Public Key Extractor
Extract the public key from certificates or private keys.
Public Key Extractor
Runs entirely in your browser
This tool executes locally using standard browser APIs (for example window.crypto.getRandomValues or crypto.subtle where applicable). Your input is not transmitted to or stored on a ScriptPulse server. See How Calculations Work.
What This Tool Does
- The Public Key Extractor pulls the public key out of a certificate or a private key file, producing a standalone PEM-encoded public key (SubjectPublicKeyInfo) you can share safely. This matters because the public half of a key pair is exactly what's meant to be distributed — for pinning, for a peer's trust configuration, for a JWK conversion — while the certificate or private key it's embedded in may carry more than you want to hand someone, or in the private key's case, must never be shared at all.
- For a private key specifically, the public key isn't a separate secret stored alongside it — it's mathematically derivable from the private key's own parameters (for RSA, from the modulus and public exponent already present in the key structure; for elliptic curve keys, from the private scalar and the curve's generator point). This tool performs that derivation locally, so the private key itself never needs to be shared just to obtain its public counterpart.
How It Works
- If given a certificate, the tool extracts the SubjectPublicKeyInfo structure directly — the certificate already contains the public key in exactly the format needed.
- If given a private key, the tool derives the corresponding public key from the private key's own parameters — the modulus and exponent for RSA, or the curve point for elliptic curve algorithms — without needing any external input.
- The resulting public key is PEM-encoded with standard PUBLIC KEY headers, in the same SubjectPublicKeyInfo format used across X.509 certificates, TLS, and most crypto libraries.
- No private key material is included in or derivable from the output — the extraction is strictly one-directional.
Usage
- Paste a PEM-formatted certificate or private key.
- Run the extraction.
- Copy the resulting standalone public key, PEM-encoded and ready to share or convert.
- Use the extracted public key for pinning, sharing with a peer, or converting to JWK format as your workflow requires.
Examples
- Extracting a public key from a server's certificate to hard-code a pinned key value in a mobile application for certificate pinning.
- Pulling the public key from a private key file before sharing it with a partner service that needs it to verify signatures your system produces.
- Extracting the public key from both a certificate and its corresponding private key file to confirm they're actually a matched pair before deploying them together.
- Preparing a public key extracted from an RSA private key for conversion into JWK format for a service that only accepts JSON Web Keys.
Real-World Use Cases
- Extracting a server's public key from its certificate to configure certificate or public-key pinning in a client application.
- Obtaining a standalone public key from a private key file to share with a peer for encryption or signature verification, without ever transmitting the private key itself.
- Preparing a public key for conversion to JWK format (using the JWK ↔ PEM Converter) when integrating with a library or service that expects JSON Web Key input.
- Confirming that a certificate and a private key you believe are paired actually share the same public key, by extracting from both and comparing the output.
Best Practices
- Always extract and share the public key specifically — never share a private key file even if only the public information is actually needed by the recipient.
- Verify a certificate and private key are genuinely paired by extracting the public key from each and comparing, especially before deploying them together in a production TLS configuration.
- Treat an extracted public key as safe to publish or distribute widely — by design, possessing only the public key reveals nothing that would let someone derive the private key.
- When a peer or service requires JWK format specifically, extract the public key first, then convert — don't attempt to hand-construct a JWK from raw key parameters.
Common Mistakes
- Sharing an entire private key file when only the public key was actually needed, unnecessarily exposing sensitive material for no operational benefit.
- Assuming a certificate and a private key are paired without verifying it — deploying a mismatched pair produces a TLS handshake failure that can be confusing to diagnose without directly comparing the public keys.
- Treating the extracted public key as if it needed to be kept confidential — it doesn't; the entire point of asymmetric cryptography is that the public half is safe to distribute freely.
- Manually retyping or reformatting a public key instead of extracting it programmatically, risking a transcription error that produces a key that looks similar but doesn't actually match.
Limitations
- This tool extracts a public key from a certificate or private key you provide; it does not validate the certificate's trust chain or the private key's own integrity beyond confirming it parses.
- It does not perform format conversion beyond PEM output — use the JWK ↔ PEM Converter if you need the extracted key in JSON Web Key format.
- All extraction happens in local browser memory; nothing is transmitted, but nothing is persisted either — copy the output before reloading the page.
Technical Reference Guide
- The SubjectPublicKeyInfo structure this tool outputs — the standard format for a standalone public key — is defined by RFC 5280, the same structure used inside X.509 certificates.
- RSA public key parameters (modulus and public exponent) that this tool derives a public key from when given an RSA private key are defined by RFC 8017 (PKCS #1).
- Elliptic curve public key derivation from a private scalar is defined by RFC 5480, which specifies how EC public keys are represented within SubjectPublicKeyInfo.
FAQ
Is it safe to extract and share a public key from my private key?
Yes — the public key is meant to be shared. Extracting it doesn't expose or weaken the private key in any way; the derivation is strictly one-directional, from private key to public key, never the reverse.
Why extract a public key from a private key instead of just using the certificate?
You may not always have a certificate on hand — for example, when working with a raw key pair before a certificate has been issued, or when the private key is used for something other than TLS, like SSH or a signing workflow.
Can I derive a private key from an extracted public key?
No — that's the entire security foundation of asymmetric cryptography. Deriving a private key from its public counterpart is computationally infeasible for properly-sized RSA or elliptic curve keys.
How do I know if a certificate and private key actually match?
Extract the public key from both and compare them directly — if they're identical, the private key is the matching half of that certificate's key pair.
What format does this tool output the public key in?
Standard PEM-encoded SubjectPublicKeyInfo — the same format used inside X.509 certificates and accepted by most TLS and crypto libraries. Use the JWK ↔ PEM Converter if you need JSON Web Key format instead.
Does this tool work with elliptic curve keys, not just RSA?
Yes — public key derivation works the same conceptually for both algorithm families, deriving the public point or modulus/exponent pair from the private key's own parameters.
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