| IO::Socket::SSL - SSL sockets with IO::Socket interface |
IO::Socket::SSL - SSL sockets with IO::Socket interface
use strict;
use IO::Socket::SSL;
# simple client
my $cl = IO::Socket::SSL->new('www.google.com:443');
print $cl "GET / HTTP/1.0\r\n\r\n";
print <$cl>;
# simple server
my $srv = IO::Socket::SSL->new(
LocalAddr => '0.0.0.0:1234',
Listen => 10,
SSL_cert_file => 'server-cert.pem',
SSL_key_file => 'server-key.pem',
);
$srv->accept;
IO::Socket::SSL makes using SSL/TLS much easier by wrapping the necessary functionality into the familiar the IO::Socket manpage interface and providing secure defaults whenever possible. This way, existing applications can be made SSL-aware without much effort, at least if you do blocking I/O and don't use select or poll.
But, under the hood, SSL is a complex beast. So there are lots of methods to make it do what you need if the default behavior is not adequate. Because it is easy to inadvertently introduce critical security bugs or just hard to debug problems, I would recommend studying the following documentation carefully.
The documentation consists of the following parts:
Additional documentation can be found in
SSL (Secure Socket Layer) or its successor TLS (Transport Layer Security) are protocols to facilitate end-to-end security. These protocols are used when accessing web sites (https), delivering or retrieving email, and in lots of other use cases. In the following documentation we will refer to both SSL and TLS as simply 'SSL'.
SSL enables end-to-end security by providing two essential functions:
Identification is the part which is the hardest to understand and the easiest to get wrong.
With SSL, the Identification is usually done with certificates inside a PKI (Public Key Infrastructure). These Certificates are comparable to an identity card, which contains information about the owner of the card. The card then is somehow signed by the issuer of the card, the CA (Certificate Agency).
To verify the identity of the peer the following must be done inside SSL:
We believe that a certificate is not a fake if we either know the certificate already or if we trust the issuer (the CA) and can verify the issuers signature on the certificate. In reality there is often a hierarchy of certificate agencies and we only directly trust the root of this hierarchy. In this case the peer not only sends his own certificate, but also all intermediate certificates. Verification will be done by building a trust path from the trusted root up to the peers certificate and checking in each step if the we can verify the issuer's signature.
This step often causes problems because the client does not know the necessary trusted root certificates. These are usually stored in a system dependent CA store, but often the browsers have their own CA store.
Check if the certificate is still valid. Each certificate has a lifetime and should not be used after that time because it might be compromised or the underlying cryptography got broken in the mean time. Check if the subject of the certificate matches the peer. This is like comparing the picture on the identity card against the person representing the identity card.When connecting to a server this is usually done by comparing the hostname used for connecting against the names represented in the certificate. A certificate might contain multiple names or wildcards, so that it can be used for multiple hosts (e.g. *.example.com and *.example.org).
Although nobody sane would accept an identity card where the picture does not match the person we see, it is a common implementation error with SSL to omit this check or get it wrong.
Check if the certificate was revoked by the issuer. This might be the case if the certificate was compromised somehow and now somebody else might use it to claim the wrong identity. Such revocations happened a lot after the heartbleed attack.For SSL there are two ways to verify a revocation, CRL and OCSP. With CRLs (Certificate Revocation List) the CA provides a list of serial numbers for revoked certificates. The client somehow has to download the list (which can be huge) and keep it up to date. With OCSP (Online Certificate Status Protocol) the client can check a single certificate directly by asking the issuer.
Revocation is the hardest part of the verification and none of today's browsers get it fully correct. But, they are still better than most other implementations which don't implement revocation checks or leave the hard parts to the developer.
When accessing a web site with SSL or delivering mail in a secure way the identity is usually only checked one way, e.g. the client wants to make sure it talks to the right server, but the server usually does not care which client it talks to. But, sometimes the server wants to identify the client too and will request a certificate from the client which the server must verify in a similar way.
