Originally published on cert-depot.com. Free, open-source self-signed certificate generator — no signup, keys never stored.
RSA vs ECDSA for Self-Signed Certificates
Which key algorithm should you pick? Short answer: ECDSA P-256 if everything you're integrating with supports it. RSA 2048 otherwise.
When you generate a self-signed certificate, you pick a key algorithm. Our generator offers RSA 2048, RSA 4096, ECDSA P-256, and ECDSA P-384. Here's how to choose.
Quick Summary
- ECDSA P-256 — default for new services. Smaller, faster, cryptographically equivalent to RSA 3072.
- RSA 2048 — maximum compatibility. If you don't know what will consume the cert, use this.
- RSA 4096 — only if a compliance checklist demands it. Slower, larger, no meaningful security advantage over RSA 3072 for normal use.
- ECDSA P-384 — for high-assurance scenarios. Overkill for most self-signed certs.
Speed
ECDSA is dramatically faster for signing. On a modern CPU:
- RSA 2048 sign: ~1 ms
- RSA 4096 sign: ~6 ms (6x slower)
- ECDSA P-256 sign: ~0.04 ms (25x faster than RSA 2048)
For a TLS handshake, this matters on high-traffic servers. For a self-signed cert in development, it's immaterial.
Key Size and Certificate Size
ECDSA keys are tiny compared to RSA:
- RSA 2048: public key is ~294 bytes, cert is ~1.2 KB
- RSA 4096: public key is ~550 bytes, cert is ~1.8 KB
- ECDSA P-256: public key is ~91 bytes, cert is ~700 bytes
Smaller certs = faster TLS handshakes, especially on mobile.
Security Equivalence
NIST publishes equivalent strength tables. Summary:
- ECDSA P-256 ≈ RSA 3072 (128-bit security)
- ECDSA P-384 ≈ RSA 7680 (192-bit security)
- RSA 2048 ≈ 112-bit security (acceptable through ~2030)
- RSA 4096 ≈ 140-bit security
Both families resist all currently known classical attacks at these sizes. Both are broken by a sufficiently large quantum computer, which doesn't exist yet.
Compatibility
RSA is universally supported. Every SSL/TLS client ever built speaks RSA.
ECDSA is supported by:
- All modern browsers (Chrome, Safari, Firefox, Edge — full support since ~2013)
- curl, wget, OpenSSL, GnuTLS, BoringSSL
- Go, Rust, Node.js, Python, Java 8+, .NET Core
- All recent Linux distributions, macOS 10.9+, Windows 7+
ECDSA is not supported by some very old embedded devices, certain industrial control systems, Java before 7, and some legacy load balancer firmware. If you're integrating with anything in that list, choose RSA.
Practical Recommendations
Local development, modern stack
Use ECDSA P-256. It's faster, smaller, and everything you care about supports it.
Enterprise / legacy integration
Use RSA 2048. You don't know what 20-year-old appliance will encounter the cert; RSA is the safe bet.
Compliance requires 4096+
Use RSA 4096 or ECDSA P-384. The compliance requirement is usually a checkbox, not a cryptographic necessity.
Air-gapped / future-proofing
Neither is quantum-safe. When post-quantum crypto is standardized (ML-DSA etc.), you'll want to regenerate anyway. Don't pick an algorithm based on quantum threats today.