(VB.NET) Validate Certificate using OCSP Protocol

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

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' 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.
Dim cert As New Chilkat.Cert
Dim success As Boolean = cert.LoadFromFile("qa_data/certs/google.crt")
If (success <> True) Then
    Debug.WriteLine(cert.LastErrorText)
    Exit Sub
End If


' Get the cert's OCSP URL.
Dim ocspUrl As String = cert.OcspUrl

' Build the JSON that will be the OCSP request.

' Possible hash algorithms are sha1, sha256, sha384, sha512.  
Dim hashAlg As String = "sha256"
Dim prng As New Chilkat.Prng
Dim json As New Chilkat.JsonObject
json.EmitCompact = False
' Read more about OCSP nonce lengths
json.UpdateString("extensions.ocspNonce",prng.GenRandom(16,"base64"))
json.I = 0
json.UpdateString("request[i].cert.hashAlg",hashAlg)
json.UpdateString("request[i].cert.issuerNameHash",cert.HashOf("IssuerDN",hashAlg,"base64"))
json.UpdateString("request[i].cert.issuerKeyHash",cert.HashOf("IssuerPublicKey",hashAlg,"base64"))
json.UpdateString("request[i].cert.serialNumber",cert.SerialNumber)

Debug.WriteLine(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"
'       }
'     }
'   ]
' }


Dim ocspRequest As New Chilkat.BinData
Dim http As New Chilkat.Http

' Convert our JSON to a binary (ASN.1) OCSP request
success = http.CreateOcspRequest(json,ocspRequest)
If (success = False) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


' Send the OCSP request to the OCSP server
Dim resp As Chilkat.HttpResponse = http.PBinaryBd("POST",ocspUrl,ocspRequest,"application/ocsp-request",False,False)
If (http.LastMethodSuccess <> True) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


' Get the binary (ASN.1) OCSP reply
Dim ocspReply As New Chilkat.BinData
resp.GetBodyBd(ocspReply)


' Convert the binary reply to JSON.
' Also returns the overall OCSP response status.
Dim jsonReply As New Chilkat.JsonObject
Dim ocspStatus As Integer = http.ParseOcspReply(ocspReply,jsonReply)

' 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) Then
    Debug.WriteLine("Invalid OCSP reply.")
    Exit Sub
End If


Debug.WriteLine("Overall OCSP Response Status: " & ocspStatus)

' Let's examine the OCSP response (in JSON).
jsonReply.EmitCompact = False
Debug.WriteLine(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:
Dim certStatus As Integer = -1
If (jsonReply.HasMember("response.cert[0].status") = True) Then
    certStatus = jsonReply.IntOf("response.cert[0].status")
End If


' Possible certStatus values are:
' -1: No status returned.
' 0: Good
' 1: Revoked
' 2: Unknown.
Debug.WriteLine("Certificate Status: " & certStatus)