SSL Certificate Generator
Generate valid X.509 v3 self-signed TLS/SSL certificates, RSA private keys, and Certificate Signing Requests (CSR) locally in your browser. Configure Subject Alternative Names (SAN) and custom validity periods with zero network transmission.
X.509 Certificate Engine
Browser-Native X.509 v3 Self-Signed TLS Certificate and CSR Generation
The SSL Certificate Generator produces cryptographically valid X.509 v3 self-signed TLS/SSL certificates, Certificate Signing Requests (CSR), and RSA private keys directly inside your web browser. Operating entirely within client-side memory, this tool enables developers to configure and test HTTPS security parameters without exposing server private keys to third-party endpoints.
This utility allows customization of all standard Public Key Infrastructure (PKI) subject fields, including Common Name (CN), Organization (O), Country (C), State (ST), Locality (L), and validity durations from 30 days to 10 years. It provides first-class support for Subject Alternative Names (SANs) for localhost, loopback IP addresses (127.0.0.1 and ::1), internal domains, and wildcard hostnames.
The workspace outputs standard PEM-encoded certificates (.crt), private keys (.key), CSRs (.csr), and combined full-chain bundles (.pem). It computes instant SHA-256 and SHA-1 certificate fingerprints, displays serial numbers, and provides clear transparency disclosures regarding self-signed certificate trust boundaries.
Core Tool Capabilities
- X.509 v3 Standard Certificate Generation: Constructs fully compliant X.509 version 3 digital certificates signed with SHA-256 and 2048-bit or 4096-bit RSA keys.
- Subject Alternative Names (SAN) Multi-Domain: Embeds custom DNS names and IP addresses into standard subjectAltName extensions for multi-host and local development testing.
- Certificate Signing Request (CSR) Export: Generates PKCS#10 Certificate Signing Requests with embedded SAN attributes for submission to commercial Certificate Authorities.
- Fast Development Presets: Includes one-click configurations for localhost development, wildcard local domains, and multi-domain internal staging environments.
- Multi-Format Export and Bundle Downloads: Exports individual .crt, .key, and .csr files alongside combined certificate and key bundle archives for web server deployments.
Local Browser Privacy
Your files are processed locally on your device. Files are not uploaded, transmitted, or stored on remote servers.
Once the page has loaded, you can disconnect your network connection and continue using this tool offline.
Target Use Cases
- • Local HTTPS Development Server Configuration
- • Microservice Mutual TLS (mTLS) Testing
- • Staging and Internal Network Encryption
- • Certificate Authority Request Preparation
Technical Specifications & Platform Limits
Standard internet TLS certificate structure.
Industry-standard cryptographic signature.
Standard Certificate Signing Request.
Zero external network requests or key storage.
Step-by-Step Workflow
Configure Domain and Subject Info
Enter the primary Common Name (e.g. localhost or dev.local) and add any required Subject Alternative Names (SANs) separated by commas.
Select Validity and Key Parameters
Choose the certificate validity duration (30 to 3650 days), RSA modulus length (2048 or 4096 bits), and organization details.
Generate Certificate and Keys
Click Generate Certificate to perform RSA keypair generation, ASN.1 structure compilation, and SHA-256 self-signing locally in memory.
Export Certificate and Private Key
Copy or download the generated .crt certificate, .key private key, .csr request, or the combined PEM bundle for your local server.
Practical Real-World Use Cases
Local HTTPS Development Server Configuration
Web developers creating localhost and 127.0.0.1 certificates with SAN extensions to test modern browser APIs requiring secure origins.
Microservice Mutual TLS (mTLS) Testing
Backend architects provisioning isolated client and server certificates for local Docker and Kubernetes service mesh testing.
Staging and Internal Network Encryption
DevOps engineers generating self-signed certificates for internal dashboards and staging reverse proxies (Nginx, Caddy, Apache).
Certificate Authority Request Preparation
System administrators generating CSRs and private keys locally before submitting the public request to enterprise or commercial CAs.
Frequently Asked Questions
- Why does my browser show a security warning when using a self-signed certificate?
- Web browsers trust only certificates signed by recognized Certificate Authorities (CAs) pre-installed in the operating system trust store. A self-signed certificate is mathematically valid, but requires manual trust installation to remove browser warnings.
- What is the purpose of Subject Alternative Names (SAN)?
- Subject Alternative Names (SAN) allow a single TLS certificate to protect multiple hostnames, IP addresses, or wildcard domains (such as localhost, 127.0.0.1, and dev.local) simultaneously, which modern browsers require for valid HTTPS validation.
- What is the difference between a self-signed certificate and a CSR?
- A self-signed certificate is a complete, usable certificate signed by its own private key. A Certificate Signing Request (CSR) contains only the public key and identity attributes formatted for submission to an external Certificate Authority.
- How do I use this certificate in Nginx or Apache?
- Save the downloaded .crt certificate file and .key private key file to your server, then reference them using ssl_certificate and ssl_certificate_key in Nginx, or SSLCertificateFile and SSLCertificateKeyFile in Apache.
- Are my generated SSL private keys uploaded to any server?
- No. All RSA key generation, X.509 encoding, and self-signing operations execute entirely in your browser memory. No private keys or certificate contents are transmitted across the network.
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