(Objective-C) Decrypt a SAML Response

Demonstrates how to decrypt a SAML response.

Note: This example requires Chilkat v9.5.0.76 or greater.

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#import <CkoHttp.h>
#import <CkoStringBuilder.h>
#import <CkoXml.h>
#import <CkoPrivateKey.h>
#import <CkoRsa.h>
#import <NSString.h>
#import <CkoBinData.h>
#import <CkoCrypt2.h>

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

// This example decrypts this SAML response:

// <?xml version="1.0" encoding="UTF-8" ?>
// <saml2p:Response Destination="https://deskflow-asp2.com/ubc/ubcdfe.dll/cwlacs" ID="_e4585eaeedbcaf7c24dff7f1ee2499f5" IssueInstant="2018-10-11T17:46:20.727Z" Version="2.0" xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol">
//     <saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">https://authentication.stg.id.ubc.ca</saml2:Issuer>
//     <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
//         <ds:SignedInfo>
//             <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
//             <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
//             <ds:Reference URI="#_e4585eaeedbcaf7c24dff7f1ee2499f5">
//                 <ds:Transforms>
//                     <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
//                     <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
//                 </ds:Transforms>
//                 <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
//                 <ds:DigestValue>1ui22tqFyYEOoWI19CMwz4n+ynxNjLDGdTeRMdi60EU=</ds:DigestValue>
//             </ds:Reference>
//         </ds:SignedInfo>
//         <ds:SignatureValue>ROg7FXV6vsp8socVhdo76/i7cRHGGKIveAiScKdujZT0QrHVqIvvbZ/RnwvEMJ9H9i/kJFAQA171
// 		Eo2kDjSdvNFQ/YcKaJUwMtAwT05yVatGV42RZKEf7ME+vpcCTR1LWZdrhat1FWCg1MNQwNWB0EL5
// 		fEP2a4jAcSTB8tFbjTAHsv7IWC39E5RVv99mACYXLa7iGZLtORANZxgYu5qQgmH6pUkI6Z1cpmf+
// 		m9mIjKM6LF0EvLfWOBWL6udZ+GsHPOLjVTJg+1S0xb9FQCYDVW1QhbjSS0icKHKTNNbrsaxllVDY
// 		m4q27YQjRh+XxugPgvsZ61Pxlto8Jbg+6jUlMQ==</ds:SignatureValue>
//         <ds:KeyInfo>
//             <ds:X509Data>
//                 <ds:X509Certificate>MIIDTTCCAjWgAwIBAgIVAJccYyIV6wly8XyddumpgnHMJ2JLMA0GCSqGSIb3DQEBCwUAMCcxJTAj
// 			BgNVBAMMHGF1dGhlbnRpY2F0aW9uLnN0Zy5pZC51YmMuY2EwHhcNMTcwMzAxMTk1NDM0WhcNMzcw
// 			...
// 			xUuh6HuHKIwQqHBz7udxbH3Zbb6jXGDJjiDHt1LRJ8xbVisFIcDlIwsGQQi0HeEJfx4P</ds:X509Certificate>
//             </ds:X509Data>
//         </ds:KeyInfo>
//     </ds:Signature>
//     <saml2p:Status>
//         <saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
//     </saml2p:Status>
//     <saml2:EncryptedAssertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
//         <xenc:EncryptedData Id="_314d80b9cf02d8eda8d686a6ffd626cf" Type="http://www.w3.org/2001/04/xmlenc#Element" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//             <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"/>
//             <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
//                 <xenc:EncryptedKey Id="_d7b6da6fb59a627ebb4a96928441ab79" Recipient="https://ubcdfe.deskflow-asp2.com" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                     <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                         <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" xmlns:ds="http://www.w3.org/2000/09/xmldsig#"/>
//                     </xenc:EncryptionMethod>
//                     <ds:KeyInfo>
//                         <ds:X509Data>
//                             <ds:X509Certificate>MIICuzCCAiQCCQD3bpigRnKMSzANBgkqhkiG9w0BAQsFADCBoTELMAkGA1UEBhMCQ0ExEDAOBgNV
// 				BAgMB09udGFyaW8xEDAOBgNVBAcMB1Rvcm9udG8xJjAkBgNVBAoMHVRhY3RpY2FsIEJ1c2luZXNz
// 				...
// 				kVRcHd1UK3q7G8FoykWjdQz/0EoMTfEZ+Md56mLOe48eMUZV2ONZuL1kDCEKw1UwkaDQI4Pf8pzx
// 				82b9rgw9wBDtvu5eFPlUGEGIBw==</ds:X509Certificate>
//                         </ds:X509Data>
//                     </ds:KeyInfo>
//                     <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                         <xenc:CipherValue>BNHfUOpgdPE5BgpN2VIZIDthMAv1rxk91qVnWyCZOG9bmUKChJtTUqMpndot7VJwYuyKFshkAdnT
// 				D79KGdlSA1xHKcVeZXXzDWglqSyYjzhDCsyOhPaI4HelMFgCLwyFz89uEpUpqlvfl8ol3Am/XnzQ
// 				Vp7V7oS76hocjUI51Qs=</xenc:CipherValue>
//                     </xenc:CipherData>
//                 </xenc:EncryptedKey>
//             </ds:KeyInfo>
//             <xenc:CipherData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
//                 <xenc:CipherValue>R6l7tmbnXrOfBgB8lA3KnwLYsLH5ZO5omQ7Hp5K05atzw2o55xmCXVMYhNneFxMtxUh6raEyHeZX
// 			PTZNgWrvdqc4GYND/R7MhRrJzk9OAq1WyoOXwbtRpwNDwWA4N2IuprPQJbvjVxaw/PesZMZwZqlp
// 			...
// 			zm9zAxahyu8Ooe8M4r3HN2cY0JxxxkZtDiulbnyA+rRtXfBRJtangvFQ4iFAnzM/Yg9hMyW9jcu0
// 			S7FzuRB9ONMxi+nh0IFWgqp+</xenc:CipherValue>
//             </xenc:CipherData>
//         </xenc:EncryptedData>
//     </saml2:EncryptedAssertion>
// </saml2p:Response>

