Signature generation and verification

Overview

The data communication between the merchant web service and the ecommpay payment platform is protected by using the TLS protocol version 1.2 or later. This ensures the confidentiality of the data being transmitted, though the protocol cannot guarantee the message integrity and ensure that the message author possesses the secret key. Therefore, every message must be digitally signed by using the secret key issued by ecommpay for the merchant and known only to the merchant and the ecommpay payment platform.

Regardless of the interface that is used for working with the payment platform, digital signatures should be included in all requests, callbacks (for the requests processed within the asynchronous interaction model), and certain responses (for the requests processed within the synchronous interaction model). The responses that do not include signatures are usually the ones that contain only auxiliary information (for example, the response stating that the request has been declined due to the incorrect data) or general information without the payment or customer details (for example, the response containing the list of available banks). In other cases, signatures are included in the responses.

Thus, before you submit a request to the ecommpay payment platform, a digital signature should be generated and included in the request; after the callbacks and responses that contain signatures have been received from the payment platform, it is necessary to verify the received data by comparing the signatures to the ones generated on the merchant side. To implement the digital signature generation and verification, you can use either your own solutions or the SDK available from ecommpay. (For more information about the SDK, see Integration using SDK). The data integrity can be compromised for various reasons, but whenever such cases are detected, this data should not be considered valid.

This section describes the algorithms for the digital signature generation and the data integrity verification, including examples with the use of these algorithms and interactive forms for testing the workflows using signatures.

Signature generation

Signing algorithm

The algorithm input includes the following:

Data to sign.
Generally, this is request body in JSON format without the signature parameter.
Signing key.
For the purposes of debugging and testing your signing algorithm implementation, you are free to use any signing key. For signing requests in production environment, you are required to use your production secret key.

Depending on the algorithm implementation, its output may be either signature or signed data. Generally, the algorithm output consists of request body in JSON format with integrated signature parameter.

The algorithm description, the example, and test form below include the most common algorithm implementation that includes request body in JSON format both as input (without the signature parameter) and output (with the signature parameter).

Thus, the algorithm includes the following steps:

Input validation. Make sure the following requirements are met:
1. Data conforms to the JSON format.
2. Data to sign does not contain any signature parameter even if it is empty.
3. The signing key is readily available.
Conversion of all the strings to UTF-8 with alphabetical sorting. Complete the following steps:
1. Encode any Boolean values as follows: replace false with 0, replace true with 1. Mind that this rule applies only to Boolean values. If any string parameter contains "false" or "true" string value, the value is not replaced with 0 or 1 but is treated as any other string value (for example the recurring: "{type: \"U\",register: true}" parameter doesn’t require replacing true with 1).
2. Convert each parameter into a string that contains the full path to the parameter (with all its parents), parameter name, and parameter value:
```
<parent_1>:...:<parent_n>:<parameter_name>:<parameter_value>
```
  where parents are the object(s) and/or arrays in which the parameter is contained. Parents are ordered by embedding level starting with the topmost one. The parent names, parameter name, and parameter value are delimited by colon (:); delete any commas between “key-value” pairs and any quotation marks that delimit string values.
3. Leave any empty parameter values empty. In other words, do not replace any empty values with blank space or null. For instance, "payment_description":"" is replaced with payment_description:.
4. Add index numbers to array elements starting with zero, for instance ["alpha", "beta", "gamma"] is replaced with three strings: 0:alpha, 1:beta, and 2:gamma.
5. Empty arrays are totally ignored and not included in the string set used to generate the signature.
6. Convert all the strings to UTF-8.
7. Sort the strings in alphabetical order and join them in a single string by using semicolon (;) as a delimiter.
Calculation of HMAC code by using the key and the SHA-512 hash function. Calculate the HMAC code for the string by using the SHA-512 hash function and secret key. The HMAC code must be calculated as a raw binary data.
Encoding the HMAC code by using the Base64 scheme. Encoding the HMAC code by using the Base64 scheme to obtain the signature for the initial data.
Adding signature. Add the signature parameter to the request body using the signature from the previous step as its value.

Example of purchase request through Gate

Suppose that you need to generate the signature for a Gate request in the following scenario:

Signing key : secret.

