SSL Certificate Check

Full TLS certificate health check using nothing but openssl. No signup required.

Prerequisites

• openssl 1.1.1 or newer on PATH (openssl version)

Trigger

• "Check the SSL cert on example.com"
• "When does my certificate expire?"
• "Is TLS 1.1 still enabled on my site?"
• "Verify my certificate chain is complete"

Workflow

Set HOST to the bare hostname (no scheme, no path). Every probe below is read-only.

1. Capture the handshake and full served chain once, then reuse the capture:

``bash openssl s_client -connect "$HOST:443" -servername "$HOST" -showcerts </dev/null >/tmp/tls-probe.txt 2>&1 openssl x509 -in /tmp/tls-probe.txt -noout -subject -issuer -enddate ` (openssl x509` parses the first PEM block — the leaf certificate.)

1. Expiry. Report the notAfter date, then bucket it with -checkend (exit 0 = still valid at that horizon):

``bash openssl x509 -in /tmp/tls-probe.txt -noout -checkend $((3086400)); echo "30d exit=$?" openssl x509 -in /tmp/tls-probe.txt -noout -checkend $((786400)); echo "7d exit=$?" `` Grade: both exit 0 → OK (>30 days). Only the 7-day probe exits 0 → WARN (8–30 days). 7-day probe exits 1 → CRITICAL (<7 days or already expired).

1. Chain completeness. From the same capture:

``bash grep -c 'BEGIN CERTIFICATE' /tmp/tls-probe.txt grep 'Verify return code' /tmp/tls-probe.txt ` Verify return code: 0 (ok)` = chain verifies. Code 20/21 ("unable to get local issuer certificate") with only 1 certificate served = server is not sending intermediates — strict clients (curl, Java, some mobile stacks) will fail even though browsers with AIA-chasing succeed. Grade CRITICAL.

1. Protocol support. TLS 1.0/1.1 are formally deprecated by RFC 8996; the deprecated probe must FAIL and modern ones must succeed:

``bash openssl sclient -connect "$HOST:443" -servername "$HOST" -tls11 </dev/null >/dev/null 2>&1; echo "tls1.1 exit=$?" openssl sclient -connect "$HOST:443" -servername "$HOST" -tls12 </dev/null >/dev/null 2>&1; echo "tls1.2 exit=$?" openssl sclient -connect "$HOST:443" -servername "$HOST" -tls13 </dev/null >/dev/null 2>&1; echo "tls1.3 exit=$?" `` Expected: tls1.1 nonzero (server refuses), tls1.2 and tls1.3 exit 0. Honesty check: if the tls1.1 probe errors with "no protocols available", your local OpenSSL was built without TLS 1.1 — report that leg as untestable, not as a pass.

1. Key size and signature algorithm:

``bash openssl x509 -in /tmp/tls-probe.txt -noout -text >/tmp/tls-cert.txt grep -E 'Public-Key|Signature Algorithm' /tmp/tls-cert.txt ` RSA must be ≥ 2048 bits, EC ≥ 256 bits (CA/Browser Forum Baseline Requirements). Signature must be SHA-256 family or better — any sha1With...` is CRITICAL.

1. SAN / hostname match:

``bash openssl x509 -in /tmp/tls-probe.txt -noout -ext subjectAltName ` $HOST must match a SAN dNSName entry; per RFC 6125 a wildcard (*.example.com`) matches exactly one label, and a CN-only match is rejected by modern clients. Mismatch = CRITICAL.

Report

## TLS Certificate Report: [host]

**Overall: [OK | WARN | CRITICAL]** — worst finding wins

| Check              | Result                          | Grade    |
|--------------------|---------------------------------|----------|
| Expiry             | notAfter [date] ([~N] days)     | OK/WARN/CRITICAL |
| Chain              | [N] certs served, verify=[code] | OK/CRITICAL |
| TLS 1.1 (RFC 8996) | [refused / ACCEPTED / untestable] | OK/CRITICAL/N-A |
| TLS 1.2 / 1.3      | [ok / missing]                  | OK/WARN  |
| Key & signature    | [RSA 2048, SHA-256]             | OK/CRITICAL |
| SAN match          | [host ∈ SANs? per RFC 6125]     | OK/CRITICAL |

### Findings
1. [CRITICAL/WARN] [finding] — [evidence line from openssl output] — [what breaks and for whom]

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