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Step 3: Construct Messages Using HTTP Signature Security

HTTP signatures use a digital signature to enable the receiver to validate the sender's authenticity and ensure that the message was not tampered with during transit. For more information about HTTP signatures, see the IETF Draft that is maintained by the IETF HTTP Working Group (https://httpwg.org).

Follow these steps to implement HTTP signatures:

Create the shared secret key pair. See Create a Shared Secret Key Pair.

Generate a hash of the message body. See Generate a Hash of the Message Body.

Generate a signature hash. See Generate the Signature Hash.

Populate the

signature

header field. See Update Header Fields.

Elements of an HTTP Message

A HTTP Message is built with the following elements:

Headers

Your message header must include these header fields:

HTTP Header Fields
HTTP Header Field	Description
v-c-merchant-id	Your `National Australia Bank` organization ID.
v-c-date	The date of the transaction in the RFC1123 format. (Thu, 18 Jul 2019 00:18:03 GMT)
Content-Type	Also known as the Multipurpose Internet Mail Extension (MIME) type, this identifies the media or file type of the resource. (application/json)
Host	The transaction endpoint. (`nabgateway-developer.nab.com.au`)

Body

The message body. For more information on setting up the body, see Generate a Hash of the Message Body.

Generate a Hash of the Message Body

This hash is used to validate the integrity of the message at the receiving end.

Follow these steps to generate the hash:

Generate the SHA-256 hash of the JSON payload (body of the message).

Encode the hashed string to Base64.

Prepend SHA-256=
to the front of the hash.

Add the message body hash to the

digest

header field.

Creating a Message Hash Using the Command Line

shasum

Tool

echo -n "{"clientReferenceInformation":{"code":"TC50171_3"},"paymentInformation":{"card":{"number":
				"4111111111111111","expirationMonth":"12","expirationYear":"2031"}},"orderInformation":{"amountDetails":
				{"totalAmount":"102.21","currency":"USD"},"billTo”:{“firstName":"John","lastName":"Doe","address1":
				"1MarketSt","locality":"sanfrancisco","administrativeArea":"CA","postalCode":"94105","country":"US",
				"email":"[email protected]","phoneNumber":"4158880000"}}}" | shasum -a 256

echo -n "6ae5459bc8a7d6a4b203e8a734d6a616725134088e13261f5bbcefc1424fc956" | base64

Creating a Message Hash Using the Command Line

base64

Tool

echo -n "6ae5459bc8a7d6a4b203e8a734d6a616725134088e13261f5bbcefc1424fc956" | base64

Creating a Message Hash Using C#

public static string GenerateDigest() {
				var digest = "";
				var bodyText = "{ your JSON payload }";
				using (var sha256hash = SHA256.Create()) {
				byte[] payloadBytes = sha256hash
				.ComputeHash(Encoding.UTF8.GetBytes(bodyText));
				digest = Convert.ToBase64String(payloadBytes);
				digest = "SHA-256=" + digest;
				}
				return digest;
				}

Creating a Message Using Java

public static String GenerateDigest() throws NoSuchAlgorithmException {
				String bodyText = "{ your JSON payload }";
				MessageDigest md = MessageDigest.getInstance("SHA-256");
				md.update(bodyText.getBytes(StandardCharsets.UTF_8));
				byte[] digest = md.digest();
				return "SHA-256=" + Base64.getEncoder().encodeToString(digest);
				}

Digest Header Field

digest: SHA-256=NmFlNTQ1OWJjOGE3ZDZhNGIyMDNlOGE3MzRkNmE2MTY3MjUxMzQwODhlMTMyNjFmNWJiY2VmYzE0MjRmYzk1Ng==

Generate the Signature Hash

The signature hash is a Base64-encoded HMAC SHA-256 hash of the header fields and their values. The following information must be included in the signature hash:

