Defaults.Exposed › October 2026 census › v10 registry › Signature algorithm
Signature algorithm
Methodology v10 · canonical ID cert-signature-algorithm · TLS (Transport Layer Security) & Certificates · scored
Uses a modern, unbroken signing algorithm (not legacy SHA-1).
Signature algorithm: definition
| Canonical ID | cert-signature-algorithm |
|---|---|
| Category | TLS & Certificates |
| Grade impact | Scored, counts toward the grade |
| Pass | The certificate is signed with a modern algorithm (SHA-256 family or better). |
| Fail | The certificate is signed with a deprecated algorithm such as SHA-1 or MD5. |
| Example (passing) | Signature Algorithm: sha256WithRSAEncryption |
Signature algorithm across the census
99.6% of domains whose certificate signature algorithm could be read are signed with a modern algorithm (SHA-256 family or better) (219,443,279 of 220,271,759, as of October 12, 2026).
Legacy signatures (SHA-1, MD5) are effectively extinct on the public web; the small remainder is dominated by long-lived private and appliance certificates.
Aggregates only: never an individual domain's result.
How this check is scored
Signature algorithm is one of the 24 scored checks in methodology v10. It carries points toward the grade, and a pass earns them. When the result cannot be determined for a domain (a timeout, a SERVFAIL, a redacted source), the check returns N/A and drops out of that domain's scoring denominator. A result that could not be determined is never counted as a fail; a determined absence is.
In the October 2026 census, 112,220,560 of the 332,492,319 graded domains had no determinable result for this check: the signature algorithm has to be read from a presented certificate, so domains without one are outside its base.
Every outcome in the census
| Outcome | Domains | Share of domains whose certificate signature algorithm could be read | In the headline figure |
|---|---|---|---|
| SHA-256 family or better | 219,443,279 | 99.6% | Yes |
| Legacy signature (such as SHA-1 or MD5) | 828,480 | 0.38% | No |
Source: the October 2026 census rollup, deduplicated per domain, as of October 12, 2026.
Against the other checks
Among the 6 TLS & Certificates checks with a published figure, Signature algorithm has the 3rd highest pass share. Next above it is Key strength: 99.9% of domains whose certificate key could be read. Next below it is Certificate expiry: 95.8% of domains whose certificate expiry date could be read. Across every check with a published figure it ranks 3rd of 24 .
Each share is measured on the check's own base, named on its page, so the ranking compares rates across different sets of domains.
Fix it
Plain-English impact, cost of ignoring it, and step-by-step remediation: How to fix TLS certificate health
Cite this check
Defaults.Exposed, "Signature algorithm (cert-signature-algorithm)", Grading Methodology v10 (census as of October 12, 2026). https://defaults.exposed/methodology/cert-signature-algorithm
Permalink: https://defaults.exposed/methodology/cert-signature-algorithm ·
All 33 checks: v10 registry ·
Machine-readable: /methodology/checks.json ·
Licence: open data