- Should I use 2048-bit or 4096-bit RSA keys?
- 2048-bit is the minimum recommended by NIST in 2026 and sufficient for most applications. Use 4096-bit for high-security requirements, long-lived certificates, or when compliance policy requires it. 4096-bit keys are ~4x slower for signing operations.
- Can I use these RSA keys for JWT signing (RS256)?
- Yes. Copy the private key to sign JWTs with RS256, RS384, or RS512 algorithms. Share the public key with services that need to verify the tokens. Standard PEM format works with jsonwebtoken (Node.js), PyJWT (Python), and all major JWT libraries.
- Is it safe to generate RSA keys in a browser?
- Yes for development and testing. The Web Crypto API provides cryptographically secure key generation. For production keys protecting sensitive data or infrastructure, use dedicated tools like OpenSSL or cloud HSM services.
- What is the difference between RSA and Ed25519?
- RSA is older and more widely supported. Ed25519 (elliptic curve) is newer, faster, and provides equivalent security with much smaller keys (256-bit vs 2048-bit). Ed25519 is now preferred for SSH keys; RSA remains standard for TLS and JWT.
- Why does my private key fail to import in my application?
- Common causes: wrong key format (PKCS#1 vs PKCS#8), missing BEGIN/END markers, line break differences (CRLF vs LF), or algorithm mismatch (expecting EC key but getting RSA). Check your library’s expected format.
- How should I store RSA private keys in production?
- Use a secrets manager (AWS Secrets Manager, HashiCorp Vault, Doppler), cloud KMS (AWS KMS, GCP KMS, Azure Key Vault), or HSM (AWS CloudHSM, YubiHSM). Never commit private keys to Git. For application configs, use environment variables or encrypted config files with restricted file permissions (chmod 600).
- Can I use this RSA key for SSH?
- Not directly — OpenSSH uses a different key format. Generate the RSA key here, save the PEM private key to a file, then convert: `ssh-keygen -p -m PEM -f your-key.pem` then `ssh-keygen -y -f your-key.pem > your-key.pub` to get the ssh-rsa public key. Easier path: just use `ssh-keygen -t ed25519` directly on your machine for new SSH keys.
- Is 2048-bit RSA still safe in 2026?
- Yes. NIST SP 800-57 marks 2048-bit RSA as acceptable through 2030. There is no known practical attack faster than the General Number Field Sieve, which would take billions of CPU-years for a 2048-bit key. For keys with a planned lifetime past 2030, upgrade to 3072-bit.
- What's the public exponent and why is it always 65537?
- The public exponent (e) is part of the public key used during encryption and signature verification. F4 = 2^16 + 1 = 65537 is the universal standard because: it's prime (required for RSA), it has only two set bits making encryption/verification very fast, and it's large enough to avoid certain low-exponent attacks. The tool always uses 65537. Custom exponents like 3 are dangerous (Bleichenbacher's attack); never use them.
- Why does my generated private key start with 'BEGIN PRIVATE KEY' instead of 'BEGIN RSA PRIVATE KEY'?
- Because the tool outputs PKCS#8 format (the modern standard), not PKCS#1 (the older format). Most current libraries accept both. To convert PKCS#8 to PKCS#1: `openssl rsa -in private.pem -traditional -out private-pkcs1.pem`. The OpenSSL `-traditional` flag forces the older PKCS#1 format.
- Can I use this for JWT signing with jose / jsonwebtoken?
- Yes — directly. Copy the private key (in PKCS#8 PEM) and use it with jsonwebtoken `jwt.sign(payload, privateKey, { algorithm: 'RS256' })` or jose `new SignJWT(payload).setProtectedHeader({alg: 'RS256'}).sign(privateKeyObject)`. Share the public key with services that need to verify. PyJWT and jose-jwt in Python accept the same format with `jwt.encode(payload, private_key, algorithm='RS256')`.
