(Objective-C) Sign JSON (or any Text) to Create a Detached PKCS7 Signature

Demonstrates how to sign JSON or any string using a certificate + private key from a .p12/.pfx to create a detached PKCS7 signature. (A detached signature is one that does not embed the original signed data.)

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#import <CkoCrypt2.h>
#import <CkoCert.h>
#import <NSString.h>

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

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];

CkoCert *cert = [[CkoCert alloc] init];
BOOL success = [cert LoadPfxFile: @"qa_data/pfx/cert_test123.pfx" password: @"test123"];
if (success != YES) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// Tell the crypt component to use this cert.
success = [crypt SetSigningCert: cert];
if (success != YES) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

crypt.HashAlgorithm = @"sha256";

// By default, all the certs in the chain of authentication are included in the signature.
// If desired, we can choose to only include the signing certificate:
crypt.IncludeCertChain = NO;

// Create the detached signature, which does NOT contain the original data.
// To create a PKCS7 signature that contains the original data, see CAdES Sign JSON
crypt.Charset = @"utf-8";
NSData detachedSig;
NSString *stringToSign = @"{ \"abc\": 123}";
detachedSig = [crypt SignString: stringToSign];
if (crypt.LastMethodSuccess == NO) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

// Verify the signature against the original data.
BOOL verified = [crypt VerifyString: stringToSign sigData: detachedSig];
if (verified == NO) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

NSLog(@"%@",@"Success!");