(Objective-C) Create XML Digital Signature having KeyName

Demonstrates how to create an XML digital signature where the KeyInfo part will contain 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.
The verifying application would use the KeyName to find and use the 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 <CkoPrivateKey.h>
#import <CkoXmlDSigGen.h>

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

// The XML to be signed in this example contains the following:

// <?xml version="1.0" encoding="UTF-8" standalone="no"?>
// <Envelope>
//   <Header>
//     <Security>
//     </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/xmlToSign.xml
// Fetch the XML and then sign it..

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

// This example uses a DSA private key for signing.  
// There are many ways of getting an DSA private key using Chilkat.  This example
// will load it from an encrypted PEM file.

// In case you would like to use it, I put the DSA private key PEM file here:
// https://www.chilkatsoft.com/exampleData/dsa1024_secret.zip
// The password is "secret".
CkoPrivateKey *dsaKey = [[CkoPrivateKey alloc] init];
success = [dsaKey LoadEncryptedPemFile: @"qa_data/dsa/dsa1024_secret.pem" password: @"secret"];
if (success != YES) {
    NSLog(@"%@",dsaKey.LastErrorText);
    return;
}

CkoXmlDSigGen *xmlSigGen = [[CkoXmlDSigGen alloc] init];

// Indicate where the XML Signature is to be inserted.
xmlSigGen.SigLocation = @"Envelope|Header|Security";

// Specify the fragment of the XML document to be signed.
// This example will sign the fragment from <Body Id="abc"> ... </Body>
[xmlSigGen AddSameDocRef: @"abc" digestMethod: @"sha256" canonMethod: @"EXCL_C14N" prefixList: @"" refType: @""];

// Provide the DSA key to be used for signing:
[xmlSigGen SetPrivateKey: dsaKey];

// Specify what we want to emit in the KeyInfo part of the Signature.
// By default, it is the KeyValue that is emitted to the KeyInfo.
// In this example,we want to emit a key name rather than the actual public key value.
xmlSigGen.KeyInfoType = @"KeyName";

// Provide a key name.  The verifying application will use the key name
// to find/load the public key to be used for verifying the signature.
// The key name is an arbitrary pre-agreed upon name that signer and verifier both know in advance.
xmlSigGen.KeyInfoKeyName = @"dsaKey_123";

// The KeyInfo part of the XML signature to be created will contain this:
// 
//     <ds:KeyInfo><ds:KeyName>dsaKey_123</ds:KeyName></ds:KeyInfo>
// 

// OK, everything's specified, so let's create the XML digital signature:
// This in-place signs the XML.  If successful, sbXml will contain the 
// XML with the digital signature at the specified location.
xmlSigGen.Behaviors = @"IndentedSignature";
success = [xmlSigGen CreateXmlDSigSb: sbXml];
if (success != YES) {
    NSLog(@"%@",xmlSigGen.LastErrorText);
    return;
}

// Examine the signed XML:
NSLog(@"%@",[sbXml GetAsString]);

[sbXml WriteFile: @"c:/chilkatsoft.com/exampleData/signedUsingKeyName.xml" charset: @"utf-8" emitBom: NO];

// Below is the signed XML that is produced.
// 
// <?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>F+HopRvLoj+9SHZxI/cGfX9SDfh+HRGZLMievGX3y/cckX1UzFuXCA==</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>
//