Certificate Key Is Smaller Than Recommended Size

Issue type: Certificate Key Is Smaller Than Recommended Size

Key:  insecure_server_certificate_key_size 

Factor: Application Security 

Severity: Low

What this finding means

SecurityScorecard flags this issue when a domain's SSL/TLS certificate is presenting a public key that is smaller than the recommended size for its key type.

Every certificate contains a public key, which is paired with a private key that stays secret on the server. The public key (inside the certificate) is what's sent to browsers during the TLS handshake, and it's what a scanner . including SecurityScorecard's - actually reads and measures; the private key is never transmitted and isn't visible externally. Since a key pair's public and private halves are always generated at the same size, a small public key size means the whole key pair, including the private half, is undersized. If that key size is too small, the encryption it enables is weaker than it should be.

Note on terminology: you may see this referred to elsewhere (including in some SecurityScorecard documentation) as a "private key" issue. Strictly speaking, the size being measured is the public key size embedded in the certificate - but since the public and private keys in a pair are always the same size, the underlying risk (a weak key pair) is the same either way.

Why a small key is a risk: a smaller key size means less computational complexity behind the encryption, which makes it comparatively easier for an attacker to break or guess the key through cryptographic attacks. That in turn raises the risk of an attacker intercepting or decrypting traffic that was meant to be confidential, undermining the confidentiality and integrity of the data exchanged over that connection.

Recommended remediation

• Reissue the certificate with a key size that meets current minimum standards for its key type (see the update below for current thresholds).
• Ensure the site enforces HTTPS across all pages and redirects HTTP traffic automatically.
• Apply a Content Security Policy (CSP) to prevent resources from loading over insecure origins.
• Periodically audit certificates across your domains/subdomains so weak keys are caught before they age into findings.

🔔 Update: EC (Elliptic Curve) key evaluation change - effective 2026-07-23

Starting with the 2026-07-23 scoring date, SecurityScorecard's evaluation logic for this issue type was corrected for EC (Elliptic Curve) keys:

• EC keys ≥ 256 bits will no longer be flagged. Previously, some EC keys were being held to the same minimum length expectations as RSA keys, which was not the correct comparison - EC cryptography achieves equivalent strength at much shorter key lengths than RSA.
• RSA key requirements are unchanged. RSA keys still need to meet the longer minimum key length that has always applied to that key type (e.g., 2048-bit or greater).

In short: if a domain was flagged for this issue solely because it presented an EC certificate with a key size of 256 bits or more, that finding should no longer appear as of the 2026-07-23 scoring run. RSA-based findings are not affected by this change. Existing finding will decay automatically with reason "Accuracy Improvement". There are no further actions to take.

Self-test: check your certificate's key type and size

You can verify which key type and size your server's certificate is presenting (i.e., the public key size, which reflects the size of the underlying key pair), and confirm whether the finding should still apply, using either of the methods below.

Option 1 — OpenSSL (command line)

# Replace example.com:443 with your domain and port
echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -text | grep -A1 "Public Key Algorithm"

Look at the output:

• If it shows id-ecPublicKey (EC/ECDSA) and the key size shown (e.g., under "Public-Key:") is ≥ 256 bits, this finding should not apply to you after 2026-07-23.
• If it shows rsaEncryption (RSA), the standard RSA minimum key length still applies (generally 2048 bits or greater required) — this update does not change RSA evaluation.

Option 2 — Browser certificate viewer

1. Visit your site over HTTPS in a browser.
2. Click the padlock icon → "Certificate" (or "Connection is secure" → "Certificate is valid").
3. Look for the certificate's Public Key Info:
   • Algorithm: shows either Elliptic Curve (or a named curve like secp256r1/prime256v1) or RSA.
   • Key Size: shown in bits.

Cross-reference against the rule above: EC + ≥256 bits = should not be flagged; RSA = existing minimum key length requirement still applies.