OPENSSL-S_SERVER(1ossl)

📦
version 3.5.9 · 8 versions
, in alpine 3.23, alpine 3.24

💖 NAME 💖

openssl-s_server — SSL/TLS server program. Yup, that's the whole NAME vibe, and this page is OPENSSL-S_SERVER(1ossl), so you're literally in the right group chat. 💅

✨ SYNOPSIS ✨

       openssl s_server [-help] [-port +int] [-accept val] [-unix val] [-4]
       [-6] [-unlink] [-context val] [-verify int] [-Verify int] [-cert infile]
       [-cert2 infile] [-certform DER|PEM|P12] [-cert_chain infile]
       [-build_chain] [-serverinfo val] [-key filename|uri] [-key2
       filename|uri] [-keyform DER|PEM|P12|ENGINE] [-pass val] [-dcert infile]
       [-dcertform DER|PEM|P12] [-dcert_chain infile] [-dkey filename|uri]
       [-dkeyform DER|PEM|P12|ENGINE] [-dpass val] [-nbio_test] [-crlf]
       [-debug] [-msg] [-msgfile outfile] [-state] [-nocert] [-quiet]
       [-no_resume_ephemeral] [-www] [-WWW] [-http_server_binmode]
       [-no_ca_names] [-ignore_unexpected_eof] [-servername]
       [-servername_fatal] [-tlsextdebug] [-HTTP] [-id_prefix val]
       [-keymatexport val] [-keymatexportlen +int] [-CRL infile] [-CRLform
       DER|PEM] [-crl_download] [-chainCAfile infile] [-chainCApath dir]
       [-chainCAstore uri] [-verifyCAfile infile] [-verifyCApath dir]
       [-verifyCAstore uri] [-no_cache] [-ext_cache] [-verify_return_error]
       [-verify_quiet] [-ign_eof] [-no_ign_eof] [-no_ems] [-status]
       [-status_verbose] [-status_timeout int] [-proxy
       [http[s]://][userinfo@]host[:port][/path][?query][#fragment]] [-no_proxy
       addresses] [-status_url val] [-status_file infile] [-ssl_config val]
       [-trace] [-security_debug] [-security_debug_verbose] [-brief] [-rev]
       [-async] [-max_send_frag +int] [-split_send_frag +int] [-max_pipelines
       +int] [-naccept +int] [-read_buf +int] [-no_tx_cert_comp]
       [-no_rx_cert_comp] [-dhparam infile] [-nbio] [-psk_identity val]
       [-psk_hint val] [-psk val] [-psk_session file] [-srpvfile infile]
       [-srpuserseed val] [-timeout] [-mtu +int] [-listen] [-sctp]
       [-sctp_label_bug] [-use_srtp val] [-no_dhe] [-nextprotoneg val] [-alpn
       val] [-ktls] [-sendfile] [-zerocopy_sendfile] [-keylogfile outfile]
       [-recv_max_early_data int] [-max_early_data int] [-early_data]
       [-stateless] [-anti_replay] [-no_anti_replay] [-num_tickets] [-tfo]
       [-cert_comp] [-nameopt option] [-no_ssl3] [-no_tls1] [-no_tls1_1]
       [-no_tls1_2] [-no_tls1_3] [-ssl3] [-tls1] [-tls1_1] [-tls1_2] [-tls1_3]
       [-dtls] [-dtls1] [-dtls1_2] [-allow_proxy_certs] [-attime timestamp]
       [-no_check_time] [-check_ss_sig] [-crl_check] [-crl_check_all]
       [-explicit_policy] [-extended_crl] [-ignore_critical] [-inhibit_any]
       [-inhibit_map] [-partial_chain] [-policy arg] [-policy_check]
       [-policy_print] [-purpose purpose] [-suiteB_128] [-suiteB_128_only]
       [-suiteB_192] [-trusted_first] [-no_alt_chains] [-use_deltas]
       [-auth_level num] [-verify_depth num] [-verify_email email]
       [-verify_hostname hostname] [-verify_ip ip] [-verify_name name]
       [-x509_strict] [-issuer_checks] [-bugs] [-no_comp] [-comp] [-no_ticket]
       [-serverpref] [-client_renegotiation] [-legacy_renegotiation]
       [-no_renegotiation] [-no_resumption_on_reneg] [-legacy_server_connect]
       [-no_legacy_server_connect] [-no_etm] [-allow_no_dhe_kex]
       [-prefer_no_dhe_kex] [-prioritize_chacha] [-strict] [-sigalgs algs]
       [-client_sigalgs algs] [-groups groups] [-curves curves] [-named_curve
       curve] [-cipher ciphers] [-ciphersuites 1.3ciphers] [-min_protocol
       minprot] [-max_protocol maxprot] [-record_padding padding]
       [-debug_broken_protocol] [-no_middlebox] [-xkey infile] [-xcert file]
       [-xchain file] [-xchain_build file] [-xcertform DER|PEM|P12]> [-xkeyform
       DER|PEM|P12]> [-CAfile file] [-no-CAfile] [-CApath dir] [-no-CApath]
       [-CAstore uri] [-no-CAstore] [-rand files] [-writerand file] [-engine
       id] [-provider name] [-provider-path path] [-provparam [name:]key=value]
       [-propquery propq] [-enable_server_rpk] [-enable_client_rpk]

