(Objective-C) JWE Using General JWE JSON Serialization

This example duplicates the example A.4 in RFC 7516 for JSON Web Encryption (JWE).

This example demonstrates the capability for encrypting the same plaintext to multiple recipients. Two recipients are present in this example.

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>
#import <CkoPrivateKey.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.

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];

// The first recipient uses the RSAES-PKCS1-v1_5 algorithm to encrypt
// the CEK.  The second uses AES Key Wrap to encrypt the CEK.  Key ID
// values are supplied for both keys.  The two JWE Per-Recipient
// Unprotected Header values used to represent these algorithms and key
// IDs are:
// 
//      {"alg":"RSA1_5","kid":"2011-04-29"}
// 
// and
// 
//      {"alg":"A128KW","kid":"7"}

CkoJsonObject *jweRecipientHdr1 = [[CkoJsonObject alloc] init];
[jweRecipientHdr1 AppendString: @"alg" value: @"RSA1_5"];
[jweRecipientHdr1 AppendString: @"kid" value: @"2011-04-29"];
int recipientIndex = 0;
[jwe SetRecipientHeader: [NSNumber numberWithInt: recipientIndex] json: jweRecipientHdr1];

CkoJsonObject *jweRecipientHdr2 = [[CkoJsonObject alloc] init];
[jweRecipientHdr2 AppendString: @"alg" value: @"A128KW"];
[jweRecipientHdr2 AppendString: @"kid" value: @"7"];
recipientIndex = 1;
[jwe SetRecipientHeader: [NSNumber numberWithInt: recipientIndex] json: jweRecipientHdr2];

// 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];

// Note: The intent of specifying a "kid" (an acronym for "Key ID") is that
// the software would somehow download the keys.jwks from https://server.example.com/keys.jwks,
// and would select the key (whatever format it may be, such as RSA, or an AES key wrap key, etc.),
// and then automatically use it. 

// This example keeps the "kid" and "jku" in their respective headers, but does not actually fetch
// the keys from some URL.  We'll just provide the keys directly..

