OPENSSL-S_SERVER(1ossl)

📦 version 3.5.0, in opensuse-leap 16.0

🎀 NAME 🎀

OPENSSL-S_SERVER(1ossl) — OpenSSL’s openssl-s_server(1ossl) / openssl s_server — SSL/TLS server program. Yes bestie, this is the page for the generic SSL/TLS server vibe. 💅

✨ SYNOPSIS ✨

okay so the whole command shape is literally this:

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]> [-xkeyform
DER|PEM]> [-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 🌸

This command implements a generic SSL/TLS server which listens for connections on a given port using SSL/TLS. That’s the whole main character energy of it, bestie: you point it at a port, and it’s ready to talk TLS. ✨

💖 OPTIONS 💖

In addition to the options below, this command also supports the common and server only options documented "Supported Command Line Commands" in SSL_CONF_cmd(3). 🫶

  • -help — Print out a usage message. Classic little helper icon. 💬
  • -port +int — The TCP port to listen on for connections. If not specified 4433 is used. 🎀
  • -accept val — The optional TCP host and port to listen on for connections. If not specified, *: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. Lowkey important. 💅
  • -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 servers 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 CA containing trusted certificates to use for verifying client certificates. 🫶
  • -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. 🌈
  • -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 — The URI of a store containing trusted certificates to use for building the server certificate chain provided to the client. The URI may indicate a single certificate, as well as a collection of them. With URIs in the "file:" scheme, this acts as -chainCAfile or -chainCApath, depending on if the URI indicates a directory or a single file. See ossl_store-file(7) for more information on the "file:" scheme. 💜

okay so, picking up right where we left off in the option buffet, bestie — no heading repeat, just vibes and flags 💅

