SSL(3) User Contributed Perl Documentation SSL(3)NAMEIO::Socket::SSL-- Nearly transparent SSL encapsulation for
IO::Socket::INET.
SYNOPSIS
use IO::Socket::SSL;
my $client = IO::Socket::SSL->new("www.example.com:https");
if ($client) {
print $client "GET / HTTP/1.0\r\n\r\n";
print <$client>;
close $client;
} else {
warn "I encountered a problem: ",
IO::Socket::SSL::errstr();
}
DESCRIPTION
This module is a true drop-in replacement for IO::Socket::INET that
uses SSL to encrypt data before it is transferred to a remote server or
client. 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, and SSL version
selection. As an extra bonus, it works perfectly with mod_perl.
If you have never used SSL before, you should read the appendix
labelled 'Using SSL' before attempting to use this module.
If you have used this module before, read on, as versions 0.93 and
above have several changes from the previous IO::Socket::SSL versions
(especially see the note about return values).
If you are using non-blocking sockets read on, as version 0.98 added
better support for non-blocking.
METHODSIO::Socket::SSL inherits its methods from IO::Socket::INET, overriding
them as necessary. If there is an SSL error, the method or operation
will return an empty list (false in all contexts). The methods that
have changed from the perspective of the user are re-documented here:
new(...)
Creates a new IO::Socket::SSL object. You may use all the friendly
options that came bundled with IO::Socket::INET, plus (optionally)
the ones that follow:
SSL_version
Sets the version of the SSL protocol used to transmit data. The
default is SSLv2/3, which auto-negotiates between SSLv2 and
SSLv3. You may specify 'SSLv2', 'SSLv3', or 'TLSv1' (case-insen‐
sitive) if you do not want this behavior.
SSL_cipher_list
If this option is set the cipher list for the connection will be
set to the given value, e.g. something like 'ALL:!LOW:!EXP:!ADH'.
Look into the OpenSSL documentation
(<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_STRINGS>)
for more details. If this option is not used the openssl builtin
default is used which is suitable for most cases.
SSL_use_cert
If this is set, 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_key_file
If your RSA private key is not in default place
(certs/server-key.pem for servers, certs/client-key.pem for
clients), then this is the option that you would use to specify a
different location. Keys should be PEM formatted, and if they
are encrypted, you will be prompted to enter a password before
the socket is formed (unless you specified the SSL_passwd_cb
option).
SSL_key
This is an EVP_PKEY* and can be used instead of SSL_key_file.
Useful if you don't have your key in a file but create it dynami‐
cally or get it from a string (see openssl PEM_read_bio_Pri‐
vateKey etc for getting a EVP_PKEY* from a string).
SSL_cert_file
If your SSL certificate is not in the default place
(certs/server-cert.pem for servers, certs/client-cert.pem for
clients), then you should use this option to specify the location
of your certificate. Note that a key and certificate are only
required for an SSL server, so you do not need to bother with
these trifling options should you be setting up an unauthenti‐
cated client.
SSL_cert
This is an X509* or an array of X509*. The first X509* is the
internal representation of the certificate while the following
ones are extra certificates. Useful if you create your certifi‐
cate dynamically (like in a SSL intercepting proxy) or get it
from a string (see openssl PEM_read_bio_X509 etc for getting a
X509* from a string).
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 com‐
mand in openssl for more information.
SSL_dh
Like SSL_dh_file, but instead of giving a file you use a pre‐
loaded or generated DH*.
SSL_passwd_cb
If your private key is encrypted, you might not want the default
password prompt from Net::SSLeay. This option takes a reference
to a subroutine that should return the password required to
decrypt your private key.
SSL_ca_file
If you want to verify that the peer certificate has been signed
by a reputable certificate authority, then you should use this
option to locate the file containing the certificate(s) of the
reputable certificate authorities if it is not already in the
file certs/my-ca.pem.
SSL_ca_path
If you are unusually friendly with the OpenSSL documentation, you
might have set yourself up a directory containing several trusted
certificates as separate files as well as an index of the cer‐
tificates. If you want to use that directory for validation pur‐
poses, and that directory is not ca/, then use this option to
point IO::Socket::SSL to the right place to look.
SSL_verify_mode
This option sets the verification mode for the peer certificate.
The default (0x00) does no authentication. You may combine 0x01
(verify peer), 0x02 (fail verification if no peer certificate
exists; ignored for clients), and 0x04 (verify client once) to
change the default.
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 indi‐
cates what OpenSSL thinks of the certificate, 2) a C-style memory
address of the certificate store, 3) a string containing the cer‐
tificate's issuer attributes and owner attributes, and 4) a
string containing any errors encountered (0 if no errors). 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.
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. See the
Net::SSLeay documentation for more details. Note that this func‐
tionality appears to be broken with OpenSSL < v0.9.7b, so its use
with lower versions will result in an error.
SSL_reuse_ctx
If you have already set the above options (SSL_version through
SSL_check_crl; this does not include SSL_cipher_list yet) for a
previous instance of IO::Socket::SSL, then you can reuse the SSL
context of that instance by passing it as the value for the
SSL_reuse_ctx parameter. You may also create a new instance of
the IO::Socket::SSL::SSL_Context class, using any context options
that you desire without specifying connection options, and pass
that here instead.
