(Objective-C) Swift Alliance LAU XML Signature

Calculating the LAU for Swift Alliance File Act XML using HMAC SHA256. (The XML signature, also referred to as Local Authentication (LAU), is computed using the algorithm HMAC based on SHA-256.)

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#import <CkoStringBuilder.h>
#import <CkoXmlDSigGen.h>

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

// We begin with the following XML:

// <?xml version="1.0" encoding="UTF-8"?>
// <Saa:DataPDU xmlns:Saa="urn:swift:saa:xsd:saa.2.0" xmlns:Sw="urn:swift:snl:ns.Sw" xmlns:SwInt="urn:swift:snl:ns.SwInt" xmlns:SwGbl="urn:swift:snl:ns.SwGbl" xmlns:SwSec="urn:swift:snl:ns.SwSec">
//     <Saa:Revision>2.0.6</Saa:Revision>
//     <Saa:Header>
//         <Saa:Message>
//             <Saa:SenderReference>Ref760FA1234</Saa:SenderReference>
//             <Saa:MessageIdentifier>tsrv.fin.mt7xx.gteesstandbys</Saa:MessageIdentifier>
//             <Saa:Format>File</Saa:Format>
//             <Saa:SubFormat>Input</Saa:SubFormat>
//             <Saa:Sender>
//                 <Saa:DN>cn=su8,o=ptsqgbbb,o=swift</Saa:DN>
//                 <Saa:FullName>
//                     <Saa:X1>PTSQGBBBXXX</Saa:X1>
//                 </Saa:FullName>
//             </Saa:Sender>
//             <Saa:Receiver>
//                 <Saa:DN>cn=abc,ou=saa,o=xxx,o=swift</Saa:DN>
//                 <Saa:FullName>
//                     <Saa:X1>PTSXXXXXXXX</Saa:X1>
//                     <Saa:X2>saa</Saa:X2>
//                 </Saa:FullName>
//             </Saa:Receiver>
//             <Saa:InterfaceInfo>
//                 <Saa:UserReference>CRE...</Saa:UserReference>
//                 <Saa:MessageCreator>ApplicationInterface</Saa:MessageCreator>
//                 <Saa:MessageContext>Original</Saa:MessageContext>
//                 <Saa:MessageNature>Financial</Saa:MessageNature>
//             </Saa:InterfaceInfo>
//             <Saa:NetworkInfo>
//                 <Saa:Priority>Normal</Saa:Priority>
//                 <Saa:IsPossibleDuplicate>true</Saa:IsPossibleDuplicate>
//                 <Saa:Service>swift.corp.fast!x</Saa:Service>
//                 <Saa:Network>Application</Saa:Network>
//                 <Saa:SessionNr>0080</Saa:SessionNr>
//                 <Saa:SeqNr>000001</Saa:SeqNr>
//                 <Saa:SWIFTNetNetworkInfo>
//                     <Saa:RequestType>tsrv.fin.mt7xx.gteesstandbys</Saa:RequestType>
//                     <Saa:Reference>2f949999-d32e-49eb-9999-9a819b9b9c0d</Saa:Reference>
//                     <Saa:FileInfo>SwCompression=Zip</Saa:FileInfo>
//                 </Saa:SWIFTNetNetworkInfo>
//             </Saa:NetworkInfo>
//             <Saa:SecurityInfo>
//                 <Saa:SWIFTNetSecurityInfo>
//                     <Saa:FileDigestAlgorithm>SHA-256</Saa:FileDigestAlgorithm>
//                     <Saa:FileDigestValue>9tnnjIgsowPSU+ehm8Rb0J5TvZIvhCYnySzFkpur1aw=</Saa:FileDigestValue>
//                 </Saa:SWIFTNetSecurityInfo>
//             </Saa:SecurityInfo>
//             <Saa:FileLogicalName>Payload.ZIP</Saa:FileLogicalName>
//             <Saa:ExpiryDateTime>20210712074808</Saa:ExpiryDateTime>
//         </Saa:Message>
//     </Saa:Header>
//     <Saa:Body>Payload.ZIP</Saa:Body>
// </Saa:DataPDU>

// Load the XML file to be signed.
CkoStringBuilder *sbXml = [[CkoStringBuilder alloc] init];
BOOL success = [sbXml LoadFile: @"c:/someDir/fileToSign.xml" charset: @"utf-8"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load XML file.");
    return;
}

// We need to add a "LAU" XML element just before the "</Saa:DataPDU>"
int numReplaced = [[sbXml Replace: @"</Saa:DataPDU>" replacement: @"<LAU xmlns=\"urn:swift:saa:xsd:saa.2.0\"></LAU></Saa:DataPDU>"] intValue];

CkoXmlDSigGen *gen = [[CkoXmlDSigGen alloc] init];
gen.SigLocation = @"Saa:DataPDU|LAU";
gen.SigLocationMod = [NSNumber numberWithInt:0];
gen.SigNamespacePrefix = @"ds";
gen.SigNamespaceUri = @"http://www.w3.org/2000/09/xmldsig#";
gen.SignedInfoCanonAlg = @"EXCL_C14N";
gen.SignedInfoDigestMethod = @"sha256";
gen.Behaviors = @"CompactSignedXml";

// Sign the entire document.
[gen AddSameDocRef: @"" digestMethod: @"sha256" canonMethod: @"EXCL_C14N" prefixList: @"" refType: @""];

// Set our HMAC key
[gen SetHmacKey: @"Abcdef0123456789Abcdef0123456789" encoding: @"ascii"];

// Sign the XML:
success = [gen CreateXmlDSigSb: sbXml];
if (success == NO) {
    NSLog(@"%@",gen.LastErrorText);
    return;
}

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

// Save the signed XML to a file.
success = [sbXml WriteFile: @"c:/someDir/signedFile.xml" charset: @"utf-8" emitBom: NO];