IO::Socket::SSL(3pm) User Contributed Perl Documentation IO::Socket::SSL(3pm)NAMEIO::Socket::SSL-- SSL sockets with IO::Socket interface
SYNOPSIS
use strict;
use IO::Socket::SSL;
# simple HTTP client -----------------------------------------------
my $client = IO::Socket::SSL->new(
# where to connect
PeerHost => "www.example.com",
PeerPort => "https",
# certificate verification
SSL_verify_mode => SSL_VERIFY_PEER,
SSL_ca_path => '/etc/ssl/certs', # typical CA path on Linux
# on OpenBSD instead: SSL_ca_file => '/etc/ssl/cert.pem'
# easy hostname verification
SSL_verifycn_name => 'foo.bar', # defaults to PeerHost
SSL_verifycn_scheme => '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 ....
# use non-blocking socket (BEWARE OF SELECT!) -------------------
my $cl = IO::Socket::SSL->new($dst);
$cl->blocking(0);
my $sel = IO::Select->new($cl);
while (1) {
# with SSL a call for reading n bytes does not result in reading of n
# bytes from the socket, but instead it must read at least one full SSL
# frame. If the socket has no new bytes, but there are unprocessed data
# from the SSL frame can_read will block!
# wait for data on socket
$sel->can_read();
# new data on socket or eof
READ:
# this does not read only 1 byte from socket, but reads the complete SSL
# frame and then just returns one byte. On subsequent calls it than
# returns more byte of the same SSL frame until it needs to read the
# next frame.
my $n = sysread( $cl,my $buf,1);
if ( ! defined $n ) {
die $! if not ${EAGAIN};
next if $SSL_ERROR == SSL_WANT_READ;
if ( $SSL_ERROR == SSL_WANT_WRITE ) {
# need to write data on renegotiation
$sel->can_write;
next;
}
die "something went wrong: $SSL_ERROR";
} elsif ( ! $n ) {
last; # eof
} else {
# read next bytes
# we might have still data within the current SSL frame
# thus first process these data instead of waiting on the underlying
# socket object
goto READ if $self->pending; # goto sysread
next; # goto $sel->can_read
}
}
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 section 'Using
SSL' before attempting to use this module.
If you used IO::Socket before you should read the following section
'Differences to IO::Socket'.
If you want to use SSL with non-blocking sockets and/or within an event
loop please read very carefully the sections about non-blocking I/O and
polling of SSL sockets.
If you are trying to use it with threads see the BUGS section.
Differences to IO::Socket
Although IO::Socket::SSL tries to behave similar to IO::Socket there
are some important differences due to the way SSL works:
· buffered input
Data are transmitted inside the SSL protocol using encrypted
frames, which can only be decrypted once the full frame is
received. So if you use "read" or "sysread" to receive less data
than the SSL frame contains, it will read the whole frame, return
part of it and buffer the rest for later reads. This does not make
a difference for simple programs, but if you use select-loops or
polling or non-blocking I/O please read the related sections.
· SSL handshakes
Before any encryption can be done the peers have to agree to common
algorithms, verify certificates etc. So a handshake needs to be
done before any payload is send or received and might additionally
happen later in the connection again.
This has important implications when doing non-blocking or event-
based I/O (please read the related sections), but means also, that
connect and accept calls include the SSL handshake and thus might
block or fail, if the peer does not behave like expected. For
instance accept will wait infinitly if a TCP client connects to the
socket but does not initiate an SSL handshake.
METHODSIO::Socket::SSL inherits from another IO::Socket module. The choice of
the super class depends on the installed modules:
· 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.
· If IO::Socket::INET6 is installed it will use this module as super
class, transparently providing IPv6 and IPv4 support.
· 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 the super class (e.g.
IO::Socket::IP, IO::Socket::INET, ...) plus (optionally) the ones
described below. If you don't specify any SSL related options it
will do it's best in using secure defaults, e.g. chosing good
ciphers, enabling proper verification etc.
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 'SSLv23:!SSLv2' which 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:!aNULL'. Look into the OpenSSL documentation
(<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_STRINGS>)
for more details.
Unless you fail to contact your peer because of no shared ciphers
it is recommended to leave this option at the default setting.
The default setting prefers ciphers with forward secrecy,
disables anonymous authentication and disables known insecure
ciphers like MD5, DES etc. This gives a grade A result at the
tests of SSL Labs. To use the less secure OpenSSL builtin
default (whatever this is) set SSL_cipher_list to ''.
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. This option
defaults to true to make use of our secure cipher list setting.
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 | SSL_cert | SSL_key_file | SSL_key
If you create a server you usually need to specify a server
certificate which should be verified by the client. Same is true
for client certificates, which should be verified by the server.
The certificate can be given as a file in PEM format with
SSL_cert_file or as an internal representation of a X509* object
with SSL_cert.
For each certificate a key is need, which can either be given as
a file in PEM format with SSL_key_file or as an internal
representation of a EVP_PKEY* object with SSL_key.
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>>.
In case certs and keys are needed but not given it might fall
back to builtin defaults, see "Defaults for Cert, Key and CA".
