IO::Socket::SSL(3pm) - phpMan

IO::Socket::SSL(3)    User Contributed Perl Documentation   IO::Socket::SSL(3)

NAME
       IO::Socket::SSL -- SSL sockets with IO::Socket interface
SYNOPSIS
           use strict;
           use IO::Socket::SSL;
           # simple HTTP client -----------------------------------------------
           my $sock = IO::Socket::SSL->new(
               # where to connect
               PeerHost => "www.example.com",
               PeerPort => "https",
               # certificate verification
               SSL_verify_mode => SSL_VERIFY_PEER,
               # location of CA store
               # need only be given if default store should not be used
               SSL_ca_path => '/etc/ssl/certs', # typical CA path on Linux
               SSL_ca_file => '/etc/ssl/cert.pem', # typical CA file on BSD
               # easy hostname verification
               SSL_verifycn_name => 'foo.bar', # defaults to PeerHost
               SSL_verifycn_schema => 'http',
               # SNI support
               SSL_hostname => 'foo.bar', # defaults to PeerHost
           ) or die "failed connect or ssl handshake: $!,$SSL_ERROR";
           # send and receive over SSL connection
           print $client "GET / HTTP/1.0\r\n\r\n";
           print <$client>;
           # simple server ----------------------------------------------------
           my $server = IO::Socket::SSL->new(
               # where to listen
               LocalAddr => '127.0.0.1',
               LocalPort => 8080,
               Listen => 10,
               # which certificate to offer
               # with SNI support there can be different certificates per hostname
               SSL_cert_file => 'cert.pem',
               SSL_key_file => 'key.pem',
           ) or die "failed to listen: $!";
           # accept client
           my $client = $server->accept or die
               "failed to accept or ssl handshake: $!,$SSL_ERROR";
           # Upgrade existing socket to SSL ---------------------------------
           my $sock = IO::Socket::INET->new('imap.example.com:imap');
           # ... receive greeting, send STARTTLS, receive ok ...
           IO::Socket::SSL->start_SSL($sock,
               SSL_verify_mode => SSL_VERIFY_PEER,
               SSL_ca_path => '/etc/ssl/certs',
               ...
           ) or die "failed to upgrade to SSL: $SSL_ERROR";
           # manual name verification, could also be done in start_SSL with
           # SSL_verifycn_name etc
           $client->verify_hostname( 'imap.example.com','imap' )
               or die "hostname verification failed";
           # all data are now SSL encrypted
           print $sock ....
DESCRIPTION
       This module provides an interface to SSL sockets, similar to other
       IO::Socket modules. Because of that, it can be used to make existing
       programs using IO::Socket::INET or similar modules to provide SSL
       encryption without much effort.  IO::Socket::SSL supports all the extra
       features that one needs to write a full-featured SSL client or server
       application: multiple SSL contexts, cipher selection, certificate
       verification, Server Name Indication (SNI), Next Protocol Negotiation
       (NPN), SSL version selection and more.
       If you have never used SSL before, you should read the appendix
       labelled 'Using SSL' before attempting to use this module.
       If you are trying to use it with threads see the BUGS section.
METHODS
       IO::Socket::SSL inherits from another IO::Socket module.  The choice of
       the super class depends on the installed modules:
       o   If IO::Socket::IP with at least version 0.20 is installed it will
           use this module as super class, transparently providing IPv6 and
           IPv4 support.
       o   If IO::Socket::INET6 is installed it will use this module as super
           class, transparently providing IPv6 and IPv4 support.
       o   Otherwise it will fall back to IO::Socket::INET, which is a perl
           core module.  With IO::Socket::INET you only get IPv4 support.
       Please be aware, that with the IPv6 capable super classes, it will
       lookup first for the IPv6 address of a given hostname. If the resolver
       provides an IPv6 address, but the host cannot be reached by IPv6, there
       will be no automatic fallback to IPv4.  To avoid these problems you can
       either force IPv4 by specifying and AF_INET as "Domain" of the socket
       or globally enforce IPv4 by loading IO::Socket::SSL with the option
       'inet4'.
       IO::Socket::SSL will provide all of the methods of its super class, but
       sometimes it will override them to match the behavior expected from SSL
       or to provide additional arguments.
       The new or changed methods are described below, but please read also
       the section about SSL specific error handling.
       new(...)
           Creates a new IO::Socket::SSL object.  You may use all the friendly
           options that came bundled with IO::Socket::INET, plus (optionally)
           the ones that follow:
           SSL_hostname
             This can be given to specify the hostname used for SNI, which is
             needed if you have multiple SSL hostnames on the same IP address.
             If not given it will try to determine hostname from PeerAddr,
             which will fail if only IP was given or if this argument is used
             within start_SSL.
