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 all the parameters or JavaScript object configObj with all its parameters except for 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 JavaScript object configObj. Generally, the algorithm output consists of the object with integrated signature parameter.

The algorithm description, the example, and test form below include the most common algorithm implementation that includes JavaScrpt object configObj 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 JavaScript object 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 parameters sorted in natural order. 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. 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:.
3. Convert all strings to UTF-8.
4. Sort the strings in natural sort order and join them in a single string by using semicolon (;) as a delimiter.
Calculating 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 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 JavaScript object configObj using the signature from the previous step as its value.

Example of purchase request through Payment Page

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

Secret key obtained from the ecommpay support service: secret.

The configObj object that does not yet contain the signature parameter is the following:

{
"project_id": 12345, 
"payment_id": "X03936", 
"payment_amount": 2035, 
"payment_currency": "USD",
"payment_description": "Guyliner purchase",
"customer_first_name": "Jack",
"customer_id": "user007",
"customer_last_name": "Sparrow",
"customer_phone": "02081234567",
"close_on_missclick": true,
"signature": "<signature that needs to be generated>" 
}

The task is to generate the signature; in other words, you need to compute the value for the signature parameter. The signature is generated as follows:

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

{
"project_id": 12345, 
"payment_id": "X03936", 
"payment_amount": 2035, 
"payment_currency": "USD",
"payment_description": "Guyliner purchase",
"customer_first_name": "Jack",
"customer_id": "user007",
"customer_last_name": "Sparrow",
"customer_phone": "02081234567",
"close_on_missclick": true,
"signature": "<signature that needs to be generated>" 
}

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

project_id:12345 
payment_id:X03936
payment_amount:2035
payment_currency:USD
payment_description:Guyliner purchase
customer_first_name:Jack
customer_id:user007
customer_last_name:Sparrow
customer_phone:02081234567
close_on_missclick:1

Sort the strings in natural sort order:

close_on_missclick:1
customer_first_name:Jack
customer_id:user007
customer_last_name:Sparrow
customer_phone:02081234567
payment_amount:2035
payment_currency:USD
payment_description:Guyliner purchase
payment_id:X03936
project_id:12345

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

close_on_missclick:1;customer_first_name:Jack;customer_id:user007;customer_last_name:Sparrow;customer_phone:02081234567;payment_amount:2035;payment_currency:USD;payment_description:Guyliner purchase;payment_id:X03936;project_id:12345

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:
```
SyA3cx/dmFrwjRcpbnwEK9zaklWKR9buIfTctQob/EHUTutFLpI0zWpSDFEWEwbZt/04i83395RCdEhtUMw83A==
```

Add the resulting signature in the configObj object:

{
"project_id": 12345, 
"payment_id": "X03936", 
"payment_amount": 2035, 
"payment_currency": "USD",
"payment_description": "Guyliner purchase",
"customer_first_name": "Jack",
"customer_id": "user007",
"customer_last_name": "Sparrow",
"customer_phone": "02081234567",
"close_on_missclick": true,
"signature": "SyA3cx/dmFrwjRcpbnwEK9zaklWKR9buIfTctQob/EHUTutFLpI0zWpSDFEWEwbZt/04i83395RCdEhtUMw83A==" 
}

Request signature generation form

Note: To ensure correct processing of parameters specified in real requests, familiarise yourself with the requirements for encoding nested objects listed in Parameters for opening payment form and the articles describing the capabilities of the payment form. When you specify nested objects that do not conform to these requirements, the signature in the interactive testing form will still be generated according to the algorithm, but this signature cannot be used for real requests because it is generated with the use of incorrect input data.

Signature verification

Verification algorithm

The algorithm input includes the following:

Signed data to verify.
Generally, this is a 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 a 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 parameters sorted in natural order.
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 of a callback in the following scenario:

Signing key : secret.

