TLS handshake failed means the client and server couldn’t establish a TLS connection. The handshake failed at one of: protocol negotiation, cipher selection, certificate verification, or hostname matching. The team that uses Sectigo’s troubleshooting guide and checks the seven common causes resolves 95% of these in minutes.
Table of contents
- The handshake steps
- Cause 1: expired certificate
- Cause 2: TLS version mismatch
- Cause 3: cipher suite mismatch
- Cause 4: missing intermediate cert
- Cause 5: hostname mismatch
- Cause 6: clock skew
- Cause 7: firewall / DPI
- Debugging with openssl
- FAQ
The handshake steps
TLS handshake has 4 steps that can fail:
- ClientHello / ServerHello: protocol version (TLS 1.2 vs 1.3) and cipher suite.
- Server certificate: chain validation, expiry, hostname.
- Key exchange: client key share, server key share.
- Finished: both sides verify the handshake.
The team that has verbose error messages from openssl s_client or browser dev tools finds the failing step.
Cause 1: expired certificate
The cert has passed its expiry date:
# Check cert expiry
openssl s_client -connect example.com:443 -servername example.com < /dev/null 2>/dev/null | openssl x509 -noout -datesThe team that sees notAfter in the past has an expired cert. Fix: renew.
Cause 2: TLS version mismatch
Server only supports TLS 1.0/1.1, client only supports TLS 1.2/1.3:
# Test specific TLS version
openssl s_client -connect example.com:443 -tls1_2
openssl s_client -connect example.com:443 -tls1_3The team that sees handshake failure only with old TLS versions has server-side protocol mismatch. Fix: enable modern TLS on server.
Cause 3: cipher suite mismatch
Client and server have no common cipher:
# See offered ciphers
openssl s_client -connect example.com:443 -cipher 'ALL'The team that has a strict cipher config (e.g., only AEAD ciphers) and an old client has mismatch. Fix: relax server config or upgrade client.
Cause 4: missing intermediate cert
Server presents leaf cert but not the intermediate. Client can’t verify chain:
# Verify chain
openssl s_client -connect example.com:443 -showcerts
# Look for "verify return code"The team that sees unable to get local issuer certificate has missing intermediate. Fix: install full chain on server.
Cause 5: hostname mismatch
Cert is for example.com but client connected to www.example.com:
openssl s_client -connect www.example.com:443 -servername www.example.com
# Look for "verify return code: 62" (hostname mismatch)The team that uses the wrong hostname or has a cert without both names has mismatch. Fix: SAN with both hostnames.
Cause 6: clock skew
Client or server clock is wrong:
date
# Check on both sidesThe team that has a clock 5+ minutes off has handshake failure on cert validation. Fix: NTP.
Cause 7: firewall / DPI
Corporate firewall or middlebox intercepts TLS and breaks handshake:
# Test from outside (different network)
curl -v https://example.com/The team that sees the failure only on certain networks has a middlebox. Fix: try from unrestricted network.
Debugging with openssl
Verbose:
openssl s_client -connect example.com:443 -servername example.com -debug -msgThe team that uses -debug -msg sees the handshake messages.
FAQ
What’s the difference between ‘handshake failed’ and ‘connection refused’?
Connection refused = TCP couldn’t connect (service down, firewall). Handshake failed = TCP connected but TLS failed (cert, cipher, version issue).
Why does the browser work but curl doesn’t?
Browser has a different TLS library and certificate store than curl. The team that uses openssl s_client (which uses the system OpenSSL) for testing has more accurate diagnosis.
Is the cert self-signed?
openssl s_client ... | openssl x509 -noout -issuer -subject shows the issuer. If issuer = subject, it’s self-signed.
Can I disable TLS verification for testing?
Yes - curl -k or wget --no-check-certificate. NEVER use in production. The team that tests with -k verifies the cert is the problem; then fixes the actual cert.
How long does a TLS handshake take?
1 round trip on modern networks (~50-100ms). TLS 1.3 is 1-RTT (vs TLS 1.2’s 2-RTT). Resumption is 0-RTT or 1-RTT.
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