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RSA Key Strength Analyzer

Analyze RSA key strength and security

About RSA Key Strength Analyzer

Our free RSA Key Strength Analyzer examines RSA certificate keys for size adequacy, weak key detection, and NIST SP 800-57 compliance. Verifies RSA key sizes including 1024-bit, 2048-bit, and 4096-bit keys and provides security recommendations based on current cryptographic standards.

How to Use

  1. Enter the domain name whose RSA certificate key you want to analyze
  2. Click "Run" to fetch and analyze the RSA key parameters
  3. Review the key size, strength rating, and compliance recommendations

Use Cases

  • •Key strength auditing to ensure minimum 2048-bit RSA keys are used
  • •NIST SP 800-57 compliance checking for government and regulated industries
  • •Certificate lifecycle management to plan key rotation schedules

Frequently Asked Questions

NIST recommends 2048-bit RSA keys as the minimum for secure deployments through 2030. 4096-bit keys provide additional security margin but require more computational resources. 1024-bit keys are considered weak and should be replaced immediately.
Our analyzer checks for common weak key patterns including keys smaller than 2048 bits, keys generated with flawed random number generators, and keys with known vulnerabilities like ROCA. Enter your domain and the scanner will flag any issues found.
NIST recommends planning for migration to post-quantum cryptography by 2030. For now, 2048-bit RSA remains secure for most applications, but organizations should monitor quantum computing developments and prepare for eventual cryptographic transitions.
It is the accepted floor and it will hold for the foreseeable future. Facturing at that size is beyond reach, so the practical answer is yes. The nuance is margin: 2048 bits works with roughly the security equivalent of a 112-bit symmetric cipher, which is fine today and below where long-lived data should aim. For certificates that must stay valid for years, that distinction starts to matter.
Usually not. A P-256 curve key is comparable to a 3072-bit RSA key in strength while being far smaller, and 4096-bit RSA costs additional bandwidth in every handshake for security headroom nobody needs in practice. Moving to a curve-based certificate is the better trade unless a specific compliance profile demands RSA and forbids curves.
Because the certificate it connected to holds an elliptic-curve or Ed25519 key. That is not a fault — it is the modern default for many large providers. The page refuses to grade a curve key on an RSA scale, since comparing its 256 bits against RSA thresholds would produce a misleading insecure verdict. Use the ECDSA or Ed25519 page for curve keys.
Marginally, and measurably at the top end. A 4096-bit RSA public key is roughly 512 bytes against 294 for 2048 bits, added to every full handshake without session resumption. After the initial connection the difference is negligible, but on high-traffic sites serving mostly cache misses it is real, and it is another argument for curve keys over very large RSA.
Only if the key type confirms it — which is exactly what this page now checks rather than assuming. A site serving an EC key can display a bit count that means something quite different. If the certificate details show an elliptic-curve algorithm, trust the dedicated curve pages for grading and treat the RSA scale as inapplicable.

How the Verdict Is Reached

Retrieve the certificate, read the public key, and grade its size against the thresholds that matter for RSA in TLS today.

  1. 1Confirm the key really is RSA. An earlier version of this page reported key type as RSA unconditionally, so a site serving an elliptic-curve certificate was graded on an RSA scale it does not belong to. Non-RSA certificates are now named as such and pointed at the dedicated curve pages.
  2. 2Grade the size: below 2048 bits is insecure and the recommendation is to move immediately; 2048 to 4095 is good, with 4096 offered as headroom for long-lived certificates; 4096 and above is excellent.
  3. 3Report the measured bits read from the parsed key, alongside the grade and any recommendation. A certificate that could not be retrieved returns an explicit unknown rather than a zero-bit certificate pretending to be a measurement.

One caveat worth carrying into any decision: 2048-bit RSA is the accepted floor, not a comfortable target. Advancing to a curve-based key is the cheaper path to margin than 4096 bits, which costs handshake bandwidth on every connection without much practical gain.

Tips & Best Practices

  • •Use RSA keys of at least 2048 bits for security
  • •Consider RSA 4096-bit keys for high-security applications
  • •RSA 1024-bit keys are insecure and must be replaced
  • •Monitor RSA key strength across your certificate infrastructure

Technical Details

Algorithm: RSA key strength and security analysis
Size: 1024, 2048, 3072, 4096-bit key comparison
Performance: RSA key size impact on performance
Output: RSA strength assessment with recommendations

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