Simple Message Queue (formerly MNS):Verify a signature on an HTTP server

Step 1: Retrieve the X509 certificate

In an HTTP request that is sent from SMQ to an endpoint, the x-mns-signing-cert-url header specifies a string that indicates the URL of the signature certificate. You must perform Base64 decoding on the string to retrieve the URL of the signature certificate and retrieve the public key from the certificate.

Step 2: Construct a string-to-sign

Construct a string-to-sign based on the following pseudocode:

StringToSign = HttpMethod + "\n" 
         + CONTENT-MD5 + "\n"     
         + CONTENT-TYPE + "\n" 
         + DATE + "\n" 
         + CanonicalizedMNSHeaders
         + CanonicalizedResource;

The following table describes the parameters.

Example:

POST
ZDgxNjY5ZjFlMDQ5MGM0YWMwMWE5ODlmZDVlYmQxYjI=
text/xml;charset=utf-8
Wed, 25 May 2016 10:46:14 GMT
x-mns-request-id:57458276F0E3D56D7C00****
x-mns-signing-cert-url:aHR0cDovL21uc3Rlc3Qub3NzLWNuLWhhbmd6aG91LmFsaXl1bmNzLmNvbS94NTA5X3B1YmxpY19jZXJ0aWZpY2F0ZS5w****
x-mns-version:2015-06-06
/notifications       

Step 3: Decrypt the Authorization header

After you perform Base64 decoding on the Authorization header, you can decrypt the decoded value by using the public key retrieved in Step 1.

Step 4: Verify the signature

Compare the string-to-sign that is generated in Step 2 with the decrypted string that is generated in Step 3. If the two strings are the same, the request from SMQ is valid. Otherwise, reject the request.

Java sample code

public class SignDemo {
    private Boolean authenticate(String method, String uri, Map<String, String> headers) {
        try {
            // Retrieve the URL of the signature certificate. 
            if (!headers.containsKey("x-mns-signing-cert-url")) {
                System.out.println("x-mns-signing-cert-url Header not found");
                return false;
            }
            String cert = headers.get("x-mns-signing-cert-url");
            if (cert.isEmpty()) {
                System.out.println("x-mns-signing-cert-url empty");
                return false;
            }
            cert = new String(Base64.decodeBase64(cert));
            System.out.println("x-mns-signing-cert-url:\t" + cert);

            // Use the URL to retrieve the certificate and retrieve the public key from the certificate. 
            URL url = new URL(cert);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            DataInputStream in = new DataInputStream(conn.getInputStream());
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            Certificate c = cf.generateCertificate(in);
            PublicKey pk = c.getPublicKey();

            // Retrieve the string-to-sign. 
            String str2sign = getSignStr(method, uri, headers);
            System.out.println("String2Sign:\t" + str2sign);

            // Decode the Authorization header in Base64. 
            String signature = headers.get("Authorization");
            byte[] decodedSign = Base64.decodeBase64(signature);

            // Verify the signature. 
            java.security.Signature signetcheck = java.security.Signature.getInstance("SHA1withRSA");
            signetcheck.initVerify(pk);
            signetcheck.update(str2sign.getBytes());
            Boolean res = signetcheck.verify(decodedSign);
            return res;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    private String getSignStr(String method, String uri, Map<String, String> headers) {
        StringBuilder sb = new StringBuilder();
        sb.append(method);
        sb.append("\n");
        sb.append(safeGetHeader(headers, "Content-md5"));
        sb.append("\n");
        sb.append(safeGetHeader(headers, "Content-Type"));
        sb.append("\n");
        sb.append(safeGetHeader(headers, "Date"));
        sb.append("\n");

        List<String> tmp = new ArrayList<String>();
        for (Map.Entry<String, String> entry : headers.entrySet()) {
            if (entry.getKey().startsWith("x-mns-")) {
                tmp.add(entry.getKey() + ":" + entry.getValue());
            }
        }
        Collections.sort(tmp);

        for (String kv : tmp) {
            sb.append(kv);
            sb.append("\n");
        }

        sb.append(uri);
        return sb.toString();
    }

    private String safeGetHeader(Map<String, String> headers, String name) {
        if (headers.containsKey(name)) {
            return headers.get(name);
        } else {
            return "";
        }
    }

    public static void main(String[] args) {
        SignDemo sd = new SignDemo();
        Map<String, String> headers = new HashMap<String, String>();
        headers.put("Authorization", "Mko2Azg9fhCw8qR6G7AeAFMyzjO9qn7LDA5/t9E+6X5XURXTqBUuhpK+K55UNhrnlE2UdDkRrwDxsaDP5ajQ****");
        headers.put("Content-md5", "M2ViOTE2ZDEyOTlkODBjMjVkNzM4YjNhNWI3ZWQ1****");
        headers.put("Content-Type", "text/xml;charset=utf-8");
        headers.put("Date", "Tue, 23 Feb 2016 09:41:06 GMT");
        headers.put("x-mns-request-id", "56CC2932F0E3D5BD5306****");
        headers.put("x-mns-signing-cert-url", "aHR0cDovL21uc3Rlc3Qub3NzLWNuLWhhbmd6aG91LmFsaXl1bmNzLmNvbS94NTA5X3B1YmxpY19jZXJ0aWZpY2F0ZS5w****");
        headers.put("x-mns-version", "2015-06-06");
        Boolean res = sd.authenticate("POST", "/notifications", headers);
        System.out.println("Authenticate result:" + res);
    }
}