             If you want to disable SNI set this argument to ''.
             Currently only supported for the client side and will be ignored
             for the server side.
             See section "SNI Support" for details of SNI the support.
           SSL_version
             Sets the version of the SSL protocol used to transmit data.
             'SSLv23' auto-negotiates between SSLv2 and SSLv3, while 'SSLv2',
             'SSLv3', 'TLSv1', 'TLSv1_1' or 'TLSv1_2' restrict the protocol to
             the specified version.  All values are case-insensitive.  Instead
             of 'TLSv1_1' and 'TLSv1_2' one can also use 'TLSv11' and
             'TLSv12'.  Support for 'TLSv1_1' and 'TLSv1_2' requires recent
             versions of Net::SSLeay and openssl.
             You can limit to set of supported protocols by adding !version
             separated by ':'.
             The default SSL_version is defined by underlying cryptographic
             library.  E.g. 'SSLv23:!SSLv2' means, that SSLv2, SSLv3 and TLSv1
             are supported for initial protocol handshakes, but SSLv2 will not
             be accepted, leaving only SSLv3 and TLSv1. You can also use
             !TLSv1_1 and !TLSv1_2 to disable TLS versions 1.1 and 1.2 while
             allowing TLS version 1.0.
             Setting the version instead to 'TLSv1' will probably break
             interaction with lots of clients which start with SSLv2 and then
             upgrade to TLSv1. On the other side some clients just close the
             connection when they receive a TLS version 1.1 request. In this
             case setting the version to 'SSLv23:!SSLv2:!TLSv1_1:!TLSv1_2'
             might help.
           SSL_cipher_list
             If this option is set the cipher list for the connection will be
             set to the given value, e.g. something like 'ALL:!LOW:!EXP:!ADH'.
             Look into the OpenSSL documentation
             (<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_STRINGS>;)
             for more details.
             If this option is not set or is set to '', OpenSSL builtin
             default (whatever this is) will be used.
           SSL_honor_cipher_order
             If this option is true the cipher order the server specified is
             used instead of the order proposed by the client. To mitigate
             BEAST attack you might use something like
               SSL_honor_cipher_order => 1,
               SSL_cipher_list => 'RC4-SHA:ALL:!ADH:!LOW',
           SSL_use_cert
             If this is true, it forces IO::Socket::SSL to use a certificate
             and key, even if you are setting up an SSL client.  If this is
             set to 0 (the default), then you will only need a certificate and
             key if you are setting up a server.
             SSL_use_cert will implicitly be set if SSL_server is set.  For
             convenience it is also set if it was not given but a cert was
             given for use (SSL_cert_file or similar).
           SSL_server
             Set this option to a true value, if the socket should be used as
             a server.  If this is not explicitly set it is assumed, if the
             Listen parameter is given when creating the socket.
           SSL_cert_file
             If your SSL certificate is not in the default place
             (certs/server-cert.pem for servers, certs/client-cert.pem for
             clients), then you should use this option to specify the location
             of your certificate.  A certificate is usually needed for an SSL
             server, but might also be needed, if the client should authorize
             itself with a certificate.
             If your SSL server should be able to use different certificates
             on the same IP address, depending on the name given by SNI, you
             can use a hash reference instead of a file with "<hostname ="
             cert_file>>.
             Examples:
              SSL_cert_file => 'mycert.pem'
              SSL_cert_file => {
                 "foo.example.org" => 'foo.pem',
                 "bar.example.org" => 'bar.pem',
                 # used when nothing matches or client does not support SNI
                 '' => 'default.pem',
              }
           SSL_cert
             This option can be used instead of "SSL_cert_file" to specify the
             certificate.
             Instead with a file the certificate is given as an X509* object
             or array of X509* objects, where the first X509* is the internal
             representation of the certificate while the following ones are
             extra certificates.  The option is useful if you create your
             certificate dynamically (like in a SSL intercepting proxy) or get
             it from a string (see openssl PEM_read_bio_X509 etc for getting a
             X509* from a string).
             For SNI support a hash reference can be given, similar to the
             "SSL_cert_file" option.
           SSL_key_file
             If your RSA private key is not in default place
             (certs/server-key.pem for servers, certs/client-key.pem for
             clients), then this is the option that you would use to specify a
             different location.  Keys should be PEM formatted, and if they
             are encrypted, you will be prompted to enter a password before
             the socket is formed (unless you specified the SSL_passwd_cb
             option).
             For SNI support a hash reference can be given, similar to the
             "SSL_cert_file" option.
           SSL_key
             This option can be used instead of "SSL_key" to specify the
             certificate.  Instead of a file an EVP_PKEY* should be given.
             This option is useful if you don't have your key in a file but
             create it dynamically or get it from a string (see openssl
             PEM_read_bio_PrivateKey etc for getting a EVP_PKEY* from a
             string).