A basic SSL client is simple:
my $client = IO::Socket::SSL->new('www.example.com:443')
or die "error=$!, ssl_error=$SSL_ERROR";
This will take the OpenSSL default CA store as the store for the trusted CA. This usually works on UNIX systems. If there are no certificates in the store it will try use the Mozilla::CA manpage which provides the default CAs of Firefox.
In the default settings, the IO::Socket::SSL manpage will use a safer cipher set and SSL
version, do a proper hostname check against the certificate, and use SNI (server
name indication) to send the hostname inside the SSL handshake. This is
necessary to work with servers which have different certificates behind the
same IP address.
It will also check the revocation of the certificate with OCSP, but currently
only if the server provides OCSP stapling (for deeper checks see
ocsp_resolver method).
Lots of options can be used to change ciphers, SSL version, location of CA and much more. See documentation of methods for details.
With protocols like SMTP it is necessary to upgrade an existing socket to SSL. This can be done like this:
my $client = IO::Socket::INET->new('mx.example.com:25') or die $!;
# .. read greeting from server
# .. send EHLO and read response
# .. send STARTTLS command and read response
# .. if response was successful we can upgrade the socket to SSL now:
IO::Socket::SSL->start_SSL($client,
# explicitly set hostname we should use for SNI
SSL_hostname => 'mx.example.com'
) or die $SSL_ERROR;
A more complete example for a simple HTTP client:
my $client = IO::Socket::SSL->new(
# where to connect
PeerHost => "www.example.com",
PeerPort => "https",
# certificate verification - VERIFY_PEER is default
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
# or just use default path on system:
IO::Socket::SSL::default_ca(), # either explicitly
# or implicitly by not giving SSL_ca_*
# easy hostname verification
# It will use PeerHost as default name a verification
# scheme as default, which is safe enough for most purposes.
SSL_verifycn_name => 'foo.bar',
SSL_verifycn_scheme => 'http',
# SNI support - defaults to PeerHost
SSL_hostname => 'foo.bar',
) 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>;
And to do revocation checks with OCSP (only available with OpenSSL 1.0.0 or higher and the Net::SSLeay manpage 1.59 or higher):
# default will try OCSP stapling and check only leaf certificate
my $client = IO::Socket::SSL->new($dst);
# better yet: require checking of full chain
my $client = IO::Socket::SSL->new(
PeerAddr => $dst,
SSL_ocsp_mode => SSL_OCSP_FULL_CHAIN,
);
# even better: make OCSP errors fatal
# (this will probably fail with lots of sites because of bad OCSP setups)
# also use common OCSP response cache
my $ocsp_cache = IO::Socket::SSL::OCSP_Cache->new;
my $client = IO::Socket::SSL->new(
PeerAddr => $dst,
SSL_ocsp_mode => SSL_OCSP_FULL_CHAIN|SSL_OCSP_FAIL_HARD,
SSL_ocsp_cache => $ocsp_cache,
);
# disable OCSP stapling in case server has problems with it
my $client = IO::Socket::SSL->new(
PeerAddr => $dst,
SSL_ocsp_mode => SSL_OCSP_NO_STAPLE,
);
# check any certificates which are not yet checked by OCSP stapling or
# where we have already cached results. For your own resolving combine
# $ocsp->requests with $ocsp->add_response(uri,response).
my $ocsp = $client->ocsp_resolver();
my $errors = $ocsp->resolve_blocking();
if ($errors) {
warn "OCSP verification failed: $errors";
close($client);
}
A basic SSL server looks similar to other the IO::Socket manpage servers, only that it also contains settings for certificate and key:
# 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";
This will automatically use a secure set of ciphers and SSL version and also supports Forward Secrecy with (Elliptic-Curve) Diffie-Hellmann Key Exchange.
