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Sapient: Secure API toolkit

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Sapient secures your PHP applications' server-to-server HTTP(S) traffic even in the wake of a TLS security breakdown (compromised certificate authority, etc.).

Sapient allows you to quickly and easily add application-layer cryptography to your API requests and responses. Requires PHP 7.

Sapient was designed and implemented by the PHP security and cryptography team at Paragon Initiative Enterprises.

See our blog post about using Sapient to harden your PHP-powered APIs for more information about its design rationale and motivation.

The cryptography is provided by sodium_compat (which, in turn, will use the libsodium extension in PECL if it's installed).

Because sodium_compat operates on strings rather than resources (a.k.a. streams), Sapient is not suitable for extremely large messages on systems with very low available memory. Sapient only encrypts or authenticates message bodies; if you need headers to be encrypted or authenticated, that's the job of Transport-Layer Security (TLS).

Features at a Glance

  • Works with both Request and Response objects (PSR-7)
    • Includes a Guzzle adapter for HTTP clients
  • Secure APIs:
    • Shared-key encryption
      • XChaCha20-Poly1305
    • Shared-key authentication
      • HMAC-SHA512-256
    • Anonymous public-key encryption
      • X25519 + BLAKE2b + XChaCha20-Poly1305
    • Public-key digital signatures
      • Ed25519
  • Works with arrays
    • i.e. the methods with "Json" in the name
    • Sends/receives signed or encrypted JSON
  • Works with strings
    • i.e. the methods without "Json" in the name
  • Digital signatures and authentication are backwards-compatible with unsigned JSON API clients and servers
    • The signaure and authentication tag will go into HTTP headers, rather than the request/response body.

Additionally, Sapient is covered by both unit tests (provided by PHPUnit) and automated static analysis (provided by Psalm).

Sapient Adapters

If you're looking to integrate Sapient into an existing framework:

If your framework correctly implements PSR-7, you most likely do not need an adapter. However, some adapters provide convenience methods that make rapid development easier.

To learn more about adapters, see the documentation for AdapterInterface.

Example 1: Signed PSR-7 Responses

This demonstrats a minimal implementation that adds Ed25519 signatures to your existing PSR-7 HTTP responses.

Server-Side: Signing an HTTP Response

<?php
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningSecretKey;
use Psr\Http\Message\ResponseInterface;

/**
 * @var ResponseInterface $response
 *
 * Let's assume we have a valid ResponseInterface object already.
 * (Most likely, after doing normal framework things.)  
 */

$sapient = new Sapient();
$serverSignSecret = new SigningSecretKey(
    Base64UrlSafe::decode(
        'q6KSHArUnD0sEa-KWpBCYLka805gdA6lVG2mbeM9kq82_Cwg1n7XLQXXXHF538URRov8xV7CF2AX20xh_moQTA=='
    )
);

$signedResponse = $sapient->signResponse($response, $serverSignSecret);

Client-Side: Verifying the Signature

<?php
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningPublicKey;
use ParagonIE\Sapient\Exception\{
    HeaderMissingException,
    InvalidMessageException
};
use Psr\Http\Message\ResponseInterface;

/**
 * @var ResponseInterface $response
 *
 * Let's assume we have a valid ResponseInterface object already.
 * (Most likely the result of an HTTP request to the server.)  
 */

$sapient = new Sapient();
$serverPublicKey = new SigningPublicKey(
    Base64UrlSafe::decode(
        'NvwsINZ-1y0F11xxed_FEUaL_MVewhdgF9tMYf5qEEw='
    )
);

try {
    $verified = $sapient->verifySignedResponse($response, $serverPublicKey);
} catch (HeaderMissingException $ex) {
    /* The server didn't provide a header. Discard and log the error! */
} catch (InvalidMessageException $ex) {
    /* Invalid signature for the message. Discard and log the error! */
}

Example 2: Mutually Signed JSON API with the Guzzle Adapter

This example takes advantage of an Adapter the provides the convenience methods described in ConvenienceInterface.

Client-Side: Sending a Signed Request, Verifying the Response

<?php
use GuzzleHttp\Client;
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Adapter\Guzzle as GuzzleAdapter;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningPublicKey;
use ParagonIE\Sapient\CryptographyKeys\SigningSecretKey;
use ParagonIE\Sapient\Exception\InvalidMessageException;

$http = new Client([
    'base_uri' => 'https://your-api.example.com'
]);
$sapient = new Sapient(new GuzzleAdapter($http));

// Keys
$clientSigningKey = new SigningSecretKey(
    Base64UrlSafe::decode(
        'AHxoibWhTylBMgFzJp6GGgYto24PVbQ-ognw9SPnvKppfti72R8By8XnIMTJ8HbDTks7jK5GmAnvtzaj3rbcTA=='
    )
);
$serverPublicKey = new SigningPublicKey(
    Base64UrlSafe::decode(
        'NvwsINZ-1y0F11xxed_FEUaL_MVewhdgF9tMYf5qEEw='
    )
);

// We use an array to define our message
$myMessage = [
    'date' => (new DateTime)->format(DateTime::ATOM),
    'body' => [
        'test' => 'hello world!'        
    ]
];

// Create the signed request:
$request = $sapient->createSignedJsonRequest(
    'POST',
     '/my/api/endpoint',
     $myMessage,
     $clientSigningKey
);

$response = $http->send($request);
try {
    /** @var array $verifiedResponse */
    $verifiedResponse = $sapient->decodeSignedJsonResponse(
        $response,
        $serverPublicKey
    );
} catch (InvalidMessageException $ex) {
    \http_response_code(500);
    exit;
}

Server-Side: Verifying a Signed Request, Signing a Response

 <?php
use GuzzleHttp\Client;
use GuzzleHttp\Psr7\ServerRequest;
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Adapter\Guzzle as GuzzleAdapter;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningPublicKey;
use ParagonIE\Sapient\CryptographyKeys\SigningSecretKey;
use ParagonIE\Sapient\Exception\InvalidMessageException;

$http = new Client([
    'base_uri' => 'https://your-api.example.com'
]);
$sapient = new Sapient(new GuzzleAdapter($http));
 
$clientPublicKey = new SigningPublicKey(
    Base64UrlSafe::decode(
        'aX7Yu9kfAcvF5yDEyfB2w05LO4yuRpgJ77c2o9623Ew='
    )
);
$request = ServerRequest::fromGlobals();
try {
    /** @var array $decodedRequest */
    $decodedRequest = $sapient->decodeSignedJsonRequest(
        $request,
        $clientPublicKey
    );
} catch (InvalidMessageException $ex) {
    \http_response_code(500);
    exit;
}

/* Business logic goes here */

// Signing a response:
$serverSignSecret = new SigningSecretKey(
    Base64UrlSafe::decode(
        'q6KSHArUnD0sEa-KWpBCYLka805gdA6lVG2mbeM9kq82_Cwg1n7XLQXXXHF538URRov8xV7CF2AX20xh_moQTA=='
    )
);

$responseMessage = [
    'date' => (new DateTime)->format(DateTime::ATOM),
    'body' => [
        'status' => 'OK',
        'message' => 'We got your message loud and clear.'
    ]
];

$response = $sapient->createSignedJsonResponse(
    200,
    $responseMessage,
    $serverSignSecret
);
/* If your framework speaks PSR-7, just return the response object and let it
   take care of the rest. */