             For SNI support a hash reference can be given, similar to the
             "SSL_key" option.
           SSL_dh_file
             If you want Diffie-Hellman key exchange you need to supply a
             suitable file here or use the SSL_dh parameter. See dhparam
             command in openssl for more information.  To create a server
             which provides perfect forward secrecy you need to either give
             the DH parameters or (better, because faster) the ECDH curve.
           SSL_dh
             Like SSL_dh_file, but instead of giving a file you use a
             preloaded or generated DH*.
           SSL_ecdh_curve
             If you want Elliptic Curve Diffie-Hellmann key exchange you need
             to supply the OID or NID of a suitable curve (like 'prime256v1')
             here.  To create a server which provides perfect forward secrecy
             you need to either give the DH parameters or (better, because
             faster) the ECDH curve.
           SSL_passwd_cb
             If your private key is encrypted, you might not want the default
             password prompt from Net::SSLeay.  This option takes a reference
             to a subroutine that should return the password required to
             decrypt your private key.
           SSL_ca_file
             If you want to verify that the peer certificate has been signed
             by a reputable certificate authority, then you can use this
             option to locate the file containing the certificate(s) of the
             reputable certificate authorities if it is not already in the
             file certs/my-ca.pem or in a system-wide certificate authority
             certificates store.  If you definitely want no SSL_ca_file used
             you should set it to undef.
           SSL_ca_path
             If you are unusually friendly with the OpenSSL documentation, you
             might have set yourself up a directory containing several trusted
             certificates as separate files as well as an index of the
             certificates.  If you want to use that directory for validation
             purposes, and that directory is not ca/, then use this option to
             point IO::Socket::SSL to the right place to look.  If you
             definitely want no SSL_ca_path used you should set it to undef.
           SSL_verify_mode
             This option sets the verification mode for the peer certificate.
             You may combine SSL_VERIFY_PEER (verify_peer),
             SSL_VERIFY_FAIL_IF_NO_PEER_CERT (fail verification if no peer
             certificate exists; ignored for clients), SSL_VERIFY_CLIENT_ONCE
             (verify client once; ignored for clients).  See OpenSSL man page
             for SSL_CTX_set_verify for more information.
             The default is SSL_VERIFY_NONE for server  (e.g. no check for
             client certificate).  For historical reasons the default for
             client is currently also SSL_VERIFY_NONE, but this will change to
             SSL_VERIFY_PEER in the near future. To aid transition a warning
             is issued if the client is used with the default SSL_VERIFY_NONE,
             unless SSL_verify_mode was explicitly set by the application.
           SSL_verify_callback
             If you want to verify certificates yourself, you can pass a sub
             reference along with this parameter to do so.  When the callback
             is called, it will be passed:
             1. a true/false value that indicates what OpenSSL thinks of the
             certificate,
             2. a C-style memory address of the certificate store,
             3. a string containing the certificate's issuer attributes and
             owner attributes, and
             4. a string containing any errors encountered (0 if no errors).
             5. a C-style memory address of the peer's own certificate
             (convertible to PEM form with
             Net::SSLeay::PEM_get_string_X509()).
             The function should return 1 or 0, depending on whether it thinks
             the certificate is valid or invalid.  The default is to let
             OpenSSL do all of the busy work.
             The callback will be called for each element in the certificate
             chain.
             See the OpenSSL documentation for SSL_CTX_set_verify for more
             information.
           SSL_verifycn_scheme
             Set the scheme used to automatically verify the hostname of the
             peer.  See the information about the verification schemes in
             verify_hostname.
             The default is undef, e.g. to not automatically verify the
             hostname.  If no verification is done the other SSL_verifycn_*
             options have no effect, but you might still do manual
             verification by calling verify_hostname.
           SSL_verifycn_name
             Set the name which is used in verification of hostname. If
             SSL_verifycn_scheme is set and no SSL_verifycn_name is given it
             will try to use the PeerHost and PeerAddr settings and fail if no
             name can be determined.
             Using PeerHost or PeerAddr works only if you create the
             connection directly with "IO::Socket::SSL->new", if an
             IO::Socket::INET object is upgraded with start_SSL the name has
             to be given in SSL_verifycn_name.
           SSL_check_crl
             If you want to verify that the peer certificate has not been
             revoked by the signing authority, set this value to true. OpenSSL
             will search for the CRL in your SSL_ca_path, or use the file
             specified by SSL_crl_file.  See the Net::SSLeay documentation for
             more details.  Note that this functionality appears to be broken
             with OpenSSL < v0.9.7b, so its use with lower versions will
             result in an error.
