I am new to OAuth and I used this tutorial to generate access token from client app to target app. The code itself is working fine, but the access token I generated has invalid signature when I decoded on https://jwt.io/
Here's the code from the tutorial
public class ServicePrincipal
{
/// <summary>
/// The variables below are standard Azure AD terms from our various samples
/// We set these in the Azure Portal for this app for security and to make it easy to change (you can reuse this code in other apps this way)
/// You can name each of these what you want as long as you keep all of this straight
/// </summary>
static string authority = ""; // the AD Authority used for login. For example: https://login.microsoftonline.com/myadnamehere.onmicrosoft.com
static string clientId = ""; // client app's client id
static string clientSecret = ""; // client app's secret key
static string resource = ""; // target app's App ID URL
/// <summary>
/// wrapper that passes the above variables
/// </summary>
/// <returns></returns>
static public async Task<AuthenticationResult> GetS2SAccessTokenForProdMSAAsync()
{
return await GetS2SAccessToken(authority, resource, clientId, clientSecret);
}
static async Task<AuthenticationResult> GetS2SAccessToken(string authority, string resource, string clientId, string clientSecret)
{
var clientCredential = new ClientCredential(clientId, clientSecret);
AuthenticationContext context = new AuthenticationContext(authority, false);
AuthenticationResult authenticationResult = await context.AcquireTokenAsync(
resource, // the resource (app) we are going to access with the token
clientCredential); // the client credentials
return authenticationResult;
}
}
There is another piece of code I found that can also generate the access token:
AuthenticationContext authenticationContext =
new AuthenticationContext({authority});
ClientCredential clientCredential = new ClientCredential({client app id}, {client app secret});
try
{
AuthenticationResult result =
await authenticationContext.AcquireTokenAsync({target app's App ID URL},
clientCredential);
}
catch (Exception e)
{
return false;
}
Both of the code gave me invalid signature access token with version 1.0
There are two issues here:
I noticed is that when I decode the access token, it shows "ver": "1.0". Does it mean it is using OAuth1.0? Because I suppose to use OAuth 2.0.. Why would the code generate token that create OAuth1.0 not OAuth2.0?
Why would it be invalid signature?
I tried the same code with yours, got the same situation invalid signature, but when I changed the jwt ALGORITHM to HS256, I got the Signature Verified.
And the signature:
And the differences about RRS256 and HS256:
RS256 (RSA Signature with SHA-256) is an asymmetric algorithm, and it uses a public/private key pair: the identity provider has a private (secret) key used to generate the signature, and the consumer of the JWT gets a public key to validate the signature. Since the public key, as opposed to the private key, doesn't need to be kept secured, most identity providers make it easily available for consumers to obtain and use (usually through a metadata URL).
HS256 (HMAC with SHA-256), on the other hand, is a symmetric algorithm, with only one (secret) key that is shared between the two parties. Since the same key is used both to generate the signature and to validate it, care must be taken to ensure that the key is not compromised.
Are you posting your key into the form at jwt.io? Try to make a real rest call using the token in the authorization header. If everything is working and jwt isn't, maybe it's on them.
I noticed is that when I decode the access token, it shows "ver": "1.0". Does it mean it is using OAuth1.0? Because I suppose to use OAuth 2.0.. Why would the code generate token that create OAuth1.0 not OAuth2.0?
You are using OAuth2.0 , the ver:"1.0" means the JWT token is issued by Azure AD V1.0 Endpoint .
Why would it be invalid signature?
The API needs to check if the algorithm, as specified by the JWT header (property alg), matches the one expected by the API . AAD use RS256 , so you should change to RS256:
The normal way is to build from modulus and exponent , finding them from https://login.microsoftonline.com/common/discovery/keys matching kid and x5t from the token . Any use online tool like https://play.golang.org/ to get public key consists of two components: n and e. You can also use x5c value , click here for samples .
I am using the following code to encode the SAMLRequest value to the endpoint, i.e. the XYZ when calling https://login.microsoftonline.com/common/saml2?SAMLRequest=XYZ.
