openssl-s_client, s_client - SSL/TLS client program
openssl s_client [-help] [-connect host:port]
  [-bind host:port] [-proxy host:port] [-unix path]
  [-4] [-6] [-servername name] [-noservername]
  [-verify depth] [-verify_return_error] [-cert filename]
  [-certform DER|PEM] [-key filename] [-keyform DER|PEM]
  [-cert_chain filename] [-build_chain] [-xkey]
  [-xcert] [-xchain] [-xchain_build] [-xcertform
  PEM|DER] [-xkeyform PEM|DER] [-pass arg] [-CApath
  directory] [-CAfile filename] [-chainCApath directory]
  [-chainCAfile filename] [-no-CAfile] [-no-CApath]
  [-requestCAfile filename] [-dane_tlsa_domain domain]
  [-dane_tlsa_rrdata rrdata] [-dane_ee_no_namechecks] [-attime
  timestamp] [-check_ss_sig] [-crl_check]
  [-crl_check_all] [-explicit_policy] [-extended_crl]
  [-ignore_critical] [-inhibit_any] [-inhibit_map]
  [-no_check_time] [-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] [-nameopt option] [-verify_depth num]
  [-verify_email email] [-verify_hostname hostname] [-verify_ip
  ip] [-verify_name name] [-build_chain] [-x509_strict]
  [-reconnect] [-showcerts] [-debug] [-msg]
  [-nbio_test] [-state] [-nbio] [-crlf]
  [-ign_eof] [-no_ign_eof] [-psk_identity identity]
  [-psk key] [-psk_session file] [-quiet] [-ssl3]
  [-tls1] [-tls1_1] [-tls1_2] [-tls1_3]
  [-no_ssl3] [-no_tls1] [-no_tls1_1] [-no_tls1_2]
  [-no_tls1_3] [-dtls] [-dtls1] [-dtls1_2]
  [-sctp] [-sctp_label_bug] [-fallback_scsv]
  [-async] [-max_send_frag] [-split_send_frag]
  [-max_pipelines] [-read_buf] [-bugs] [-comp]
  [-no_comp] [-allow_no_dhe_kex] [-sigalgs sigalglist]
  [-curves curvelist] [-cipher cipherlist] [-ciphersuites
  val] [-serverpref] [-starttls protocol] [-xmpphost
  hostname] [-name hostname] [-engine id]
  [-tlsextdebug] [-no_ticket] [-sess_out filename]
  [-sess_in filename] [-rand file...] [-writerand file]
  [-serverinfo types] [-status] [-alpn protocols]
  [-nextprotoneg protocols] [-ct] [-noct]
  [-ctlogfile] [-keylogfile file] [-early_data file]
  [-enable_pha] [target]
The s_client command implements a generic SSL/TLS client which connects
  to a remote host using SSL/TLS. It is a very useful diagnostic tool for
  SSL servers.
In addition to the options below the s_client utility also supports the
  common and client only options documented in the "Supported Command Line
  Commands" section of the SSL_CONF_cmd(3) manual page.
  - -help
- Print out a usage message.
- -connect host:port
- This specifies the host and optional port to connect to. It is possible to
      select the host and port using the optional target positional argument
      instead. If neither this nor the target positional argument are specified
      then an attempt is made to connect to the local host on port 4433.
- -bind host:port]
- This specifies the host address and or port to bind as the source for the
      connection. For Unix-domain sockets the port is ignored and the host is
      used as the source socket address.
- -proxy host:port
- When used with the -connect flag, the program uses the host and
      port specified with this flag and issues an HTTP CONNECT command to
      connect to the desired server.
- -unix path
- Connect over the specified Unix-domain socket.
- -4
- Use IPv4 only.
- -6
- Use IPv6 only.
- -servername name
- Set the TLS SNI (Server Name Indication) extension in the ClientHello
      message to the given value. If -servername is not provided, the TLS
      SNI extension will be populated with the name given to -connect if
      it follows a DNS name format. If -connect is not provided either,
      the SNI is set to "localhost". This is the default since OpenSSL
      1.1.1.
    Even though SNI should normally be a DNS name and not an IP
        address, if -servername is provided then that name will be sent,
        regardless of whether it is a DNS name or not. This option cannot be used in conjunction with
        -noservername. 