If you are doing a forking or threading server, we recommend that you do the SSL handshake inside the new process/thread so that the master is free for new connections. We recommend this because a client with improper or slow SSL handshake could make the server block in the handshake which would be bad to do on the listening socket:
# inet server
my $server = IO::Socket::INET->new(
# where to listen
LocalAddr => '127.0.0.1',
LocalPort => 8080,
Listen => 10,
);
# accept client
my $client = $server->accept or die;
# SSL upgrade client (in new process/thread)
IO::Socket::SSL->start_SSL($client,
SSL_server => 1,
SSL_cert_file => 'cert.pem',
SSL_key_file => 'key.pem',
) or die "failed to ssl handshake: $SSL_ERROR";
Like with normal sockets, neither forking nor threading servers scale well. It is recommended to use non-blocking sockets instead, see Using Non-Blocking Sockets
This is a list of typical errors seen with the use of the IO::Socket::SSL manpage:
SSL_verify_mode.
As described in Essential Information About SSL/TLS, a proper identification of the peer is essential and failing to verify makes Man-In-The-Middle attacks possible.
Nevertheless, lots of scripts and even public modules or applications disable verification, because it is probably the easiest way to make the thing work and usually nobody notices any security problems anyway.
If the verification does not succeed with the default settings, one can do the following:
SSL_ca_file or
SSL_ca_path to specify a different CA store.
If the validation fails because the certificate is self-signed and that's what
you expect, you can use the SSL_fingerprint option to accept specific
certificates by their certificate fingerprint.
If the validation failed because the hostname does not match and you cannot
access the host with the name given in the certificate, you can use
SSL_verifycn_name to specify they hostname you expect in the certificate.
A common error pattern is also to disable verification if they found no CA
store (different modules look at different ``default'' places).
Because the IO::Socket::SSL manpage is now able to provide a usable CA store on most
platforms (UNIX, Mac OSX and Windows) it is better to use the defaults provided
by the IO::Socket::SSL manpage.
If necessary these can be checked with the default_ca method.
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 packaged 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 16kByte all the time.
16kByte is the maximum size of an SSL frame and because sysread returns data
from only a single SSL frame you can guarantee that there are no pending
data.
See also Using Non-Blocking Sockets.
Set 'SSL_version' or 'SSL_cipher_list' to a ``better'' value.the IO::Socket::SSL manpage tries to set these values to reasonable, secure values which are compatible with the rest of the world. But, there are some scripts or modules out there which tried to be smart and get more secure or compatible settings. Unfortunately, they did this years ago and never updated these values, so they are still forced to do only 'TLSv1' (instead of also using TLSv12 or TLSv11). Or they set 'HIGH' as the cipher list and thought they were secure, but did not notice that 'HIGH' includes anonymous ciphers, e.g. without identification of the peer.
So it is recommended to leave the settings at the secure defaults which the IO::Socket::SSL manpage sets and which get updated from time to time to better fit the real world.
Make SSL settings inaccessible by the user, together with bad builtin settings.Some modules use the IO::Socket::SSL manpage, but don't make the SSL settings available to the user. This is often combined with bad builtin settings or defaults (like switching verification off).
Thus the user needs to hack around these restrictions by using
set_args_filter_hack or similar.
Constants like SSL_VERIFY_PEER or SSL_WANT_READ should be used as
constants and not be put inside quotes, because they represent numerical values.
SSL is a complex protocol with multiple implementations and each of these has their own quirks. While most of these implementations work together, it often gets problematic with older versions, minimal versions in load balancers, or plain wrong setups.
Unfortunately these problems are hard to debug.
Helpful for debugging are a knowledge of SSL internals, wireshark and the use of
the debug settings of the IO::Socket::SSL manpage and the Net::SSLeay manpage, which can both be
set with $IO::Socket::SSL::DEBUG.
The following debugs levels are defined, but used not in any consistent way:
Also, analyze-ssl.pl from the ssl-tools repository at
https://github.com/noxxi/p5-ssl-tools might be a helpful tool when debugging
SSL problems, as do the openssl command line tool and a check with a
different SSL implementation (e.g. a web browser).