Is this the correct way to encode it?
private static string DeflateEncode(string val)
{
var memoryStream = new MemoryStream();
using (var writer = new StreamWriter(new DeflateStream(memoryStream, CompressionMode.Compress, true), new UTF8Encoding(false)))
{
writer.Write(val);
writer.Close();
return Convert.ToBase64String(memoryStream.GetBuffer(), 0, (int)memoryStream.Length, Base64FormattingOptions.None);
}
}
If you just want to convert string to a base64 encoded string, then you can use the following way:
var encoded = Convert.ToBase64String(System.Text.Encoding.Default.GetBytes(val));
Console.WriteLine(encoded);
return encoded;
Yes, that looks correct for the Http Redirect binding.
But don't do this yourself unless you really know what you are doing. Sending the AuthnRequest is the simple part. Correctly validating the received response, including guarding for Xml signature wrapping attacks is hard. Use an existing library, there are both commercial and open source libraries available.
When the user is authenticated I put a signed token in the response authorization header.
Every furthere access on a ressource url is only allowed with a valid signed token.
When I create the token and valdiate it:
var principal = tokenHandler.ValidateToken(tokenString, validationParameters);
then I get the principal (user who made the request) when the signed key is the same which got
used by creating the token.
That I can use the same signed key after authentication and during the ressource request to validate the token I have created this class:
public static class ApiConstants
{
private static readonly RNGCryptoServiceProvider CryptoProvider = new RNGCryptoServiceProvider(new byte[33]);
private static byte[] key = new byte[32];
static ApiConstants()
{
CryptoProvider.GetBytes(key);
}
public static byte[] GetSignedKey()
{
return key;
}
}
Is there anything wrong that I put this code in a static class which is actually my full purpose as I want the filling up of the byte array with random numbers to happen only one time!?
Is there still something I can improve?
You Can't make the signature token as static. because then it will become as global variable and shared by all request(thread). Also you will face concurrency issue with static field.
If you want to make it session specific. then you need to store in a session variable not in a static field.
In my build process, I want to include a timestamp from an RFC-3161-compliant TSA. At run time, the code will verify this timestamp, preferably without the assistance of a third-party library. (This is a .NET application, so I have standard hash and asymmetric cryptography functionality readily at my disposal.)
RFC 3161, with its reliance on ASN.1 and X.690 and whatnot, is not simple to implement, so for now at least, I'm using Bouncy Castle to generate the TimeStampReq (request) and parse the TimeStampResp (response). I just can't quite figure out how to validate the response.
So far, I've figured out how to extract the signature itself, the public cert, the time the timestamp was created, and the message imprint digest and nonce that I sent (for build-time validation). What I can't figure out is how to put this data together to generate the data that was hashed and signed.
Here's a rough idea of what I'm doing and what I'm trying to do. This is test code, so I've taken some shortcuts. I'll have to clean a couple of things up and do them the right way once I get something that works.
Timestamp generation at build time:
// a lot of fully-qualified type names here to make sure it's clear what I'm using
static void WriteTimestampToBuild(){
var dataToTimestamp = Encoding.UTF8.GetBytes("The rain in Spain falls mainly on the plain");
var hashToTimestamp = new System.Security.Cryptography.SHA1Cng().ComputeHash(dataToTimestamp);
var nonce = GetRandomNonce();
var tsr = GetTimestamp(hashToTimestamp, nonce, "http://some.rfc3161-compliant.server");
var tst = tsr.TimeStampToken;
var tsi = tst.TimeStampInfo;
ValidateNonceAndHash(tsi, hashToTimestamp, nonce);
var cms = tst.ToCmsSignedData();
var signer =
cms.GetSignerInfos().GetSigners()
.Cast<Org.BouncyCastle.Cms.SignerInformation>().First();
// TODO: handle multiple signers?
var signature = signer.GetSignature();
var cert =
tst.GetCertificates("Collection").GetMatches(signer.SignerID)
.Cast<Org.BouncyCastle.X509.X509Certificate>().First();
// TODO: handle multiple certs (for one or multiple signers)?
ValidateCert(cert);
var timeString = tsi.TstInfo.GenTime.TimeString;
var time = tsi.GenTime; // not sure which is more useful
// TODO: Do I care about tsi.TstInfo.Accuracy or tsi.GenTimeAccuracy?
var serialNumber = tsi.SerialNumber.ToByteArray(); // do I care?
WriteToBuild(cert.GetEncoded(), signature, timeString/*or time*/, serialNumber);
// TODO: Do I need to store any more values?
