Terminal data encryption

1. A method comprising:

receiving, with one or more servers of a payment processing network, an altered key and an identifier of a point of sale device, the altered key having first cryptographic properties resulting from being formed at least in part by an alteration of an initial key with a public key, the first cryptographic properties including an ability to obtain the initial key by further altering the altered key, the initial key having second cryptographic properties resulting from being generated based at least in part on an initialization interaction between the point of sale device and a first portable consumer device, the second cryptographic properties including the initial key being a terminal-specific symmetric key that is unavailable for interception prior to the initialization interaction, wherein the receiving of the altered key with the one or more servers of the payment processing network inhibits unauthorized interception of the unaltered initial key;

further altering, with the one or more servers, the altered key to obtain the initial key, the further altering of the altered key enabled at least in part by the altered key having been formed at least in part by the alteration of the initial key with the public key;

sending, with the one or more servers, the initial key to a key storage location;

associating the initial key that is stored at the key storage location with the received identifier of the point of sale device;

receiving, with the one or more servers, altered transaction data associated with a plurality of financial transactions that are conducted using the point of sale device;

determining, with the one or more servers, that the altered transaction data was altered with the initial key that is stored at the key storage location based at least in part on the associated identifier of the point of sale device; and

further altering, with the one or more servers, the altered transaction data using the initial key that is stored at the key storage location, the further altering of the altered transaction data enabled at least in part by the initial key having been generated based at least in part on the initialization interaction between the point of sale device and the first portable consumer device.

2. The method of claim 1 wherein the identifier is a terminal ID.

3. The method of claim 1 wherein the altered key is an encrypted symmetric key that was encrypted using a public key.

4. The method of claim 1 wherein the first portable consumer device is a payment card.

5. The method of claim 1 wherein the initial key is a symmetric key and wherein the key storage location is in the point of sale device.

6. The method of claim 1 further comprising:

receiving, with the one or more servers, an altered identifier based at least in part on the identifier,

wherein receiving the altered key and the altered identifier data is part of a special initialization transaction that is different from a transaction associated with a purchase at least in that the initialization transaction is initial with respect to later transactions associated with purchases.

7. The method of claim 1 wherein the initialization interaction comprises using the first portable consumer device to interact with the point of sale device in a financial transaction, and wherein altering comprises encrypting.

8. The method of claim 7 wherein the encrypting comprises performing an encryption process, the point of sale device being capable of performing the encryption process.

9. The method of claim 8 wherein the encryption process comprises elliptical curve cryptography.

10. The method of claim 1 wherein a host computer is coupled to the point of sale device.

11. The method of claim 10 wherein the public key is stored in the host computer.

12. The method of claim 10 wherein the host computer generates the initial key.

13. The method of claim 10 wherein the host computer performs the altering.