(Objective-C) Create and Verify an Opaque PKCS7/CMS Signature

Demonstrates how to create a PKCS7 opaque signature, and also how to verify an opaque signature. An opaque signature is different than a detached PKCS7 signature in that it contains the original data. Verifying an opaque signature retrieves the original content.

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#import <CkoCrypt2.h>
#import <CkoCert.h>
#import <CkoPrivateKey.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];

// A certificate and private key is needed to create a signature.
// Chilkat provides many different ways to load a certificate and private key, such
// as from a PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
// This example will load the certificate from a .crt and the private key from a .key file

CkoCert *cert = [[CkoCert alloc] init];
// The LoadFromFile method will automatically detect the format and load it.
BOOL success = [cert LoadFromFile: @"qa_data/certs/test_12345678a.cer"];
if (success != YES) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// Our private key is in an encrypted PKCS8 format.
// If you don't know the format of your key, but you do know it's encrypted,
// and requires a password, then just call any of the Chilkat methods that load
// a private key w/ a password argument.  Chilkat will auto-detect the format
// and load it correctly even if it's not the format indicated by the method name..
CkoPrivateKey *privKey = [[CkoPrivateKey alloc] init];
NSString *password = @"12345678a";
success = [privKey LoadPkcs8EncryptedFile: @"qa_data/certs/test_12345678a.key" password: password];
if (success != YES) {
    NSLog(@"%@",privKey.LastErrorText);
    return;
}

// Set properties required for signing.

// Tell it to use the cert and private key we've loaded.
success = [crypt SetSigningCert2: cert key: privKey];
if (success != YES) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

// Indicate we want the opaque signature in base64 format:
crypt.EncodingMode = @"base64";

// Sign the string using the "utf-8" byte representation:
crypt.Charset = @"utf-8";

// Create the opaque signature:
NSString *originalData = @"This is the string to be signed.";
NSString *opaqueSig = [crypt OpaqueSignStringENC: originalData];
if (crypt.LastMethodSuccess != YES) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

NSLog(@"%@",opaqueSig);

// The output looks like this:
// MIIPgQYJKoZIhvcNAQcCoIIPcjCCD24CAQExCzAJBgUrDgMCGgUAMC8GCSqGSIb3DQEHAaAiBCBUaGlzIGlzIHRoZSBzdHJpbmcgdG8gYmUgc...

// ----------------------------------------------------------------------------------------------
// Now let's verify the signature and retrieve the original data.
// We'll use a new Crypt2 object to keep things completely separate...

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

vCrypt.EncodingMode = @"base64";
vCrypt.Charset = @"utf-8";

NSString *extractedData = [vCrypt OpaqueVerifyStringENC: opaqueSig];
if (vCrypt.LastMethodSuccess != YES) {
    NSLog(@"%@",vCrypt.LastErrorText);
    return;
}

NSLog(@"%@%@",@"The extracted data: ",extractedData);

// The output is:
// The extracted data: This is the string to be signed.