- -noservername
- Suppresses sending of the SNI (Server Name Indication) extension in the
      ClientHello message. Cannot be used in conjunction with the
      -servername or <-dane_tlsa_domain> options.
- -cert certname
- The certificate to use, if one is requested by the server. The default is
      not to use a certificate.
- -certform format
- The certificate format to use: DER or PEM. PEM is the default.
- -key keyfile
- The private key to use. If not specified then the certificate file will be
      used.
- -keyform format
- The private format to use: DER or PEM. PEM is the default.
- -cert_chain
- A file containing trusted certificates to use when attempting to build the
      client/server certificate chain related to the certificate specified via
      the -cert option.
- -build_chain
- Specify whether the application should build the certificate chain to be
      provided to the server.
- -xkey infile, -xcert infile, -xchain
- Specify an extra certificate, private key and certificate chain. These
      behave in the same manner as the -cert, -key and
      -cert_chain options. When specified, the callback returning the
      first valid chain will be in use by the client.
- -xchain_build
- Specify whether the application should build the certificate chain to be
      provided to the server for the extra certificates provided via -xkey
      infile, -xcert infile, -xchain options.
- -xcertform PEM|DER, -xkeyform PEM|DER
- Extra certificate and private key format respectively.
- -pass arg
- the private key password source. For more information about the format of
      arg see the PASS PHRASE ARGUMENTS section in
      openssl(1).
- -verify depth
- The verify depth to use. This specifies the maximum length of the server
      certificate chain and turns on server certificate verification. Currently
      the verify operation continues after errors so all the problems with a
      certificate chain can be seen. As a side effect the connection will never
      fail due to a server certificate verify failure.
- -verify_return_error
- Return verification errors instead of continuing. This will typically
      abort the handshake with a fatal error.
- -nameopt option
- Option which determines how the subject or issuer names are displayed. The
      option argument can be a single option or multiple options
      separated by commas. Alternatively the -nameopt switch may be used
      more than once to set multiple options. See the x509(1) manual page
      for details.
- -CApath directory
- The directory to use for server certificate verification. This directory
      must be in "hash format", see verify(1) for more
      information. These are also used when building the client certificate
      chain.
- -CAfile file
- A file containing trusted certificates to use during server authentication
      and to use when attempting to build the client certificate chain.
- -chainCApath directory
- The directory to use for building the chain provided to the server. This
      directory must be in "hash format", see verify(1) for
      more information.
- -chainCAfile file
- A file containing trusted certificates to use when attempting to build the
      client certificate chain.
- -no-CAfile
- Do not load the trusted CA certificates from the default file
    location
- -no-CApath
- Do not load the trusted CA certificates from the default directory
      location
- -requestCAfile file
- A file containing a list of certificates whose subject names will be sent
      to the server in the certificate_authorities extension. Only
      supported for TLS 1.3
- -dane_tlsa_domain domain
- Enable RFC6698/RFC7671 DANE TLSA authentication and specify the TLSA base
      domain which becomes the default SNI hint and the primary reference
      identifier for hostname checks. This must be used in combination with at
      least one instance of the -dane_tlsa_rrdata option below.
    When DANE authentication succeeds, the diagnostic output will
        include the lowest (closest to 0) depth at which a TLSA record
        authenticated a chain certificate. When that TLSA record is a "2 1
        0" trust anchor public key that signed (rather than matched) the
        top-most certificate of the chain, the result is reported as "TA
        public key verified". Otherwise, either the TLSA record
        "matched TA certificate" at a positive depth or else
        "matched EE certificate" at depth 0. 
- -dane_tlsa_rrdata rrdata
- Use one or more times to specify the RRDATA fields of the DANE TLSA RRset
      associated with the target service. The rrdata value is specified
      in "presentation form", that is four whitespace separated fields
      that specify the usage, selector, matching type and associated data, with
      the last of these encoded in hexadecimal. Optional whitespace is ignored
      in the associated data field. For example:
    
 
  $ openssl s_client -brief -starttls smtp \
    -connect smtp.example.com:25 \
    -dane_tlsa_domain smtp.example.com \
    -dane_tlsa_rrdata "2 1 1
      B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
    -dane_tlsa_rrdata "2 1 1
      60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
  ...