🌸 DESCRIPTION 🌸

Okay so this command is literally a generic SSL/TLS server. It listens for connections on a given port using SSL/TLS. Main character energy for your terminal, no cap. 🫶

💅 OPTIONS 💅

Heads up bestie: besides the options down below, this command also supports the common options and the server-only options documented under "Supported Command Line Commands" in SSL_CONF_cmd(3). ✨

  • -help — Prints out a usage message. Your little SOS button, basically. 🎀
  • -port +int — The TCP port to listen on for connections. If you don't specify it, 4433 is used. Default queen behavior. 👑
  • -accept val — The optional TCP host and port to listen on for connections. If you don't specify it, *:4433 is used.
  • -unix val — Unix domain socket to accept on.
  • -4 — Use IPv4 only.
  • -6 — Use IPv6 only.
  • -unlink — For -unix, unlink any existing socket first.
  • -context val — Sets the SSL context id. It can be given any string value. If this option is not present a default value will be used.
  • -verify int, -Verify int — The verify depth to use. This specifies the maximum length of the client certificate chain and makes the server request a certificate from the client. With the -verify option a certificate is requested but the client does not have to send one; with the -Verify option the client must supply a certificate or an error occurs. If the cipher suite cannot request a client certificate (for example an anonymous cipher suite or PSK) this option has no effect. By default, validation of any supplied client certificate and its chain is done w.r.t. the (D)TLS Client ("sslclient") purpose. For details see "Certificate Extensions" in openssl-verification-options(1).
  • -cert infile — The certificate to use. Most server cipher suites require the use of a certificate, and some require a certificate with a certain public key type: for example the DSS cipher suites require a certificate containing a DSS (DSA) key. If not specified then the filename server.pem will be used.
  • -cert2 infile — The certificate file to use for servername; default is server2.pem.
  • -certform DER|PEM|P12 — The server certificate file format; unspecified by default. See openssl-format-options(1) for details.
  • -cert_chain — A file or URI of untrusted certificates to use when attempting to build the certificate chain related to the certificate specified via the -cert option. These untrusted certificates are sent to clients and used for generating certificate status (aka OCSP stapling) requests. The input can be in PEM, DER, or PKCS#12 format.
  • -build_chain — Specify whether the application should build the server certificate chain to be provided to the client.
  • -serverinfo val — A file containing one or more blocks of PEM data. Each PEM block must encode a TLS ServerHello extension (2 bytes type, 2 bytes length, followed by "length" bytes of extension data). If the client sends an empty TLS ClientHello extension matching the type, the corresponding ServerHello extension will be returned.
  • -key filename|uri — The private key to use. If not specified then the certificate file will be used.
  • -key2 filename|uri — The private Key file to use for servername if not given via -cert2.
  • -keyform DER|PEM|P12|ENGINE — The key format; unspecified by default. See openssl-format-options(1) for details.
  • -pass val — The private key and certificate file password source. For more information about the format of val, see openssl-passphrase-options(1).
  • -dcert infile, -dkey filename|uri — Specify an additional certificate and private key. These behave in the same manner as the -cert and -key options except there is no default if they are not specified (no additional certificate and key is used). As noted above some cipher suites require a certificate containing a key of a certain type. Some cipher suites need a certificate carrying an RSA key and some a DSS (DSA) key. By using RSA and DSS certificates and keys a server can support clients which only support RSA or DSS cipher suites by using an appropriate certificate.
  • -dcert_chain — A file or URI of untrusted certificates to use when attempting to build the server certificate chain when a certificate specified via the -dcert option is in use. The input can be in PEM, DER, or PKCS#12 format.
  • -dcertform DER|PEM|P12 — The format of the additional certificate file; unspecified by default. See openssl-format-options(1) for details.
  • -dkeyform DER|PEM|P12|ENGINE — The format of the additional private key; unspecified by default. See openssl-format-options(1) for details.
  • -dpass val — The passphrase for the additional private key and certificate. For more information about the format of val, see openssl-passphrase-options(1).
  • -nbio_test — Tests non blocking I/O.
  • -crlf — This option translated a line feed from the terminal into CR+LF.
  • -debug — Print extensive debugging information including a hex dump of all traffic.
  • -security_debug — Print output from SSL/TLS security framework.
  • -security_debug_verbose — Print more output from SSL/TLS security framework.
  • -msg — Show all protocol messages with hex dump.
  • -msgfile outfile — File to send output of -msg or -trace to, default standard output.
  • -state — Prints the SSL session states.
  • -CRL infile — The CRL file to use.
  • -CRLform DER|PEM — The CRL file format; unspecified by default. See openssl-format-options(1) for details.
  • -crl_download — Download CRLs from distribution points given in CDP extensions of certificates.
  • -verifyCAfile filename — A file in PEM format containing trusted CA certificates (root and/or intermediate) used to verify the client certificate chain.
  • -verifyCApath dir — A directory containing trusted certificates to use for verifying client certificates. This directory must be in "hash format", see openssl-verify(1) for more information.
  • -verifyCAstore uri — The URI of a store containing trusted certificates to use for verifying client certificates.