// The sample encrypted SAML response and RSA private key are available online:
CkoHttp *http = [[CkoHttp alloc] init];
CkoStringBuilder *sbSamlResponse = [[CkoStringBuilder alloc] init];
CkoStringBuilder *sbPrivateKeyPem = [[CkoStringBuilder alloc] init];
BOOL success = [http QuickGetSb: @"https://chilkatdownload.com/data/samlresponse.xml" sbContent: sbSamlResponse];
if (success == YES) {
    success = [http QuickGetSb: @"https://chilkatdownload.com/data/samlresponse_privkey.pem" sbContent: sbPrivateKeyPem];
}

if (success != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

CkoXml *xml = [[CkoXml alloc] init];
[xml LoadSb: sbSamlResponse autoTrim: YES];

// Load the RSA private key..
CkoPrivateKey *privkey = [[CkoPrivateKey alloc] init];
success = [privkey LoadPem: [sbPrivateKeyPem GetAsString]];
if (success != YES) {
    NSLog(@"%@",privkey.LastErrorText);
    return;
}

// Prepare an RSA object w/ the private key...
CkoRsa *rsa = [[CkoRsa alloc] init];
success = [rsa ImportPrivateKeyObj: privkey];
if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// RSA will be used to decrypt the xenc:EncryptedKey
// The bytes to be decrypted are in xenc:CipherValue (in base64 format)
NSString *encryptedAesKey = [xml GetChildContent: @"saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:CipherData|xenc:CipherValue"];
if (xml.LastMethodSuccess != YES) {
    NSLog(@"%@",@"Encrypted AES key not found.");
    return;
}

NSLog(@"%@%@",@"Encrypted AES key (base64) = ",encryptedAesKey);