The following problems are not uncommon:
It is a regular problem that administrators fail to include all necessary certificates into their server setup, e.g. everything needed to build the trust chain from the trusted root. If they check the setup with the browser everything looks ok, because browsers work around these problems by caching any intermediate certificates and apply them to new connections if certificates are missing.
But, fresh browser profiles which have never seen these intermediates cannot fill in the missing certificates and fail to verify; the same is true with the IO::Socket::SSL manpage.
Old versions of servers or load balancers which do not understand specific TLS versions or croak on specific data.From time to time one encounters an SSL peer, which just closes the connection
inside the SSL handshake. This can usually be worked around by downgrading the
SSL version, e.g. by setting SSL_version. Modern Browsers usually deal with
such servers by automatically downgrading the SSL version and repeat the
connection attempt until they succeed.
Worse servers do not close the underlying TCP connection but instead just drop the relevant packet. This is harder to detect because it looks like a stalled connection. But downgrading the SSL version often works here too.
A cause of such problems are often load balancers or security devices, which have hardware acceleration and only a minimal (and less robust) SSL stack. They can often be detected because they support much fewer ciphers than other implementations.
Bad or old OpenSSL versions.the IO::Socket::SSL manpage uses OpenSSL with the help of the the Net::SSLeay manpage library. It is recommend to have a recent version of this library, because it has more features and usually fewer known bugs.
Validation of client certificates fail.Make sure that the purpose of the certificate allows use as ssl client (check
with openssl x509 -purpose, that the necessary root certificate is in the
path specified by SSL_ca* (or the default path) and that any intermediate
certificates needed to build the trust chain are sent by the client.
If you have a non-blocking socket, the expected behavior on read, write, accept
or connect is to set $! to EWOULDBLOCK if the operation can not be completed
immediately. Note that EWOULDBLOCK is the same as EAGAIN on UNIX systems, but
is different on Windows.
With SSL, handshakes might occur at any time, even within an established
connection. In these 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 EAGAIN like expected, and additionally
$SSL_ERROR is set to either SSL_WANT_READ or SSL_WANT_WRITE.
Thus if you get EWOULDBLOCK 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 the IO::Socket manpage 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. the IO::Socket::IP manpage,
the IO::Socket::INET manpage..) 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 this you are safer by doing a TCP accept and later upgrade the
TCP socket in a non-blocking way with start_SSL and accept_SSL.
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 ${EWOULDBLOCK};
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 $cl->pending; # goto sysread
next; # goto $sel->can_read
}
}
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 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 the IO::Socket::SSL manpage.
With a supported version, SNI is used automatically on the client side, if it
can determine the hostname from PeerAddr or PeerHost (which are synonyms
in the underlying IO::Socket:: classes and thus should never be set both or at
least not to different values).
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 the Net::SSLeay manpage 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.
It is often required to first exchange some plain data and then upgrade the socket to SSL after some kind of STARTTLS command. Protocols like FTPS even need a way to downgrade the socket again back to plain.
The common way to do this would be to create a normal socket and use start_SSL
to upgrade and stop_SSL to downgrade:
my $sock = IO::Socket::INET->new(...) or die $!;
... exchange plain data on $sock until starttls command ...
IO::Socket::SSL->start_SSL($sock,%sslargs) or die $SSL_ERROR;
... now $sock is a IO::Socket::SSL object ...
... exchange data with SSL on $sock until stoptls command ...
$sock->stop_SSL or die $SSL_ERROR;
... now $sock is again a IO::Socket::INET object ...
But, lots of modules just derive directly from the IO::Socket::INET manpage. While this base class can be replaced with the IO::Socket::SSL manpage, these modules cannot easily support different base classes for SSL and plain data and switch between these classes on a starttls command.
To help in this case, the IO::Socket::SSL manpage can be reduced to a plain socket on
startup, and connect_SSL/accept_SSL/start_SSL can be used to enable SSL and
stop_SSL to talk plain again:
my $sock = IO::Socket::SSL->new(
PeerAddr => ...
