(Objective-C) Create a JWS Using ECDSA P-256 SHA-256

Creates and validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

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

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#import <CkoStringBuilder.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.

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

// Use the following ECC key loaded from JWK format.
CkoStringBuilder *sbJwk = [[CkoStringBuilder alloc] init];
[sbJwk Append: @"{\"kty\":\"EC\","];
[sbJwk Append: @"\"crv\":\"P-256\","];
[sbJwk Append: @"\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\","];
[sbJwk Append: @"\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\","];
[sbJwk Append: @"\"d\":\"jpsQnnGQmL-YBIffH1136cspYG6-0iY7X1fCE9-E9LI\""];
[sbJwk Append: @"}"];

CkoPrivateKey *eccKey = [[CkoPrivateKey alloc] init];
// Note: This example loads the ECDSA key from JWK format.  Any format can be loaded
// into the private key object. (See the online reference documentation..)
BOOL success = [eccKey LoadJwk: [sbJwk GetAsString]];
if (success != YES) {
    NSLog(@"%@",eccKey.LastErrorText);
    return;
}

// Create the JWS Protected Header
CkoJsonObject *jwsProtHdr = [[CkoJsonObject alloc] init];
[jwsProtHdr AppendString: @"alg" value: @"ES256"];

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

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

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

// 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);

// Note: ECC signatures use random values, so the output will be different each time a signature is produced.
// sample output:
// JWS: eyJhbGciOiJFUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.J6EGTNkeuEjehHHBu0SOKzifm8r35wbx49A5964pxzB7gannyZZPMkK7vmlaPJ-K8Xmm8cZsQySAPC12Xd8avw

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

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

CkoPublicKey *eccPubKey = [eccKey GetPublicKey];

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

// 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 ECC 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": "ES256"
// }