon sending each selection signal to the card reader.

7. The method of claim 1 , wherein the selection input or the modification input comprises a user tap of one or more buttons displayed on an interface presented by the mobile device.

8. The method of claim 1 , wherein the character is an integer, wherein the modification input increments or decrements the character based on the user input at a first sensor or a second sensor included in the mobile device, respectively, and wherein said modifying the character based on the modification input comprises:

incrementing or decrementing the character to produce the modified character based on the user tap of the first sensor or the second sensor, respectively.

9. A method for processing payment transactions between a card, a card reader and a mobile device separate from the card reader, the method comprising:

displaying, by the mobile device, a user interface that is configured to receive user input that selects or modifies a character displayed by the card reader, where the user input is a modification input that causes the card reader to modify the character or a selection input that causes the card reader to store the character;

receiving, by the mobile device, user input at the user interface;

sending, by the mobile device, data representing the user input to the card reader;

in the event that the user input is a selection input, displaying, by the mobile device, an indication of the user input on the user interface;

receiving, by the mobile device, transaction data from the card reader; and

transmitting, by the mobile device, the transaction data to a payment processing system.

10. The method of claim 9 , where the transaction data includes an encrypted password, and where the encrypted password was encrypted at the card reader.

11. The method of claim 9 , where the transaction data includes a password authentication message generated by the card.

12. The method of claim 9 , where displaying the user interface comprises displaying a number of empty spots equal to a preset length of the password, and where displaying the indication of the user input comprises displaying the indication at an empty spot upon sending data representing the selection input to the card reader.

13. The method of claim 1 , wherein the card reader is attached to an audio jack of the mobile device.

14. The method of claim 1 , wherein the card reader is configured to wirelessly communicate with the mobile device across a network.

15. The method of claim 9 , further comprising:

if the user input is a selection input, transmitting, by the mobile device, a signal to the card reader that prompts the card reader to modify the character displayed by the card reader.

16. A card reader comprising:

a display configured to display a character;

a microcontroller configured to process data indicative of user input received at a mobile device with which the card reader communicates; and

a memory that includes instructions, which, when executed by the microcontroller, cause the card reader to perform operations including:

receive a request for a password from a card swiped at the card reader;

determine a value for each character of the password through user input at the mobile device by

displaying, on the display, a character selected by the card reader;

receiving the data representing the user input from the mobile device;

determining whether the user input is a modification input or a selection input;

in the event that the user input is a modification input:

modifying the character based on the modification input to produce a modified character; and

displaying, on the display, the modified character;

in the event that the user input is a selection input:

receiving a selection signal from the mobile device, wherein the mobile device is configured to display an indication of the user input upon receiving the selection input; and

storing a selected character specified by the selection input in the memory; and

repeating the determining of the value of each character of the password until the password is completed.

17. The card reader of claim 16 , wherein the character is an integer and wherein the modification input increments or decrements the character.

18. The card reader of claim 16 , further comprising circuitry that communicates with the mobile device through an audio jack.

19. The card reader of claim 16 , further comprising circuitry that communicates with the mobile device wirelessly.

20. The card reader of claim 16 , wherein the display is a segment display or an electrophoretic ink display.

21. The card reader of claim 16 , further comprising a plurality of light emitting diodes, where one of the plurality of light emitting diodes is configured to turn on for each selected character.

22. A method for processing payment transactions between a card, a card reader, and a mobile device separate from the card reader, the method comprising:

receiving, at the card reader, a request for a password from the card;

displaying, by the mobile device, a user interface that is configured to receive user input that selects or modifies a character displayed by the card reader, where the user input is a modification input that causes the card reader to modify the character or a selection input that causes the card reader to store the character;

displaying, on a graphical display of the card reader, a character selected by the card reader;

receiving, by the mobile device, user input at the user interface;

transmitting, by the mobile device, data representing the user input to the card reader;

determining, by the card reader, that the user input is a modification input;

responsive to determining that the user input is a modification input:

modifying, by the card reader, the character based on the modification input to produce a modified character; and

displaying, on the graphical display of the card reader, the modified character;

determining, by the card reader, that the user input is a selection input;

responsive to determining that the user input is a selection input:

receiving, by the card reader, a selection signal from the mobile device, which displays an indication of the user input upon receiving the selection input; and

storing, by the card reader, a selected character specified by the selection input;

repeating, by the card reader, the determining of the value of each character of the password until the password is completed;

creating, by the card reader, transaction data;

transmitting, by the card reader, the transaction data to the mobile device; and

transmitting, by the mobile device, the transaction data to a payment processing system.