SSL_startHandshake => 0,
%sslargs
) or die $!;
... exchange plain data on $sock until starttls command ...
$sock->connect_SSL or die $SSL_ERROR;
... now $sock is a IO::Socket::SSL object ...
... exchange data with SSL on $sock until stoptls command ...
$sock->stop_SSL or die $SSL_ERROR;
... $sock is still a IO::Socket::SSL object ...
... but data exchanged again in plain ...
the IO::Socket::SSL manpage behaves similarly to other the IO::Socket manpage modules and thus could be integrated in the same way, but you have to take special care when using non-blocking I/O (like for handling timeouts) or using select or poll. Please study the documentation on how to deal with these differences.
Also, it is recommended to not set or touch most of the SSL_* options, so
that they keep their secure defaults. It is also recommended to let the user
override these SSL specific settings without the need of global settings or hacks
like set_args_filter_hack.
The notable exception is SSL_verifycn_scheme.
This should be set to the hostname verification scheme required by the module or
protocol.
the IO::Socket::SSL manpage inherits from another the IO::Socket manpage module. The choice of the super class depends on the installed modules:
Please be aware that with the IPv6 capable super classes, it will look 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 enforce IPv4 for a specific socket by
using the Domain or Family option with the value AF_INET as described in
the IO::Socket::IP manpage. Alternatively you can enforce IPv4 globally by loading
the IO::Socket::SSL manpage with the option 'inet4', in which case it will use the IPv4
only class the IO::Socket::INET manpage as the super class.
the IO::Socket::SSL manpage 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 also read the section about SSL specific error handling.
$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 the errstr method give a dualvar similar to $!, e.g.
providing an error number in numeric context or an error description in string
context.
Listen parameter is given
when creating the socket.
PeerAddr, which will fail if only an IP was given or if
this argument is used within start_SSL.
If you want to disable SNI, set this argument to ''.
Currently only supported for the client side and will be ignored for the server side.
See section ``SNI Support'' for details of SNI the support.
accept_SSL or connect_SSL.
Before the handshake is started read/write/etc. can be used to exchange plain
data.
SSL_ca_file) or directory (SSL_ca_path) containing the
certificate(s) of the trusted certificate authorities.
SSL_ca_path can also be an array or a string containing multiple path, where
the path are separated by the platform specific separator. This separator is
; on DOS, Windows, Netware, , on VMS and : for all the other systems.
If multiple path are given at least one of these must be accessible.
You can also give a list of X509* certificate handles (like you get from
the Net::SSLeay manpage or the IO::Socket::SSL::Utils::PEM_xxx2cert manpage) with SSL_ca. These
will be added to the CA store before path and file and thus take precedence.
If neither SSL_ca, nor SSL_ca_file or SSL_ca_path are set it will use
default_ca() to determine the user-set or system defaults.
If you really don't want to set a CA set SSL_ca_file or SSL_ca_path to
\undef or SSL_ca to an empty list. (unfortunately '' is used by some
modules using the IO::Socket::SSL manpage when CA is not explicitly given).
SSL_ca and SSL_ca_file.
'algo$hex_fingerprint'. algo is a fingerprint algorithm
supported by OpenSSL, e.g. 'sha1','sha256'... and hex_fingerprint is the
hexadecimal representation of the binary fingerprint.
To get the fingerprint of an established connection you can use
get_fingerprint.
You can specify a list of fingerprints in case you have several acceptable certificates. If a fingerprint matches the topmost certificate no additional validations can make the verification fail.
If given as a list of X509* please note, that the all the chain certificates (e.g. all except the first) will be ``consumed'' by openssl and will be freed if the SSL context gets destroyed - so you should never free them yourself. But the servers certificate (e.g. the first) will not be consumed by openssl and thus must be freed by the application.