Preliminary request body version where the value for the signature is missing:

{
    "general": {
        "project_id": 3254,
        "payment_id": "id_38202316",
       "signature": "<digital signature to generate>" 
    },
    "customer": {
        "id": "585741",
        "email": "johndoe@mycompany.com",
        "first_name": "John",
        "last_name": "Doe",
        "address": "Downing str., 23",
        "identify": {
            "doc_number": "54122312544"
        },
        "ip_address": "111.222.333.444"
    },
    "payment": {
        "amount": 10800,
        "currency": "USD",
        "description": "Computer keyboards"
    },
    "receipt_data": {
        "positions": [
            {
                "quantity": "10",
                "amount": "108",
                "description": "Computer keyboard"
            }
        ]
    },
    "return_url": {
        "success": "https://paymentpage.mycompany.com/complete-redirect?id=success",
        "decline": "https://paymentpage.mycompany.com/complete-redirect?id=decline"
    }
}

The task is to generate the signature; in other words, you need to compute the value for the signature parameter and add it in the request. Complete the following steps:

Make sure there is no signature parameter in your request even if it is empty:

{
    "general": {
        "project_id": 3254,
        "payment_id": "id_38202316",
       "signature": "<digital signature to generate>" 
    },
    "customer": {
        "id": "585741",
        "email": "johndoe@mycompany.com",
        "first_name": "John",
        "last_name": "Doe",
        "address": "Downing str., 23",
        "identify": {
            "doc_number": "54122312544"
        },
        "ip_address": "111.222.333.444"
    },
    "payment": {
        "amount": 10800,
        "currency": "USD",
        "description": "Computer  keyboards"
    },
    "receipt_data": {
        "positions": [
            {
                "quantity": "10",
                "amount": "108",
                "description": "Computer keyboard"
            }
        ]
    },
    "return_url": {
        "success": "https://paymentpage.mycompany.com/complete-redirect?id=success",
        "decline": "https://paymentpage.mycompany.com/complete-redirect?id=decline"
    }
}

Convert all the strings to UTF-8 as per algorithm description:

general:project_id:3254
general:payment_id:id_38202316
customer:id:585741
customer:email:johndoe@mycompany.com
customer:first_name:John
customer:last_name:Doe
customer:address:Downing str., 23
customer:identify:doc_number:54122312544
customer:ip_address:111.222.333.444
payment:amount:10800
payment:currency:USD
payment:description:Computer keyboards
receipt_data:positions:0:quantity:10
receipt_data:positions:0:amount:108
receipt_data:positions:0:description:Computer keyboard
return_url:success:https://paymentpage.mycompany.com/complete-redirect?id=success
return_url:decline:https://paymentpage.mycompany.com/complete-redirect?id=decline

Sort the strings in alphabetical order:

customer:address:Downing str., 23
customer:email:johndoe@mycompany.com
customer:first_name:John
customer:id:585741
customer:identify:doc_number:54122312544
customer:ip_address:111.222.333.444
customer:last_name:Doe
general:payment_id:id_38202316
general:project_id:3254
payment:amount:10800
payment:currency:USD
payment:description:Computer keyboards
receipt_data:positions:0:amount:108
receipt_data:positions:0:description:Computer keyboard
receipt_data:positions:0:quantity:10
return_url:decline:https://paymentpage.mycompany.com/complete-redirect?id=decline
return_url:success:https://paymentpage.mycompany.com/complete-redirect?id=success

Join all the strings in a single string by using semicolon (;) as a delimiter:

customer:address:Downing str., 23;customer:email:johndoe@mycompany.com;customer:first_name:John;customer:id:585741;customer:identify:doc_number:54122312544;customer:ip_address:111.222.333.444;customer:last_name:Doe;general:payment_id:id_38202316;general:project_id:3254;payment:amount:10800;payment:currency:USD;payment:description:Computer keyboards;receipt_data:positions:0:amount:108;receipt_data:positions:0:description:Computer keyboard;receipt_data:positions:0:quantity:10;return_url:decline:https://paymentpage.mycompany.com/complete-redirect?id=decline;return_url:success:https://paymentpage.mycompany.com/complete-redirect?id=success

