(Objective-C) Create XML Signature with Certificate's Private Key

Demonstrates how to create an XML digital signature using a certificate's RSA private key. This example loads the certificate from a PFX, and uses the cert's associated private key to sign. The public key is embedded in the XML signature as a ds:KeyInfo / ds:KeyValue / dsRSAKeyValue element.

This example requires Chilkat v9.5.0.71 or greater.

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#import <NSString.h>
#import <CkoHttp.h>
#import <CkoStringBuilder.h>
#import <CkoCert.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 SOAP XML to be signed in this example contains the following:

// <?xml version="1.0" encoding="UTF-8" standalone="no" ?>
// <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
//     <SOAP-ENV:Header>
//         <wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" SOAP-ENV:mustUnderstand="1"></wsse:Security>
//     </SOAP-ENV:Header>
//     <SOAP-ENV:Body xmlns:SOAP-SEC="http://schemas.xmlsoap.org/soap/security/2000-12" SOAP-SEC:id="Body">
//         <z:FooBar xmlns:z="http://example.com" />
//     </SOAP-ENV:Body>
// </SOAP-ENV:Envelope>
// 

// The above XML is available at https://www.chilkatsoft.com/exampleData/soapToSign.xml
// Fetch the XML and then sign it..

NSString *url = @"https://www.chilkatsoft.com/exampleData/soapToSign.xml";
CkoHttp *http = [[CkoHttp alloc] init];
CkoStringBuilder *sbSoapXml = [[CkoStringBuilder alloc] init];
BOOL success = [http QuickGetSb: url sbContent: sbSoapXml];
if (success != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

// Load a PFX file containing the certificate + private key.
CkoCert *cert = [[CkoCert alloc] init];
success = [cert LoadPfxFile: @"/somedir/myPfx.pfx" password: @"pfx_password"];
if (success != YES) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// Get the RSA private key for signing...
CkoPrivateKey *rsaKey = [cert ExportPrivateKey];
if (cert.LastMethodSuccess != YES) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// To create the XML digital signature (i.e. embed the signature within
// the SOAP XML), we specify what is desired, and then call the method to 
// create the XML signature.
// 
// For example, the application must provide the following:
//     - Where to put the signature.
//     - What to sign.
//     - The algorithms to be used.
//     - The key to be used for signing.
// 

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

// In this example, we're going to put the signature within the wsse:Security element.
// To specify the location, set the SigLocation property to the XML path to this element,
// using vertical bar characters to separate tags.
xmlSigGen.SigLocation = @"SOAP-ENV:Envelope|SOAP-ENV:Header|wsse:Security";

// An XML digital signature contains one or more references.  These are references to the parts
// of the XML document to be signed (a same document reference), or can be external references.
// This example will add a single same-document reference.  We'll add a reference to the XML fragment
// at SOAP-ENV:Body, which is indicated by providing the value of the "ID" attribute (where "ID" is case
// insensitive).  For each same-document reference, we must also indicate the hash algorithm and XML canonicalization
// algorithm to be used.  For this example we'll choose SHA-256 and Exclusive XML Canonicalization.
[xmlSigGen AddSameDocRef: @"Body" digestMethod: @"sha256" canonMethod: @"EXCL_C14N" prefixList: @"" refType: @""];

// Let's provide the RSA key to be used for signing:
[xmlSigGen SetPrivateKey: rsaKey];

// We're leaving the following properties at their default values:
// 
//    - SigNamespacePrefix (default is "ds")
//    - SigningAlg (for RSA keys. The default is PKCS1-v1_5, can be changed to RSASSA-PSS.)
//    - SignedInfoCanonAlg  (default is EXCL_C14N)
//    - SignedInfoDigestMethod (default is sha256)
//    - KeyInfoType (default is "KeyValue", where the RSA public key is included in the Signature)

// Note: Each Reference has it's own specified algorithms for XML canonicalization and hashing,
// and the actual signature part (the SignedInfo) has it's own algorithms for the same.
// They may or may not be the same.  In this example, we use Exclusive XML Canonicalization and SHA-256 throughout.

