(Objective-C) Verify XML Digital Signature having KeyName

Demonstrates how to verify an XML digital signature where the KeyInfo part contains the KeyName element.
In this case, the public key is not specifically stored in the signed XML.
Rather, application specific information about the key is stored in the KeyName element.
This example uses the KeyName to find and matching public key.

This example requires Chilkat v9.5.0.69 or greater.

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

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

// The signed XML to be verified in this example contains the following:
// 
// <?xml version="1.0" encoding="UTF-8" standalone="no"?>
// <Envelope>
//   <Header>
//     <Security>
//     <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/2009/xmldsig11#dsa-sha256"/><ds:Reference URI="#abc"><ds:Transforms><ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/></ds:Transforms><ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/><ds:DigestValue>XTjDIHSEsDNTO9yn4cKtyXjRUjPFXkOQOLYI5mueZhk=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>NXOIMevGCqFl0Dwtp2KkqkT05GRV8CjmHZ9LhFpt8/d7+lkIi7mITA==</ds:SignatureValue><ds:KeyInfo><ds:KeyName>dsaKey_123</ds:KeyName></ds:KeyInfo></ds:Signature></Security>
//   </Header>
//   <Body Id="abc">
//     <z:FooBar xmlns:z="https://www.example-code.com"/>
//   </Body>
// </Envelope>
// 

// The above XML is available at https://www.chilkatsoft.com/exampleData/signedUsingKeyName.xml
// First we'll fetch the signed XML:

NSString *url = @"https://www.chilkatsoft.com/exampleData/signedUsingKeyName.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;
}

// (The Chilkat XML Digital Signature API has the capability to handle XML documents with multiple signatures.
// We know in advance that this signed XML has just one Signature, so we leave the dsig.Selector property at the
// default value of 0.)

// Let's get the KeyInfo XML so we can then get the KeyName.
CkoXml *xmlKeyInfo = [verifier GetKeyInfo];
if (verifier.LastMethodSuccess == NO) {
    NSLog(@"%@",@"There is no KeyInfo available in the Signature.");
    return;
}

// Examine the XML:
NSLog(@"%@",[xmlKeyInfo GetXml]);

// The KeyInfo XML that is returned looks like this:
// 
// 	<ds:KeyInfo>
// 	    <ds:KeyName>dsaKey_123</ds:KeyName>
// 	</ds:KeyInfo>
// 

// Get the KeyName.
CkoStringBuilder *sbKeyName = [[CkoStringBuilder alloc] init];
[sbKeyName Append: [xmlKeyInfo GetChildContent: @"*:KeyName"]];

// sbKeyName contains "dsaKey_123"
NSLog(@"%@",[sbKeyName GetAsString]);

// The application now locates and loads the public key for verification
// based on the key name.  This example will do the following:
// If the key name equals "dsaKey_123", then load the DSA key from
// "qa_data/dsa/dsa1024_public.pem"
// 

if ([sbKeyName ContentsEqual: @"dsaKey_123" caseSensitive: NO] == NO) {
    NSLog(@"%@",@"I don't know this key...");
    return;
}

// The DSA public key used in this example is available at:
// https://www.chilkatsoft.com/exampleData/dsa1024_public.zip
CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
success = [pubKey LoadFromFile: @"qa_data/dsa/dsa1024_public.pem"];
if (success != YES) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

// Provide the DSA public key to the XML DSig verifier:
[verifier SetPublicKey: pubKey];

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