Step-by-Step Guide to Exporting Certificates and Handling NCRYPT_KEY_HANDLE Issues in OpenSSL

Step-by-Step Guide to Exporting Certificates and Handling NCRYPT_KEY_HANDLE Issues in OpenSSL

This guide walks you through the process of exporting a certificate in PEM format while addressing common issues, such as receiving unexpected values when mapping the blob and handling the NCRYPT_KEY_HANDLE correctly. Specifically, the issue discussed here involves successfully exporting the blob, but facing difficulties with the encryption or key handle, which is not functioning as expected.

Problem Overview

You’ve successfully exported the certificate into a blob but are encountering the following issues:

  • NCRYPT_KEY_HANDLE (hExportKey) is set to NULL, leading you to suspect that the blob may not be encrypted.
  • When mapping the blob header to _BCRYPT_RSAKEY_BLOB, you receive unusual values like:
    • Magic = 833680480
    • BitLength = 634
    • Other unexpectedly large values.

Step-by-Step Guide to Solving the Issues

Step 1: Understand NCRYPT_KEY_HANDLE and the Blob Export Process

Before diving into fixing the issue, make sure you fully understand how the NCryptExportKey function works and how the key blob is structured.

  • Key Blob Export: When a key is exported, it is wrapped in a key blob. This blob contains all necessary data, such as the public key and other key parameters. It allows you to export both private and public keys for use in other processes.
  • RSA Private Key Export: In your case, you are attempting to export an RSA private key using the NCryptExportKey function.

Step 2: Correct Usage of NCRYPT_KEY_HANDLE

If hExportKey is set to NULL in your code, it typically means the key is not being encrypted during export. This is common when exporting just the key data, without any encryption or wrapping.

  • No Encryption: Setting hExportKey to NULL indicates that no encryption is applied to the key export. If encryption is required, you need to modify your code accordingly.

Step 3: Understand the Blob Header

When mapping the header of _BCRYPT_RSAKEY_BLOB, strange values like Magic = 833680480 and BitLength = 634 suggest that there may be an issue with how the blob is being mapped, or that the values within the blob are not properly defined.

  • Key Blob Header: The key blob header includes fields such as Magic, BitLength, cbPublicExp, and cbModulus, which represent the RSA key’s size and other details. Understanding these values correctly is essential to interpreting the blob data accurately.

Step 4: Proper Use of the NCryptExportKey Function

To resolve issues during the export process, ensure that all parameters are correctly set in the NCryptExportKey function. Here’s an example:


SECURITY_STATUS status = NCryptExportKey(
    hKey,
    hExportKey,
    pszBlobType,
    pParameterList,
    pbOutput,
    cbOutput,
    &pcbResult,
    dwFlags
);
  • Parameters to Check:
    • hKey: The handle for the key.
    • pszBlobType: The type of blob to export.
    • hExportKey: If NULL, the key export will not be encrypted.

Ensure that these parameters are set correctly to avoid issues with the export process.

Step 5: Verify Data Integrity

If you are encountering strange values like Magic, BitLength, and cbPublicExp, it’s crucial to ensure that you are reading the data correctly. These values often occur when the data is misinterpreted or read incorrectly.

  • Data Misinterpretation: Ensure the data is correctly interpreted. You may need to check if the blob is being read in the correct format or check for potential issues in the mapping process.

Conclusion

In this guide, we have outlined the proper use of NCRYPT_KEY_HANDLE, the blob export process, and strategies to address related issues. By following these steps, you can resolve issues related to key export and blob mapping effectively:

  • Understand the Export Process: Know how the key is exported and how the blob is structured.
  • Correct Use of Key Handle: Ensure the NCRYPT_KEY_HANDLE is used correctly, and encryption is applied if necessary.
  • Accurate Blob Mapping: Carefully map the blob header to avoid strange values.
  • Verify Parameters and Integrity: Ensure all parameters are correct and verify data integrity during export.

By following these steps, you can troubleshoot and resolve issues with NCRYPT_KEY_HANDLE and key export processes.