Examples:
SSL_cert_file => 'mycert.pem',
SSL_key_file => 'mykey.pem',
SSL_cert_file => {
"foo.example.org" => 'foo-cert.pem',
"bar.example.org" => 'bar-cert.pem',
# used when nothing matches or client does not support SNI
'' => 'default-cert.pem',
}
SSL_key_file => {
"foo.example.org" => 'foo-key.pem',
"bar.example.org" => 'bar-key.pem',
# used when nothing matches or client does not support SNI
'' => 'default-key.pem',
}
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 forward secrecy you need to either give the DH
parameters or (better, because faster) the ECDH curve.
If neither "SSL_dh_file" not "SSL_dh" is set a builtin DH
parameter with a length of 2048 bit is used to offer DH key
exchange by default. If you don't want this (e.g. disable DH key
exchange) explicitly set this or the "SSL_dh" parameter to undef.
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 forward secrecy you need
to either give the DH parameters or (better, because faster) the
ECDH curve.
This parameter defaults to 'prime256v1' (builtin of OpenSSL) to
offer ECDH key exchange by default. If you don't want this
explicitly set it to undef.
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 | SSL_ca_path
Usually you want to verify that the peer certificate has been
signed by a trusted certificate authority. In this case you
should use this option to specify the file (SSL_ca_file) or
directory (SSL_ca_path) containing the certificate(s) of the
trusted certificate authorities. If both SSL_ca_file and
SSL_ca_path are undefined and not builtin defaults (see "Defaults
for Cert, Key and CA".) can be used, it will try to use the
system defaults used built into the OpenSSL library. If you
really don't want to set a CA set this key to ''.
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) and SSL_VERIFY_PEER for client (check server
certificate).
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 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_key
Specifies a key to use for lookups and inserts into client-side
session cache. Per default ip:port of destination will be used,
but sometimes you want to share the same session over multiple
ports on the same server (like with FTPS).
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.
accept
This behaves similar to the accept function of the underlying
socket class, but additionally does the initial SSL handshake. But
because the underlying socket class does return a blocking file
handle even when accept is called on a non-blocking socket, the SSL
handshake on the new file object will be done in a blocking way.
Please see the section about non-blocking I/O for details. If you
don't like this behavior you should do accept on the TCP socket and
then upgrade it with "start_SSL" later.
connect(...)
This behaves similar to the connnect function but also does an SSL
handshake. Because you cannot give SSL specific arguments to this
function, you should better either use "new" to create a connect
SSL socket or "start_SSL" to upgrade an established TCP socket to
SSL.
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.
Not using a real ssl shutdown on a socket will make session
caching unusable.
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 sent.
Otherwise a bidirectional shutdown will be done where it waits
for the close_notify of the peer too.
Because a unidirectional shutdown is enough to keep session cache
working it defaults to fast shutdown inside close.
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.
sysread( BUF, LEN, [ OFFSET ] )
This function behaves from the outside the same as sysread in other
IO::Socket objects, e.g. it returns at most LEN bytes of data. But
in reality it reads not only LEN bytes from the underlying socket,
but at a single SSL frame. It then returns up to LEN bytes it
decrypted from this SSL frame. If the frame contained more data
than requested it will return only LEN data, buffer the rest and
return it on futher read calls. This means, that it might be
possible to read data, even if the underlying socket is not
readable, so using poll or select might not be sufficient.
sysread will only return data from a single SSL frame, e.g. either
the pending data from the already buffered frame or it will read a
frame from the underlying socket and return the decrypted data. It
will not return data spanning several SSL frames in a single call.
Also, calls to sysread might fail, because it must first finish an
SSL handshake.
To understand these behaviors is essential, if you write
applications which use event loops and/or non-blocking sockets.
Please read the specific sections in this documentation.
syswrite( BUF, [ LEN, [ OFFSET ]] )
This functions behaves from the outside the same as syswrite in
other IO::Socket objects, e.g. it will write at most LEN bytes to
the socket, but there is no guarantee, that all LEN bytes are
written. It will return the number of bytes written. syswrite will
write all the data within a single SSL frame, which means, that no
more than 16.384 bytes, which is the maximum size of an SSL frame,
can be written at once.
For non-blocking sockets SSL specific behavior applies. Pease read
the specific section in this documentation.
peek( BUF, LEN, [ OFFSET ])
This function has exactly the same syntax as sysread, and performs
nearly the same task 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 gives you the number of bytes available without
reading from the underlying socket object. This function is
essential if you work with event loops, please see the section
about polling SSL sockets.
get_cipher()
Returns the string form of the cipher that the IO::Socket::SSL
object is using.
get_sslversion()
Returns the string representation of the SSL version of an
established connection.
get_sslversion_int()
Returns the integer representation of the SSL version of an
established connection.
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 $! is set to EAGAIN
and the ssl error to SSL_WANT_READ or SSL_WANT_WRITE. In this case
the call should be retried again with the same arguments once the
socket is ready.