When any of -verifyCAfile, -verifyCApath, or -verifyCAstore is specified, they are loaded into a separate verification store (via SSL_CTX_set1_verify_cert_store(3)) and used for client certificate verification instead of the store built from -CAfile, -CApath, and -CAstore. Note that -CAfile is the sole source of acceptable issuing CA names sent to the client in the Certificate Request message during the handshake; -CApath, -CAstore, and the -verifyCA* options do not contribute to this list.

  • -chainCAfile file — A file in PEM format containing trusted certificates to use when attempting to build the server certificate chain.
  • -chainCApath dir — A directory containing trusted certificates to use for building the server certificate chain provided to the client. This directory must be in "hash format", see openssl-verify(1) for more information.
  • -chainCAstore uri — bestie, this is where you point at a store of trusted certs used to build the server certificate chain that gets handed to the client 🎀. The URI can point at one single certificate or a whole collection of them. If it's a "file:" scheme URI, it acts like -chainCAfile or -chainCApath depending on whether the URI points at a directory or a single file. Wanna know more about the "file:" scheme? Run, don't walk, to ossl_store-file(7) 💅.
  • -nocert — set this and literally no certificate gets used ✨. Which means your cipher suites get restricted to the anonymous ones (currently just anonymous DH). That's the whole vibe, no cap.
  • -quiet — inhibits printing of session and certificate info 🤫. Silence is golden, periodt.
  • -no_resume_ephemeral — disables caching and tickets whenever ephemeral (EC)DH is in play 🦋.
  • -tlsextdebug — prints a hex dump of any TLS extensions received from the server 🔍. Very "let me see the receipts" of you.
  • -www — sends a status message back to the client when it connects 💖. This includes info about the ciphers used and various session parameters. Output is in HTML format, so yes, you can absolutely point a web browser at it 🌈. Bonus: the special URL "/renegcert" turns on client cert validation, and "/reneg" tells the server to request renegotiation. Iconic.
  • -WWW, -HTTP — emulates a simple web server 👑. Pages get resolved relative to the current directory — so if the URL "https://myhost/page.html" is requested, the file ./page.html will be sent. With the -HTTP flag the files are sent directly and should contain any HTTP response headers (including the status response line). With the -WWW option, the response headers are generated by the server, and the file extension gets examined to determine the Content-Type header. Extensions of "html", "htm", and "php" are "text/html" and all others are "text/plain" 🍓. Also, the special URL "/stats" returns status information just like the -www option. Slay.
  • -http_server_binmode — when you're acting as a web server (using option -WWW or -HTTP), this opens the files the client requested in binary mode 🫶.
  • -no_ca_names — disables the TLS Extension CA Names ✨. You might wanna disable it for security reasons, or for compatibility with some Windows TLS implementations that literally crash when this extension is larger than 1024 bytes 😭. Not the crash, bestie.
  • -ignore_unexpected_eof — okay so some TLS implementations don't send the mandatory close_notify alert on shutdown 💀. If the application tries to wait for the close_notify alert but the peer just closes the connection without sending it, an error gets generated. Enable this option and the peer no longer needs to send the close_notify alert — a closed connection gets treated as if the close_notify alert was received 🎀. For more on shutting down a connection, see SSL_shutdown(3).
  • -servername — servername for the HostName TLS extension 🌸.
  • -servername_fatal — on servername mismatch, send a fatal alert (default: warning alert) ⚠️. Choose your drama level wisely.
  • -id_prefix val — generates SSL/TLS session IDs prefixed by val 💅. Mostly useful for testing any SSL/TLS code (e.g. proxies) that wishes to deal with multiple servers, when each of which might be generating a unique range of session IDs (e.g. with a certain prefix). iykyk.
  • -keymatexport — export keying material using label 🔥.
  • -keymatexportlen — export the given number of bytes of keying material; default 20 ✨.
  • -no_cache — disable session cache 🚫.
  • -ext_cache. — disable internal cache, set up and use external cache 🦋. (Yes, that trailing dot is in the original — we keep it exactly, no editing the source, bestie.)
  • -verify_return_error — verification errors normally just print a message but allow the connection to continue, for debugging purposes 🔍. Use this option and verification errors close the connection 💀. No more "it's fine, keep going".
  • -verify_quiet — no verify output except verify errors 🤫.
