Primary account number (PAN) length issuer identifier in payment account number data field of a transaction authorization request message

1. A method comprising:

obtaining transaction data relating to a purchase transaction;

retrieving an account indicator of a payment account for payment of the purchase transaction;

transforming the retrieved account indicator based on the obtained transaction data to generate a transformed account indicator;

encrypting the transformed account indicator with a cryptographic key to generate an encrypted and transformed account indicator;

storing an issuer identifier associated with the cryptographic key in a payment account field of an authorization request and storing the encrypted and transformed account indicator in a different field of the authorization request, wherein the issuer identifier does not contain an identifier of a payment account; and

transmitting the authorization request to a payment terminal device.

2. The method of claim 1 , wherein the transmitting comprises transmitting the authorization request to a POS (point of sale) terminal.

3. The method of claim 1 , further comprising:

retrieving a device identifier;

transforming the device identifier based on the obtained transaction data to generate a transformed device identifier; and

encrypting the transformed device identifier based on the cryptographic key to generate an encrypted and transformed device identifier; and

storing the encrypted and transformed device identifier in a third field of the authorization request.

4. The method of claim 1 , further comprising:

forming a mask from the transaction data;

and wherein:

said transforming the account indicator includes applying the mask to the account identifier.

5. The method of claim 4 , wherein said applying the mask includes performing an XOR function with respect to the mask and the account identifier.

6. The method of claim 1 , wherein the account identifier is an original payment token different from the encrypted account indicator.

7. The method of claim 6 , wherein the retrieving, transforming and encrypting are performed by a payment-enabled mobile device.

8. The method of claim 7 , wherein the original payment token is retrieved from a remote device.

9. The method of claim 7 , wherein the original payment token is retrieved from a secure element in the payment-enabled mobile device.

10. A method comprising:

obtaining transaction data relating to a purchase transaction;

retrieving an account indicator of a payment account for payment of the purchase transaction;

transforming the retrieved account indicator based on the obtained transaction data to generate a transformed account indicator;

encrypting the transformed account indicator with a cryptographic key to generate an encrypted and transformed account indicator;

storing a primary account number (PAN)-length issuer identifier associated with the cryptographic key in a payment account field of an authorization request and storing the encrypted and transformed account indicator in a different field of the authorization request; and

transmitting the authorization request to a payment terminal device.