}
static Org.BouncyCastle.Math.BigInteger GetRandomNonce(){
var rng = System.Security.Cryptography.RandomNumberGenerator.Create();
var bytes = new byte[10]; // TODO: make it a random length within a range
rng.GetBytes(bytes);
return new Org.BouncyCastle.Math.BigInteger(bytes);
}
static Org.BouncyCastle.Tsp.TimeStampResponse GetTimestamp(byte[] hash, Org.BouncyCastle.Math.BigInteger nonce, string url){
var reqgen = new Org.BouncyCastle.Tsp.TimeStampRequestGenerator();
reqgen.SetCertReq(true);
var tsrequest = reqgen.Generate(Org.BouncyCastle.Tsp.TspAlgorithms.Sha1, hash, nonce);
var data = tsrequest.GetEncoded();
var webreq = WebRequest.CreateHttp(url);
webreq.Method = "POST";
webreq.ContentType = "application/timestamp-query";
webreq.ContentLength = data.Length;
using(var reqStream = webreq.GetRequestStream())
reqStream.Write(data, 0, data.Length);
using(var respStream = webreq.GetResponse().GetResponseStream())
return new Org.BouncyCastle.Tsp.TimeStampResponse(respStream);
}
static void ValidateNonceAndHash(Org.BouncyCastle.Tsp.TimeStampTokenInfo tsi, byte[] hashToTimestamp, Org.BouncyCastle.Math.BigInteger nonce){
if(tsi.Nonce != nonce)
throw new Exception("Nonce doesn't match. Man-in-the-middle attack?");
var messageImprintDigest = tsi.GetMessageImprintDigest();
var hashMismatch =
messageImprintDigest.Length != hashToTimestamp.Length ||
Enumerable.Range(0, messageImprintDigest.Length).Any(i=>
messageImprintDigest[i] != hashToTimestamp[i]
);
if(hashMismatch)
throw new Exception("Message imprint doesn't match. Man-in-the-middle attack?");
}
static void ValidateCert(Org.BouncyCastle.X509.X509Certificate cert){
// not shown, but basic X509Chain validation; throw exception on failure
// TODO: Validate certificate subject and policy
}
static void WriteToBuild(byte[] cert, byte[] signature, string time/*or DateTime time*/, byte[] serialNumber){
// not shown
}
Timestamp verification at run time (client site):
// a lot of fully-qualified type names here to make sure it's clear what I'm using
static void VerifyTimestamp(){
var timestampedData = Encoding.UTF8.GetBytes("The rain in Spain falls mainly on the plain");
var timestampedHash = new System.Security.Cryptography.SHA1Cng().ComputeHash(timestampedData);
byte[] certContents;
byte[] signature;
string time; // or DateTime time
byte[] serialNumber;
GetDataStoredDuringBuild(out certContents, out signature, out time, out serialNumber);
var cert = new System.Security.Cryptography.X509Certificates.X509Certificate2(certContents);
ValidateCert(cert);
var signedData = MagicallyCombineThisStuff(timestampedHash, time, serialNumber);
// TODO: What other stuff do I need to magically combine?
VerifySignature(signedData, signature, cert);
// not shown: Use time from timestamp to validate cert for other signed data
}
static void GetDataStoredDuringBuild(out byte[] certContents, out byte[] signature, out string/*or DateTime*/ time, out byte[] serialNumber){
// not shown
}
static void ValidateCert(System.Security.Cryptography.X509Certificates.X509Certificate2 cert){
// not shown, but basic X509Chain validation; throw exception on failure
}
static byte[] MagicallyCombineThisStuff(byte[] timestampedhash, string/*or DateTime*/ time, byte[] serialNumber){
// HELP!
}
static void VerifySignature(byte[] signedData, byte[] signature, System.Security.Cryptography.X509Certificates.X509Certificate2 cert){
var key = (RSACryptoServiceProvider)cert.PublicKey.Key;
// TODO: Handle DSA keys, too
var okay = key.VerifyData(signedData, CryptoConfig.MapNameToOID("SHA1"), signature);
// TODO: Make sure to use the same hash algorithm as the TSA
if(!okay)
throw new Exception("Timestamp doesn't match! Don't trust this!");
}
As you might guess, where I think I'm stuck is the MagicallyCombineThisStuff function.
I finally figured it out myself. It should come as no surprise, but the answer is nauseatingly complex and indirect.
The missing pieces to the puzzle were in RFC 5652. I didn't really understand the TimeStampResp structure until I read (well, skimmed through) that document.