For each certificate a key is need, which can either be given as a file with SSL_key_file or as an internal representation of a EVP_PKEY* object with SSL_key (like you get from the Net::SSLeay manpage or the IO::Socket::SSL::Utils::PEM_xxx2key manpage). If a key was already given within the PKCS#12 file specified by SSL_cert_file it will ignore any SSL_key or SSL_key_file. If no SSL_key or SSL_key_file was given it will try to use the PEM file given with SSL_cert_file again, maybe it contains the key too.
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_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).
Independent from the handshake format you can limit to set of accepted SSL versions by adding !version separated by ':'.
The default SSL_version is 'SSLv23:!SSLv3:!SSLv2' which means, that the handshake format is compatible to SSL2.0 and higher, but that the successful handshake is limited to TLS1.0 and higher, that is no SSL2.0 or SSL3.0 because both of these versions have serious security issues and should not be used anymore. You can also use !TLSv1_1 and !TLSv1_2 to disable TLS versions 1.1 and 1.2 while still allowing TLS version 1.0.
Setting the version instead to 'TLSv1' might break interaction with older clients, which need and SSL2.0 compatible handshake. 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:!SSLv3:!TLSv1_1:!TLSv1_2' might help.
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 ''.
In case different cipher lists are needed for different SNI hosts a hash can be given with the host as key and the cipher suite as value, similar to SSL_cert*.
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.
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.
You can check if ECDH support is available by calling
IO::Socket::SSL->can_ecdh.
The default is SSL_VERIFY_NONE for server (e.g. no check for client certificate) and SSL_VERIFY_PEER for client (check server certificate).
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.
If you don't specify a scheme it will use 'default', but only complain loudly if the name verification fails instead of letting the whole certificate verification fail. THIS WILL CHANGE, e.g. it will let the certificate verification fail in the future if the hostname does not match the certificate !!!! To override the name used in verification use SSL_verifycn_name.
The scheme 'default' is a superset of the usual schemes, which will accept the hostname in common name and subjectAltName and allow wildcards everywhere. While using this scheme is way more secure than no name verification at all you better should use the scheme specific to your application protocol, e.g. 'http', 'ftp'...
If you are really sure, that you don't want to verify the identity using the hostname you can use 'none' as a scheme. In this case you'd better have alternative forms of verification, like a certificate fingerprint or do a manual verification later by calling verify_hostname yourself.
If not specified it will simply use the builtin default of the IO::Socket::SSL::PublicSuffix manpage, you can create another object with from_string or from_file of this module.
To disable verification of public suffix set this option to ''.
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 or
SSL_hostname.
Any other OCSP checking needs to be done manually with ocsp_resolver.
The following flags can be combined with |:
Soft errors inside a stapled response are never considered hard, e.g. it is expected that in this case an OCSP request will be send to the responsible OCSP responder.
ocsp_resolver so that all certificates from the peer
chain will be checked, otherwise only the leaf certificate will be checked
against revocation.
<$cb-($ssl,$resp)>>.
If the peer did not provide a stapled OCSP response the function will be called
with $resp=undef.
Because the OCSP response handle is no longer valid after leaving this function
it should not by copied or freed. If access to the response is necessary after
leaving this function it can be serialized with
Net::SSLeay::i2d_OCSP_RESPONSE.
If no such callback is provided, it will use the default one, which verifies the
response and uses it to check if the certificate(s) of the connection got
revoked.
You can either create a new cache with
<IO::Socket::SSL::OCSP_Cache-new([size]) >> or implement your own cache,
which needs to have methods put($key,\%entry) and get($key)-\%entry>
where entry is the hash representation of the OCSP response with fields like
nextUpdate. The default implementation of the cache will consider responses
valid as long as nextUpdate is less then the current time.
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.
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);
}
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.
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.
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.
next_proto_negotiated.
Next Protocol Negotiation (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.
alpn_selected.
Application-Layer Protocol Negotiation (ALPN) is available with Net::SSLeay
1.56+ and openssl-1.0.2+. More details about the extension are in RFC7301. To
check support you might call IO::Socket::SSL-can_alpn() >. If you use this
option with an unsupported Net::SSLeay/OpenSSL it will throw an error.
