How to Create a Self-Signed Certificate on Windows

Most Windows administrators, who are familiar with PKI, know about the MakeCert.exetool, which allows to create self-signed certificates. This tool is part of the Microsoft .NET Framework SDK and Microsoft Windows SDK. You can create a self-signed certificate using the built-in PowerShell cmdlet New-SelfSignedCertificate without using additional tools.

New-SelfSignedCertificate: Creating a Self-Signed Certificate with PowerShell

To create a self-signed certificate with PowerShell, you can use the built-in New-SelfSignedCertificate cmdlet, which is a part of the PowerShell PKI (Public Key Infrastructure) module:

To list all available cmdlets in the PKI module, run the command:

Get-Command -Module PKI

It is recommended to use self-signed certificates for testing/developing tasks or to provide certificates for internal Intranet services (IIS, Exchange, Web Application Proxy, LDAPS, ADRMS, DirectAccess, etc.) if you cannot deploy PKI/CA infrastructure or purchase a trusted certificate from an external provider.

To create a certificate, you have to specify the values of –DnsName (name of a server, the name may be arbitrary and even different from the current hostname) and -CertStoreLocation (a local certificate store in which the generated certificate will be placed).

To create a new SSL certificate (with the default SSLServerAuthentication type) for the DNS name test.contoso.com (use an FQDN name) and place it to the personal certificates on a computer, run the following command:

New-SelfSignedCertificate -DnsName test.contoso.com -CertStoreLocation cert:\LocalMachine\My

The command will return the Thumbprint, Subject, and EnhancedKeyUsageList of the new certificate. By default, such a certificate can be used for Client Authentication (1.3.6.1.5.5.7.3.2) or Server Authentication (1.3.6.1.5.5.7.3.1).

New-SelfSignedCertificate : CertEnroll::CX509Enrollment::_CreateRequest: Access denied. 0x80090010 (-2146893808 NTE_PERM)

New-SelfSignedCertificate: CertEnroll::CX509Enrollment::_CreateRequest: Provider type not defined. 0x80090017 (-2146893801 NTE_PROV_TYPE_NOT_DEF).

By default, a self-signed certificate is generated with the following settings:

• Cryptographic algorithm: RSA;
• Key length: 2048 bit;
• Acceptable key usage: Client Authentication and Server Authentication;
• The certificate can be used for: Digital Signature, Key Encipherment;
• Certificate validity period: 1 year;
• Crypto provider: Microsoft Software Key Storage Provider.

This command creates a new certificate and imports it into the computer’s personal certificate store. Open the certlm.msc MMC snap-in and make sure that a new certificate appears in the Personal section of the computer’s certificate store.

Using the Get-ChildItem cmdlet, you can display all the parameters of the created certificate by its Thumbprint:

Get-ChildItem -Path "Cert:\LocalMachine\My" | Where-Object Thumbprint -eq 2175A76B10F843676951965F52A718F635FFA043 | Select-Object *

PSPath                   : Microsoft.PowerShell.Security\Certificate::LocalMachine\My\2175A76B10F843676951965F52A718F635FFA043
PSParentPath             : Microsoft.PowerShell.Security\Certificate::LocalMachine\My
PSChildName              : 2175A76B10F843676951965F52A718F635FFA043
PSDrive                  : Cert
PSProvider               : Microsoft.PowerShell.Security\Certificate
PSIsContainer            : False
EnhancedKeyUsageList     : {Client Authentication (1.3.6.1.5.5.7.3.2), Server Authentication (1.3.6.1.5.5.7.3.1)}
DnsNameList              : {test.contoso.com}
SendAsTrustedIssuer      : False
EnrollmentPolicyEndPoint : Microsoft.CertificateServices.Commands.EnrollmentEndPointProperty
EnrollmentServerEndPoint : Microsoft.CertificateServices.Commands.EnrollmentEndPointProperty
PolicyId                 :
Archived                 : False
Extensions               : {System.Security.Cryptography.Oid, System.Security.Cryptography.Oid,
System.Security.Cryptography.Oid, System.Security.Cryptography.Oid}
FriendlyName             :
IssuerName               : System.Security.Cryptography.X509Certificates.X500DistinguishedName
NotAfter                 : 12/4/2023 5:35:15 PM
NotBefore                : 12/4/2022 5:15:15 PM
HasPrivateKey            : True
PrivateKey               :
PublicKey                : System.Security.Cryptography.X509Certificates.PublicKey
RawData                  : {48, 130, 3, 45...}
SerialNumber             : 6797F5E3F870478D4D3798BEB291DBF3
SubjectName              : System.Security.Cryptography.X509Certificates.X500DistinguishedName
SignatureAlgorithm       : System.Security.Cryptography.Oid
Thumbprint               : 2175A76B10F843676951965F52A718F635FFA043
Version                  : 3
Handle                   : 2834444631568
Issuer                   : CN=test.contoso.com
Subject                  : CN=test.contoso.com

