(Objective-C) Create XML Signature with External XML Reference

Demonstrates how to create an XML digital signature where the referenced data is external. In this case, the data is an XML file located at the following URL: https://www.chilkatsoft.com/data/helloWorld.xml

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#import <CkoXml.h>
#import <CkoCert.h>
#import <CkoXmlDSigGen.h>
#import <CkoHttp.h>
#import <CkoStringBuilder.h>
#import <CkoXmlDSig.h>
#import <NSString.h>

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

// This example inserts an XML signature in the following XML:

// <?xml version="1.0" encoding="UTF-8" standalone="no"?>
// <abc>
//   <xyz>
// 	<name>helloWorld.xml</name>
// 	<url>https://www.chilkatsoft.com/data/helloWorld.xml</url>
//   </xyz>
// </abc>

// Build the above XML to be signed.
CkoXml *xml = [[CkoXml alloc] init];
xml.Tag = @"abc";
[xml UpdateChildContent: @"xyz|name" value: @"helloWorld.xml"];
[xml UpdateChildContent: @"xyz|url" value: @"https://www.chilkatsoft.com/data/helloWorld.xml"];

CkoCert *cert = [[CkoCert alloc] init];

BOOL success = [cert LoadPfxFile: @"qa_data/pfx/test_secret.pfx" password: @"secret"];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

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

// Indicate the location within the XML the Signature will be inserted.
gen.SigLocation = @"abc|xyz";

// Get the content of the XML data to be referenced.
CkoHttp *http = [[CkoHttp alloc] init];
CkoStringBuilder *sbExternalXml = [[CkoStringBuilder alloc] init];
success = [http QuickGetSb: @"https://www.chilkatsoft.com/data/helloWorld.xml" sbContent: sbExternalXml];
if (success == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

success = [gen AddExternalXmlRef: @"https://www.chilkatsoft.com/data/helloWorld.xml" content: sbExternalXml digestMethod: @"sha256" canonMethod: @"EXCL_C14N" refType: @""];
if (success == NO) {
    NSLog(@"%@",gen.LastErrorText);
    return;
}

// Provide the private key for signing via the certificate, and indicate that
// we want the base64 of the certificate embedded in the KeyInfo.
gen.KeyInfoType = @"X509Data";
gen.X509Type = @"Certificate";

BOOL bUsePrivateKey = YES;
success = [gen SetX509Cert: cert usePrivateKey: bUsePrivateKey];
if (success != YES) {
    NSLog(@"%@",gen.LastErrorText);
    return;
}

// Indicate we want an indented signature for readability.
// This can be removed after debugging is finished..
gen.Behaviors = @"IndentedSignature";

// Now create and insert the Signature
CkoStringBuilder *sbXml = [[CkoStringBuilder alloc] init];
[xml GetXmlSb: sbXml];
success = [gen CreateXmlDSigSb: sbXml];
if (success != YES) {
    NSLog(@"%@",gen.LastErrorText);
    return;
}

// Examine the XML with the digital signature inserted
NSLog(@"%@",[sbXml GetAsString]);

// Here is the output:

// <?xml version="1.0" encoding="utf-8"?>
// <abc>
//     <xyz>
//         <name>helloWorld.xml</name>
//         <url>https://www.chilkatsoft.com/data/helloWorld.xml</url>
//     <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#rsa-sha256"/>
//     <ds:Reference URI="https://www.chilkatsoft.com/data/helloWorld.xml">
//       <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>H/s775OZhel6wdBhe02l4LK6m0lkplOisKxAbVwWxp0=</ds:DigestValue>
//     </ds:Reference>
//   </ds:SignedInfo>
//   <ds:SignatureValue>UruwnBqh..Ll4IzUA==</ds:SignatureValue>
//   <ds:KeyInfo>
//     <ds:X509Data>
//       <ds:X509Certificate>MIIHAz...nUZWCaDE=</ds:X509Certificate>
//     </ds:X509Data>
//   </ds:KeyInfo>
// </ds:Signature></xyz>
// </abc>

// Let's verify the signature...
CkoXmlDSig *verifier = [[CkoXmlDSig alloc] init];
success = [verifier LoadSignatureSb: sbXml];
if (success != YES) {
    NSLog(@"%@",verifier.LastErrorText);
    return;
}

// Let's examine the external references, and fetch the data for each..
CkoStringBuilder *sbExternalData = [[CkoStringBuilder alloc] init];
int numRefs = [verifier.NumReferences intValue];
int i = 0;
while (i < numRefs) {
    BOOL bExternal = [verifier IsReferenceExternal: [NSNumber numberWithInt: i]];
    if (bExternal == YES) {
        NSString *uri = [verifier ReferenceUri: [NSNumber numberWithInt: i]];

        // We're assuming the URI is an https:// or http:// URL...
        // Let's also assume we know that the referenced data is text and we want the utf-8 byte representation.
        [sbExternalData Clear];
        success = [http QuickGetSb: uri sbContent: sbExternalData];
        if (success == NO) {
            NSLog(@"%@",http.LastErrorText);
            return;
        }

        // Because the referenced external data was explicitly XML, it was the canonicalized XML that was digested.
        // We need to canonicalize the XML in the same way as when signed.
        NSString *canonXml = [verifier CanonicalizeXml: [sbExternalData GetAsString] version: @"EXCL_C14N" withComments: NO];
        [sbExternalData SetString: canonXml];

        success = [verifier SetRefDataSb: [NSNumber numberWithInt: i] sb: sbExternalData charset: @"utf-8"];
        if (success == NO) {
            NSLog(@"%@",verifier.LastErrorText);
            return;
        }

    }

    i = i + 1;
}

// Now that we have the external data available, we can verify the reference digest(s) and the signature.
BOOL bVerified = [verifier VerifySignature: YES];
if (bVerified != YES) {
    NSLog(@"%@",verifier.LastErrorText);
    return;
}

NSLog(@"%@",@"Signature verified!");