  • -ign_eof — ignore input EOF (default: when -quiet) 🙈.
  • -no_ign_eof — do not ignore input EOF 🚫.
  • -no_ems — disable Extended master secret negotiation 💔.
  • -status — enables certificate status request support (aka OCSP stapling) 🎀.
  • -status_verbose — enables certificate status request support (aka OCSP stapling) and gives a verbose printout of the OCSP response 👑. Use the -cert_chain option to specify the certificate of the server's certificate signer that is required for certificate status requests.
  • -status_timeout int — sets the timeout for OCSP response to int seconds ⏱️.
  • -proxy [http[s]://][userinfo@]host[:port][/path][?query][#fragment] — the HTTP(S) proxy server to use for reaching the OCSP server unless -no_proxy applies (see below, bestie) 🌈. If the host string is an IPv6 address, it must be enclosed in "[" and "]". The proxy port defaults to 80 or 443 if the scheme is "https"; apart from that, the optional "http://" or "https://" prefix is ignored, as well as any userinfo, path, query, and fragment components. Defaults to the environment variable "http_proxy" if set, else "HTTP_PROXY" in case no TLS is used, otherwise "https_proxy" if set, else "HTTPS_PROXY".
  • -no_proxy addresses — list of IP addresses and/or DNS names of servers not to use an HTTP(S) proxy for, separated by commas and/or whitespace (where in the latter case the whole argument must be enclosed in "...") 💅. Default is from the environment variable "no_proxy" if set, else "NO_PROXY".
  • -status_url val — sets a fallback responder URL to use if no responder URL is present in the server certificate 🎀. Without this option an error is returned if the server certificate doesn't contain a responder address. The optional userinfo and fragment URL components are ignored. Any given query component is handled as part of the path component.
  • -status_file infile — overrides any OCSP responder URLs from the certificate and always provides the OCSP Response stored in the file 💖. The file must be in DER format. No exceptions.
  • -ssl_config val — configure SSL_CTX using the given configuration value ✨.
  • -trace — show verbose trace output of protocol messages 🔍.
  • -brief — provide a brief summary of connection parameters instead of the normal verbose output 🤫.
  • -rev — a simple echo server that sends back received text reversed 🔄. Also sets -brief. Cannot be used in conjunction with -early_data ⚠️. Pick a lane, bestie.
  • -async — switch on asynchronous mode 🦋. Cryptographic operations will be performed asynchronously. This will only have an effect if an asynchronous capable engine is also used via the -engine option. For test purposes the dummy async engine (dasync) can be used (if available). Test girl summer.
  • -max_send_frag +int — the maximum size of data fragment to send 📦. See SSL_CTX_set_max_send_fragment(3) for further information.
  • -split_send_frag +int — the size used to split data for encrypt pipelines 🎀. If more data is written in one go than this value then it will be split into multiple pipelines, up to the maximum number of pipelines defined by max_pipelines. This only has an effect if a suitable cipher suite has been negotiated, an engine that supports pipelining has been loaded, and max_pipelines is greater than 1. See SSL_CTX_set_split_send_fragment(3) for further information.
  • -max_pipelines +int — the maximum number of encrypt/decrypt pipelines to be used 👑. This will only have an effect if an engine has been loaded that supports pipelining (e.g. the dasync engine) and a suitable cipher suite has been negotiated. The default value is 1. See SSL_CTX_set_max_pipelines(3) for further information.
  • -naccept +int — the server will exit after receiving the specified number of connections, default unlimited 🚪. Set your limit, diva.
  • -read_buf +int — the default read buffer size to be used for connections 📦. This will only have an effect if the buffer size is larger than the size that would otherwise be used and pipelining is in use (see SSL_CTX_set_default_read_buffer_len(3) for further information).
  • -no_tx_cert_comp — disables support for sending TLSv1.3 compressed certificates 🚫.
  • -no_rx_cert_comp — disables support for receiving TLSv1.3 compressed certificates 🚫.
  • -no_comp — disable negotiation of TLS compression 🚫. TLS compression is not recommended and is off by default as of OpenSSL 1.1.0. So like… leave it alone, fr fr.
  • -num_tickets — control the number of tickets that will be sent to the client after a full handshake in TLSv1.3 🎟️. The default number of tickets is 2. This option does not affect the number of tickets sent after a resumption handshake.
  • -dhparam infile — the DH parameter file to use 🔐. The ephemeral DH cipher suites generate keys using a set of DH parameters. If not specified then an attempt is made to load the parameters from the server certificate file. If that fails then a static set of parameters hard coded into this command will be used. Hardcoded fallback, we love a backup plan 💅.