You can create a certificate chain. First, a root certificate (CA) is created. Then based on it, an SSL server certificate is generated:

$rootCert = New-SelfSignedCertificate -Subject 'CN=TestRootCA,O=TestRootCA,OU=TestRootCA' -KeyExportPolicy Exportable  -KeyUsage CertSign,CRLSign,DigitalSignature -KeyLength 2048 -KeyUsageProperty All -KeyAlgorithm 'RSA'  -HashAlgorithm 'SHA256'  -Provider 'Microsoft Enhanced RSA and AES Cryptographic Provider'
New-SelfSignedCertificate -CertStoreLocation cert:\LocalMachine\My -DnsName "test2.contoso.com" -Signer $rootCert -KeyUsage KeyEncipherment,DigitalSignature

To change the certificate key length and encryption algorithm, you need to use the -KeyAlgorithm, -KeyLength, and -HashAlgorithm options. For example:

New-SelfSignedCertificate -KeyAlgorithm RSA -KeyLength 2048 -HashAlgorithm "SHA256" …

The Microsoft Platform Crypto Provider allows you to use the device’s Trusted Platform Module chip (TPM 2.0) to protect the key.

New-SelfSignedCertificate -Type Custom -Provider "Microsoft Platform Crypto Provider" ...

You can generate a document encryption certificate to protect your document and email. Use the DocumentEncryptionCert type when creating a cert:

$Params = @{
"DnsName" = "myhostname"
"CertStoreLocation" = "Cert:\\CurrentUser\\My"
"KeyUsage" = "KeyEncipherment","DataEncipherment","KeyAgreement"
"Type" = "DocumentEncryptionCert"
}
$doccert=New-SelfSignedCertificate @Params

Check the certificate EnhancedKeyUsageList value:

$doccert|select EnhancedKeyUsageList

{Document Encryption (1.3.6.1.4.1.311.80.1)}

Create a Certificate with the Subject Alternative Name (SAN) Using PowerShell

The New-SelfSignedCertificate cmdlet allows you to create a certificate with several different Subject Alternative Names (SANs).

You can deploy this public key or the certificate file itself on all user computers and servers in the Active Directory domain using GPO (How to deploy certificates to users with GPO?).

Generating a Self-Signed Certificate for Code Signing on Windows

In PowerShell 3.0, the New-SelfSifgnedCertificate cmdlet only generates SSL certificates which cannot be used to sign the driver code, application, or script (unlike the certificates generated by the MakeCert utility).

You can use the New-SelfSifgnedCertificate cmdlet to issue Code Signing certificates in PowerShell version 5.0 and newer.

To create a self-signed certificate for sign application code, run the command:

$cert = New-SelfSignedCertificate -Subject "My Code Signing Certificate” -Type CodeSigningCert -CertStoreLocation cert:\LocalMachine\My

Now you can sign your PowerShell script file with a self-signed certificate:

Set-AuthenticodeSignature -FilePath C:\PS\my_posh_script.ps1 -Certificate $cert

If you are receiving an UnknownError warning when executing the command, this means that the certificate is not trusted, because it is located in the user’s personal certificates store.

You need to move it to the Trusted Root Certificate store (don’t forget to periodically scan the Windows certificate root store for untrusted and suspicious certificates and update the lists of trusted root certificates).

Move-Item -Path $cert.PSPath -Destination "Cert:\CurrentUser\Root"

Now you can use this self-signed certificate to sign your PowerShell scripts, drivers, or applications.

Creating SHA-256 Self-Signed SSL Certificate in IIS on Windows Server

Please note that when creating a self-signed certificate for IIS through the Internet Information Manager console (using Create Self-Signed Certificate action menu item), an SSL certificate is created using the SHA-1 encryption algorithm. Such certificates are considered untrusted by many browsers and cannot be used to establish a secure connection (or you may see other SSL warnings and errors). The New-SelfSignedCertificate cmdlet allows you to create a more popular type of certificate using the SHA-256 encryption algorithm.

You can bind a self-signed SHA-256 certificate generated with PowerShell to an IIS site on Windows Server. If you create an SSL certificate using PowerShell and place it in the computer’s certificate store, it will automatically be available to IIS sites.

Open the IIS Manager console (inetmgr.exe), select your site, and then select the certificate you created in the Site Binding options. Save your changes.

You can also bind an SSL certificate by its thumbprint to an IIS site:

New-IISSiteBinding -Name "Default Web Site" -BindingInformation "*:443:" -CertificateThumbPrint $yourCert.Thumbprint -CertStoreLocation "Cert:\LocalMachine\My" -Protocol https