// Recipient 0 uses this RSA key:
CkoStringBuilder *sbJwk = [[CkoStringBuilder alloc] init];
[sbJwk Append: @"{\"kty\":\"RSA\","];
[sbJwk Append: @"\"n\":\"sXchDaQebHnPiGvyDOAT4saGEUetSyo9MKLOoWFsueri23bOdgWp4Dy1Wl"];
[sbJwk Append: @"UzewbgBHod5pcM9H95GQRV3JDXboIRROSBigeC5yjU1hGzHHyXss8UDpre"];
[sbJwk Append: @"cbAYxknTcQkhslANGRUZmdTOQ5qTRsLAt6BTYuyvVRdhS8exSZEy_c4gs_"];
[sbJwk Append: @"7svlJJQ4H9_NxsiIoLwAEk7-Q3UXERGYw_75IDrGA84-lA_-Ct4eTlXHBI"];
[sbJwk Append: @"Y2EaV7t7LjJaynVJCpkv4LKjTTAumiGUIuQhrNhZLuF_RJLqHpM2kgWFLU"];
[sbJwk Append: @"7-VTdL1VbC2tejvcI2BlMkEpk1BzBZI0KQB0GaDWFLN-aEAw3vRw\","];
[sbJwk Append: @"\"e\":\"AQAB\","];
[sbJwk Append: @"\"d\":\"VFCWOqXr8nvZNyaaJLXdnNPXZKRaWCjkU5Q2egQQpTBMwhprMzWzpR8Sxq"];
[sbJwk Append: @"1OPThh_J6MUD8Z35wky9b8eEO0pwNS8xlh1lOFRRBoNqDIKVOku0aZb-ry"];
[sbJwk Append: @"nq8cxjDTLZQ6Fz7jSjR1Klop-YKaUHc9GsEofQqYruPhzSA-QgajZGPbE_"];
[sbJwk Append: @"0ZaVDJHfyd7UUBUKunFMScbflYAAOYJqVIVwaYR5zWEEceUjNnTNo_CVSj"];
[sbJwk Append: @"-VvXLO5VZfCUAVLgW4dpf1SrtZjSt34YLsRarSb127reG_DUwg9Ch-Kyvj"];
[sbJwk Append: @"T1SkHgUWRVGcyly7uvVGRSDwsXypdrNinPA4jlhoNdizK2zF2CWQ\","];
[sbJwk Append: @"\"p\":\"9gY2w6I6S6L0juEKsbeDAwpd9WMfgqFoeA9vEyEUuk4kLwBKcoe1x4HG68"];
[sbJwk Append: @"ik918hdDSE9vDQSccA3xXHOAFOPJ8R9EeIAbTi1VwBYnbTp87X-xcPWlEP"];
[sbJwk Append: @"krdoUKW60tgs1aNd_Nnc9LEVVPMS390zbFxt8TN_biaBgelNgbC95sM\","];
[sbJwk Append: @"\"q\":\"uKlCKvKv_ZJMVcdIs5vVSU_6cPtYI1ljWytExV_skstvRSNi9r66jdd9-y"];
[sbJwk Append: @"BhVfuG4shsp2j7rGnIio901RBeHo6TPKWVVykPu1iYhQXw1jIABfw-MVsN"];
[sbJwk Append: @"-3bQ76WLdt2SDxsHs7q7zPyUyHXmps7ycZ5c72wGkUwNOjYelmkiNS0\","];
[sbJwk Append: @"\"dp\":\"w0kZbV63cVRvVX6yk3C8cMxo2qCM4Y8nsq1lmMSYhG4EcL6FWbX5h9yuv"];
[sbJwk Append: @"ngs4iLEFk6eALoUS4vIWEwcL4txw9LsWH_zKI-hwoReoP77cOdSL4AVcra"];
[sbJwk Append: @"Hawlkpyd2TWjE5evgbhWtOxnZee3cXJBkAi64Ik6jZxbvk-RR3pEhnCs\","];
[sbJwk Append: @"\"dq\":\"o_8V14SezckO6CNLKs_btPdFiO9_kC1DsuUTd2LAfIIVeMZ7jn1Gus_Ff"];
[sbJwk Append: @"7B7IVx3p5KuBGOVF8L-qifLb6nQnLysgHDh132NDioZkhH7mI7hPG-PYE_"];
[sbJwk Append: @"odApKdnqECHWw0J-F0JWnUd6D2B_1TvF9mXA2Qx-iGYn8OVV1Bsmp6qU\","];
[sbJwk Append: @"\"qi\":\"eNho5yRBEBxhGBtQRww9QirZsB66TrfFReG_CcteI1aCneT0ELGhYlRlC"];
[sbJwk Append: @"tUkTRclIfuEPmNsNDPbLoLqqCVznFbvdB7x-Tl-m0l_eFTj2KiqwGqE9PZ"];
[sbJwk Append: @"B9nNTwMVvH3VRRSLWACvPnSiwP8N5Usy-WRXS-V7TbpxIhvepTfE0NNo\""];
[sbJwk Append: @"}"];

// Load this JWK into a Chilkat private key object.
CkoPrivateKey *rsaPrivKey = [[CkoPrivateKey alloc] init];
success = [rsaPrivKey LoadJwk: [sbJwk GetAsString]];
if (success != YES) {
    NSLog(@"%@",rsaPrivKey.LastErrorText);
    return;
}

// Get the public key for encryption.  (The RSA private key is used for decryption.)
CkoPublicKey *rsaPubKey = [rsaPrivKey GetPublicKey];
recipientIndex = 0;
[jwe SetPublicKey: [NSNumber numberWithInt: recipientIndex] pubKey: rsaPubKey];

// Recipient 1 uses AES Key Wrap
NSString *aesWrappingKey = @"GawgguFyGrWKav7AX4VKUg";
recipientIndex = 1;
[jwe SetWrappingKey: [NSNumber numberWithInt: recipientIndex] encodedKey: aesWrappingKey encoding: @"base64url"];

// OK.. everything has been specified.
// Now encrypt.  Chilkat will use the general JSON serialization because it is only
// possible serializationto use given there are multiple recipients. 
NSString *strJwe = [jwe Encrypt: plaintext charset: @"utf-8"];
if (jwe.LastMethodSuccess != YES) {
    NSLog(@"%@",jwe.LastErrorText);
    return;
}

