| Error Message | Likely Cause | Solution | | :--- | :--- | :--- | | Unable to load config file | Missing openssl.cnf | Set OPENSSL_CONF=C:\Program Files\OpenSSL-Win64\bin\openssl.cfg | | 'openssl' is not recognized | PATH missing | Reinstall with “Add to PATH” or use full path | | error:0D0D60C3:asn1 encoding routines | Wrong format (DER vs PEM) | Use -inform DER or convert with openssl x509 -inform der -in cert.cer | | Can't open C:\Program Files\OpenSSL-Win64\bin\private\cakey.pem | Permission denied (Windows UAC) | Run CMD/PowerShell |
There are several reasons why you might want to use OpenSSL on Windows: openssl on windows
Verifying that your IIS or Apache server is correctly serving certificates. | Error Message | Likely Cause | Solution
| Feature | OpenSSL on Windows | Windows CNG (via certreq , certutil ) | | :--- | :--- | :--- | | | Yes (same commands on Linux/macOS) | No (Windows only) | | TLS Client/Server | Full s_client , s_server | None (requires .NET or WinHTTP) | | Performance | Good (optimized assembler) | Excellent (kernel-mode acceleration) | | Key Storage | Files (PEM, DER) | Hardware Security Module (HSM), TPM, Certificate Store | | Scripting Language | Batch/PowerShell | PowerShell (native objects) | DER) | Hardware Security Module (HSM)