Note that some client implementations may encounter problems if both NPN and ALPN are specified. Since ALPN is intended as a replacement for NPN, try providing ALPN protocols then fall back to NPN if that fails.
start_SSL later.
new to create a connect SSL socket or start_SSL to
upgrade an established TCP socket to SSL.
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. $socket->close(SSL_no_shutdown => 1))
and one or more of the following parameters:
close() not use the SSL_shutdown()
call on the socket in question so that the close operation can complete without
problems if you have used shutdown() or are working on a copy of a socket.
Not using a real ssl shutdown on a socket will make session caching unusable.
SSL_shutdown(3)) will be sent. Otherwise a bidirectional
shutdown will be done where it waits for the close_notify of the peer too.
Because a unidirectional shutdown is enough to keep session cache working it defaults to fast shutdown inside close.
sysread will only return data from a single SSL frame, e.g. either the pending data from the already buffered frame or it will read a frame from the underlying socket and return the decrypted data. It will not return data spanning several SSL frames in a single call.
Also, calls to sysread might fail, because it must first finish an SSL handshake.
To understand these behaviors is essential, if you write applications which use event loops and/or non-blocking sockets. Please read the specific sections in this documentation.
For non-blocking sockets SSL specific behavior applies. Pease read the specific section in this documentation.
peek() with the same arguments will return the same results. This function
requires OpenSSL 0.9.6a or later to work.
algo$digest_hex, where algo is the used algorithm, default 'sha256'.
If no certificate is given the peer certificate of the connection is used.
algo, default 'sha256'.
If no certificate is given the peer certificate of the connection is used.
dump_peer_certificate() method of
Net::SSLeay.
The following fields can be queried:
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.
peer_certificate but will return the sites own
certificate. The same arguments for $field can be used.
If no $field is given the certificate handle from the underlying OpenSSL will
be returned. This handle will only be valid as long as the SSL connection exists
and if used afterwards it might result in strange crashes of the application.
This function depends on a version of Net::SSLeay >= 1.58 .
SSL_verifycn_publicsuffix parameter for an explanation of suffix
checking and for the possible values.
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. RFC 6125 provides a good overview.
To ease the verification the following schemes are predefined (both protocol name and rfcXXXX name can be used):
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:
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.
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().
ALPN support is available with Net::SSLeay 1.56+ and openssl-1.0.2+.
To check support, use IO::Socket::SSL->can_alpn().
| 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 $SSL_ERROR against the exported symbols
SSL_WANT_READ and SSL_WANT_WRITE.
start_SSL($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.
connect_SSL() and accept_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 EWOULDBLOCK 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 necessary in case you want to
downgrade the socket and continue to use it as a plain socket.
After stop_SSL the socket can again be used to exchange plain data.
new or upgraded with start_SSL and SSL_startHandshake was
set to false.
They will return undef until the handshake succeeded or an error got thrown.
As long as the function returns undef and $! is set to EWOULDBLOCK one could
retry the call after the socket got readable (SSL_WANT_READ) or writeable
(SSL_WANT_WRITE).
SSL_ocsp_mode: by default only the leaf
certificate will be checked, but with SSL_OCSP_FULL_CHAIN all chain
certificates will be checked.
Because to create an OCSP request the certificate and its issuer certificate need to be known it is not possible to check certificates when the trust chain is incomplete or if the certificate is self-signed.
The OCSP resolver gets created by calling $ssl-ocsp_resolver> and provides
the following methods:
SSL_ocsp_mode of
SSL_OCSP_FAIL_HARD any soft error (e.g. failures to get signed information
about the certificates) will be considered a hard error too.
The OCSP resolving will stop on the first hard error.
The method will return undef as long as no hard errors occurred and still
requests to be resolved. If all requests got resolved and no hard errors
occurred the method will return ''.
error(s) which occurred when asking the OCSP responders.
