X-Payments:API

API versions supported

API v1.1: X-Payments 1.0.2-1.0.5
API v1.2: X-Payments 1.0.6, 2.0.0, 2.0.1
API v1.3: X-Payments 2.1.0, 2.1.1
API v1.4: X-Payments 2.1.2 (Nov 2014), 2.1.3 (Feb 2015)
API v1.5: X-Payments 2.2 (June 2015)
API v1.6: X-Payments 3.0.0 (June 2016)
API v1.7: X-Payments 3.0.2 (August 2016)
API v1.8: X-Payments 3.1.0 (July 2017)
API v1.9: X-Payments 3.1.2 (April 2018)

API requests

All API requests are made to the https ://<xpayments_url>/api.php URL. Only HTTPS protocol is used. A request is an XML document that is encrypted using RSA method with a key generated by X-Payments.

Request/Response encryption

• Encryption method used: RSA;
• Key length: 2048 bit;
• A private key is created with a 32 character password;
• The password is generated randomly;
• The number of password characters varies from 33 to 127.

For each online store X-Payments generates 2 pairs of keys:

1. a public and a private key to encrypt requests/responses from the online store to X-Payments;
2. a public and a private key to encrypt requests/responses from X-Payments to the online store.

So when the online store sends a request to X-Payments, this request is encrypted using the public key from the first pair, X-Payments decrypts it using the private key of the first pair. Then X-Payments response is encrypted using the public key of the second pair, and the online store decrypts this response using the private key of the second pair.

To ensure full-featured two-way communication between X-Payments and an online store, you need to copy tree values from the X-Payments interface:

• Public key from the first pair (Online store -> X-Payments),
• Private key from the second pair (X-Payments -> Online store),
• Private key password,

and have them stored on the side of the online store by an appropriate X-Payments connector.

Encryption and communication

I. Encryption
Data is passed as an XML string.

1. Get the Salt block.
   • Generate a 32-character string formed of random characters from 33 to 255.
2. Get the CRC block.
   • Generate MD5 in the binary format of the passed data.
   • Prepend it with the "     MD5" prefix (the five preceding spaces are mandatory!)
3. Get the Data block.
   • For each Salt, CRC and Data calculate the length: it is formatted as a 12-digit number, e.g. 000000000032.
   • Compose the data block. Write consecutively: length of Salt, Salt, length of CRC, CRC, length of Data, Data.
4. Split the data into chunks of 128 characters.
5. Encrypt each chunk consecutively using the public key.
6. Encode each chunk with base64.
7. Compose the encrypted data.
   • Start with the "API" prefix.
   • Write the encrypted and encoded chunks separated with line-breaks.

II. Send the request

POST the encrypted data to https ://<xpayments_url>/api.php in the following format:

 cart_id=<CART_D>&request=<REQUEST>

where:

- <CART_ID> is the Store ID;
- <REQUEST> is the encrypted XML

III. Decrypt the response
The response is a string starting with "API".

1. Remove the leading "API" word. If the response does not start with "API", it means that it is incorrect.
2. Split and decode the encrypted chunks.
   • Chunks are separated by line-breaks.
   • Each chunk is encoded with base64.
3. Decrypt each chunk using the private key.
4. Combine the decrypted chunks together in a single line.
5. Validate the CRC of the encrypted response.

IV. CRC Validation.
A response is received in a single line. It contains the following data, consecutively: length of Salt, Salt, length of CRC, CRC, length of Data, Data.

1. Extract Salt
   • Get the salt length from the first 12 characters.
   • Shift the salt block by its length.
2. Extract CRC:
   • Get the CRC length from the first 12 characters.
   • Shift the CRC block by its length.
   • Remove the "     MD5" prefix from CRC.
3. Extract data
   • Get the data length from the first 12 characters
   • Shift the data block by its length
4. Calculate the MD5 checksum in the binary format of the received data.
5. Compare it with CRC.

cURL as a means of sending requests

Using libcurl v.7.10 and above is recommended.

TTL should be specified depending on the performance of the server where X-Payments is installed. The recommended value is 120 seconds.

Use the latest TLSv1.2, since the previous protocols and implementations contain security vulnerabilities, and thus must not be used according to PCI DSS.

Data types

Data types used:

• string - a UTF-8 string;
• email - an email address no longer than 255 characters;
• URL - a URL address no longer than 255 characters;
• currency - a floating point number denoting a certain sum of money. The mantissa size is the same as the payment currency mantissa size, but not longer than 3. All the exceeding characters will be truncated.
• integer - an integer number.