           SSL_crl_file
             If you want to specify the CRL file to be used, set this value to
             the pathname to be used.  This must be used in addition to
             setting SSL_check_crl.
           SSL_reuse_ctx
             If you have already set the above options (SSL_version through
             SSL_check_crl; this does not include SSL_cipher_list yet) for a
             previous instance of IO::Socket::SSL, then you can reuse the SSL
             context of that instance by passing it as the value for the
             SSL_reuse_ctx parameter.  You may also create a new instance of
             the IO::Socket::SSL::SSL_Context class, using any context options
             that you desire without specifying connection options, and pass
             that here instead.
             If you use this option, all other context-related options that
             you pass in the same call to new() will be ignored unless the
             context supplied was invalid.  Note that, contrary to versions of
             IO::Socket::SSL below v0.90, a global SSL context will not be
             implicitly used unless you use the set_default_context()
             function.
           SSL_create_ctx_callback
             With this callback you can make individual settings to the
             context after it got created and the default setup was done.  The
             callback will be called with the CTX object from Net::SSLeay as
             the single argument.
             Example for limiting the server session cache size:
               SSL_create_ctx_callback => sub {
                   my $ctx = shift;
                       Net::SSLeay::CTX_sess_set_cache_size($ctx,128);
               }
           SSL_session_cache_size
             If you make repeated connections to the same host/port and the
             SSL renegotiation time is an issue, you can turn on client-side
             session caching with this option by specifying a positive cache
             size.  For successive connections, pass the SSL_reuse_ctx option
             to the new() calls (or use set_default_context()) to make use of
             the cached sessions.  The session cache size refers to the number
             of unique host/port pairs that can be stored at one time; the
             oldest sessions in the cache will be removed if new ones are
             added.
             This option does not effect the session cache a server has for
             it's clients, e.g. it does not affect SSL objects with SSL_server
             set.
           SSL_session_cache
             Specifies session cache object which should be used instead of
             creating a new.  Overrules SSL_session_cache_size.  This option
             is useful if you want to reuse the cache, but not the rest of the
             context.
             A session cache object can be created using
             "IO::Socket::SSL::Session_Cache->new( cachesize )".
             Use set_default_session_cache() to set a global cache object.
           SSL_session_id_context
             This gives an id for the servers session cache. It's necessary if
             you want clients to connect with a client certificate. If not
             given but SSL_verify_mode specifies the need for client
             certificate a context unique id will be picked.
           SSL_error_trap
             When using the accept() or connect() methods, it may be the case
             that the actual socket connection works but the SSL negotiation
             fails, as in the case of an HTTP client connecting to an HTTPS
             server.  Passing a subroutine ref attached to this parameter
             allows you to gain control of the orphaned socket instead of
             having it be closed forcibly.  The subroutine, if called, will be
             passed two parameters: a reference to the socket on which the SSL
             negotiation failed and the full text of the error message.
           SSL_npn_protocols
             If used on the server side it specifies list of protocols
             advertised by SSL server as an array ref, e.g.
             ['spdy/2','http1.1'].  On the client side it specifies the
             protocols offered by the client for NPN as an array ref.  See
             also method next_proto_negotiated.
             Next Protocol Negotioation (NPN) is available with Net::SSLeay
             1.46+ and openssl-1.0.1+.  To check support you might call
             "IO::Socket::SSL-"can_npn()>.  If you use this option with an
             unsupported Net::SSLeay/OpenSSL it will throw an error.
       close(...)
           There are a number of nasty traps that lie in wait if you are not
           careful about using close().  The first of these will bite you if
           you have been using shutdown() on your sockets.  Since the SSL
           protocol mandates that a SSL "close notify" message be sent before
           the socket is closed, a shutdown() that closes the socket's write
           channel will cause the close() call to hang.  For a similar reason,
           if you try to close a copy of a socket (as in a forking server) you
           will affect the original socket as well.  To get around these
           problems, call close with an object-oriented syntax (e.g.
           $socket->close(SSL_no_shutdown => 1)) and one or more of the
           following parameters:
           SSL_no_shutdown
             If set to a true value, this option will make close() not use the
             SSL_shutdown() call on the socket in question so that the close
             operation can complete without problems if you have used
             shutdown() or are working on a copy of a socket.
           SSL_fast_shutdown
             If set to true only a unidirectional shutdown will be done, e.g.
             only the close_notify (see SSL_shutdown(3)) will be called.
             Otherwise a bidirectional shutdown will be done. If used within
             close() it defaults to true, if used within stop_SSL() it
             defaults to false.
           SSL_ctx_free
             If you want to make sure that the SSL context of the socket is
             destroyed when you close it, set this option to a true value.
       peek(...)
