(Objective-C) JWE Using Flattened JWE JSON Serialization

This example duplicates the example A.5 in RFC 7516 for JSON Web Encryption (JWE).

This example demonstrates using the flattened JWE JSON Serialization syntax. This example demonstrates the capability for encrypting the plaintext to a single recipient in a flattened JSON structure.

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 <CkoStringBuilder.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: {"enc":"A128CBC-HS256"}
CkoJsonObject *jweProtHdr = [[CkoJsonObject alloc] init];
[jweProtHdr AppendString: @"enc" value: @"A128CBC-HS256"];
[jwe SetProtectedHeader: jweProtHdr];

// We have a single recipient that uses AES Key Wrap to encrypt the CEK.
// 
//      {"alg":"A128KW","kid":"7"}

CkoJsonObject *jweRecipientHdr = [[CkoJsonObject alloc] init];
[jweRecipientHdr AppendString: @"alg" value: @"A128KW"];
[jweRecipientHdr AppendString: @"kid" value: @"7"];
int recipientIndex = 0;
[jwe SetRecipientHeader: [NSNumber numberWithInt: recipientIndex] json: jweRecipientHdr];

// Set the Shared Unprotected Header:  {"jku":"https://server.example.com/keys.jwks"}
CkoJsonObject *jweUnprotHdr = [[CkoJsonObject alloc] init];
[jweUnprotHdr AppendString: @"jku" value: @"https://server.example.com/keys.jwks"];
[jwe SetUnprotectedHeader: jweUnprotHdr];

// Set the AES key wrapping key.
NSString *aesWrappingKey = @"GawgguFyGrWKav7AX4VKUg";
recipientIndex = 0;
[jwe SetWrappingKey: [NSNumber numberWithInt: recipientIndex] encodedKey: aesWrappingKey encoding: @"base64url"];

// OK.. everything has been specified.
// Now encrypt.  
// Indicate that we prefer the flattened JSON serialization.
jwe.PreferFlattened = YES;
NSString *strJwe = [jwe Encrypt: plaintext charset: @"utf-8"];
if (jwe.LastMethodSuccess != YES) {
    NSLog(@"%@",jwe.LastErrorText);
    return;
}

// The JWE is produced in the most compact form possible (a single line).
// Let's load it into a JSON object and examine in a non-compact pretty-printed format:
CkoJsonObject *jsonTemp = [[CkoJsonObject alloc] init];
[jsonTemp Load: strJwe];
jsonTemp.EmitCompact = NO;
NSLog(@"%@",[jsonTemp Emit]);

// The JWE looks like this:
// (Note: Because of random values used in the encryption process, your encrypted results will be different.)

// 	{ 
// 	  "protected": "eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0",
// 	  "unprotected": { 
// 	    "jku": "https://server.example.com/keys.jwks"
// 	  },
// 	  "header": { 
// 	    "alg": "A128KW",
// 	    "kid": "7"
// 	  },
// 	  "encrypted_key": "FW7z9VxOvnF2ClicvUT4HTeqcdyh90C6qytfEFJsOb77FOwTfYrc3w",
// 	  "iv": "O6Ly5-eML3zTs-_fNX3D5Q",
// 	  "ciphertext": "Q8NLmeac9JhLh0CQPuG_7D9wVDb55eToCh0g5-FQ4M0",
// 	  "tag": "slzlo6-J9C7wSDF4dh_kBg"
// 	} 

// Now decrypt......................................

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

// Set the AES wrap key..
recipientIndex = 0;
[jwe2 SetWrappingKey: [NSNumber numberWithInt: recipientIndex] encodedKey: aesWrappingKey encoding: @"base64url"];

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

NSLog(@"%@",@"original text decrypted with AES key wrap key: ");
NSLog(@"%@",originalPlaintext);

// ---------------------------------------------------------------------------------
// It should also be possible to decrypt the flattened JWE as shown in RFC 7516, Appendix A.5
// because it was produced using the same key.

CkoStringBuilder *sbJwe = [[CkoStringBuilder alloc] init];

[sbJwe Append: @"{"];
[sbJwe Append: @"\"protected\":"];
[sbJwe Append: @"\"eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0\","];
[sbJwe Append: @"\"unprotected\":"];
[sbJwe Append: @"{\"jku\":\"https://server.example.com/keys.jwks\"},"];
[sbJwe Append: @"\"header\":"];
[sbJwe Append: @"{\"alg\":\"A128KW\",\"kid\":\"7\"},"];
[sbJwe Append: @"\"encrypted_key\":"];
[sbJwe Append: @"\"6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ\","];
[sbJwe Append: @"\"iv\":"];
[sbJwe Append: @"\"AxY8DCtDaGlsbGljb3RoZQ\","];
[sbJwe Append: @"\"ciphertext\":"];
[sbJwe Append: @"\"KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY\","];
[sbJwe Append: @"\"tag\":"];
[sbJwe Append: @"\"Mz-VPPyU4RlcuYv1IwIvzw\""];
[sbJwe Append: @"}"];

success = [jwe2 LoadJweSb: sbJwe];
if (success != YES) {
    NSLog(@"%@",jwe2.LastErrorText);
    return;
}

recipientIndex = 0;
[jwe2 SetWrappingKey: [NSNumber numberWithInt: recipientIndex] encodedKey: aesWrappingKey encoding: @"base64url"];

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

NSLog(@"%@",@"original text decrypted from published flattened JWE: ");
NSLog(@"%@",originalPlaintext);

// The output:

// original text decrypted with AES key wrap key: 
// Live long and prosper.
// original text decrypted from published flattened JWE: 
// Live long and prosper.