Authentication

The SVB Developer API requires an additional layer of security in the form of request signing via HMAC. Request signing uses a second secret key that is never transmitted over the wire to the API. This mitigates two additional attack vectors that a single API token does not:

• an attacker is unable to replay a previous request to the API; and
• an attacker is unable to modify the API request during transmission.

HMAC signing can be implemented in any language.

Algorithm

To sign a request, you’ll need a few things:

• a crypto library that supports HMAC-SHA-256;
• your secret HMAC signing key;
• your HTTP request contents; and
• the current time (from a reasonably accurate clock).

The signature is calculated using the following fields:

Using this Algorithm

1. Let + be a function that concatenates strings, and let "\n"indicate a newline character;
2. Let HMAC be a function that calculates an HMAC from a string and a secret key, and let HEX be a function that returns the string hexadecimal representation of its input; then
3. The signature is:

HEX( HMAC( your_secret_key,
           timestamp + "\n" +
           method + "\n" +
           path + "\n" +
           query + "\n" +
           body ))

Notes:

• body is only used for JSON bodies with the application/jsontype. if the body is any other type or is missing, then an empty string should be used instead.
• The only endpoint that uses a non-JSON body is /v1/files. That endpoint uses the multipart/form-data type and an empty string should be used for body when computing the signature.
• path always begins with a slash.
• query omits the leading question mark, and is an empty string if there is no query string.
  
  

Headers

After calculating the signature, add the following two HTTP headers to your request:

• X-Timestamp: timestamp, from step (2) above
• X-Signature: the request signature

For a request to be considered valid, it must have a timestamp within 30 seconds of the server’s time as well as a valid signature.

Python Example

Here is Python code sample to compute the signature of a request to create a VCN:

from hashlib import sha256
import hmac, time

secret = 'FNAqNywCi0hmo845Ni43p06mx3l4ub7C'
timestamp = str(int(time.time()))
method = 'POST'
path = '/v1/vcn'
params = 'show_card_number=true'
body = '{"data": {"total_card_amount": 12345, "valid_ending_on": "2018-12-25"}}'

message = "\n".join([timestamp, method, path, params, body])
signature = hmac.new(secret, message, sha256).digest().encode("hex")

Postman Example

Here is javascript code that can be put into a postman collection. In postman there is a tab called "Pre-request Script" which you can insert the code below:

Note: Signature variable on the below Postman script is the secret that is shared by the SVB team. If Postman script is used, there is no need to manually add X-Signature and X-Timestamp on the request headers.

let apigee = 1;
var signature = "";
const { Property, Url } = require('postman-collection');
var moment = require("moment")
var requestTimeStamp = moment(new Date().toUTCString()).valueOf() / 1000;
let resolvedUrl = Property.replaceSubstitutions(pm.request.url.toJSON(), 
pm.variables.toObject()),newUrl = new Url(resolvedUrl);
var dataUrl = requestTimeStamp + "\n" + pm.request.method + "\n" + 
newUrl.getPath() + "\n" + newUrl.getQueryString() + "\n";

while (dataUrl.indexOf("{{") >= 0) {
 var variableName = dataUrl.substring(dataUrl.indexOf("{{") + 2, 
 dataUrl.indexOf("}}"));

 var variableValue = pm.globals.get(variableName);
 dataUrl = dataUrl.replace("{{" + variableName + "}}", variableValue);
}

while (apigee && dataUrl.indexOf("[") >= 0) {
 dataUrl = dataUrl.replace("[", "%5B")
}

while (apigee && dataUrl.indexOf("]") >= 0) {
 dataUrl = dataUrl.replace("]", "%5D")
}

while (apigee && dataUrl.indexOf("\"") >= 0) {
 dataUrl = dataUrl.replace("\"", "%22")
}


if (pm.request.body)
 dataUrl = dataUrl.concat(pm.request.body);
console.log(dataUrl)

var hmac = CryptoJS.algo.HMAC.create(CryptoJS.algo.SHA256, signature);
var hash = hmac.update(dataUrl).finalize();

pm.request.headers.add({ 'key': 'X-Timestamp', 'value': requestTimeStamp });
pm.request.headers.add({ 'key': 'X-Signature', 'value': '' + hash });

We recommend IP whitelisting as an additional means of controlling access to the SVB Developer API whenever possible. While some architectures may preclude IP whitelisting as a viable means of protection, this additional level of security can help mitigate certain attacks. The Developer API can whitelist individual addresses or CIDR ranges of IP addresses as needed.