Generate RSA-2048, RSA-3072, or RSA-4096 key pairs in PEM format for signing and encryption, entirely in-browser.
Two very different files come out of this button: a short public key you can hand to anyone, and a long private key that must never leave your machine. Both are PEM text blocks you can paste into servers, apps, and config files, and the whole job runs in the browser, so no key material is ever uploaded. The recurring surprise is the direction of no-return: the public key cannot be reversed into the private key, so losing the private key is permanent - no reset, no recovery.
A concrete input and expected output from the current implementation.
Input
Select 2048-bit and click Generate. There is no text to type - the tool supplies the randomness itself.
Expected output
-----BEGIN PUBLIC KEY----- MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A <360 more base64 characters encoding the generated modulus and the exponent 65537, wrapped at 64 per line> -----END PUBLIC KEY----- The example elides the middle of the body; the saved file frames the full base64 between two boundary lines, in rows of at most 64 characters.
The first base64 line is fixed: it encodes the 24-byte DER header shared by every RSA-2048 public key in this format - the SubjectPublicKeyInfo structure, the rsaEncryption identifier (1.2.840.113549.1.1.1), and the bit-string header. The remainder encodes the random modulus (a 257-byte DER integer including its leading zero) and the exponent 65537, so the body changes on every generation and cannot be predicted.
PEM is plain ASCII: a header line, base64 text, and a footer line. The public key wraps a SubjectPublicKeyInfo structure carrying the modulus n and the public exponent e, usually 65537. The private key wraps the same modulus plus the private exponent and the two secret primes. The header line - BEGIN PUBLIC KEY, BEGIN PRIVATE KEY, or BEGIN RSA PRIVATE KEY - tells you which structure is inside.
RSA's security rests on a one-way computation: the modulus n is the product of two large primes p and q, and finding p and q from n is considered infeasible at these sizes. Data encrypted with the public key can only be decrypted with the private key, and a signature made with the private key verifies with the public key. Generation starts by picking those two primes at random.
Only with conversion. OpenSSH wants its own format, not PEM: convert the public key with ssh-keygen -i -m PKCS8 -f key.pem, or just generate the pair with ssh-keygen in the first place. This tool's PEM output fits OpenSSL, TLS, and cloud workflows directly.
Not automatically. Larger keys make factoring the modulus harder, but 2048-bit RSA is not known to be broken, and NIST's SP 800-57 Part 1 rates it acceptable through 2030, recommending 3072-bit for use beyond that. Bigger keys are slower to generate and slower at every operation, so size them to how long the key must stay strong.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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