The callback body contains the following information:

Figure 1. Callback body

{
    "customer": {
        "id": "782572"
    },
    "account": {
        "number": "424242******4242",
        "token": "c8175453f68ec7c8fb3f052b8d786c661261efebcb91155327a6c7b8f8e66359",
        "type": "visa",
        "card_holder": "TEST TEST",
        "expiry_month": "01",
        "expiry_year": "2025"
    },
    "project_id": 28051,
    "payment": {
        "id": "5242723",
        "type": "purchase",
        "status": "success",
        "date": "2023-03-10T12:26:17+0000",
        "method": "card",
        "sum": {
            "amount": 5200,
            "currency": "EUR"
        },
        "description": ""
    },
    "operation": {
        "sum_initial": {
            "amount": 5200,
            "currency": "EUR"
        },
        "sum_converted": {
            "amount": 5200,
            "currency": "EUR"
        },
        "code": "0",
        "message": "Success",
        "provider": {
            "id": 6,
            "payment_id": "16784511766816",
            "auth_code": "563253",
            "endpoint_id": 6,
            "date": "2023-03-10T10:26:17+0000"
        },
        "id": 5028800010128225,
        "type": "sale",
        "status": "success",
        "date": "2023-03-10T12:26:17+0000",
        "created_date": "2023-03-10T12:26:15+0000",
        "request_id": "1f6d3ac37444142f5bd27e7491faa360633fd5a2-fc98e73d475fa4cd6ee02fc6340c964f0267b3d8-05028801"
    },
    "signature": "IszjSnH+UqFp88DF0giI/jUTDHOnfPxc83j2VD/jN4loB9wbHwiO5+KvHfdFE4nBPHhhxD6TXbOkGnRINFTTmg=="
}

The signature is verified as follows:

Remove the signature parameter and its value from the callback:

{
    "customer": {
        "id": "782572"
    },
    "account": {
        "number": "424242******4242",
        "token": "c8175453f68ec7c8fb3f052b8d786c661261efebcb91155327a6c7b8f8e66359",
        "type": "visa",
        "card_holder": "TEST TEST",
        "expiry_month": "01",
        "expiry_year": "2025"
    },
    "project_id": 28051,
    "payment": {
        "id": "5242723",
        "type": "purchase",
        "status": "success",
        "date": "2023-03-10T12:26:17+0000",
        "method": "card",
        "sum": {
            "amount": 5200,
            "currency": "EUR"
        },
        "description": ""
    },
    "operation": {
        "sum_initial": {
            "amount": 5200,
            "currency": "EUR"
        },
        "sum_converted": {
            "amount": 5200,
            "currency": "EUR"
        },
        "code": "0",
        "message": "Success",
        "provider": {
            "id": 6,
            "payment_id": "16784511766816",
            "auth_code": "563253",
            "endpoint_id": 6,
            "date": "2023-03-10T10:26:17+0000"
        },
        "id": 5028800010128225,
        "type": "sale",
        "status": "success",
        "date": "2023-03-10T12:26:17+0000",
        "created_date": "2023-03-10T12:26:15+0000",
        "request_id": "1f6d3ac37444142f5bd27e7491faa360633fd5a2-fc98e73d475fa4cd6ee02fc6340c964f0267b3d8-05028801"
    },
    "signature": "IszjSnH+UqFp88DF0giI/jUTDHOnfPxc83j2VD/jN4loB9wbHwiO5+KvHfdFE4nBPHhhxD6TXbOkGnRINFTTmg=="
}

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

customer:id:782572
account:number:424242******4242
account:token:c8175453f68ec7c8fb3f052b8d786c661261efebcb91155327a6c7b8f8e66359
account:type:visa
account:card_holder:TEST TEST
account:expiry_month:01
account:expiry_year:2025
project_id:28051
payment:id:5242723
payment:type:purchase
payment:status:success
payment:date:2023-03-10T12:26:17+0000
payment:method:card
payment:sum:amount:5200
payment:sum:currency:EUR
payment:description:
operation:sum_initial:amount:5200
operation:sum_initial:currency:EUR
operation:sum_converted:amount:5200
operation:sum_converted:currency:EUR
operation:code:0
operation:message:Success
operation:provider:id:6
operation:provider:payment_id:16784511766816
operation:provider:auth_code:563253
operation:provider:endpoint_id:6
operation:provider:date:2023-03-10T10:26:17+0000
operation:id:5028800010128225
operation:type:sale
operation:status:success
operation:date:2023-03-10T12:26:17+0000
operation:created_date:2023-03-10T12:26:15+0000
operation:request_id:1f6d3ac37444142f5bd27e7491faa360633fd5a2-fc98e73d475fa4cd6ee02fc6340c964f0267b3d8-05028801