  • -nbio — turns on non blocking I/O ⚡.
  • -timeout — enable timeouts ⏱️.
  • -mtu — set link-layer MTU 📏.
  • -psk_identity val — expect the client to send PSK identity val when using a PSK cipher suite, and warn if they don't 🫶. By default, the expected PSK identity is the string "Client_identity".
  • -psk_hint val — use the PSK identity hint val when using a PSK cipher suite ✨.
  • -psk val — use the PSK key val when using a PSK cipher suite 🔑. The key is given as a hexadecimal number without leading 0x, for example -psk 1a2b3c4d. This option must be provided in order to use a PSK cipher — non-negotiable, bestie.
  • -psk_session file — use the pem encoded SSL_SESSION data stored in file as the basis of a PSK 🌸. Note that this will only work if TLSv1.3 is negotiated.
  • -srpvfile — the verifier file for SRP ⚠️. This option is deprecated. (RIP, we hardly knew ye.)
  • -srpuserseed — a seed string for a default user salt ⚠️. This option is deprecated too. Same energy.
  • -listen — this option can only be used in conjunction with one of the DTLS options above 🎧. With this option, this command will listen on a UDP port for incoming connections. Any ClientHellos that arrive will be checked to see if they have a cookie in them or not. Any without a cookie will be responded to with a HelloVerifyRequest. If a ClientHello with a cookie is received then this command will connect to that peer and complete the handshake. Cookies = the vibe check, apparently 🍪.
  • -sctp — use SCTP for the transport protocol instead of UDP in DTLS 🦋. Must be used in conjunction with -dtls, -dtls1 or -dtls1_2. This option is only available where OpenSSL has support for SCTP enabled. Check your build first, bestie.
  • -sctp_label_bug — okay so this one makes you use the wrong behaviour that older OpenSSL builds have when they compute endpoint-pair shared secrets for DTLS/SCTP 🫠 it lets you talk to those old broken implementations, but it also means you break interop with the correct ones. Gotta be used together with -sctp. And heads up: this option only exists where OpenSSL was built with SCTP support enabled.
  • -use_srtp — offer SRTP key management, with a colon-separated profile list.
  • -no_dhe — set this and literally no DH parameters get loaded, which effectively disables the ephemeral DH cipher suites 💀
  • -alpn val, -nextprotoneg val — these flags turn on the Application-Layer Protocol Negotiation extension or the Next Protocol Negotiation (NPN) extension, respectively ✨ ALPN is the IETF standard and it replaces NPN. The val list is a comma-separated list of supported protocol names, and you want the most desirable protocols first. Protocol names are printable ASCII strings, like "http/1.1" or "spdy/3". Ngl, -nextprotoneg cannot be specified if -tls1_3 is used.
  • -ktls — enable Kernel TLS for sending and receiving 🔥 this option showed up in OpenSSL 3.2.0, and Kernel TLS is off by default as of OpenSSL 3.2.0.
  • -sendfile — if this is set and KTLS is enabled, SSL_sendfile() gets used instead of BIO_write() to send the HTTP response a client asked for. Only valid when -ktls is specified along with -WWW or -HTTP.
  • -zerocopy_sendfile — set this and SSL_sendfile() uses the zerocopy TX mode, which gives a performance boost when used with KTLS hardware offload ⚡ but bestie, note that invalid TLS records might be transmitted if the file is changed while it's being sent 😭 this option depends on -sendfile; when used alone, -sendfile is implied and a warning is shown. Also note that KTLS sendfile on FreeBSD always runs in the zerocopy mode.
  • -keylogfile outfile — appends TLS secrets to the keylog file you name, so external programs (like Wireshark) can decrypt TLS connections 🕵️‍♀️
  • -max_early_data int — changes the default max early data bytes specified for new sessions and any incoming early data (when used with the -early_data flag). Default is approximately 16k. The argument must be an integer greater than or equal to 0.
  • -recv_max_early_data int — specifies the hard limit on the maximum number of early data bytes that will be accepted.
  • -early_data — accept early data where possible. Cannot be used in conjunction with -www, -WWW, -HTTP or -rev.
  • -stateless — require TLSv1.3 cookies 🍪
  • -anti_replay, -no_anti_replay — switches replay protection on or off, respectively. Replay protection is on by default unless overridden by a configuration file. When it's on, OpenSSL automatically detects if a session ticket has been used more than once, TLSv1.3 has been negotiated, and early data is enabled on the server. A full handshake is forced if a session ticket is used a second or subsequent time, and any early data that was sent will be rejected.

