(Objective-C) Validate JWS Using RSASSA-PKCS1-v1_5 SHA-256

Validates a JSON Web Signature (JWS) that uses RSASSA-PKCS1-v1_5 SHA-256.

Note: This example requires Chilkat v9.5.0.66 or greater.

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#import <CkoStringBuilder.h>
#import <CkoPublicKey.h>
#import <CkoJws.h>
#import <CkoJsonObject.h>

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

// Note: This example requires Chilkat v9.5.0.66 or greater.

// This example takes a JSON signature in compact serialization format,
// and uses an RSA public key to validate and recover the protected header and payload.

// We only need a public key for signature validation.  This is the RSA public key
// that is used:

//      {"kty":"RSA", 
//       "n":"ofgWCuLjybRlzo0tZWJjNiuSfb4p4fAkd_wWJcyQoTbji9k0l8W26mPddx
//            HmfHQp-Vaw-4qPCJrcS2mJPMEzP1Pt0Bm4d4QlL-yRT-SFd2lZS-pCgNMs
//            D1W_YpRPEwOWvG6b32690r2jZ47soMZo9wGzjb_7OMg0LOL-bSf63kpaSH
//            SXndS5z5rexMdbBYUsLA9e-KXBdQOS-UTo7WTBEMa2R2CapHg665xsmtdV
//            MTBQY4uDZlxvb3qCo5ZwKh9kG4LT6_I5IhlJH7aGhyxXFvUK-DWNmoudF8
//            NAco9_h9iaGNj8q2ethFkMLs91kzk2PAcDTW9gb54h4FRWyuXpoQ", 
//       "e":"AQAB"
//      }

CkoStringBuilder *sbPubKey = [[CkoStringBuilder alloc] init];
[sbPubKey Append: @"{\"kty\":\"RSA\","];
[sbPubKey Append: @"\"n\":\"ofgWCuLjybRlzo0tZWJjNiuSfb4p4fAkd_wWJcyQoTbji9k0l8W26mPddx"];
[sbPubKey Append: @"HmfHQp-Vaw-4qPCJrcS2mJPMEzP1Pt0Bm4d4QlL-yRT-SFd2lZS-pCgNMs"];
[sbPubKey Append: @"D1W_YpRPEwOWvG6b32690r2jZ47soMZo9wGzjb_7OMg0LOL-bSf63kpaSH"];
[sbPubKey Append: @"SXndS5z5rexMdbBYUsLA9e-KXBdQOS-UTo7WTBEMa2R2CapHg665xsmtdV"];
[sbPubKey Append: @"MTBQY4uDZlxvb3qCo5ZwKh9kG4LT6_I5IhlJH7aGhyxXFvUK-DWNmoudF8"];
[sbPubKey Append: @"NAco9_h9iaGNj8q2ethFkMLs91kzk2PAcDTW9gb54h4FRWyuXpoQ\","];
[sbPubKey Append: @"\"e\":\"AQAB\""];
[sbPubKey Append: @"}"];

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
BOOL success = [pubKey LoadFromString: [sbPubKey GetAsString]];
if (success != YES) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

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

// Set the RSA public key:
int signatureIndex = 0;
[jws SetPublicKey: [NSNumber numberWithInt: signatureIndex] pubKey: pubKey];

// Load the JWS.
CkoStringBuilder *sbJws = [[CkoStringBuilder alloc] init];
[sbJws Append: @"eyJhbGciOiJSUzI1NiJ9"];
[sbJws Append: @"."];
[sbJws Append: @"eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt"];
[sbJws Append: @"cGxlLmNvbS9pc19yb290Ijp0cnVlfQ"];
[sbJws Append: @"."];
[sbJws Append: @"cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7"];
[sbJws Append: @"AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4"];
[sbJws Append: @"BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K"];
[sbJws Append: @"0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqv"];
[sbJws Append: @"hJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrB"];
[sbJws Append: @"p0igcN_IoypGlUPQGe77Rw"];

success = [jws LoadJwsSb: sbJws];
if (success != YES) {
    NSLog(@"%@",jws.LastErrorText);
    return;
}

// Validate the 1st (and only) signature at index 0..
int v = [[jws 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(@"%@",jws.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.");
NSLog(@"%@",@"--");

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

// Examine the protected header:
CkoJsonObject *joseHeader = [jws GetProtectedHeader: [NSNumber numberWithInt: signatureIndex]];
if (jws.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.
// 	--
// 	Recovered content:
// 	{"iss":"joe", 
// 	 "exp":1300819380,
// 	 "http://example.com/is_root":true}
// 	--
// 	Protected (JOSE) header:
// 	{ 
// 	  "alg": "RS256"
// 	}