(Objective-C) Verify HMAC XML Digital Signature

Demonstrates how to validate an XML digital signature signed with an HMAC key.

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#import <NSString.h>
#import <CkoHttp.h>
#import <CkoStringBuilder.h>
#import <CkoXmlDSig.h>

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// The XML containing the Signature to be verified contains the following:

// <?xml version="1.0" encoding="UTF-8" standalone="no"?>
// <collection Id="root">
// 	<album>
// 		<title>Questions, unanswered</title>
// 		<artist>Steve and the flubberblubs</artist>
// 		<year>1989</year>
// 		<t:tracks xmlns:t="http://test.xades4j/tracks">
// 			<t:song length="4:05" tracknumber="1">
// 				<t:title>What do you know?</t:title>
// 				<t:artist>Steve and the flubberblubs</t:artist>
// 				<t:lastplayed>2006-10-17-08:31</t:lastplayed>
// 			</t:song>
// 			<t:song length="3:45" tracknumber="2">
// 				<t:title>Who do you know?</t:title>
// 				<t:artist>Steve and the flubberblubs</t:artist>
// 				<t:lastplayed>2006-10-17-08:35</t:lastplayed>
// 			</t:song>
// 			<t:song length="5:14" tracknumber="3">
// 				<t:title>When do you know?</t:title>
// 				<t:artist>Steve and the flubberblubs</t:artist>
// 				<t:lastplayed>2006-10-17-08:39</t:lastplayed>
// 			</t:song>
// 			<t:song length="4:19" tracknumber="4">
// 				<t:title>Do you know?</t:title>
// 				<t:artist>Steve and the flubberblubs</t:artist>
// 				<t:lastplayed>2006-10-17-08:44</t:lastplayed>
// 			</t:song>
// 		</t:tracks>
// 	</album>
// <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"><ds:SignedInfo><ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/><ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#hmac-sha256"/><ds:Reference URI="#root"><ds:Transforms><ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/></ds:Transforms><ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/><ds:DigestValue>rD/g8soqKz8EiPUBhEWfcQacS0ta4ULHX3dKMEH6ZoQ=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>R8dXP95VRYJBfL6d0Peogybdk27+R+JIfX8jnVu0NOI=</ds:SignatureValue></ds:Signature></collection>

// The above XML is available at https://www.chilkatsoft.com/exampleData/hmacSigned.xml
// First fetch the XML..

NSString *url = @"https://www.chilkatsoft.com/exampleData/hmacSigned.xml";
CkoHttp *http = [[CkoHttp alloc] init];
CkoStringBuilder *sbXml = [[CkoStringBuilder alloc] init];
BOOL success = [http QuickGetSb: url sbContent: sbXml];
if (success != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

CkoXmlDSig *verifier = [[CkoXmlDSig alloc] init];

// Load the XML containing the signature to be verified.
success = [verifier LoadSignatureSb: sbXml];
if (success != YES) {
    NSLog(@"%@",verifier.LastErrorText);
    return;
}

// Provide the HMAC key
// The HMAC key for this signature is the us-ascii bytes of the string "secret",
// It can be set in any of the following ways (and also more ways not shown here..)
[verifier SetHmacKey: @"secret" encoding: @"ascii"];
// or
[verifier SetHmacKey: @"c2VjcmV0" encoding: @"base64"];
// or
[verifier SetHmacKey: @"736563726574" encoding: @"hex"];

// Verify the signature
BOOL bVerified = [verifier VerifySignature: YES];
NSLog(@"%@%d",@"Signature verified = ",bVerified);