SSL routines:tls_post_process_client_hello:no shared cipher

openssl s_server (OpenSSL 3.x) logs "error:0A0000C1:SSL routines:tls_post_process_client_hello:no shared cipher:<source>"; nginx logs "SSL_do_handshake() failed (SSL: error:0A0000C1:SSL routines::no shared cipher) while SSL handshaking" at info level, so it is invisible with the default error_log level. OpenSSL 1.1.1 used code 1417A0C1.

OpenSSL (server side: nginx, Apache, Postfix, openssl s_server) — SSL_R_NO_SHARED_CIPHER

What it means

This is the server's view of a failed handshake: none of the cipher suites in the client's ClientHello is both enabled on the server and usable with the server's certificate key. The server then sends handshake_failure (alert 40) to the client. It appears in server logs, not in client output.

Why it happens

• The cipher list does not fit the certificate's key type

  common

  An ECDSA certificate with only ECDHE-RSA-* suites enabled (or an RSA certificate with only ECDHE-ECDSA-*) leaves no usable TLS 1.2 suite, so every TLS 1.2 client fails.

• A hand-trimmed cipher list excludes real clients

  common

  Lists reduced to one or two suites, or to CHACHA20 only, lock out clients (and monitoring tools) that prefer other modern suites.

• Very old clients

  occasional

  Clients limited to RSA key exchange, CBC or 3DES suites (old Java, embedded devices) cannot connect to a modern configuration; decide deliberately whether to support them.

How to fix it

1. 1.

   Check the certificate key against the suites

   ECDHE-ECDSA-* suites need an ECDSA certificate, ECDHE-RSA-* an RSA one; servers with both certificates can list both families.

   # ECDSA key + only ECDHE-RSA suites (or the reverse) leaves nothing usable
   openssl x509 -in server.pem -noout -text | grep 'Public Key Algorithm'
   openssl ciphers -v 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256'

2. 2.

   List the suites the server really accepts

   Enumerate them from outside and compare with the clients you need to support.

   # Which TLS 1.2 suites does the server accept? (nmap needed)
   nmap --script ssl-enum-ciphers -p 443 api.example.com

3. 3.

   Use a well-tested suite list

   Start from a generated modern or intermediate configuration rather than trimming lists by hand.

   # nginx: suites for both RSA and ECDSA certificates, TLS 1.3 enabled
   ssl_protocols TLSv1.2 TLSv1.3;
   ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;

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