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Tools / RSA keypair generator

RSA keypair generator

Generate cryptographically secure RSA keypairs using the browser SubtleCrypto engine. Outputs standard PKCS#8 private keys and SPKI public keys in PEM format for SSH, JWT signing, and SSL certificates.

Runs entirely in your browser

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About this tool

RSA keypairs underpin a lot of everyday security: SSH logins, signing JSON Web Tokens, and the certificates behind HTTPS. A keypair consists of a private key you keep secret and a public key you can share freely; data encrypted or verified with one relates mathematically to the other. This tool generates cryptographically secure RSA keypairs at 2048-bit or 4096-bit strength using the browser’s SubtleCrypto engine.

The output is in the standard PEM formats you will actually need — PKCS#8 for the private key and SPKI for the public key — so the keys drop straight into tools and libraries that expect them. Generating in the browser via SubtleCrypto means the keys are produced with a proper cryptographic random source and never sent to a server, which is essential for a private key.

On key size: 2048-bit is the common baseline and is widely considered adequate today, while 4096-bit offers a larger margin at the cost of slower operations. Whatever you choose, the private key’s security is only as good as how you store it — keep it out of shared locations and never paste a private key you intend to keep into an untrusted site.

Frequently asked questions

What is the difference between the public and private key?
The private key must be kept secret; the public key can be shared. They are mathematically linked so that signatures made with the private key verify with the public one, and data can be secured for the holder of the private key.
Should I choose 2048-bit or 4096-bit?
2048-bit is a widely accepted baseline and faster; 4096-bit gives a larger security margin but slower operations. Choose based on your requirements — many systems standardise on 2048-bit unless a policy requires more.
Are the keys generated privately?
Yes. Keys are generated in your browser with the SubtleCrypto engine and are not transmitted to any server, which is critical for keeping the private key secret.
What are PKCS#8 and SPKI?
They are the standard PEM encodings for the private key (PKCS#8) and public key (SPKI). Most SSH, JWT and TLS tooling expects keys in these formats, so they are ready to use as generated.
How should I store my private key?
Keep it somewhere access-controlled and never commit it to a repository or paste it into untrusted sites. Anyone with the private key can impersonate you, so its confidentiality is the whole security of the pair.

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