Step 3B: Digest Hash Calculation {#restgs-http-message-conf-payload-hash}
=========================================================================

The value of the digest HTTP header is a hashed version of the HTTP message body that you must calculate. This hash value validates the integrity of your message by the receiver.  
Follow these steps to calculate the digest hash:

1. Generate the SHA-256 hash of the JSON payload (message body).
2. Encode the hashed string to Base64.
3. Prepend **SHA-256=** to the front of the hash.
4. Add the message body hash to the digest HTTP header field.  
   Creating a Message Hash Using the Command Line `shasum` Tool

```keyword
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":"test@bankofamerica.com","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);
				}
```