// The strJwe is 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"
// 	  },
// 	  "recipients": [
// 	    { 
// 	      "header": { 
// 	        "alg": "RSA1_5",
// 	        "kid": "2011-04-29"
// 	      },
// 	      "encrypted_key": "WlUggejR-vStJVNKgjG2mQrVv74aga1FFutT8E-n-yJEOTsOVnGjhj1NW_Snd9DqHAhFrc7NEvKCFplKWGnusBZxxjm1JpdUa0MIpkGmncJHQQdfm21vcbEUbDmfqVY79SnEis3tih1D3qmyp_Bxti4byDAHJIOJv_cj0Sx8oHZzgGtOLjtHsydyo1MtBIqI0w86i_uhUuraihZ3ngj67YZ6uqpR6lulkPIVohfF3oJ0D3Ay_XOCHWlHYkTg6VZsa0FDrPtfB2pG3TxTBPwI4IMj5uF_D3zrg51dCYKU1Gah71ujLaXRE5q9XF7oOknxiWQuWc7Ox8JP03lSx-DiVA"
// 	    },
// 	    { 
// 	      "header": { 
// 	        "alg": "A128KW",
// 	        "kid": "7"
// 	      },
// 	      "encrypted_key": "8diBP2aUUB_Jl5WxCuMJLN6HsppE3rhSjcecee0fBcwB31zbPAVejQ"
// 	    } 
// 	  ],
// 	  "iv": "JqahFKx5Z8SFT_LnkfOq0Q",
// 	  "ciphertext": "YcSdjlszsaY1ADcs4Vw85H_WoAqnkDIJaJsTkmCj05s",
// 	  "tag": "G3KF2CZ-DMhm0cqUbhJKMA"
// 	} 

// To decrypt, we don't need both recipient keys.  We can decrypt with one key or the other.
// The FindRecipient method can be used to find a particular recipient index.

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

// Let's say we have the AES key wrap key, and we know the "kid" equals "7".
BOOL caseSensitive = NO;
recipientIndex = [[jwe2 FindRecipient: @"kid" paramValue: @"7" caseSensitive: caseSensitive] intValue];
if (recipientIndex < 0) {
    NSLog(@"%@",@"Unable to find recipient with kid=7");
    return;
}

// Set the AES wrap key for the recipient index.
[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);

// Now, let's do the same with the RSA private key:
recipientIndex = [[jwe2 FindRecipient: @"kid" paramValue: @"2011-04-29" caseSensitive: caseSensitive] intValue];
if (recipientIndex < 0) {
    NSLog(@"%@",@"Unable to find recipient with kid=2011-04-29");
    return;
}

// Set the RSA private key for the recipient index.
[jwe2 SetPrivateKey: [NSNumber numberWithInt: recipientIndex] privKey: rsaPrivKey];

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

NSLog(@"%@",@"original text decrypted with RSA private key: ");
NSLog(@"%@",originalPlaintext);

// ---------------------------------------------------------------------------------
// It should also be possible to decrypt the JWE as shown in RFC 7516, Appendix A.4.7
// because it was produced using the same keys.

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: @"\"recipients\":["];
[sbJwe Append: @"{\"header\":"];
[sbJwe Append: @"{\"alg\":\"RSA1_5\",\"kid\":\"2011-04-29\"},"];
[sbJwe Append: @"\"encrypted_key\":"];
[sbJwe Append: @"\"UGhIOguC7IuEvf_NPVaXsGMoLOmwvc1GyqlIKOK1nN94nHPoltGRhWhw7Zx0-"];
[sbJwe Append: @"kFm1NJn8LE9XShH59_i8J0PH5ZZyNfGy2xGdULU7sHNF6Gp2vPLgNZ__deLKx"];
[sbJwe Append: @"GHZ7PcHALUzoOegEI-8E66jX2E4zyJKx-YxzZIItRzC5hlRirb6Y5Cl_p-ko3"];
[sbJwe Append: @"YvkkysZIFNPccxRU7qve1WYPxqbb2Yw8kZqa2rMWI5ng8OtvzlV7elprCbuPh"];
[sbJwe Append: @"cCdZ6XDP0_F8rkXds2vE4X-ncOIM8hAYHHi29NX0mcKiRaD0-D-ljQTP-cFPg"];
[sbJwe Append: @"wCp6X-nZZd9OHBv-B3oWh2TbqmScqXMR4gp_A\"},"];
[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;
}

// We can decrypt with either key.  Let's use the AES key wrap key...
recipientIndex = [[jwe2 FindRecipient: @"kid" paramValue: @"7" caseSensitive: caseSensitive] intValue];
if (recipientIndex < 0) {
    NSLog(@"%@",@"Unable to find recipient with kid=7");
    return;
}

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

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

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

// The output:

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