A .CER file is a digital certificate typically encoded in X.509 format. These certificates are used for authentication, encryption, and digital signatures in various security protocols like SSL/TLS.

The simplest way to view certificate details is through Windows' built-in Certificate Manager:

certmgr.msc

Then follow these steps:

1. Navigate to "Trusted Root Certification Authorities" → "Certificates"
2. Right-click the certificate → "Open"
3. Examine details in the "Details" tab

For more technical analysis, OpenSSL provides powerful tools:

openssl x509 -in certificate.cer -text -noout

This command outputs:

• Version number
• Serial number
• Signature algorithm
• Issuer details
• Validity period
• Subject details
• Public key information
• Extensions (if present)

Here's a C# example using System.Security.Cryptography:

using System;
using System.Security.Cryptography.X509Certificates;

class Program {
    static void Main() {
        X509Certificate2 cert = new X509Certificate2("certificate.cer");
        Console.WriteLine($"Subject: {cert.Subject}");
        Console.WriteLine($"Issuer: {cert.Issuer}");
        Console.WriteLine($"Valid From: {cert.GetEffectiveDateString()}");
        Console.WriteLine($"Valid Until: {cert.GetExpirationDateString()}");
        Console.WriteLine($"Thumbprint: {cert.Thumbprint}");
        Console.WriteLine($"Serial Number: {cert.SerialNumber}");
        Console.WriteLine($"Public Key: {cert.GetPublicKeyString()}");
    }
}

To verify the complete certificate chain:

openssl verify -CAfile root-ca.crt -untrusted intermediate.crt certificate.cer

You can export certificate details to various formats:

# Export to PEM format
openssl x509 -in certificate.cer -out certificate.pem -outform PEM

# Export to DER format
openssl x509 -in certificate.cer -out certificate.der -outform DER

# Export public key only
openssl x509 -in certificate.cer -pubkey -noout > publickey.pem

Field	Description
CN (Common Name)	Typically the domain name for SSL certificates
O (Organization)	Legal entity that owns the certificate
OU (Organizational Unit)	Department within the organization
L (Locality)	City where organization is located
S (State)	State or province
C (Country)	Two-letter country code
Subject Alternative Names	Additional domains covered by the certificate

When working with .CER files, you might encounter:

• "Invalid certificate format" - Try converting between DER and PEM formats
• "Certificate expired" - Check validity dates in the output
• "Untrusted certificate" - Verify the certificate chain is complete

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A .CER file is a digital certificate that typically contains public key information and is used for authentication and encryption purposes. These files are commonly used in SSL/TLS configurations, code signing, and client authentication.

The simplest way to view a .CER file is through Windows Explorer:

1. Double-click the .CER file
2. Click the "Details" tab in the certificate viewer
3. Explore the various fields like Issuer, Validity Period, Public Key, etc.

For more advanced inspection:

1. Press Win+R and type "certmgr.msc"
2. Navigate to "Trusted Root Certification Authorities" > "Certificates"
3. Right-click and select "All Tasks" > "Import" to add your certificate
4. Double-click the imported certificate to view details

Windows includes a powerful command-line tool for certificate inspection:

certutil -dump yourcertificate.cer

For more detailed output:

certutil -v -dump yourcertificate.cer

Here's how to inspect certificates using PowerShell:

$cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2
$cert.Import("C:\path\to\yourcertificate.cer")
$cert | Format-List *

To view specific properties:

$cert.Subject
$cert.Issuer
$cert.NotBefore
$cert.NotAfter
$cert.Thumbprint
$cert.PublicKey

For developers with OpenSSL installed:

openssl x509 -in yourcertificate.cer -text -noout

• Subject: The entity the certificate belongs to
• Issuer: The Certificate Authority that issued it
• Validity Period: NotBefore and NotAfter dates
• Public Key: The actual cryptographic key
• Signature Algorithm: How the certificate was signed
• Extensions: Additional certificate properties

To verify the complete trust chain:

certutil -verify yourcertificate.cer

To save certificate details to a text file:

certutil -dump yourcertificate.cer > cert_details.txt

If you encounter problems:

• Ensure the file is a valid X.509 certificate
• Check file permissions
• Verify the certificate hasn't expired
• Confirm the certificate isn't corrupted