Calculate the HMAC code for the string by using the SHA-512 hash function and secret key, and then encode the HMAC code by using the Base64 scheme:
```
VLLZzVNGevQNhr1b4TEhbC4qqHD17Kyn/M6FPNN93ttyk/amJgD/R6dayTKVvW6/QCRdq4hOf8R2w/xbUa8f2w==
```

Add the resulting signature in the request body:

{
    "general": {
        "project_id": 3254,
        "payment_id": "id_38202316",
       "signature": "VLLZzVNGevQNhr1b4TEhbC4qqHD17Kyn/M6FPNN93ttyk/amJgD/R6dayTKVvW6/QCRdq4hOf8R2w/xbUa8f2w=="
    },
    "customer": {
        "id": "585741",
        "email": "johndoe@mycompany.com",
        "first_name": "John",
        "last_name": "Doe",
        "address": "Downing str., 23",
        "identify": {
            "doc_number": "54122312544"
        },
        "ip_address": "111.222.333.444"
    },
    "payment": {
        "amount": 10800,
        "currency": "USD",
        "description": "Computer keyboards"
    },
    "receipt_data": {
        "positions": [
            {
                "quantity": "10",
                "amount": "108",
                "description": "Computer keyboard"
            }
        ]
    },
    "return_url": {
        "success": "https://paymentpage.mycompany.com/complete-redirect?id=success",
        "decline": "https://paymentpage.mycompany.com/complete-redirect?id=decline"
    }
}

Request signature generation form

Signature verification

Verification algorithm

The algorithm input includes the following:

Signed data to verify.
Generally, this is callback or response body in JSON format with the signature parameter.
Verification key. It must be the same key that was previously used for signing the data to verify.

Depending on the algorithm implementation, its output may be either a generated signature or the information whether the generated signature matches the one included in the response or callback.

The algorithm description, the example, and test form below use the most common algorithm implementation that includes callback or response body in JSON format as input (without the signature parameter) and output (with the signature parameter) which is the result of signature verification.

Thus, the algorithm includes the following steps:

Input validation Make sure the following requirements are met:
1. Data conforms to the JSON format.
2. Data to sign contains a signature parameter with the signature value.
3. The signing key is readily available.
Extracting signature from the data to verify. Store the value of the signature parameter value for further reference and remove the parameter from the input data.
Generate signature for the data to verify. Complete steps 2 through 4 as specified in the signature generation algorithm description. (For more details, see the following link):
1. Conversion of all the strings to UTF-8 with alphabetical sorting.
2. Calculation of HMAC code by using the key and the SHA-512 hash function.
3. Encoding the HMAC code by using the Base64 scheme.
Signature matching Compare the generated signature with the signature stored in step 2. If the signatures match, the data are authentic and its integrity is considered confirmed; otherwise, the data is considered compromised and cannot be used for production purposes.

Example of callback verification

Suppose that you need to verify the signature a callback in the following scenario:

Signing key : secret.

The callback body contains the following information:

Figure: Callback body

{
  "request_id": "17cd0535c5ffecf5-335e5b5e",
  "transaction": {
    "id": 82452138542211,
    "date": "2019-10-09T07:13:36+0000",
    "type": "purchase"
  },
  "payment": {
    "id": "123456789",
    "method": "webmoney",
    "date": "2019-10-09T07:13:36+0000",
    "result_code": "9999",
    "result_message": "Awaiting processing",
    "status": "awaiting redirect result",
    "is_new_attempts_available": false,
    "attempts_timeout": 0,
    "cascading_with_redirect": false,
    "provider_id": 1234
  },
  "sum_real": {
    "amount": 29100,
    "currency": "USD"
  },
  "account": {
    "number": "79879496816"
  },
  "return_url": {
    "method": "GET",
    "body": {
      "shop": "1234567",
      "transaction": 45712154,
      "iframe": "true",
      "successUrl": "https://mysite.com/process/success",
      "failUrl": "https://mysite.com/process/failure",
      "target": "iframe"
    },
    "encrypted": []
  },
  "rrn": "",
  "general": {
    "project_id": 123,
    "payment_id": "457822332658",
    "signature": "NtDutuRiksyHeBhhUs+nQxQ1FcMSueoACb4vENju0APgHgeZfRfMj46289v1vD4hJ1a8Yhg=="
  },
  "description": "TEST_1543831735980",
  "sum_request": {
    "amount": 29100,
    "currency": "USD"
  },
  "operations": [
    {
      "id": 45712154,
      "type": "sale",
      "status": "awaiting redirect result",
      "date": "2019-10-09T07:13:36+0000",
      "processing_time": null,
      "request_id": "3bd75dc1977cc8c05b50855b-544f7f6af3d989dd42ef8e6ff02df56eef7c5f4e-521457",
      "sum": {
        "amount": 29100,
        "currency": "USD"
      },
      "code": "9999",
      "message": "Awaiting processing"
    }
  ]
}

