Signature

Introduction

The signature with private and public keys is done to ensure the identity of the parties sending and receiving the information.

All requests from the merchant shall be signed with the merchant's private key, Trustly will verify the signature of the request using the merchant's public key.
All responses from Trustly are signed with Trustly's private key and should be verified by the merchant using Trustly's public key.

Key generation

You can generate your private and public keys with OpenSSL:

openssl genrsa -out private.pem 2048

openssl rsa -pubout -in private.pem -out public.pem -outform PEM

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If you are using Windows you will have to install OpenSSL for Windows in order to run the OpenSSL commands above.

The file public.pem should then be sent to your integration manager at Trustly ([email protected]).

Trustly's public keys

Trustly's public keys for TEST and LIVE:

Serializing and signing your request

The Signature is a Base64 encoding of the RSA signature of [Method concatenated with UUID concatenated with a serialization of the Data{} object]. The serialization is done by concatenating all scalars, hash keys, hash values and array values together, sorted ASCIIbetically. ("Null" is treated as an empty string.)

Please see the simple PHP example below for clarification, and try our signature tester, it will show you how to serialize and sign any data.

function serialize_data($object) {
    $serialized = '';
    if( is_array($object) ) {
        ksort($object); //Sort keys
        foreach($object as $key => $value) {
            if(is_numeric($key)) { //Array
                $serialized .= serialize_data($value);
            } else { //Hash
                $serialized .= $key . serialize_data($value);
            }
        }
    } else return $object; //Scalar
    return $serialized;
}

function sign($method, $uuid, $data) {
    $merchant_private_key = openssl_get_privatekey(file_get_contents(
                                'merchant_private_key.pem'
                            ));
    $plaintext = $method . $uuid . serialize_data($data);
    openssl_sign($plaintext, $signature, $merchant_private_key);
    return base64_encode($signature);
}

function verify($method, $uuid, $data, $signature_from_trustly) {
    $trustly_public_key = openssl_get_publickey(file_get_contents(
                                'trustly_public_key.pem'
                            ));
    $plaintext = $method . $uuid . serialize_data($data);
    return openssl_verify($plaintext,
                            base64_decode($signature_from_trustly),
                            $trustly_public_key
                         );
}

Below is an example of a JSON object and how it should be serialized:

{
    "MyKey": "MyValue",
    "MyArray": [
        "Element1",
        "Element2",
        {
            "mykey2": "myvalue2"
        }
    ]
}

The JSON data above would result in the serialized string below:

MyArrayElement1Element2mykey2myvalue2MyKeyMyValue