Clicking on a website and finding no padlock icon in the address bar, but instead a warning page displaying "This website's security certificate has a problem" or "Your connection is not private," indicates an SSL error. Does this mean the website is broken? Does this mean visitor information has been leaked? Most SSL errors don't mean the website has been hacked, but rather that there's a configuration problem somewhere in the security handshake process. Understanding these errors and knowing how to deal with them can help you access the internet securely and efficiently.

To understand these errors, you first need to understand what SSL/TLS does. When you access a website using HTTPS, the browser and server perform a "security handshake." There are three core actions: First, the server presents its digital certificate, issued by a trusted third-party authority (Certificate Authority, CA), like an official ID card for the website, proving "I am example.com." Second, the browser verifies this ID card: Was it issued by a trusted authority? Is it valid? Does the domain name match? Third, after successful verification, both parties negotiate an encryption key, and all subsequent communication is encrypted using this key to prevent eavesdropping or tampering. SSL errors can occur at any stage of the verification or negotiation process.

The most common SSL errors have different root causes and risk levels. Certificate expiration is the most frequent, like an expired ID card; the browser will clearly display "Certificate expired or not yet valid." This is usually due to website administrator negligence in failing to renew the certificate on time. While it may affect access, it generally doesn't indicate a security risk to the website itself. A certificate mismatch with the website domain will display "Certificate is for another domain," for example, a certificate issued for `www.example.com`, but you are accessing `example.com` (missing a subdomain). This configuration error is also common.

More alarming are incomplete certificate chains or self-signed certificates. Legitimate certificates are typically issued by a root CA and intermediate CAs in a hierarchical manner. If intermediate certificates are forgotten during server configuration, the browser cannot build a complete trust chain and will report "This certificate issuer is not trusted." A self-signed certificate is like an ID card issued by the website itself, without any recognized authority's endorsement; the browser naturally cannot trust it. This type of error is common in internal systems, test environments, or some older equipment. The highest risk is encountering a "This connection is untrusted" warning or a serious alert indicating a potential man-in-the-middle attack. This is sometimes due to a system time error, but there is indeed a possibility that a malicious attacker is forging certificates to try and eavesdrop on your communications.

When this error occurs, you can follow a troubleshooting path from easy to difficult, starting with yourself and then moving to the website. First, check your own device and network. 1. Verify that your computer or mobile phone's system date and time are accurate. If the system time is significantly off (e.g., still from 2000), the browser will determine that all valid certificates are "not yet valid." 2. Try clearing your browser cache and SSL state. Old, erroneous caches can cause new problems. Search for "clear browsing data" in Chrome settings, select "cached images and files," and you can further clear the "SSL certificates" cache in the "Security" settings. 3. Temporarily switch networks. Sometimes company networks or public Wi-Fi may conduct traffic audits, implanting their own root certificates, causing browser alerts. Switch to your mobile hotspot to test; if the error disappears, the problem is likely on the original network.

Second, carefully check the certificate details. On your browser's warning page (in Chrome, click the small text next to "Advanced" -> "Continue," but do not proceed directly), there's usually a "View Certificate" option. Clicking it will show you detailed certificate information: ensure the domain "issued to" matches the one you're accessing; check if the "expiration date" is within a reasonable range; and verify if the "issuer" is a reputable organization like DigiCert, Let's Encrypt, or Sectigo. Be extra cautious if the issuer is unfamiliar or shows as "self-signed."

For website administrators or developers, troubleshooting SSL errors reported by users needs to be done on the server side. First, use an online SSL certificate testing tool (such as SSL Labs' SSL Test). Enter your domain name, and it will generate a very detailed report, clearly indicating whether the certificate has expired, the chain is complete, and whether supported encryption protocols are outdated, among other issues. Second, you can perform a quick diagnostic using command-line tools. On a server or local computer, the `openssl` command can be used to simulate a handshake and view the certificate chain:

# Check certificate details and chain

openssl s_client -connect example.com:443 -servername example.com

# Check certificate expiration time

echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -noout -dates

If the certificate chain is incomplete, you need to contact the certificate provider or server administrator to ensure that in the web server (such as Nginx, Apache) configuration, in addition to the domain certificate (.crt file), the intermediate certificate content provided by the provider is correctly attached to the certificate file. If the certificate is expired or mismatched, you need to contact the administrator to repurchase and reissue the correct domain certificate and deploy it to the server. For self-signed certificates used in internal testing environments, you can choose to export them and manually import them into the "Trusted Root Certification Authorities" store in your operating system or browser. However, this reduces security and should only be used in trusted, closed environments.

In summary, when faced with SSL errors, ordinary users should develop the habit of first checking their own time and cache, and then carefully reviewing the certificate information, remaining vigilant about errors on important websites. Website administrators should make good use of testing tools to ensure that certificate configurations are complete and correct.