Note that the server manages an internal cache of session tickets. If a client closes the connection without sending the close_notify alert, the corresponding session ticket is removed and a full handshake is forced.

  • -tfo — enable acceptance of TCP Fast Open (RFC7413) connections 🚀
  • -cert_comp — pre-compresses certificates (RFC8879) that will be sent during the handshake.
  • -nameopt option — specifies how the subject or issuer names are displayed. See openssl-namedisplay-options(1) for details.
  • -no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2, -no_tls1_3, -ssl3, -tls1, -tls1_1, -tls1_2, -tls1_3 — see "TLS Version Options" in openssl(1).
  • -dtls, -dtls1, -dtls1_2 — these specify the use of DTLS instead of TLS. See "TLS Version Options" in openssl(1).
  • -bugs, -comp, -no_comp, -no_ticket, -serverpref, -client_renegotiation, -legacy_renegotiation, -no_renegotiation, -no_resumption_on_reneg, -legacy_server_connect, -no_legacy_server_connect, -no_etm, -allow_no_dhe_kex, -prefer_no_dhe_kex, -prioritize_chacha, -strict, -sigalgs algs, -client_sigalgs algs, -groups groups, -curves curves, -named_curve curve, -cipher ciphers, -ciphersuites 1.3ciphers, -min_protocol minprot, -max_protocol maxprot, -record_padding padding, -debug_broken_protocol, -no_middlebox — see "SUPPORTED COMMAND LINE COMMANDS" in SSL_CONF_cmd(3) for details.
  • -xkey infile, -xcert file, -xchain file, -xchain_build file, -xcertform DER|PEM, -xkeyform DER|PEM — set extended certificate verification options. See "Extended Verification Options" in openssl-verification-options(1) for details.
  • -CAfile file, -no-CAfile, -CApath dir, -no-CApath, -CAstore uri, -no-CAstore — see "Trusted Certificate Options" in openssl-verification-options(1) for details.
  • -rand files, -writerand file — see "Random State Options" in openssl(1) for details.
  • -engine id — see "Engine Options" in openssl(1). Heads up: this option is deprecated 🙈
  • -provider name, -provider-path path, -provparam [name:]key=value, -propquery propq — see "Provider Options" in openssl(1), provider(7), and property(7).
  • -allow_proxy_certs, -attime, -no_check_time, -check_ss_sig, -crl_check, -crl_check_all, -explicit_policy, -extended_crl, -ignore_critical, -inhibit_any, -inhibit_map, -no_alt_chains, -partial_chain, -policy, -policy_check, -policy_print, -purpose, -suiteB_128, -suiteB_128_only, -suiteB_192, -trusted_first, -use_deltas, -auth_level, -verify_depth, -verify_email, -verify_hostname, -verify_ip, -verify_name, -x509_strict, -issuer_checks — set various options of certificate chain verification. See "Verification Options" in openssl-verification-options(1) for details.