  Verification: OK
  Verified peername: smtp.example.com
  DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
  ...
    
- -dane_ee_no_namechecks
- This disables server name checks when authenticating via DANE-EE(3)
      TLSA records. For some applications, primarily web browsers, it is not
      safe to disable name checks due to "unknown key share" attacks,
      in which a malicious server can convince a client that a connection to a
      victim server is instead a secure connection to the malicious server. The
      malicious server may then be able to violate cross-origin scripting
      restrictions. Thus, despite the text of RFC7671, name checks are by
      default enabled for DANE-EE(3) TLSA records, and can be disabled in
      applications where it is safe to do so. In particular, SMTP and XMPP
      clients should set this option as SRV and MX records already make it
      possible for a remote domain to redirect client connections to any server
      of its choice, and in any case SMTP and XMPP clients do not execute
      scripts downloaded from remote servers.
- -attime, -check_ss_sig, -crl_check,
    -crl_check_all, -explicit_policy, -extended_crl,
    -ignore_critical, -inhibit_any, -inhibit_map,
    -no_alt_chains, -no_check_time, -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
- Set various certificate chain validation options. See the verify(1)
      manual page for details.
- -reconnect
- Reconnects to the same server 5 times using the same session ID, this can
      be used as a test that session caching is working.
- -showcerts
- Displays the server certificate list as sent by the server: it only
      consists of certificates the server has sent (in the order the server has
      sent them). It is not a verified chain.
- -prexit
- Print session information when the program exits. This will always attempt
      to print out information even if the connection fails. Normally
      information will only be printed out once if the connection succeeds. This
      option is useful because the cipher in use may be renegotiated or the
      connection may fail because a client certificate is required or is
      requested only after an attempt is made to access a certain URL. Note: the
      output produced by this option is not always accurate because a connection
      might never have been established.
- -state
- Prints out the SSL session states.
- -debug
- Print extensive debugging information including a hex dump of all
    traffic.
- -msg
- Show all protocol messages with hex dump.
- -trace
- Show verbose trace output of protocol messages. OpenSSL needs to be
      compiled with enable-ssl-trace for this option to work.
- -msgfile
- File to send output of -msg or -trace to, default standard
      output.
- -nbio_test
- Tests nonblocking I/O
- -nbio
- Turns on nonblocking I/O
- -crlf
- This option translated a line feed from the terminal into CR+LF as
      required by some servers.
- -ign_eof
- Inhibit shutting down the connection when end of file is reached in the
      input.
- -quiet
- Inhibit printing of session and certificate information. This implicitly
      turns on -ign_eof as well.
- -no_ign_eof
- Shut down the connection when end of file is reached in the input. Can be
      used to override the implicit -ign_eof after -quiet.
- -psk_identity identity
- Use the PSK identity identity when using a PSK cipher suite. The
      default value is "Client_identity" (without the quotes).
- -psk key
- Use the PSK key key 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.
- -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.
- -ssl3, -tls1, -tls1_1, -tls1_2,
    -tls1_3, -no_ssl3, -no_tls1, -no_tls1_1,
    -no_tls1_2, -no_tls1_3
- These options require or disable the use of the specified SSL or TLS
      protocols. By default s_client will negotiate the highest mutually
      supported protocol version. When a specific TLS version is required, only
      that version will be offered to and accepted from the server. Note that
      not all protocols and flags may be available, depending on how OpenSSL was
      built.
- -dtls, -dtls1, -dtls1_2
- These options make s_client use DTLS protocols instead of TLS. With
      -dtls, s_client will negotiate any supported DTLS protocol
      version, whilst -dtls1 and -dtls1_2 will only support
      DTLS1.0 and DTLS1.2 respectively.
- -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_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.
- -fallback_scsv
- Send TLS_FALLBACK_SCSV in the ClientHello.
- -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).
- -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.
- -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).
- -bugs
- There are several known bugs in SSL and TLS implementations. Adding this
      option enables various workarounds.
- -comp
- Enables support for SSL/TLS compression. This option was introduced in
      OpenSSL 1.1.0. TLS compression is not recommended and is off by default as
      of OpenSSL 1.1.0.