ISO 4217 Alpha-3 in the upper register is always used as the payment currency code.

ISO 639-1 Alpha-2 in the lower register is always used as the language code.

API Requests from the store to X-Payments

Admin area/X-Payments configuration

• Test connection request
• Payment configurations list request
  

Payment creation (Regular payment and tokenization)

• Payment initialisation request
  
• Charge again transaction request (Tokenization)

Payment information

• Payment information request
  
• Detailed payment and transaction information request

Actions on payments (secondary actions)

• Capture authorized transaction request
  
• Void authorized transaction request
  
• Refund captured transaction request
  
• Accept potentially fraudulent transaction request
  
• Decline potentially fraudulent transaction request

Callback requests (web-hooks) from X-Payments to the store

• Callback request with service payment information
  
• Check cart callback request

Browser-related

• Redirecting a customer to the cardholder data entering page
  
• Communication between X-Payments iframe and the store

Code samples

We have prepared some code samples written in PHP demonstrating communication with X-Payments, request encryption and response decryption. The recommended way to use this code is console PHP (i.e. via command line) on the *nix OS.

To use the code samples:

1. Download the archive with code samples.
2. Upload it on the server.
3. Extract the files and execute the script as follows:

[user@host]$ ls -la
total 72
drwxrwxr-x  2 user user  4096 Nov 18 14:26 .
drwxrwxr-x 17 user user  4096 Sep  5 07:24 ..
-rw-r--r--  1 user user 11141 Nov 18 14:24 API.php
-rw-r--r--  1 user user   656 Nov 16 01:54 connect_test.php
-rw-r--r--  1 user user   500 Nov 16 01:55 payment_accept.php
-rw-r--r--  1 user user   503 Nov 16 01:54 payment_capture.php
-rw-r--r--  1 user user   576 Nov 16 01:54 payment_confs_get.php
-rw-r--r--  1 user user   502 Nov 16 01:54 payment_decline.php
-rw-r--r--  1 user user   528 Nov 16 01:54 payment_get_additional_info.php
-rw-r--r--  1 user user   493 Nov 16 01:56 payment_get_info.php
-rw-r--r--  1 user user  1958 Nov 18 14:26 payment_init.php
-rw-r--r--  1 user user   707 Nov 16 01:54 payment_recharge.php
-rw-r--r--  1 user user  2073 Nov 16 01:54 payment_recharge.with.cart.php
-rw-r--r--  1 user user   498 Nov 16 01:54 payment_refund.php
-rw-r--r--  1 user user   496 Nov 16 01:54 payment_void.php
-rw-r--r--  1 user user   819 Nov 16 01:54 redirect.html
[user@host]$ php connect_test.php
<data>
  <hashCode>202cb962ac59075b964b07152d234b70</hashCode>
  <error></error>
  <error_message></error_message>
  <is_error_message></is_error_message>
  <version>3.0.2</version>
</data>

Notes on using the code samples:

• The code is provided as is, and is supposed to be used for demonstration only. We will not be held responsible for any damage caused by using this code on production deployments/live installations. Please use it at your own risk.
• To simplify the code, some sensitive information (like the private key and the private key passphrase) was hard-coded in the script. This way, storing the keys "as is" is strongly not recommended. Instead, the keys should be stored encrypted in some way.
• For the salt generation, the openssl_random_pseudo_bytes() function is used. However, it has known issues; make sure it generates a cryptographically secure sequence. Please check: https://bugs.php.net/bug.php?id=70014. If necessary, you may use another way to generate a cryptographically secure random string. See: http://stackoverflow.com/questions/31492921/cryptographically-secure-random-string-function.
• The keys hard-coded in the sample are taken from the X-Payments installation at https://demo.xpayments.com. So some operations work out of the box, e.g. payment initialization, payment information, test request, obtaining payment configurations, etc. But some operations will give an error, since the actual payment information on the demo stand can be changed. This applies to secondary operations: capture, void, refund, etc. To see the successful result, you should change the txnId fields hard-coded in the scripts.

Appendix A. Status codes.

Payment status codes

1 - New

2 - Authorized

3 - Declined

4 - Charged

5 - Refunded

6 - Partially refunded

Operation status codes

0 - transaction failed

1 - transaction is successful

2 - transaction is successful and is duplicate

See also

• X-Payments connection manuals