Let me describe in brief the TimeStampReq and TimeStampResp structures. The interesting fields of the request are:
a "message imprint", which is the hash of the data to be timestamped
the OID of the hash algorithm used to create the message imprint
an optional "nonce", which is a client-chosen identifier used to verify that the response is generated specifically for this request. This is effectively just a salt, used to avoid replay attacks and to detect errors.
The meat of the response is a CMS SignedData structure. Among the fields in this structure are:
the certificate(s) used to sign the response
an EncapsulatedContentInfo member containing a TSTInfo structure. This structure, importantly, contains:
the message imprint that was sent in the request
the nonce that was sent in the request
the time certified by the TSA
a set of SignerInfo structures, with typically just one structure in the set. For each SignerInfo, the interesting fields within the structure are:
a sequence of "signed attributes". The DER-encoded BLOB of this sequence is what is actually signed. Among these attributes are:
the time certified by the TSA (again)
a hash of the DER-encoded BLOB of the TSTInfo structure
an issuer and serial number or subject key identifier that identifies the signer's certificate from the set of certificates found in the SignedData structure
the signature itself
The basic process of validating the timestamp is as follows:
Read the data that was timestamped, and recompute the message imprint using the same hashing algorithm used in the timestamp request.
Read the nonce used in the timestamp request, which must be stored along with the timestamp for this purpose.
Read and parse the TimeStampResp structure.
Verify that the TSTInfo structure contains the correct message imprint and nonce.
From the TimeStampResp, read the certificate(s).
For each SignerInfo:
Find the certificate for that signer (there should be exactly one).
Verify the certificate.
Using that certificate, verify the signer's signature.
Verify that the signed attributes contain the correct hash of the TSTInfo structure
If everything is okay, then we know that all signed attributes are valid, since they're signed, and since those attributes contain a hash of the TSTInfo structure, then we know that's okay, too. We have therefore validated that the timestamped data is unchanged since the time given by the TSA.
Because the signed data is a DER-encoded BLOB (which contains a hash of the different DER-encoded BLOB containing the information the verifier actually cares about), there's no getting around having some sort of library on the client (verifier) that understands X.690 encoding and ASN.1 types. Therefore, I conceded to including Bouncy Castle in the client as well as in the build process, since there's no way I have time to implement those standards myself.
My code to add and verify timestamps is similar to the following:
Timestamp generation at build time:
// a lot of fully-qualified type names here to make sure it's clear what I'm using
static void WriteTimestampToBuild(){
var dataToTimestamp = ... // see OP
var hashToTimestamp = ... // see OP
var nonce = ... // see OP
var tsq = GetTimestampRequest(hashToTimestamp, nonce);
var tsr = GetTimestampResponse(tsq, "http://some.rfc3161-compliant.server");
ValidateTimestamp(tsq, tsr);
WriteToBuild("tsq-hashalg", Encoding.UTF8.GetBytes("SHA1"));
WriteToBuild("nonce", nonce.ToByteArray());
WriteToBuild("timestamp", tsr.GetEncoded());
}
static Org.BouncyCastle.Tsp.TimeStampRequest GetTimestampRequest(byte[] hash, Org.BouncyCastle.Math.BigInteger nonce){
var reqgen = new TimeStampRequestGenerator();
reqgen.SetCertReq(true);
return reqgen.Generate(TspAlgorithms.Sha1/*assumption*/, hash, nonce);
}
static void GetTimestampResponse(Org.BouncyCastle.Tsp.TimeStampRequest tsq, string url){
// similar to OP
}
static void ValidateTimestamp(Org.BouncyCastle.Tsp.TimeStampRequest tsq, Org.BouncyCastle.Tsp.TimeStampResponse tsr){
// same as client code, see below
}
static void WriteToBuild(string key, byte[] value){
// not shown
}
Timestamp verification at run time (client site):
/* Just like in the OP, I've used fully-qualified names here to avoid confusion.
* In my real code, I'm not doing that, for readability's sake.