// Finally, we're going to set one property that's optional, but commonly used.
// It's the SignedInfoPrefixList.  In this case, we're using Exclusive Canonicalization, and the signature
// will be placed in a location within the XML document where namespace prefixes are used in the ancestors.
// Specifically, the "wsse" and "SOAP-ENV" namespace prefixes are used.
xmlSigGen.SignedInfoPrefixList = @"wsse SOAP-ENV";

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

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

// This is the signed SOAP XML.
// Chilkat emits the Signature in compact form on a single line.  Whitespace in XML signatures
// matters.  Chilkat's opinion is that writing the Signature without whitespace minimizes the chance
// for problems with whatever software might be verifying the signature.

// <?xml version="1.0" encoding="UTF-8" standalone="no" ?>
// <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
//     <SOAP-ENV:Header>
//         <wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" SOAP-ENV:mustUnderstand="1"><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#"><InclusiveNamespaces xmlns="http://www.w3.org/2001/10/xml-exc-c14n#" PrefixList="wsse SOAP-ENV"/></ds:CanonicalizationMethod><ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/><ds:Reference URI="#Body"><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>OwgHPZNfDkXnZsjpfzXqAcT3RV3HzmTsEy2bP44FJ0M=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>C+7FWngUpJ33Q1yq8uuscjCyPN2IO4cJhpMv03Jrrht1V+4gvJQLIBk6HHjo1uPQyfYj6zji3pg+fOyGUptp17CsRvjCzSpP35vB2lEzHeS8dcY8XfrEtTP/0FNn75LmhhkOPy0wjWkgDVbgzhXpEk9az8r8fQVTM3vrcmXT+WdMWJXKBRFt6PLAhsFt0scOFTWAkLGyCwygzimDKX2nT63TOit9BigtIx7fPRuMkbybMKCGGABq2DiEbvrPOiN3SUYpyMNR9KehRAGN+OWnESaDC6DhOvbKR88XHkM+GeaRe9PWdrRHrwGfp3qgolKjR/wFRSa1YGSBKAhDJFBcdg==</ds:SignatureValue><ds:KeyInfo><ds:KeyValue><ds:RSAKeyValue><ds:Modulus>sXeRhM55P13FbpNcXAMR3olbw2Wa6keZIHu5YTZYUBTlYWId+pNiwUz3zFIEo+0IfYR0H27ybIycQO+1IIzJofUFNMAL3tZps2OKPlsjuCPls6kXpXhv/gvhux8LrCtp4PcKWqJ6QVOZKChc7WAx40qFWzHi57ueqRTv3x0kESqGg/VjsqyTEvb55psJO2RsfhLT7+YVh3hImRM3RDaJdkTkPuOxeFyT6N7VXD09329sLuS3QkUbE9zEKDnz9X3d8dEQdJhSI9ba5fxl8R7fu8pB67ElfzFml96X1jLFtzy1pzOT5Fc4ROcaqlYckVzdBq9sxezm6MYmDBjNAcibRw==</ds:Modulus><ds:Exponent>AQAB</ds:Exponent></ds:RSAKeyValue></ds:KeyValue></ds:KeyInfo></ds:Signature></wsse:Security>
//     </SOAP-ENV:Header>
//     <SOAP-ENV:Body xmlns:SOAP-SEC="http://schemas.xmlsoap.org/soap/security/2000-12" SOAP-SEC:id="Body">
//         <z:FooBar xmlns:z="http://example.com" />
//     </SOAP-ENV:Body>
// </SOAP-ENV:Envelope>

// Here's the signature part formatted for easier reading.
// (Adding whitespace to the SignedInfo breaks the signature, so you wouldn't want to do this..)

//     <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#">
//                 <InclusiveNamespaces xmlns="http://www.w3.org/2001/10/xml-exc-c14n#" PrefixList="wsse SOAP-ENV" />
//             </ds:CanonicalizationMethod>
//             <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" />
//             <ds:Reference URI="#Body">
//                 <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>OwgHPZNfDkXnZsjpfzXqAcT3RV3HzmTsEy2bP44FJ0M=</ds:DigestValue>
//             </ds:Reference>
//         </ds:SignedInfo>
//         <ds:SignatureValue>C+7FWngUp....BKAhDJFBcdg==</ds:SignatureValue>
//         <ds:KeyInfo>
//             <ds:KeyValue>
//                 <ds:RSAKeyValue>
//                     <ds:Modulus>sXeRhM55P13FbpNcXAMR....MYmDBjNAcibRw==</ds:Modulus>
//                     <ds:Exponent>AQAB</ds:Exponent>
//                 </ds:RSAKeyValue>
//             </ds:KeyValue>
//         </ds:KeyInfo>
//     </ds:Signature>