For calling from "stop_SSL" "SSL_fast_shutdown" default to false,
e.g. it waits for the close_notify of the peer. This is necesarry
in case you want to downgrade the socket and continue to use it as
a plain socket.
IO::Socket::SSL->new_from_fd($fd, [mode], %sslargs)
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.
Internally the given $fd will be upgraded to a socket object using
the "new_from_fd" method of the super class (IO::Socket::INET or
similar) and then "start_SSL" will be called using the given
%sslargs. If $fd is already an IO::Socket object you should better
call "start_SSL" directly.
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'
IO::Socket::SSL::set_client_defaults(%args)
Similar to "set_defaults", but only sets the defaults for client
mode.
IO::Socket::SSL::set_server_defaults(%args)
Similar to "set_defaults", but only sets the defaults for server
mode.
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.
Defaults for Cert, Key and CA
Only if no SSL_key*, no SSL_cert* and no SSL_ca* options are given it
will fall back to the following builtin defaults:
SSL_cert_file
Depending on the SSL_server setting it will be either
"certs/server-cert.pem" or "certs/client-cert.pem".
SSL_key_file
Depending on the SSL_server setting it will be either
"certs/server-key.pem" or "certs/client-key.pem".
SSL_ca_file | SSL_ca_path
It will set SSL_ca_file to "certs/my-ca.pem" if it exist.
Otherwise it will set SSL_ca_path to "ca/" if it exist.
Please note, that these defaults are depreciated and will be removed in
the near future, e.g. you should specify all the certificates and keys
you use. If you don't specify a CA file or path it will fall back to
the system default built into OpenSSL.
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.
Polling of SSL Sockets (e.g. select, poll and other event loops)
If you sysread one byte on a normal socket it will result in a syscall
to read one byte. Thus, if more than one byte is available on the
socket it will be kept in the network stack of your OS and the next
select or poll call will return the socket as readable. But, with SSL
you don't deliver single bytes. Multiple data bytes are packet and
encrypted together in an SSL frame. Decryption can only be done on the
whole frame, so a sysread for one byte actually reads the complete SSL
frame from the socket, decrypts it and returns the first decrypted
byte. Further sysreads will return more bytes from the same frame until
all bytes are returned and the next SSL frame will be read from the
socket.
Thus, in order to decide if you can read more data (e.g. if sysread
will block) you must check, if there are still data in the current SSL
frame by calling "pending" and if there are no data pending you might
check the underlying socket with select or poll. Another way might be
if you try to sysread at least 16k all the time. 16k is the maximum
size of an SSL frame and because sysread returns data from only a
single SSL frame you guarantee this way, that there are no pending
data. Please see the example on top of this documentation on how to
use SSL within a select loop.
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 handshakes might occure at any time, even within an
established connections. In this cases it is necessary to finish the
handshake, before you can read or write data. This might result in
situations, where you want to read but must first finish the write of a
handshake or where you want to write but must first finish a read. 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.
Also, I would advise against using "accept" with a non-blocking SSL
object, because it might block and this is not what most would expect.
The reason for this is that accept on a non-blocking TCP socket (e.g.
IO::Socket::IP, IO::Socket::INET..) results in a new TCP socket, which
does not inherit the non-blocking behavior of the master socket. And
thus the initial SSL handshake on the new socket inside
"IO::Socket::SSL::accept" will be done in a blocking way. To work
around it you should better do an TCP accept and later upgrade the TCP
socket in a non-blocking way with "start_SSL" and "accept_SSL".
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::SSLqw(debug0);
No debugging (default).
use IO::Socket::SSLqw(debug1);
Print out errors from IO::Socket::SSL and ciphers from Net::SSLeay.
use IO::Socket::SSLqw(debug2);
Print also information about call flow from IO::Socket::SSL and
progress information from Net::SSLeay.
use IO::Socket::SSLqw(debug3);
Print also some data dumps from IO::Socket::SSL and from
Net::SSLeay.
EXAMPLES
See the 'example' directory.
BUGSIO::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.
LIMITATIONSIO::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, e.g. you need to authenticate the person.
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" (signed) by someone
(a CA, e.g. 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 signing
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? So most common case is that at least the
server has a certificate which the client can verify, but the server
may also ask back for a certificate to authenticate the client. To
verify that a certificate is trusted, one checks if the certificate is
signed by the expected CA (Certificate Authority), which often means
any CA installed on the system (IO::Socket::SSL tries to use the CAs
installed on the system by default). So if you trust the CA, trust the
number theory and trust the used algorithms you can be confident, that
no-one is reading your data.
Beside the authentication using certificates there is also anonymous
authentication, which effectivly means no authentication. In this case
it is easy for somebody in between to intercept the connection, e.g.
playing man in the middle and nobody notices. By default
IO::Socket::SSL uses only ciphers which require certificates and which
are safe enough, but if you want to set your own cipher_list make sure,
that you explicitly exclude anonymous authentication. E.g. setting the
cipher list to HIGH is not enough, you should use at least HIGH:!aNULL.
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 v5.18.2 2014-01-16 IO::Socket::SSL(3pm)