(Objective-C) JWE using A256GCMKW

This example demonstrates creating a JCE with AES GCM key wrap.

Chilkat Objective-C Library Downloads MAC OS X (Cocoa) Libs iOS Libs

#import <NSString.h>
#import <CkoJwe.h>
#import <CkoJsonObject.h>
#import <CkoPrng.h>

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

BOOL success;
NSString *plaintext = @"My text to enrypt";

CkoJwe *jwe = [[CkoJwe alloc] init];

// First build the JWE Protected Header: 

//         {
//             "alg": "A256GCMKW",
//             "kid": "18ec08e1-bfa9-4d95-b205-2b4dd1d4321d",
//             "tag": "kfPduVQ3T3H6vnewt--ksw",
//             "iv": "KkYT0GX_2jHlfqN_",
//             "enc": "A128CBC-HS256"
//         }

CkoJsonObject *jweProtHdr = [[CkoJsonObject alloc] init];
[jweProtHdr AppendString: @"alg" value: @"A256GCMKW"];
// kid is optional
[jweProtHdr AppendString: @"kid" value: @"18ec08e1-bfa9-4d95-b205-2b4dd1d4321d"];
// tag is optional
[jweProtHdr AppendString: @"tag" value: @"kfPduVQ3T3H6vnewt--ksw"];
[jweProtHdr AppendString: @"enc" value: @"A256GCM"];
// the iv should be 16 random chars.
CkoPrng *prng = [[CkoPrng alloc] init];
[jweProtHdr AppendString: @"iv" value: [prng RandomString: [NSNumber numberWithInt: 16] bDigits: YES bLower: YES bUpper: YES]];
[jwe SetProtectedHeader: jweProtHdr];

NSLog(@"%@%@",@"JWE Protected Header: ",[jweProtHdr Emit]);
NSLog(@"%@",@"--");

// Given that we have 256-bit AES, our key should be 32 bytes.
// The ascii string here is 32 bytes, therefore the 2nd arg is "ascii" to use these
// ascii chars directly as the key.
NSString *aesWrappingKey = @"2baf4f730f5e4542b428593ef9cceb0e";
[jwe SetWrappingKey: [NSNumber numberWithInt: 0] encodedKey: aesWrappingKey encoding: @"ascii"];

// Encrypt and return the JWE:
NSString *strJwe = [jwe Encrypt: plaintext charset: @"utf-8"];
if (jwe.LastMethodSuccess != YES) {
    NSLog(@"%@",jwe.LastErrorText);
    return;
}

// Show the JWE we just created:
NSLog(@"%@",strJwe);

// Decrypt the JWE that was just produced.
// 1) Load the JWE.
// 2) Set the AES wrapping key.
// 3) Decrypt.
CkoJwe *jwe2 = [[CkoJwe alloc] init];
success = [jwe2 LoadJwe: strJwe];
if (success != YES) {
    NSLog(@"%@",jwe2.LastErrorText);
    return;
}

// Set the AES wrap key.  Important to use "ascii"
[jwe2 SetWrappingKey: [NSNumber numberWithInt: 0] encodedKey: aesWrappingKey encoding: @"ascii"];

// Decrypt.
NSString *originalPlaintext = [jwe2 Decrypt: [NSNumber numberWithInt: 0] charset: @"utf-8"];
if (jwe2.LastMethodSuccess != YES) {
    NSLog(@"%@",jwe2.LastErrorText);
    return;
}

NSLog(@"%@",@"original text: ");
NSLog(@"%@",originalPlaintext);