*/
static DateTime GetTimestamp(){
var timestampedData = ReadFromBuild("timestamped-data");
var hashAlg = Encoding.UTF8.GetString(ReadFromBuild("tsq-hashalg"));
var timestampedHash = System.Security.Cryptography.HashAlgorithm.Create(hashAlg).ComputeHash(timestampedData);
var nonce = new Org.BouncyCastle.Math.BigInteger(ReadFromBuild("nonce"));
var tsq = new Org.BouncyCastle.Tsp.TimeStampRequestGenerator().Generate(System.Security.Cryptography.CryptoConfig.MapNameToOID(hashAlg), timestampedHash, nonce);
var tsr = new Org.BouncyCastle.Tsp.TimeStampResponse(ReadFromBuild("timestamp"));
ValidateTimestamp(tsq, tsr);
// if we got here, the timestamp is okay, so we can trust the time it alleges
return tsr.TimeStampToken.TimeStampInfo.GenTime;
}
static void ValidateTimestamp(Org.BouncyCastle.Tsp.TimeStampRequest tsq, Org.BouncyCastle.Tsp.TimeStampResponse tsr){
/* This compares the nonce and message imprint and whatnot in the TSTInfo.
* It throws an exception if they don't match. This doesn't validate the
* certs or signatures, though. We still have to do that in order to trust
* this data.
*/
tsr.Validate(tsq);
var tst = tsr.TimeStampToken;
var timestamp = tst.TimeStampInfo.GenTime;
var signers = tst.ToCmsSignedData().GetSignerInfos().GetSigners().Cast<Org.BouncyCastle.Cms.SignerInformation>();
var certs = tst.GetCertificates("Collection");
foreach(var signer in signers){
var signerCerts = certs.GetMatches(signer.SignerID).Cast<Org.BouncyCastle.X509.X509Certificate>().ToList();
if(signerCerts.Count != 1)
throw new Exception("Expected exactly one certificate for each signer in the timestamp");
if(!signerCerts[0].IsValid(timestamp)){
/* IsValid only checks whether the given time is within the certificate's
* validity period. It doesn't verify that it's a valid certificate or
* that it hasn't been revoked. It would probably be better to do that
* kind of thing, just like I'm doing for the signing certificate itself.
* What's more, I'm not sure it's a good idea to trust the timestamp given
* by the TSA to verify the validity of the TSA's certificate. If the
* TSA's certificate is compromised, then an unauthorized third party could
* generate a TimeStampResp with any timestamp they wanted. But this is a
* chicken-and-egg scenario that my brain is now too tired to keep thinking
* about.
*/
throw new Exception("The timestamp authority's certificate is expired or not yet valid.");
}
if(!signer.Verify(signerCerts[0])){ // might throw an exception, might not ... depends on what's wrong
/* I'm pretty sure that signer.Verify verifies the signature and that the
* signed attributes contains a hash of the TSTInfo. It also does some
* stuff that I didn't identify in my list above.
* Some verification errors cause it to throw an exception, some just
* cause it to return false. If it throws an exception, that's great,
* because that's what I'm counting on. If it returns false, let's
* throw an exception of our own.
*/
throw new Exception("Invalid signature");
}
}
}
static byte[] ReadFromBuild(string key){
// not shown
}
I am not sure to understand why you want to rebuild the data structure signed in the response. Actually if you want to extract the signed data from the time-stamp server response you can do this:
var tsr = GetTimestamp(hashToTimestamp, nonce, "http://some.rfc3161-compliant.server");
var tst = tsr.TimeStampToken;
var tsi = tst.TimeStampInfo;
var signature = // Get the signature
var certificate = // Get the signer certificate
var signedData = tsi.GetEncoded(); // Similar to tsi.TstInfo.GetEncoded();
VerifySignature(signedData, signature, certificate)
If you want to rebuild the data structure, you need to create a new Org.BouncyCastle.Asn1.Tsp.TstInfo instance (tsi.TstInfo is a Org.BouncyCastle.Asn1.Tsp.TstInfo object) with all elements contained in the response.
In RFC 3161 the signed data structure is defined as this ASN.1 sequence:
TSTInfo ::= SEQUENCE {
version INTEGER { v1(1) },
policy TSAPolicyId,
messageImprint MessageImprint,
-- MUST have the same value as the similar field in
-- TimeStampReq
serialNumber INTEGER,
-- Time-Stamping users MUST be ready to accommodate integers
-- up to 160 bits.
genTime GeneralizedTime,
accuracy Accuracy OPTIONAL,
ordering BOOLEAN DEFAULT FALSE,
nonce INTEGER OPTIONAL,
-- MUST be present if the similar field was present
-- in TimeStampReq. In that case it MUST have the same value.
tsa [0] GeneralName OPTIONAL,
extensions [1] IMPLICIT Extensions OPTIONAL }
Congratulations on getting that tricky protocol work done!