CkoBinData *bdAesKey = [[CkoBinData alloc] init];
[bdAesKey AppendEncoded: encryptedAesKey encoding: @"base64"];

CkoStringBuilder *sbRsaAlg = [[CkoStringBuilder alloc] init];
[sbRsaAlg Append: [xml ChilkatPath: @"saml2:EncryptedAssertion|xenc:EncryptedData|ds:KeyInfo|xenc:EncryptedKey|xenc:EncryptionMethod|(Algorithm)"]];
NSLog(@"%@%@",@"sbRsaAlg contains: ",[sbRsaAlg GetAsString]);
if ([sbRsaAlg Contains: @"rsa-oaep" caseSensitive: YES] == YES) {
    rsa.OaepPadding = YES;
}

// Note: The DecryptBd method is introduced in Chilkat v9.5.0.76
success = [rsa DecryptBd: bdAesKey usePrivateKey: YES];
if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

NSLog(@"%@%@",@"Decrypted AES key (hex) = ",[bdAesKey GetEncoded: @"hex"]);

// Get the encrypted XML (in base64) to be decrypted w/ the AES key.
NSString *encrypted64 = [xml GetChildContent: @"saml2:EncryptedAssertion|xenc:EncryptedData|xenc:CipherData|xenc:CipherValue"];
if (xml.LastMethodSuccess != YES) {
    NSLog(@"%@",@"Encrypted data not found.");
    return;
}

CkoBinData *bdEncrypted = [[CkoBinData alloc] init];
[bdEncrypted AppendEncoded: encrypted64 encoding: @"base64"];

// Get the symmetric algorithm:  "http://www.w3.org/2001/04/xmlenc#aes128-cbc"
// and set the symmetric decrypt properties.
CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];
CkoStringBuilder *sbAlg = [[CkoStringBuilder alloc] init];
[sbAlg Append: [xml ChilkatPath: @"saml2:EncryptedAssertion|xenc:EncryptedData|xenc:EncryptionMethod|(Algorithm)"]];
if ([sbAlg Contains: @"aes128-cbc" caseSensitive: YES] == YES) {
    crypt.CryptAlgorithm = @"aes";
    crypt.KeyLength = [NSNumber numberWithInt:128];
    crypt.CipherMode = @"cbc";
    // The 1st 16 bytes of the encrypted data are the AES IV.
    [crypt SetEncodedIV: [bdEncrypted GetEncodedChunk: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 16] encoding: @"hex"] encoding: @"hex"];
    [bdEncrypted RemoveChunk: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 16]];
}

// Other algorithms, key lengths, etc, can be supported by checking for different Algorithm attribute values..

[crypt SetEncodedKey: [bdAesKey GetEncoded: @"hex"] encoding: @"hex"];

// AES decrypt...
success = [crypt DecryptBd: bdEncrypted];
if (success != YES) {
    NSLog(@"%@",crypt.LastErrorText);
    return;
}

// Get the decrypted XML
NSString *decryptedXml = [bdEncrypted GetString: @"utf-8"];
NSLog(@"%@",@"Decrypted XML:");
NSLog(@"%@",decryptedXml);

// The decrypted XML looks like this:

// <saml2:Assertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" ID="_226e565c548db7986d165d7d969b48b4" IssueInstant="2018-10-11T17:46:20.727Z" Version="2.0">
// ...
// ...
// ...
// </saml2:Assertion>

CkoXml *xmlAssertion = [[CkoXml alloc] init];
[xmlAssertion LoadXml: decryptedXml];

// Replace the saml2:EncryptedAssertion XML subtree with the saml2:Assertion XML.
CkoXml *xmlEncryptedAssertion = [xml FindChild: @"saml2:EncryptedAssertion"];
[xmlEncryptedAssertion SwapTree: xmlAssertion];

// The decrypted XML assertion has now replaced the encrypted XML assertion.
// Examine the fully decrypted XML document:
NSLog(@"%@",@"Full XML SAML document with decrypted assertion:");
NSLog(@"%@",[xml GetXml]);