Header Fields
Header Field	Description
Date	From the header, the date and time in the RFC1123 format. For example: Date: Thu, 18 Jul 2023, 22:18:03.
Digest	The Base64-encoded SHA-256 hash of the message body. For more information, see Generate a Hash of the Message Body. For example: Digest: SHA-256=gXWufV4Zc7VkN9Wkv9jh/JuAVclqDusx3vkyo3uJFWU= . Do not include the digest with GET requests.
Host	From the header, the endpoint host. For example: `nabgateway-developer.nab.com.au` .
v-c-merchant-id	From the header, the merchant ID associated with the request. For example: v-c-merchant-id: mymerchantid .
request-target	The HTTP method and endpoint resource path. For example: request-target: post /pts/v2/payments/ .

Follow these steps to generate the signature hash value:

Generate a byte array of the secret key generated previously. For more information, see Create a Shared Secret Key Pair.

Generate the HMAC SHA-256 key object using the byte array of the secret key.

Concatenate a string of the required information listed above.

For more information, see Creating the Validation String
below.

Generate a byte array of the validation string.

Use the HMAC SHA-256 key object to create the HMAC SHA-256 hash of the validation string byte array.

Base64 encode the HMAC SHA-256 hash.

Signature Hash

signature=”OuKeDxj+Mg2Bh9cBnZ/25IXJs5n+qj93FvPKYpnqtTE=”

Creating the Validation String

To create the validation string, concatenate the required information in the same order as listed in the signature header field parameter. Each item must be on a separate line, and each line should be terminated with a new line character

Validation String Example

host: nabgateway-developer.nab.com.au\n
date: Thu, 18 Jul 2019 00:18:03 GMT\n
request-target: post /pts/v2/payments/\n
digest: SHA-256=gXWufV4Zc7VkN9Wkv9jh/JuAVclqDusx3vkyo3uJFWU=\n
v-c-merchant-id: mymerchantid

Generating a Signature Hash in C#

private static string GenerateSignatureFromParams(string signatureParams, string secretKey) {
var sigBytes = Encoding.UTF8.GetBytes(signatureParams);
var decodedSecret = Convert.FromBase64String(secretKey);
var hmacSha256 = new HMACSHA256(decodedSecret);
var messageHash = hmacSha256.ComputeHash(sigBytes);
return Convert.ToBase64String(messageHash);
}

Generating a Signature Hash in Java

public static String GenerateSignatureFromParams(String keyString, 
String signatureParams) throws InvalidKeyException, NoSuchAlgorithmException {
byte[] decodedKey = Base64.getDecoder().decode(keyString);
SecretKey originalKey = new SecretKeySpec(decodedKey, 0, decodedKey.length, "HmacSHA256");
Mac hmacSha256 = Mac.getInstance("HmacSHA256");
hmacSha256.init(originalKey);
hmacSha256.update(signatureParams.getBytes());
byte[] HmachSha256DigestBytes = hmacSha256.doFinal();
return Base64.getEncoder().encodeToString(HmachSha256DigestBytes);}

Update Header Fields

When the signature is generated, you can populate the

signature

header field. The

signature

header field includes these parameters:

Signatures
Signature Parameter	Description
keyid	The serial number of the signing certificate/key pair. Obtain this in the `Gateway Portal` Key Management area. For more information, see Create a Shared Secret Key Pair.
algorithm	The HMAC SHA256 algorithm used to encrypt the signature. It should be formatted: HmacSHA256 .
headers	This ordered list of the fields included in the signature: host v-c-date request-target digest v-c-merchant-id
signature	The signature hash.

Signature Header Field Format

Signature:"keyid:"[keyid]",algorithm="[encryption algoritm]",headers="field1" "field2" "field3" "etc.", signature="[signature hash]"

Signature Header Example

Signature:"keyid="123abcki-key1-key2-key3-keyid1234567", 
algorithm="HmacSHA256", headers="host date request-target digest v-c-merchant-id", 
signature="hrptKYTtn/VfwAdUqkrQ0HT7jqAbagAbFC6nRGXrNzE="