See also a Python client implementation at rfc3161ng 2.0.4.
Note that with the RFC 3161 TSP protocol, as discussed at Web Science and Digital Libraries Research Group: 2017-04-20: Trusted Timestamping of Mementos and other publications, you and your relying parties must trust that the Time-Stamping Authority (TSA) is operated properly and securely. It is of course very difficult, if not impossible, to really secure online servers like those run by most TSAs.
As also discussed in that paper, with comparisons to TSP, now that the world has a variety of public blockchains in which trust is distributed and (sometimes) carefully monitored, there are new trusted timestamping options (providing "proof of existence" for documents). For example see
OriginStamp - Trusted Timestamping with Bitcoin. The protocol is much much simpler, and they provide client code for a large variety of languages. While their online server could also be compromised, the client can check whether their hashes were properly embedded in the Bitcoin blockchain and thus bypass the need to trust the OriginStamp service itself.
One downside is that timestamps are only posted once a day, unless an extra payment is made. Bitcoin transactions have become rather expensive, so the service is looking at supporting other blockchains also to drive costs back down and make it cheaper to get more timely postings.
Update: check out Stellar and Keybase
For free, efficient, lightning-fast, widely-vetted timestamps, check out the Stellar blockchain protocol, and the STELLARAPI.IO service.
For security purposes, I try to allow only Mandrill's IP(s) to access these urls.
Does anyone know them?
Mandrill's signature is located in the HTTP response header: Authenticating-webhook-requests
In the request header find: X-Mandrill-Signature. This is a base64 of the hashcode, signed using web-hook key. This key is secret to your webhook only.
We have a range of IPs used for webhooks, but they can (and likely will) change or have new ones added as we scale. An alternative would be to add a query string to the webhook URL you add in Mandrill, and then check for that query string when a POST comes in so you can verify it's coming from Mandrill.
Just replace the constants and use this function:
<?php
function generateSignature($post)
{
$signed_data = WEB_HOOK_URL;
ksort($post);
foreach ($post as $key => $value) {
$signed_data .= $key;
$signed_data .= $value;
}
return base64_encode(hash_hmac('sha1', $signed_data, WEB_HOOK_AUTH_KEY, true));
}
//---
if (generateSignature($_POST) != $_SERVER['HTTP_X_MANDRILL_SIGNATURE']) {
//Invalid
}
?>
As described in mandrill's docs, they provide a signature to check if the request really came from them. to build the request there's a few steps:
start with the exact url of your webhook (mind slashes and params)
sort the post variables by key (in case of mandrill, you'll only have one post parameter: mandrill_events)
add key and value to the url, without any delimiter
hmac the url with your secret key (you can get the key from the web-interface) and base64 it.
compare the result with the X-Mandrill-Signature header
here's a sample implementation in python:
import hmac, hashlib
def check_mailchimp_signature(params, url, key):
signature = hmac.new(key, url, hashlib.sha1)
for key in sorted(params):
signature.update(key)
signature.update(params[key])
return signature.digest().encode("base64").rstrip("\n")
205.201.136.0/16
I have just whitelisted them in my server's firewall.
We don't need to white list the Ip they are using. Instead of that they have provided their own way to authenticate the webhook request.
When you are creating the mandrill webhook it will generate the key. It will come under the response we are getting to our post URL which is provided in the webhook.
public async Task<IHttpActionResult> MandrillEmailWebhookResponse()
{
string mandrillEvents = HttpContext.Current.Request.Form["mandrill_events"].Replace("mandrill_events=", "");
// validate the request is coming from mandrill API
string url = ConfigurationManager.AppSettings["mandrillWebhookUrl"];
string MandrillKey = ConfigurationManager.AppSettings["mandrillWebHookKey"];
url += "mandrill_events";
url += mandrillEvents;
byte[] byteKey = System.Text.Encoding.ASCII.GetBytes(MandrillKey);
byte[] byteValue = System.Text.Encoding.ASCII.GetBytes(url);
HMACSHA1 myhmacsha1 = new HMACSHA1(byteKey);
byte[] hashValue = myhmacsha1.ComputeHash(byteValue);
string generatedSignature = Convert.ToBase64String(hashValue);
string mandrillSignature = HttpContext.Current.Request.Headers["X-Mandrill-Signature"].ToString();
if (generatedSignature == mandrillSignature)
{
// validation = "Validation successful";
// do the updating using the response data
}
}