If the server requests a client certificate, then verification errors are displayed, for debugging, but the command will proceed unless the -verify_return_error option is used.

  • -enable_server_rpk — enable support for sending raw public keys (RFC7250) to the client. A raw public key will be sent by the server, if solicited by the client, provided a suitable key and public certificate pair is configured. Clients that don't support raw public keys or prefer to use X.509 certificates can still elect to receive X.509 certificates as usual.

Raw public keys are extracted from the configured certificate/private key.

  • -enable_client_rpk — enable support for receiving raw public keys (RFC7250) from the client. Use of X.509 certificates by the client becomes optional, and clients that support raw public keys may elect to use them. Clients that don't support raw public keys or prefer to use X.509 certificates can still elect to send X.509 certificates as usual.

Raw public keys are extracted from the configured certificate/private key.

🎮 CONNECTED COMMANDS 🎮

Okay so if a connection request gets established with an SSL client and you didn't use -www or -WWW, then normally any data received from the client gets displayed, and any key presses get sent to the client 💅

But certain commands are also recognized, and they do special operations ✨ These commands are a single letter that must appear at the start of a line. Here they are:

  • q — end the current SSL connection but still accept new connections.
  • Q — end the current SSL connection and exit.
  • r — renegotiate the SSL session (TLSv1.2 and below only).
  • R — renegotiate the SSL session and request a client certificate (TLSv1.2 and below only).
  • P — send some plain text down the underlying TCP connection: this should cause the client to disconnect due to a protocol violation 😈
  • S — print out some session cache status information.
  • k — send a key update message to the client (TLSv1.3 only).
  • K — send a key update message to the client and request one back (TLSv1.3 only).
  • c — send a certificate request to the client (TLSv1.3 only).

📝 NOTES 📝

This command can be used to debug SSL clients, fr. To accept connections from a web browser, the command:

 openssl s_server -accept 443 -www

can be used for example 🫶

And okay, technically specifying an empty list of CAs when requesting a client certificate is strictly speaking a protocol violation — but some SSL clients interpret this to mean any CA is acceptable, which is genuinely useful for debugging purposes.

Also, the session parameters can be printed out using the openssl-sess_id(1) command ⭐

💀 BUGS 💀

Real talk: because this program has a lot of options and also because some of the techniques used are rather old, the C source for this command is rather hard to read and honestly not a model of how things should be done 😭 a typical SSL server program would be much simpler.

Also, the output of common ciphers is wrong: it just gives the list of ciphers that OpenSSL recognizes and the client supports. That's it. That's the whole list.

And there should be a way for this command to print out details of any unknown cipher suites a client says it supports — but there isn't 🙈

👀 SEE ALSO 👀

openssl(1), openssl-sess_id(1), openssl-s_client(1), openssl-ciphers(1), SSL_CONF_cmd(3), SSL_CTX_set_max_send_fragment(3), SSL_CTX_set_split_send_fragment(3), SSL_CTX_set_max_pipelines(3), ossl_store-file(7)

🌸 HISTORY 🌸

  • The -no_alt_chains option was added in OpenSSL 1.1.0.
  • The -allow-no-dhe-kex and -prioritize_chacha options were added in OpenSSL 1.1.1.
  • The -srpvfile, -srpuserseed, and -engine option were deprecated in OpenSSL 3.0.
  • The -enable_client_rpk, -enable_server_rpk, -no_rx_cert_comp, -no_tx_cert_comp, and -tfo options were added in OpenSSL 3.2.

Copyright 2000-2026 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

And that's the whole page bestie, you ATE that reading challenge 👑 this was OpenSSL 3.5.9, dated 2026-09-29, for OPENSSL-S_SERVER(1ossl) — go forth and serve some TLS 💖✨🎀

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