(url,request)-tuples, e.g. which
contain the OCSP request string and the URL where it should be sent too. The
usual way to send such a request is as HTTP POST request with an content-type
of application/ocsp-request or as a GET request with the base64 and
url-encoded request is added to the path of the URL.
After you've handled all these requests and added the response with
add_response you should better call this method again to make sure, that no
more requests are outstanding. IO::Socket::SSL will combine multiple OCSP
requests for the same server inside a single request, but some server don't
give an response to all these requests, so that one has to ask again with the
remaining requests.
add_response($uri,$response)$uri. If no response was received or an error occurred
one should either retry or consider $response as empty which will trigger a
soft error.
The method returns the current value of hard_error, e.g. a defined value
when no more requests need to be done.
resolve_blocking(%args)requests and add_response which the HTTP::Tiny manpage to do all
necessary requests in a blocking way. %args will be given to the HTTP::Tiny manpage
so that you can put proxy settings etc here. the HTTP::Tiny manpage will be called with
verify_SSL of false, because the OCSP responses have their own signatures so
no extra SSL verification is needed.
If you don't want to use blocking requests you need to roll your own user agent
with requests and add_response.
Internally the given $fd will be upgraded to a socket object using the
new_from_fd method of the super class (the IO::Socket::INET manpage or similar) and
then start_SSL will be called using the given %sslargs.
If $fd is already an IO::Socket object you should better call start_SSL
directly.
undef is given it will forget any stored defaults and continue with
detection of system defaults.
If no arguments are given it will start detection of system defaults, unless it
has already stored user-set or previously detected values.
The detection of system defaults works similar to OpenSSL, e.g. it will check the directory specified in environment variable SSL_CERT_DIR or the path OPENSSLDIR/certs (SSLCERTS: on VMS) and the file specified in environment variable SSL_CERT_FILE or the path OPENSSLDIR/cert.pem (SSLCERTS:cert.pem on VMS). Contrary to OpenSSL it will check if the SSL_ca_path contains PEM files with the hash as file name and if the SSL_ca_file looks like PEM. If no usable system default can be found it will try to load and use the Mozilla::CA manpage and if not available give up detection. The result of the detection will be saved to speed up future calls.
The function returns the saved default CA as hash with SSL_ca_file and SSL_ca_path.
new() for more details.
Note that this sets the default context globally, so use with caution (esp. in
mod_perl scripts).
new() for more details.
Note that this sets the default cache globally, so use with caution.
set_defaults, but only sets the defaults for client mode.
set_defaults, but only sets the defaults for server mode.
IO::Socket::SSL::set_args_filter_hack( sub {
my ($is_server,$args) = @_;
if ( ! $is_server ) {
# client settings - enable verification with default CA
# and fallback hostname verification etc
delete @{$args}{qw(
SSL_verify_mode
SSL_ca_file
SSL_ca_path
SSL_verifycn_scheme
SSL_version
)};
# and add some fingerprints for known certs which are signed by
# unknown CAs or are self-signed
$args->{SSL_fingerprint} = ...
}
});
With the short setting set_args_filter_hack('use_defaults') it will prefer
the default settings in all cases. These default settings can be modified with
set_defaults, set_client_defaults and set_server_defaults.
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:
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.
The following functions are deprecated and are only retained for compatibility:
context_init()socketToSSL() and socket_to_SSL()start_SSL() instead
kill_socket()close() instead
get_peer_certificate()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()subject_name()
See the 'example' directory, the tests in 't' and also the tools in 'util'.
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.
IO::Socket::INET, IO::Socket::INET6, IO::Socket::IP, Net::SSLeay.
Many thanks to all who added patches or reported bugs or helped IO::Socket::SSL another way. Please keep reporting bugs and help with patches, even if they just fix the documentation.
Special thanks to the team of Net::SSLeay for the good cooperation.
Steffen Ullrich, <sullr at cpan.org> 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.
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) 2006-2014 Steffen Ullrich.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| IO::Socket::SSL - SSL sockets with IO::Socket interface |