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SSL/TLS Certificate Decoder

DeveloperNetworkingSecurity

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INPUT

Auto Process

OUTPUT

Client Side

Subject

Field	Value
Result will appear here

Issuer

Field	Value
Result will appear here

Validity

Field	Value
Result will appear here

Certificate Details

Property	Value
Result will appear here

Extensions

Extension	Value
Result will appear here

Fingerprints

Algorithm	Fingerprint
Result will appear here

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Guide

SSL/TLS Certificate Decoder

Decode and analyze SSL/TLS certificates instantly. Paste any PEM-encoded certificate to see its full details — subject, issuer, validity, extensions, and security warnings.

How to Use

Paste your PEM-encoded certificate (starting with —–BEGIN CERTIFICATE—–) into the input field. The tool instantly decodes and displays all certificate details including subject information, issuer chain, validity dates, public key details, and security analysis.

Features

Certificate Details – Subject, Issuer, Serial Number, Version, Signature Algorithm
Validity Analysis – Not Before/After dates with color-coded expiry countdown
Public Key Info – Algorithm type and key size
Extensions – SANs, Key Usage, Extended Key Usage
Fingerprints – SHA-256 and SHA-1 certificate fingerprints
Security Warnings – Detects expired, self-signed, weak key, and SHA-1 signatures

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 FAQ

How does SSL/TLS certificate verification work?

SSL/TLS certificate verification follows a chain of trust model. When a browser connects to a website, the server presents its certificate. The browser checks that the certificate is signed by a trusted Certificate Authority (CA), that the domain name matches, and that the certificate hasn't expired or been revoked. The CA's certificate is in turn signed by a higher-level CA, forming a chain that ends at a root CA pre-installed in the operating system or browser. If any link in this chain is broken or untrusted, the connection is rejected.
What is the difference between DER and PEM certificate encoding?

DER (Distinguished Encoding Rules) is a binary format for encoding certificates — compact but not human-readable. PEM (Privacy Enhanced Mail) is simply DER data encoded in Base64 and wrapped between '-----BEGIN CERTIFICATE-----' and '-----END CERTIFICATE-----' headers. PEM is more common because it can be safely copied and pasted in text, embedded in configuration files, and transmitted via email. Most tools and servers accept PEM format, while DER is used in some Java keystores and Windows certificate stores.
What do X.509 certificate fields like CN, SAN, and CA mean?

X.509 is the standard format for public key certificates. CN (Common Name) historically held the domain name the certificate was issued for, though modern certificates use SAN instead. SAN (Subject Alternative Name) lists all domains and IPs the certificate covers, supporting multiple domains on one cert. The CA (Certificate Authority) flag in the Basic Constraints extension indicates whether the certificate can sign other certificates. Other important fields include the validity period, key usage restrictions, and the signature algorithm used.