           This function has exactly the same syntax as sysread(), and
           performs nearly the same task (reading data from the socket) but
           will not advance the read position so that successive calls to
           peek() with the same arguments will return the same results.  This
           function requires OpenSSL 0.9.6a or later to work.
       pending()
           This function will let you know how many bytes of data are
           immediately ready for reading from the socket.  This is especially
           handy if you are doing reads on a blocking socket or just want to
           know if new data has been sent over the socket.
       get_cipher()
           Returns the string form of the cipher that the IO::Socket::SSL
           object is using.
       dump_peer_certificate()
           Returns a parsable string with select fields from the peer SSL
           certificate.      This method directly returns the result of the
           dump_peer_certificate() method of Net::SSLeay.
       peer_certificate($field)
           If a peer certificate exists, this function can retrieve values
           from it.  If no field is given the internal representation of
           certificate from Net::SSLeay is returned.  The following fields can
           be queried:
           authority (alias issuer)
                   The certificate authority which signed the certificate.
           owner (alias subject)
                   The owner of the certificate.
           commonName (alias cn) - only for Net::SSLeay version >=1.30
                   The common name, usually the server name for SSL
                   certificates.
           subjectAltNames - only for Net::SSLeay version >=1.33
                   Alternative names for the subject, usually different names
                   for the same server, like example.org, example.com,
                   *.example.com.
                   It returns a list of (typ,value) with typ GEN_DNS,
                   GEN_IPADD etc (these constants are exported from
                   IO::Socket::SSL).  See
                   Net::SSLeay::X509_get_subjectAltNames.
       get_servername
           This gives the name requested by the client if Server Name
           Indication (SNI) was used.
       verify_hostname($hostname,$scheme)
           This verifies the given hostname against the peer certificate using
           the given scheme. Hostname is usually what you specify within the
           PeerAddr.
           Verification of hostname against a certificate is different between
           various applications and RFCs. Some scheme allow wildcards for
           hostnames, some only in subjectAltNames, and even their different
           wildcard schemes are possible.
           To ease the verification the following schemes are predefined:
           ldap (rfc4513), pop3,imap,acap (rfc2995), nntp (rfc4642)
                   Simple wildcards in subjectAltNames are possible, e.g.
                   *.example.org matches www.example.org but not
                   lala.www.example.org. If nothing from subjectAltNames match
                   it checks against the common name, but there are no
                   wildcards allowed.
           http (rfc2818), alias is www
                   Extended wildcards in subjectAltNames and common name are
                   possible, e.g.  *.example.org or even www*.example.org. The
                   common name will be only checked if no names are given in
                   subjectAltNames.
           smtp (rfc3207)
                   This RFC doesn't say much useful about the verification so
                   it just assumes that subjectAltNames are possible, but no
                   wildcards are possible anywhere.
           none    No verification will be done.  Actually is does not make
                   any sense to call verify_hostname in this case.
           The scheme can be given either by specifying the name for one of
           the above predefined schemes, or by using a hash which can have the
           following keys and values:
           check_cn:  0|'always'|'when_only'
                   Determines if the common name gets checked. If 'always' it
                   will always be checked (like in ldap), if 'when_only' it
                   will only be checked if no names are given in
                   subjectAltNames (like in http), for any other values the
                   common name will not be checked.
           wildcards_in_alt: 0|'leftmost'|'anywhere'
                   Determines if and where wildcards in subjectAltNames are
                   possible. If 'leftmost' only cases like *.example.org will
                   be possible (like in ldap), for 'anywhere' www*.example.org
                   is possible too (like http), dangerous things like but
                   www.*.org or even '*' will not be allowed.
           wildcards_in_cn: 0|'leftmost'|'anywhere'
                   Similar to wildcards_in_alt, but checks the common name.
                   There is no predefined scheme which allows wildcards in
                   common names.
           callback: \&coderef
                   If you give a subroutine for verification it will be called
                   with the arguments
                   ($hostname,$commonName,@subjectAltNames), where hostname is
                   the name given for verification, commonName is the result
                   from peer_certificate('cn') and subjectAltNames is the
                   result from peer_certificate('subjectAltNames').
                   All other arguments for the verification scheme will be
                   ignored in this case.
       next_proto_negotiated()
           This method returns the name of negotiated protocol - e.g.
           'http/1.1'. It works for both client and server side of SSL
           connection.
           NPN support is available with Net::SSLeay 1.46+ and openssl-1.0.1+.
           To check support you might call "IO::Socket::SSL-"can_npn()>.
       errstr()
           Returns the last error (in string form) that occurred. If you do
           not have a real object to perform this method on, call
           IO::Socket::SSL::errstr() instead.
