(Objective-C) JWE using PBES2 Key Wrapping

Demonstrates how to create and decrypt a JWE that using PBES2 key wrapping.

This example demonstrates PBES2 with HMAC SHA-256 and A128KW wrapping. It is also possible to do the following by simply changing the "alg" parameter:

• PBES2 with HMAC SHA-384 and A192KW wrapping
• PBES2 with HMAC SHA-512 and A256KW wrapping

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

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#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.

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

BOOL success;
NSString *plaintext = @"Live long and prosper.";

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

// First build the JWE Protected Header..
CkoJsonObject *jweProtHdr = [[CkoJsonObject alloc] init];
[jweProtHdr AppendString: @"alg" value: @"PBES2-HS256+A128KW"];
[jweProtHdr AppendString: @"enc" value: @"A128GCM"];

// PBES2 requires two additional parameters:
// 1) A random salt parameter ("p2s") containing 8 or more bytes in base64url format.
// 2) An iteration count parameter ("p2c").  A minimum count of 1000 is recommended.
//    The iteration count is intended to make the PBES2 computation more expensive (time consuming)
//    to prevent brute-force attacks.
CkoPrng *prng = [[CkoPrng alloc] init];
[jweProtHdr AppendString: @"p2s" value: [prng GenRandom: [NSNumber numberWithInt: 16] encoding: @"base64url"]];
[jweProtHdr AppendString: @"p2c" value: @"1000"];

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

// Don't forget to actually provide the protected header to the JWE object:
[jwe SetProtectedHeader: jweProtHdr];

// Set the PBES2 password
int recipientIndex = 0;
[jwe SetPassword: [NSNumber numberWithInt: recipientIndex] password: @"top secret"];

// 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.
CkoJwe *jwe2 = [[CkoJwe alloc] init];
success = [jwe2 LoadJwe: strJwe];
if (success != YES) {
    NSLog(@"%@",jwe2.LastErrorText);
    return;
}

// Set the PBES2 password
[jwe2 SetPassword: [NSNumber numberWithInt: recipientIndex] password: @"top secret"];

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

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

// Sample output:

// JWE Protected Header: {"alg":"PBES2-HS256+A128KW","enc":"A128GCM","p2s":"z39rTEfRy1T1Yn_D1mZRlg","p2c":"1000"}
// --
// eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJlbmMiOiJBMTI4R0NNIiwicDJzIjoiejM5clRFZlJ5MVQxWW5fRDFtWlJsZyIsInAyYyI6IjEwMDAifQ.koYt6PrFmYwcwdcT7ZcvXHA1d-Xez5h4.luGlbvEnZp-7IsBOj42Yhw.YMTcfLf8Qe4zazozGV2OAu3cUdQ8Kg.rWub47ESWkc6IqZJTvSTmg
// original text: 
// Live long and prosper.