  • -nocert — if this is set, no certificate gets used at all. That restricts the cipher suites available to the anonymous ones (currently just anonymous DH). lowkey niche but slay for testing.
  • -quiet — inhibits printing of session and certificate info. shhh ✨
  • -no_resume_ephemeral — disables caching and tickets if ephemeral (EC)DH is used. no cap, it just says no to resuming with ephemeral keys.
  • -tlsextdebug — prints a hex dump of any TLS extensions received from the server. it’s giving “look at the bytes, bestie” 🔍
  • -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 this option can be used with a web browser. the special URL "/renegcert" turns on client cert validation, and "/reneg" tells the server to request renegotiation. iconic little web moment 🌐
  • -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. if the -HTTP flag is used, the files are sent directly, and should contain any HTTP response headers (including the status response line). if the -WWW option is used, the response headers are generated by the server, and the file extension is examined to determine the Content-Type header. extensions of "html", "htm", and "php" are "text/html" and all others are "text/plain". in addition, the special URL "/stats" will return status information like the -www option. web server era fr fr 🫶
  • -http_server_binmode — when acting as web-server (using option -WWW or -HTTP), open files requested by the client in binary mode. bytes stay bytes 💾
  • -no_ca_names — disables TLS Extension CA Names. you may want to disable it for security reasons or for compatibility with some Windows TLS implementations crashing when this extension is larger than 1024 bytes. compatibility drama, but make it secure 🔒
  • -ignore_unexpected_eof — some TLS implementations do not send the mandatory close_notify alert on shutdown. if the application tries to wait for the close_notify alert but the peer closes the connection without sending it, an error is generated. when this option is enabled, the peer does not need to send the close_notify alert and a closed connection will be treated as if the close_notify alert was received. for more information on shutting down a connection, see SSL_shutdown(3). emotional support close_notify 😭
  • -servername — servername for the HostName TLS extension. name drop, but make it TLS ✨
  • -servername_fatal — on servername mismatch, send a fatal alert (default: warning alert). choose violence 💀
  • -id_prefix val — generate SSL/TLS session IDs prefixed by val. this is mostly useful for testing any SSL/TLS code (e.g. proxies) that wish to deal with multiple servers, when each of which might be generating a unique range of session IDs (e.g. with a certain prefix). idk, it’s giving organized chaos 🎀
  • -keymatexport — export keying material using label. key material, but make it export 🧚
  • -keymatexportlen — export the given number of bytes of keying material; default 20. twenty little bytes of main character energy ⭐
  • -no_cache — disables session cache. no hoarding, bestie 🙅
  • -ext_cache. — disable internal cache, set up and use external cache. external cache has entered the chat 🦋
  • -verify_return_error — verification errors normally just print a message but allow the connection to continue, for debugging purposes. if this option is used, then verification errors close the connection. ngl, that’s the strict bestie setting 🔥
  • -verify_quiet — no verify output except verify errors. quiet luxury, verification edition 💅
  • -ign_eof — ignore input EOF (default: when -quiet). don’t perceive the end of input, periodt.
  • -no_ign_eof — do not ignore input EOF. okay actually perceive it 🙈
  • -no_ems — disables Extended master secret negotiation. EMS said not today 🚫
  • -status — enables certificate status request support (aka OCSP stapling). staple that status, queen 👑
  • -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. verbose OCSP is a whole vibe 🔍
  • -status_timeout int — sets the timeout for OCSP response to int seconds. clock is ticking ⏳
  • -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. 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". proxy lore is real 🌈
  • -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". exempt list, but make it network-y 🫶
  • -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 does not 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. fallback URL said “i got you” ✨
  • -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. DER or didn’t happen 💾
  • -ssl_config val — configure SSL_CTX using the given configuration value. config time, bestie 🎀
  • -trace — show verbose trace output of protocol messages. lore dump, but for packets 🔍
  • -brief — provide a brief summary of connection parameters instead of the normal verbose output. concise queen 👑
  • -rev — simple echo server that sends back received text reversed. also sets -brief. cannot be used in conjunction with -early_data. reverse echo is lowkey iconic 🔁
  • -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). async era, if the engine says so ⚡
  • -max_send_frag +int — the maximum size of data fragment to send. see SSL_CTX_set_max_send_fragment(3) for further information. fragment size, but make it maximum 📦
  • -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. pipeline girlie behavior 🚀
  • -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. more pipelines, more drama 🌸
  • -naccept +int — the server will exit after receiving the specified number of connections, default unlimited. connection limit said “i’m leaving” 🚪
  • -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). buffer upgrade, slay 🦋
  • -no_tx_cert_comp — disables support for sending TLSv1.3 compressed certificates. no compressed certs leaving this server 🚫
  • -no_rx_cert_comp — disables support for receiving TLSv1.3 compressed certificates. no compressed certs coming in either 🙅
  • -no_comp — disable negotiation of TLS compression. TLS compression is not recommended and is off by default as of OpenSSL 1.1.0. this is a “please don’t” feature, bestie 🚨
  • -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. tickets, but make it TLSv1.3 🎟️
  • -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 this fails then a static set of parameters hard coded into this command will be used. DH param backup plan, fr fr 🔐
  • -nbio — turns on non blocking I/O. don’t block, don’t wait 💅
  • -timeout — enable timeouts. time is real ⏰
  • -mtu — set link-layer MTU. mtu said set the vibe 📏
  • -psk_identity val — expect the client to send PSK identity val when using a PSK cipher suite, and warn if they do not. by default, the expected PSK identity is the string "Client_identity". identity check, but make it PSK 🪪
  • -psk_hint val — use the PSK identity hint val when using a PSK cipher suite. hint dropped ✨
  • -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. no key, no PSK, periodt 🔑
  • -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. session file as PSK basis, iykyk 🧚
  • -srpvfile — the verifier file for SRP. this option is deprecated. old and deprecated, handle with care ⚠️
  • -srpuserseed — a seed string for a default user salt. this option is deprecated. also deprecated, bestie, don’t get attached 💀
  • -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. cookie check, then connect 🍪
  • -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. SCTP said transport glow-up 🌈
  • -sctp_label_bug — use the incorrect behaviour of older OpenSSL implementations when computing endpoint-pair shared secrets for DTLS/SCTP. this allows communication with older broken implementations but breaks interoperability with correct implementations. must be used in conjunction with -sctp. this option is only available where OpenSSL has support for SCTP enabled. bug compatibility is a choice, and it has consequences 😭
  • -use_srtp — offer SRTP key management with a colon-separated profile list. SRTP key management, slay 🎧
  • -no_dhe — set this and literally no DH params get loaded, which effectively kills off the ephemeral DH cipher suites. bye bestie 👋
  • -alpn val, -nextprotoneg val — these two turn on the Application-Layer Protocol Negotiation extension or the Next Protocol Negotiation (NPN) extension respectively. Heads up: ALPN is the IETF standard and it replaces NPN 💅. The val list is comma-separated protocol names, and you put the most desirable protocols first, queen behavior. Protocol names are printable ASCII strings, like "http/1.1" or "spdy/3". Oh and -nextprotoneg cannot be specified if -tls1_3 is used, no cap.
  • -ktls — enables Kernel TLS for sending and receiving ✨. This option was introduced 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 the client asked for. Only valid when -ktls is used along with -WWW or -HTTP, so don't try anything cute 🎀.
  • -zerocopy_sendfile — set this and SSL_sendfile() uses the zerocopy TX mode, which is a genuine performance boost when used with KTLS hardware offload 🔥. But bestie, careful: invalid TLS records might get 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, periodt.
  • -keylogfile outfile — appends TLS secrets to the keylog file you name, so outside programs (Wireshark, we see you 👀) can decrypt TLS connections.
  • -max_early_data int — changes the default max early data bytes set for new sessions and for any incoming early data (when used with the -early_data flag). The default value is approximately 16k. The argument must be an integer greater than or equal to 0, no negatives, nope.
  • -recv_max_early_data int — the hard limit on the maximum number of early data bytes that will be accepted. Hard limit means hard, bestie.
  • -early_data — accept early data where possible 🦋. Cannot be used with -www, -WWW, -HTTP or -rev. Pick a lane.
  • -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 config 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 gets forced if a session ticket is used a second or subsequent time, and any early data that was sent will be rejected. caught in 4k 🚨
  • -tfo — enable acceptance of TCP Fast Open (RFC7413) connections.
  • -cert_comp — pre-compresses certificates (RFC8879) that will be sent during the handshake. efficient queen 🌸
  • -nameopt option — specifies how subject or issuer names get displayed. See openssl-namedisplay-options(1) for the deets.
  • -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 using 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 the details, iykyk.
  • -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 the full rundown.
  • -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). This option is deprecated, so like… don't 💀.
  • -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. so it's giving "we saw the red flag but we kept walking" 🚩