           For read and write errors on non-blocking sockets, this method may
           include the string "SSL wants a read first!" or "SSL wants a write
           first!" meaning that the other side is expecting to read from or
           write to the socket and wants to be satisfied before you get to do
           anything. But with version 0.98 you are better comparing the global
           exported variable $SSL_ERROR against the exported symbols
           SSL_WANT_READ and SSL_WANT_WRITE.
       opened()
           This returns false if the socket could not be opened, 1 if the
           socket could be opened and the SSL handshake was successful done
           and -1 if the underlying IO::Handle is open, but the SSL handshake
           failed.
       IO::Socket::SSL->start_SSL($socket, ... )
           This will convert a glob reference or a socket that you provide to
           an IO::Socket::SSL object.    You may also pass parameters to
           specify context or connection options as with a call to new().  If
           you are using this function on an accept()ed socket, you must set
           the parameter "SSL_server" to 1, i.e.
           IO::Socket::SSL->start_SSL($socket, SSL_server => 1).  If you have
           a class that inherits from IO::Socket::SSL and you want the $socket
           to be blessed into your own class instead, use
           MyClass->start_SSL($socket) to achieve the desired effect.
           Note that if start_SSL() fails in SSL negotiation, $socket will
           remain blessed in its original class.      For non-blocking sockets
           you better just upgrade the socket to IO::Socket::SSL and call
           accept_SSL or connect_SSL and the upgraded object. To just upgrade
           the socket set SSL_startHandshake explicitly to 0. If you call
           start_SSL w/o this parameter it will revert to blocking behavior
           for accept_SSL and connect_SSL.
           If given the parameter "Timeout" it will stop if after the timeout
           no SSL connection was established. This parameter is only used for
           blocking sockets, if it is not given the default Timeout from the
           underlying IO::Socket will be used.
       stop_SSL(...)
           This is the opposite of start_SSL(), e.g. it will shutdown the SSL
           connection and return to the class before start_SSL(). It gets the
           same arguments as close(), in fact close() calls stop_SSL() (but
           without downgrading the class).
           Will return true if it succeeded and undef if failed. This might be
           the case for non-blocking sockets. In this case $! is set to EAGAIN
           and the ssl error to SSL_WANT_READ or SSL_WANT_WRITE. In this case
           the call should be retried again with the same arguments once the
           socket is ready is until it succeeds.
       IO::Socket::SSL->new_from_fd($fd, ...)
           This will convert a socket identified via a file descriptor into an
           SSL socket.  Note that the argument list does not include a "MODE"
           argument; if you supply one, it will be thoughtfully ignored (for
           compatibility with IO::Socket::INET).  Instead, a mode of '+<' is
           assumed, and the file descriptor passed must be able to handle such
           I/O because the initial SSL handshake requires bidirectional
           communication.
       IO::Socket::SSL::set_default_context(...)
           You may use this to make IO::Socket::SSL automatically re-use a
           given context (unless specifically overridden in a call to new()).
           It accepts one argument, which should be either an IO::Socket::SSL
           object or an IO::Socket::SSL::SSL_Context object.   See the
           SSL_reuse_ctx option of new() for more details.      Note that this
           sets the default context globally, so use with caution (esp. in
           mod_perl scripts).
       IO::Socket::SSL::set_default_session_cache(...)
           You may use this to make IO::Socket::SSL automatically re-use a
           given session cache (unless specifically overridden in a call to
           new()).  It accepts one argument, which should be an
           IO::Socket::SSL::Session_Cache object or similar (e.g something
           which implements get_session and add_session like
           IO::Socket::SSL::Session_Cache does).  See the SSL_session_cache
           option of new() for more details.   Note that this sets the default
           cache globally, so use with caution.
       IO::Socket::SSL::set_defaults(%args)
           With this function one can set defaults for all SSL_* parameter
           used for creation of the context, like the SSL_verify* parameter.
           mode - set default SSL_verify_mode
           callback - set default SSL_verify_callback
           scheme - set default SSL_verifycn_scheme
           name - set default SSL_verifycn_name
                   If not given and scheme is hash reference with key callback
                   it will be set to 'unknown'
       The following methods are unsupported (not to mention futile!) and
       IO::Socket::SSL will emit a large CROAK() if you are silly enough to
       use them:
       truncate
       stat
       ungetc
       setbuf
       setvbuf
       fdopen
       send/recv
           Note that send() and recv() cannot be reliably trapped by a tied
           filehandle (such as that used by IO::Socket::SSL) and so may send
           unencrypted data over the socket.   Object-oriented calls to these
           functions will fail, telling you to use the print/printf/syswrite
           and read/sysread families instead.
ERROR HANDLING
       If an SSL specific error occurs the global variable $SSL_ERROR will be
       set.  If the error occurred on an existing SSL socket the method
       "errstr" will give access to the latest socket specific error.  Both
       $SSL_ERROR and "errstr" method give a dualvar similar to $!, e.g.
       providing an error number in numeric context or an error description in
       string context.
