Objective-C

Verify XML Signature with External URL References

See more XML Digital Signatures Examples

Demonstrates how to verify an XML digital signature that includes references to URLs where the data to be digested is on a web server. Objective-C

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

BOOL success = NO;

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

//  The signed XML we wish to verify contains external references such as this:

//      <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref0" URI="https://www.chilkatsoft.com/images/starfish.jpg">
//        <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
//        <ds:DigestValue>AOU810yJV5Np/DnO29qpObqiTSTTCDvxGsX5ayiTYXI=</ds:DigestValue>
//      </ds:Reference>
//      <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref1" URI="https://www.chilkatsoft.com/hamlet.xml">
//        <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
//        <ds:DigestValue>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</ds:DigestValue>
//      </ds:Reference>

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

//  First load the signed XML
CkoStringBuilder *sbSignedXml = [[CkoStringBuilder alloc] init];
success = [sbSignedXml LoadFile: @"qa_data/xml_dsig_verify/signedWithExternalUrlRefs.xml" charset: @"utf-8"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load signed XML.");
    return;
}

success = [verifier LoadSignatureSb: sbSignedXml];
if (success == NO) {
    NSLog(@"%@",verifier.LastErrorText);
    return;
}

//  Iterate over each reference.  If it is an external URL reference, download the data and provide it to the verifier.
CkoStringBuilder *sbRefUri = [[CkoStringBuilder alloc] init];
CkoBinData *bd = [[CkoBinData alloc] init];
int numRefs = [verifier.NumReferences intValue];
int i = 0;
while (i < numRefs) {
    if ([verifier IsReferenceExternal: [NSNumber numberWithInt: i]] == YES) {
        [sbRefUri Clear];
        [sbRefUri Append: [verifier ReferenceUri: [NSNumber numberWithInt: i]]];
        if ([sbRefUri StartsWith: @"https://" caseSensitive: NO] == YES) {
            NSLog(@"%@%@",@"External URL Reference: ",[sbRefUri GetAsString]);

            //  Download the data at the URL and provide to the verifier.
            success = [http DownloadBd: [sbRefUri GetAsString] binData: bd];
            if (success == NO) {
                NSLog(@"%@",http.LastErrorText);
                return;
            }

            success = [verifier SetRefDataBd: [NSNumber numberWithInt: i] binData: bd];
            if (success == NO) {
                NSLog(@"%@",verifier.LastErrorText);
                return;
            }

        }

    }

    i = i + 1;
}

//  Now that we have the external data, verify the signature..
BOOL bVerified = [verifier VerifySignature: YES];
if (bVerified == NO) {
    NSLog(@"%@",verifier.LastErrorText);
}

NSLog(@"%@%d",@"Signature verified = ",bVerified);