  • -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 the client solicits it, provided a suitable key and public certificate pair is configured. Clients that don't support raw public keys, or that prefer 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 that prefer 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 neither the -www nor the -WWW option has been used, then normally any data received from the client is displayed and any key presses get sent to the client. it's a whole vibe, very chatty 💬

Certain commands are also recognized which perform special operations. These commands are a letter which must appear at the start of a line. They are listed below 👇

  • q — end the current SSL connection but still accept new connections.
  • Q — end the current SSL connection and exit. bye bestie 😭
  • 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. chaos 💀
  • 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 💅. To accept connections from a web browser, the command:

openssl s_server -accept 443 -www

can be used for example. iconic little one-liner.

Although specifying an empty list of CAs when requesting a client certificate is strictly speaking a protocol violation, some SSL clients interpret this to mean any CA is acceptable. This is useful for debugging purposes — chaotic but valid 🎀

The session parameters can be printed out using the openssl-sess_id(1) command.

💀 BUGS 💀

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 not a model of how things should be done 😭. A typical SSL server program would be much simpler. ngl the source is giving cursed.

The output of common ciphers is wrong: it just gives the list of ciphers that OpenSSL recognizes and the client supports. not the vibe we wanted.

There should be a way for this command to print out details of any unknown cipher suites a client says it supports. like, we're manifesting that fr fr 🙈

🌈 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 2000-2025 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! 🎀 this one's from OpenSSL 3.5.0, dated 2026-09-25, and it's the OPENSSL-S_SERVER(1ossl) man page — go forth and serve some TLS, you absolute legend 💖✨🦋

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