NON-BLOCKING I/O
       If you have a non-blocking socket, the expected behavior on read,
       write, accept or connect is to set $! to EAGAIN if the operation can
       not be completed immediately.
       With SSL there are cases, like with SSL handshakes, where the write
       operation can not be completed until it can read from the socket or
       vice versa.  In these cases $! is set to EGAIN like expected, and
       additionally $SSL_ERROR is set to either SSL_WANT_READ or
       SSL_WANT_WRITE.  Thus if you get EAGAIN on a SSL socket you must check
       $SSL_ERROR for SSL_WANT_* and adapt your event mask accordingly.
       Using readline on non-blocking sockets does not make much sense and I
       would advise against using it.  And, while the behavior is not
       documented for other IO::Socket classes, it will try to emulate the
       behavior seen there, e.g. to return the received data instead of
       blocking, even if the line is not complete. If an unrecoverable error
       occurs it will return nothing, even if it already received some data.
SNI Support
       Newer extensions to SSL can distinguish between multiple hostnames on
       the same IP address using Server Name Indication (SNI).
       Support for SNI on the client side was added somewhere in the OpenSSL
       0.9.8 series, but only with 1.0 a bug was fixed when the server could
       not decide about its hostname. Therefore client side SNI is only
       supported with OpenSSL 1.0 or higher in IO::Socket::SSL.  With a
       supported version, SNI is used automatically on the client side, if it
       can determine the hostname from "PeerAddr" or "PeerHost". On
       unsupported OpenSSL versions it will silently not use SNI.  The
       hostname can also be given explicitly given with "SSL_hostname", but in
       this case it will throw in error, if SNI is not supported.  To check
       for support you might call "IO::Socket::SSL-"can_client_sni()>.
       On the server side earlier versions of OpenSSL are supported, but only
       together with Net::SSLeay version >= 1.50.  To check for support you
       might call "IO::Socket::SSL-"can_server_sni()>.  If server side SNI is
       supported, you might specify different certificates per host with
       "SSL_cert*" and "SSL_key*", and check the requested name using
       "get_servername".
RETURN VALUES
       A few changes have gone into IO::Socket::SSL v0.93 and later with
       respect to return values. The behavior on success remains unchanged,
       but for all functions, the return value on error is now an empty
       list.    Therefore, the return value will be false in all contexts, but
       those who have been using the return values as arguments to subroutines
       (like "mysub(IO::Socket::SSL(...)-"new, ...)>) may run into problems.
       The moral of the story: always check the return values of these
       functions before using them in any way that you consider meaningful.
DEBUGGING
       If you are having problems using IO::Socket::SSL despite the fact that
       can recite backwards the section of this documentation labelled 'Using
       SSL', you should try enabling debugging. To specify the debug level,
       pass 'debug#' (where # is a number from 0 to 3) to IO::Socket::SSL when
       calling it.  The debug level will also be propagated to
       Net::SSLeay::trace, see also Net::SSLeay:
       use IO::Socket::SSL qw(debug0);
           No debugging (default).
       use IO::Socket::SSL qw(debug1);
           Print out errors from IO::Socket::SSL and ciphers from Net::SSLeay.
       use IO::Socket::SSL qw(debug2);
           Print also information about call flow from IO::Socket::SSL and
           progress information from Net::SSLeay.
       use IO::Socket::SSL qw(debug3);
           Print also some data dumps from IO::Socket::SSL and from
           Net::SSLeay.
EXAMPLES
       See the 'example' directory.
BUGS
       IO::Socket::SSL depends on Net::SSLeay.  Up to version 1.43 of
       Net::SSLeay it was not thread safe, although it did probably work if
       you did not use SSL_verify_callback and SSL_password_cb.
       If you use IO::Socket::SSL together with threads you should load it
       (e.g. use or require) inside the main thread before creating any other
       threads which use it.  This way it is much faster because it will be
       initialized only once. Also there are reports that it might crash the
       other way.
       Creating an IO::Socket::SSL object in one thread and closing it in
       another thread will not work.
       IO::Socket::SSL does not work together with
       Storable::fd_retrieve/fd_store.  See BUGS file for more information and
       how to work around the problem.
       Non-blocking and timeouts (which are based on non-blocking) are not
       supported on Win32, because the underlying IO::Socket::INET does not
       support non-blocking on this platform.
       If you have a server and it looks like you have a memory leak you might
       check the size of your session cache. Default for Net::SSLeay seems to
       be 20480, see the example for SSL_create_ctx_callback for how to limit
       it.
       The default for SSL_verify_mode on the client is currently
       SSL_VERIFY_NONE, which is a very bad idea, thus the default will change
       in the near future.  See documentation for SSL_verify_mode for more
       information.
