(Objective-C) Create JWS Using Private Key on a Smart Card

See more JSON Web Signatures (JWS) Examples

Creates and validates a JSON Web Signature (JWS) using the private key associated with a certificate on a smart card.

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#import <CkoCert.h>
#import <CkoPrivateKey.h>
#import <CkoJsonObject.h>
#import <CkoJws.h>
#import <NSString.h>
#import <CkoPublicKey.h>

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

// Load the certificate from a smart card.
CkoCert *cert = [[CkoCert alloc] init];
BOOL success = [cert LoadFromSmartcard: @""];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// Note: Chilkat provides many different ways to load a certificate from a smartcard or USB token,
// such as selecting a certificate if the card contains multiple certificates with private keys,
// or working with lower-level PKCS11 or ScMinidriver API's (both of which Chilkat provides).

// If the associated private key was present on the smartcard, then you can simply
// get it from the Chilkat cert object:
CkoPrivateKey *privKey = [cert ExportPrivateKey];
if (cert.LastMethodSuccess == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// You can check the key type to make sure it's RSA.
// This will output "rsa" if the key is RSA.
NSLog(@"%@%@",@"Key type = ",privKey.KeyType);

// Create the JWS Protected Header
CkoJsonObject *jwsProtHdr = [[CkoJsonObject alloc] init];
[jwsProtHdr AppendString: @"alg" value: @"RS256"];

CkoJws *jws = [[CkoJws alloc] init];

// Set the protected header:
int signatureIndex = 0;
[jws SetProtectedHeader: [NSNumber numberWithInt: signatureIndex] json: jwsProtHdr];

// Set the RSA key:
[jws SetPrivateKey: [NSNumber numberWithInt: signatureIndex] privKey: privKey];

// Set the payload.
BOOL bIncludeBom = NO;
NSString *payloadStr = @"In our village, folks say God crumbles up the old moon into stars.";
[jws SetPayload: payloadStr charset: @"utf-8" includeBom: bIncludeBom];

// Create the JWS
// By default, the compact serialization is used.
NSString *jwsCompact = [jws CreateJws];
if (jws.LastMethodSuccess != YES) {
    NSLog(@"%@",jws.LastErrorText);

    return;
}

NSLog(@"%@%@",@"JWS: ",jwsCompact);

// sample output:
// JWS: eyJhbGciOiJQUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.TRWhwRo5dMv9-8OzrInfJTwmUGYgjLfHk8lqF072ND-FmLWEBnUTOpY8oJXp8FdWw2SalbdOeNlrtlJjwk4XK8Ql2iJ_2qMCtxsvLPhKBOqFoAF4aBvTOEDVJDxf0DaBSiydEEtfTVV2iwBcjWabu5J2XieR5y7QZQtuHsn7T3qKBvCcCejN3Y2oqAT3qMHvu1fTms1r_91wBn_K7Wjd9UkZ1n02qQcUHJznR_OF2BgN7_KWIDAF9ZS9keoju2NPpPelO4yxa2XUPnehY3G7dHKoCxUEQR4d2Xc5voqDASTVCDqQS4PVOZdvT3Ein6-SanAlCwbWBbkvT8g6-5PImQ

// Now load the JWS, validate, and recover the original text.
CkoJws *jws2 = [[CkoJws alloc] init];

// Load the JWS.
success = [jws2 LoadJws: jwsCompact];

CkoPublicKey *rsaPubKey = [privKey GetPublicKey];

// Set the RSA public key used for validation.
signatureIndex = 0;
[jws2 SetPublicKey: [NSNumber numberWithInt: signatureIndex] pubKey: rsaPubKey];

// Validate the 1st (and only) signature at index 0..
int v = [[jws2 Validate: [NSNumber numberWithInt: signatureIndex]] intValue];
if (v < 0) {
    // Perhaps Chilkat was not unlocked or the trial expired..
    NSLog(@"%@",@"Method call failed for some other reason.");
    NSLog(@"%@",jws2.LastErrorText);
    return;
}

if (v == 0) {
    NSLog(@"%@",@"Invalid signature.  The RSA key was incorrect, the JWS was invalid, or both.");
    return;
}

// If we get here, the signature was validated..
NSLog(@"%@",@"Signature validated.");

// Recover the original content:
NSLog(@"%@",[jws2 GetPayload: @"utf-8"]);

// Examine the protected header:
CkoJsonObject *joseHeader = [jws2 GetProtectedHeader: [NSNumber numberWithInt: signatureIndex]];
if (jws2.LastMethodSuccess != YES) {
    NSLog(@"%@",@"No protected header found at the given index.");
    return;
}

joseHeader.EmitCompact = NO;

NSLog(@"%@",@"Protected (JOSE) header:");
NSLog(@"%@",[joseHeader Emit]);

// Output:

// 	Signature validated.
// 	In our village, folks say God crumbles up the old moon into stars.
// 	Protected (JOSE) header:
// 	{ 
// 	  "alg": "RS256"
// 	}