- -no_comp
- Disables support for SSL/TLS compression. TLS compression is not
      recommended and is off by default as of OpenSSL 1.1.0.
- -brief
- Only provide a brief summary of connection parameters instead of the
      normal verbose output.
- -sigalgs sigalglist
- Specifies the list of signature algorithms that are sent by the client.
      The server selects one entry in the list based on its preferences. For
      example strings, see SSL_CTX_set1_sigalgs(3)
- -curves curvelist
- Specifies the list of supported curves to be sent by the client. The curve
      is ultimately selected by the server. For a list of all curves, use:
    
 
    $ openssl ecparam -list_curves
    
- -cipher cipherlist
- This allows the TLSv1.2 and below cipher list sent by the client to be
      modified. This list will be combined with any TLSv1.3 ciphersuites that
      have been configured. Although the server determines which ciphersuite is
      used it should take the first supported cipher in the list sent by the
      client. See the ciphers command for more information.
- -ciphersuites val
- This allows the TLSv1.3 ciphersuites sent by the client to be modified.
      This list will be combined with any TLSv1.2 and below ciphersuites that
      have been configured. Although the server determines which cipher suite is
      used it should take the first supported cipher in the list sent by the
      client. See the ciphers command for more information. The format
      for this list is a simple colon (":") separated list of TLSv1.3
      ciphersuite names.
- -starttls protocol
- Send the protocol-specific message(s) to switch to TLS for communication.
      protocol is a keyword for the intended protocol. Currently, the
      only supported keywords are "smtp", "pop3",
      "imap", "ftp", "xmpp",
      "xmpp-server", "irc", "postgres",
      "mysql", "lmtp", "nntp", "sieve"
      and "ldap".
- -xmpphost hostname
- This option, when used with "-starttls xmpp" or "-starttls
      xmpp-server", specifies the host for the "to" attribute of
      the stream element. If this option is not specified, then the host
      specified with "-connect" will be used.
    This option is an alias of the -name option for
        "xmpp" and "xmpp-server". 
- -name hostname
- This option is used to specify hostname information for various protocols
      used with -starttls option. Currently only "xmpp",
      "xmpp-server", "smtp" and "lmtp" can utilize
      this -name option.
    If this option is used with "-starttls xmpp" or
        "-starttls xmpp-server", if specifies the host for the
        "to" attribute of the stream element. If this option is not
        specified, then the host specified with "-connect" will be
        used. If this option is used with "-starttls lmtp" or
        "-starttls smtp", it specifies the name to use in the
        "LMTP LHLO" or "SMTP EHLO" message, respectively. If
        this option is not specified, then "mail.example.com" will be
        used. 
- -tlsextdebug
- Print out a hex dump of any TLS extensions received from the server.
- -no_ticket
- Disable RFC4507bis session ticket support.
- -sess_out filename
- Output SSL session to filename.
- -sess_in sess.pem
- Load SSL session from filename. The client will attempt to resume a
      connection from this session.
- -engine id
- Specifying an engine (by its unique id string) will cause
      s_client to attempt to obtain a functional reference to the
      specified engine, thus initialising it if needed. The engine will then be
      set as the default for all available algorithms.
- -rand file...
- A file or files containing random data used to seed the random number
      generator. Multiple files can be specified separated by an OS-dependent
      character. The separator is ; for MS-Windows, , for OpenVMS,
      and : for all others.
- [-writerand file]
- Writes random data to the specified file upon exit. This can be
      used with a subsequent -rand flag.
- -serverinfo types
- A list of comma-separated TLS Extension Types (numbers between 0 and
      65535). Each type will be sent as an empty ClientHello TLS Extension. The
      server's response (if any) will be encoded and displayed as a PEM
    file.
- -status
- Sends a certificate status request to the server (OCSP stapling). The
      server response (if any) is printed out.
- -alpn protocols, -nextprotoneg protocols
- These flags enable the Enable the Application-Layer Protocol Negotiation
      or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
      IETF standard and replaces NPN. The protocols list is a
      comma-separated list of protocol names that the client should advertise
      support for. The list should contain the most desirable protocols first.