LIMITATIONS
       IO::Socket::SSL uses Net::SSLeay as the shiny interface to OpenSSL,
       which is the shiny interface to the ugliness of SSL.   As a result, you
       will need both Net::SSLeay and OpenSSL on your computer before using
       this module.
       If you have Scalar::Util (standard with Perl 5.8.0 and above) or
       WeakRef, IO::Socket::SSL sockets will auto-close when they go out of
       scope, just like IO::Socket::INET sockets.     If you do not have one
       of these modules, then IO::Socket::SSL sockets will stay open until the
       program ends or you explicitly close them.    This is due to the fact
       that a circular reference is required to make IO::Socket::SSL sockets
       act simultaneously like objects and glob references.
DEPRECATIONS
       The following functions are deprecated and are only retained for
       compatibility:
       context_init()
         use the SSL_reuse_ctx option if you want to re-use a context
       socketToSSL() and socket_to_SSL()
         use IO::Socket::SSL->start_SSL() instead
       kill_socket()
         use close() instead
       get_peer_certificate()
         use the peer_certificate() function instead.  Used to return
         X509_Certificate with methods subject_name and issuer_name.  Now
         simply returns $self which has these methods (although deprecated).
       issuer_name()
         use peer_certificate( 'issuer' ) instead
       subject_name()
         use peer_certificate( 'subject' ) instead
SEE ALSO
       IO::Socket::INET, IO::Socket::INET6, IO::Socket::IP, Net::SSLeay.
AUTHORS
       Steffen Ullrich, <steffen at genua.de> is the current maintainer.
       Peter Behroozi, <behrooz at fas.harvard.edu> (Note the lack of an "i"
       at the end of "behrooz")
       Marko Asplund, <marko.asplund at kronodoc.fi>, was the original author
       of IO::Socket::SSL.
       Patches incorporated from various people, see file Changes.
COPYRIGHT
       The original versions of this module are Copyright (C) 1999-2002 Marko
       Asplund.
       The rewrite of this module is Copyright (C) 2002-2005 Peter Behroozi.
       Versions 0.98 and newer are Copyright (C) 2006-2013 Steffen Ullrich.
       This module is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.
Appendix: Using SSL
       If you are unfamiliar with the way OpenSSL works, good references may
       be found in both the book "Network Security with OpenSSL" (Oreilly &
       Assoc.) and the web site
       <http://www.tldp.org/HOWTO/SSL-Certificates-HOWTO/>;.  Read on for a
       quick overview.
   The Long of It (Detail)
       The usual reason for using SSL is to keep your data safe.  This means
       that not only do you have to encrypt the data while it is being
       transported over a network, but you also have to make sure that the
       right person gets the data.    To accomplish this with SSL, you have to
       use certificates.   A certificate closely resembles a Government-issued
       ID (at least in places where you can trust them).     The ID contains
       some sort of identifying information such as a name and address, and is
       usually stamped with a seal of Government Approval.   Theoretically,
       this means that you may trust the information on the card and do
       business with the owner of the card.  The same ideas apply to SSL
       certificates, which have some identifying information and are "stamped"
       [most people refer to this as signing instead] by someone (a
       Certificate Authority) who you trust will adequately verify the
       identifying information.  In this case, because of some clever number
       theory, it is extremely difficult to falsify the stamping
       process.  Another useful consequence of number theory is that the
       certificate is linked to the encryption process, so you may encrypt
       data (using information on the certificate) that only the certificate
       owner can decrypt.
       What does this mean for you?  It means that at least one person in the
       party has to have an ID to get drinks :-).  Seriously, it means that
       one of the people communicating has to have a certificate to ensure
       that your data is safe.   For client/server interactions, the server
       must always have a certificate.      If the server wants to verify that
       the client is safe, then the client must also have a personal
       certificate.  To verify that a certificate is safe, one compares the
       stamped "seal" [commonly called an encrypted digest/hash/signature] on
       the certificate with the official "seal" of the Certificate Authority
       to make sure that they are the same.    To do this, you will need the
       [unfortunately named] certificate of the Certificate Authority.  With
       all these in hand, you can set up a SSL connection and be reasonably
       confident that no-one is reading your data.
   The Short of It (Summary)
       For servers, you will need to generate a cryptographic private key and
       a certificate request.  You will need to send the certificate request
       to a Certificate Authority to get a real certificate back, after which
       you can start serving people. For clients, you will not need anything
       unless the server wants validation, in which case you will also need a
       private key and a real certificate.     For more information about how
       to get these, see <http://www.modssl.org/docs/2.8/ssl_faq.html#ToC24>;.

perl v5.16.3                      2018-04-10                IO::Socket::SSL(3)