(Objective-C) Validate a JWS Using ECDSA P-521 SHA-512

Validates a JSON Web Signature (JWS) that uses ECDSA P-521 SHA-512

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 ECDSA public key to validate and recover the protected header and payload.

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

//      {"kty":"EC", 
//       "crv":"P-521", 
//       "x":"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk", 
//       "y":"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDly79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2" 
//      } 

CkoStringBuilder *sbPubKey = [[CkoStringBuilder alloc] init];
[sbPubKey Append: @"{\"kty\":\"EC\","];
[sbPubKey Append: @"\"crv\":\"P-521\","];
[sbPubKey Append: @"\"x\":\"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk\","];
[sbPubKey Append: @"\"y\":\"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDly79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2\""];
[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 ECC public key:
int signatureIndex = 0;
[jws SetPublicKey: [NSNumber numberWithInt: signatureIndex] pubKey: pubKey];

// Load the JWS.
CkoStringBuilder *sbJws = [[CkoStringBuilder alloc] init];
[sbJws Append: @"eyJhbGciOiJFUzUxMiJ9"];
[sbJws Append: @"."];
[sbJws Append: @"UGF5bG9hZA"];
[sbJws Append: @"."];
[sbJws Append: @"AdwMgeerwtHoh-l192l60hp9wAHZFVJbLfD_UxMi70cwnZOYaRI1bKPWROc-mZZq"];
[sbJws Append: @"wqT2SI-KGDKB34XO0aw_7XdtAG8GaSwFKdCAPZgoXD2YBJZCPEX3xKpRwcdOO8Kp"];
[sbJws Append: @"EHwJjyqOgzDO7iKvU8vcnwNrmxYbSW9ERBXukOXolLzeO_Jn"];

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 ECC 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:
// (the string "Payload" was the content that was signed.)

// 	Signature validated.
// 	--
// 	Recovered content:
// 	Payload
// 	--
// 	Protected (JOSE) header:
// 	{
// 	  "alg": "ES512"
// 	}