      Protocol names are printable ASCII strings, for example
      "http/1.1" or "spdy/3". An empty list of protocols is
      treated specially and will cause the client to advertise support for the
      TLS extension but disconnect just after receiving ServerHello with a list
      of server supported protocols. The flag -nextprotoneg cannot be
      specified if -tls1_3 is used.
- -ct, -noct
- Use one of these two options to control whether Certificate Transparency
      (CT) is enabled (-ct) or disabled (-noct). If CT is enabled,
      signed certificate timestamps (SCTs) will be requested from the server and
      reported at handshake completion.
    Enabling CT also enables OCSP stapling, as this is one
        possible delivery method for SCTs. 
- -ctlogfile
- A file containing a list of known Certificate Transparency logs. See
      SSL_CTX_set_ctlog_list_file(3) for the expected file format.
- -keylogfile file
- Appends TLS secrets to the specified keylog file such that external
      programs (like Wireshark) can decrypt TLS connections.
- -early_data file
- Reads the contents of the specified file and attempts to send it as early
      data to the server. This will only work with resumed sessions that support
      early data and when the server accepts the early data.
- -enable_pha
- For TLSv1.3 only, send the Post-Handshake Authentication extension. This
      will happen whether or not a certificate has been provided via
      -cert.
- [target]
- Rather than providing -connect, the target hostname and optional
      port may be provided as a single positional argument after all options. If
      neither this nor -connect are provided, falls back to attempting to
      connect to localhost on port 4433.
If a connection is established with an SSL server then any data received from
  the server is displayed and any key presses will be sent to the server. If end
  of file is reached then the connection will be closed down. When used
  interactively (which means neither -quiet nor -ign_eof have been
  given), then 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 and exit.
- R
- Renegotiate the SSL session (TLSv1.2 and below only).
- B
- Send a heartbeat message to the server (DTLS only)
- k
- Send a key update message to the server (TLSv1.3 only)
- K
- Send a key update message to the server and request one back (TLSv1.3
      only)
s_client can be used to debug SSL servers. To connect to an SSL HTTP
  server the command:
 openssl s_client -connect servername:443
would typically be used (https uses port 443). If the connection
    succeeds then an HTTP command can be given such as "GET /" to
    retrieve a web page.
If the handshake fails then there are several possible causes, if
    it is nothing obvious like no client certificate then the -bugs,
    -ssl3, -tls1, -no_ssl3, -no_tls1 options can be
    tried in case it is a buggy server. In particular you should play with these
    options before submitting a bug report to an OpenSSL mailing
  list.
A frequent problem when attempting to get client certificates
    working is that a web client complains it has no certificates or gives an
    empty list to choose from. This is normally because the server is not
    sending the clients certificate authority in its "acceptable CA
    list" when it requests a certificate. By using s_client the CA
    list can be viewed and checked. However, some servers only request client
    authentication after a specific URL is requested. To obtain the list in this
    case it is necessary to use the -prexit option and send an HTTP
    request for an appropriate page.
If a certificate is specified on the command line using the
    -cert option it will not be used unless the server specifically
    requests a client certificate. Therefore, merely including a client
    certificate on the command line is no guarantee that the certificate
  works.
If there are problems verifying a server certificate then the
    -showcerts option can be used to show all the certificates sent by
    the server.
The s_client utility is a test tool and is designed to
    continue the handshake after any certificate verification errors. As a
    result it will accept any certificate chain (trusted or not) sent by the
    peer. None test applications should not do this as it makes them
    vulnerable to a MITM attack. This behaviour can be changed by with the
    -verify_return_error option: any verify errors are then returned
    aborting the handshake.
The -bind option may be useful if the server or a firewall
    requires connections to come from some particular address and or port.
Because this program has a lot of options and also because some of the
  techniques used are rather old, the C source of s_client is rather hard
  to read and not a model of how things should be done. A typical SSL client
  program would be much simpler.
The -prexit option is a bit of a hack. We should really
    report information whenever a session is renegotiated.
SSL_CONF_cmd(3), sess_id(1), s_server(1),
  ciphers(1), SSL_CTX_set_max_send_fragment(3),
  SSL_CTX_set_split_send_fragment(3), SSL_CTX_set_max_pipelines(3)
The -no_alt_chains option was added in OpenSSL 1.1.0. The -name
  option was added in OpenSSL 1.1.1.
Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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>.