The signature is verified as follows:

Remove the signature parameter and its value from the callback:

{

  "request_id": "17cd0535c5ffecf5-335e5b5e",
  "transaction": {
    "id": 82452138542211,
    "date": "2019-10-09T07:13:36+0000",
    "type": "purchase"
  },
  "payment": {
    "id": "123456789",
    "method": "webmoney",
    "date": "2019-10-09T07:13:36+0000",
    "result_code": "9999",
    "result_message": "Awaiting processing",
    "status": "awaiting redirect result",
    "is_new_attempts_available": false,
    "attempts_timeout": 0,
    "cascading_with_redirect": false,
    "provider_id": 1234
  },
  "sum_real": {
    "amount": 29100,
    "currency": "USD"
  },
  "account": {
    "number": "79879496816"
  },
  "return_url": {
    "method": "GET",
    "body": {
      "shop": "1234567",
      "transaction": 45712154,
      "iframe": "true",
      "successUrl": "https://mysite.com/process/success",
      "failUrl": "https://mysite.com/process/failure",
      "target": "iframe"
    },
    "encrypted": []
  },
  "rrn": "",
  "general": {
    "project_id": 123,
    "payment_id": "457822332658",
    "signature": "NtDutuRiksyHeBhhUs+nQxQ1FcMSueoACb4vENju0APgHgeZfRfMj46289v1vD4hJ1a8Yhg=="
  },
  "description": "TEST_1543831735980",
  "sum_request": {
    "amount": 29100,
    "currency": "USD"
  },
  "operations": [
    {
      "id": 45712154,
      "type": "sale",
      "status": "awaiting redirect result",
      "date": "2019-10-09T07:13:36+0000",
      "processing_time": null,
      "request_id": "3bd75dc1977cc8c05b50855b-544f7f6af3d989dd42ef8e6ff02df56eef7c5f4e-521457",
      "sum": {
        "amount": 29100,
        "currency": "USD"
      },
      "code": "9999",
      "message": "Awaiting processing"
    }
  ]
}

Convert all parameter strings to UTF-8 according to the algorithm description:

request_id:17cd0535c5ffecf5-335e5b5e
transaction:id:82452138542211
transaction:date:2019-10-09T07:13:36+0000
transaction:type:purchase
payment:id:123456789
payment:method:webmoney
payment:date:2019-10-09T07:13:36+0000
payment:result_code:9999
payment:result_message:Awaiting processing
payment:status:awaiting redirect result
payment:is_new_attempts_available:0
payment:attempts_timeout:0
payment:cascading_with_redirect:0
payment:provider_id:1234
sum_real:amount:29100
sum_real:currency:USD
account:number:79879496816
return_url:method:GET
return_url:body:shop:1234567
return_url:body:transaction:45712154
return_url:body:iframe:true
return_url:body:successUrl:https://mysite.com/process/success
return_url:body:failUrl:https://mysite.com/process/failure
return_url:body:target:iframe
rrn:
general:project_id:123
general:payment_id:457822332658
description:TEST_1543831735980
sum_request:amount:29100
sum_request:currency:USD
operations:0:id:45712154
operations:0:type:sale
operations:0:status:awaiting redirect result
operations:0:date:2019-10-09T07:13:36+0000
operations:0:processing_time:
operations:0:request_id:3bd75dc1977cc8c05b50855b
operations:0:sum:amount:29100
operations:0:sum:currency:USD
operations:0:code:9999
operations:0:message:Awaiting processing