(Objective-C) Validate Certificate using OCSP Protocol

Demonstrates how to validate a certificate (check the revoked status) using the OCSP protocol.

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#import <CkoCert.h>
#import <NSString.h>
#import <CkoPrng.h>
#import <CkoJsonObject.h>
#import <CkoBinData.h>
#import <CkoHttp.h>
#import <CkoHttpResponse.h>

// Note: Requires Chilkat v9.5.0.75 or greater.

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

// This example will check the revoked status of a certificate loaded from a file.
CkoCert *cert = [[CkoCert alloc] init];
BOOL success = [cert LoadFromFile: @"qa_data/certs/google.crt"];
if (success != YES) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// Get the cert's OCSP URL.
NSString *ocspUrl = cert.OcspUrl;

// Build the JSON that will be the OCSP request.

// Possible hash algorithms are sha1, sha256, sha384, sha512.  
NSString *hashAlg = @"sha256";
CkoPrng *prng = [[CkoPrng alloc] init];
CkoJsonObject *json = [[CkoJsonObject alloc] init];
json.EmitCompact = NO;
// Read more about OCSP nonce lengths
[json UpdateString: @"extensions.ocspNonce" value: [prng GenRandom: [NSNumber numberWithInt: 16] encoding: @"base64"]];
json.I = [NSNumber numberWithInt:0];
[json UpdateString: @"request[i].cert.hashAlg" value: hashAlg];
[json UpdateString: @"request[i].cert.issuerNameHash" value: [cert HashOf: @"IssuerDN" hashAlg: hashAlg encoding: @"base64"]];
[json UpdateString: @"request[i].cert.issuerKeyHash" value: [cert HashOf: @"IssuerPublicKey" hashAlg: hashAlg encoding: @"base64"]];
[json UpdateString: @"request[i].cert.serialNumber" value: cert.SerialNumber];

NSLog(@"%@",[json Emit]);

// Our OCSP request looks something like this:
// {
//   "extensions": {
//     "ocspNonce": "qZDfbpO+nUxRzz6c/SPjE5QCAsPfpkQlRDxTnGl0gnxt7iXO"
//   },
//   "request": [
//     {
//       "cert": {
//         "hashAlg": "sha1",
//         "issuerNameHash": "9u2wY2IygZo19o11oJ0CShGqbK0=",
//         "issuerKeyHash": "d8K4UJpndnaxLcKG0IOgfqZ+uks=",
//         "serialNumber": "6175535D87BF94B6"
//       }
//     }
//   ]
// }

CkoBinData *ocspRequest = [[CkoBinData alloc] init];
CkoHttp *http = [[CkoHttp alloc] init];

// Convert our JSON to a binary (ASN.1) OCSP request
success = [http CreateOcspRequest: json ocspRequest: ocspRequest];
if (success == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

// Send the OCSP request to the OCSP server
CkoHttpResponse *resp = [http PBinaryBd: @"POST" url: ocspUrl data: ocspRequest contentType: @"application/ocsp-request" md5: NO gzip: NO];
if (http.LastMethodSuccess != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

// Get the binary (ASN.1) OCSP reply
CkoBinData *ocspReply = [[CkoBinData alloc] init];
[resp GetBodyBd: ocspReply];

// Convert the binary reply to JSON.
// Also returns the overall OCSP response status.
CkoJsonObject *jsonReply = [[CkoJsonObject alloc] init];
int ocspStatus = [[http ParseOcspReply: ocspReply replyData: jsonReply] intValue];

// The ocspStatus can have one of these values:
// -1:  The ARG1 does not contain a valid OCSP reply.
// 0:  Successful - Response has valid confirmations..
// 1: Malformed request - Illegal confirmation request.
// 2: Internal error - Internal error in issuer.
// 3: Try later -  Try again later.
// 4: Not used - This value is never returned.
// 5: Sig required - Must sign the request.
// 6: Unauthorized - Request unauthorized.

if (ocspStatus < 0) {
    NSLog(@"%@",@"Invalid OCSP reply.");
    return;
}

NSLog(@"%@%d",@"Overall OCSP Response Status: ",ocspStatus);

// Let's examine the OCSP response (in JSON).
jsonReply.EmitCompact = NO;
NSLog(@"%@",[jsonReply Emit]);

// The JSON reply looks like this:
// (Use the online tool at https://tools.chilkat.io/jsonParse.cshtml
// to generate JSON parsing code.)

// {
//   "responseStatus": 0,
//   "responseTypeOid": "1.3.6.1.5.5.7.48.1.1",
//   "responseTypeName": "ocspBasic",
//   "response": {
//     "responderIdChoice": "KeyHash",
//     "responderKeyHash": "d8K4UJpndnaxLcKG0IOgfqZ+uks=",
//     "dateTime": "20180803193937Z",
//     "cert": [
//       {
//         "hashOid": "1.3.14.3.2.26",
//         "hashAlg": "SHA-1",
//         "issuerNameHash": "9u2wY2IygZo19o11oJ0CShGqbK0=",
//         "issuerKeyHash": "d8K4UJpndnaxLcKG0IOgfqZ+uks=",
//         "serialNumber": "6175535D87BF94B6",
//         "status": 0,
//         "thisUpdate": "20180803193937Z",
//         "nextUpdate": "20180810193937Z"
//       }
//     ]
//   }
// }
// 

// The certificate status:
int certStatus = -1;
if ([jsonReply HasMember: @"response.cert[0].status"] == YES) {
    certStatus = [[jsonReply IntOf: @"response.cert[0].status"] intValue];
}

// Possible certStatus values are:
// -1: No status returned.
// 0: Good
// 1: Revoked
// 2: Unknown.
NSLog(@"%@%d",@"Certificate Status: ",certStatus);