If you use this option, all other context-related options that
you pass in the same call to new() will be ignored unless the
context supplied was invalid. Note that, contrary to versions of
IO::Socket::SSL below v0.90, a global SSL context will not be
implicitly used unless you use the set_default_context() func‐
tion.
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.
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 hav‐
ing 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 and the full text of the error message.
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 pro‐
tocol mandates that a SSL "close notify" message be sent before the
socket is closed, a shutdown() that closes the socket's write chan‐
nel 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 prob‐
lems, call close with an object-oriented syntax (e.g.
$socket->close(SSL_no_shutdown => 1)) and one or more of the fol‐
lowing parameters:
SSL_no_shutdown
If set to a true value, this option will make close() not use the
SSL_shutdown() call on the socket in question so that the close
operation can complete without problems if you have used shut‐
down() or are working on a copy of a socket.
SSL_ctx_free
If you want to make sure that the SSL context of the socket is
destroyed when you close it, set this option to a true value.
peek(...)
This function has exactly the same syntax as sysread(), and per‐
forms nearly the same task (reading data from the socket) but will
not advance the read position so that successive calls to peek()
with the same arguments will return the same results. This func‐
tion requires OpenSSL 0.9.6a or later to work.
pending()
This function will let you know how many bytes of data are immedi‐
ately ready for reading from the socket. This is especially handy
if you are doing reads on a blocking socket or just want to know if
new data has been sent over the socket.
get_cipher()
Returns the string form of the cipher that the IO::Socket::SSL
object is using.
dump_peer_certificate()
Returns a parsable string with select fields from the peer SSL cer‐
tificate. This method directly returns the result of the
dump_peer_certificate() method of Net::SSLeay.
peer_certificate($field)
If a peer certificate exists, this function can retrieve values
from it. Right now, the only fields it can return are "authority"
and "owner" (or "issuer" and "subject" if you want to use OpenSSL
names), corresponding to the certificate authority that signed the
peer certificate and the owner of the peer certificate. This func‐
tion returns a string with all the information about the particular
field in one parsable line. If no field is given it returns the
full certificate (x509).
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 $SSL_ERROR against the exported symbols
SSL_WANT_READ and SSL_WANT_WRITE.
IO::Socket::SSL->start_SSL($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, $socket will
remain blessed in its original class. For non-blocking sockets you
better just upgrade the socket to IO::Socket::SSL and call
accept_SSL or connect_SSL and the upgraded object. To just upgrade
the socket set SSL_startHandshake explicitly to 0. If you call
start_SSL w/o this parameter it will revert to blocking behavior
for accept_SSL and connect_SSL.
IO::Socket::SSL->new_from_fd($fd, ...)
This will convert a socket identified via a file descriptor into an
SSL socket. Note that the argument list does not include a "MODE"
argument; if you supply one, it will be thoughtfully ignored (for
compatibility with IO::Socket::INET). Instead, a mode of '+<' is
assumed, and the file descriptor passed must be able to handle such
I/O because the initial SSL handshake requires bidirectional commu‐
nication.
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_re‐
use_ctx option of new() for more details. Note that this sets the
default context globally, so use with caution (esp. in mod_perl
scripts).
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.
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.
IPv6
Support for IPv6 with IO::Socket::SSL is expected to work, but is
experimental, as none of the author's machines use IPv6 and hence he
cannot test IO::Socket::SSL with them. However, a few brave people
have used it without incident, so if you wish to make IO::Socket::SSL
IPv6 aware, pass the 'inet6' option to IO::Socket::SSL when calling it
(i.e. "use IO::Socket::SSLqw(inet6);"). You will need
IO::Socket::INET6 and Socket6 to use this option, and you will also
need to write "use Socket6;" before using IO::Socket::SSL. If you
absolutely do not want to use this (or want a quick change back to
IPv4), pass the 'inet4' option instead.
Currently, there is no support for using IPv4 and IPv6 simultaneously
in a single program, but it is planned for a future release.
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 4) to IO::Socket::SSL when
calling it:
use IO::Socket::SSLqw(debug0);
#No debugging (default).
use IO::Socket::SSLqw(debug1);
#Only print out errors.
use IO::Socket::SSLqw(debug2);
#Print out errors and cipher negotiation.
use IO::Socket::SSLqw(debug3);
#Print out progress, ciphers, and errors.
use IO::Socket::SSLqw(debug4);
#Print out everything, including data.
You can also set $IO::Socket::SSL::DEBUG to 0-4, but that's a bit of a
mouthful, isn't it?
EXAMPLES
See the 'example' directory.
BUGSIO::Socket::SSL is not threadsafe. This is because IO::Socket::SSL is
based on Net::SSLeay which uses a global object to access some of the
API of openssl and is therefore not threadsafe.
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 com‐
patibility:
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
get_peer_certificate()
use the peer_certificate() function instead. Used to return
X509_Certificate with methods subject_name and issuer_name. Now sim‐
ply returns $self which has these methods (although depreceated).
issuer_name()
use peer_certificate( 'issuer' ) instead
subject_name()
use peer_certificate( 'subject' ) instead
The following classes have been removed:
SSL_SSL
(not that you should have been directly accessing this anyway):
X509_Certificate
(but get_peer_certificate() will still Do The Right Thing)
SEE ALSO
IO::Socket::INET, IO::Socket::INET6, 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
Working support for non-blocking was added by Steffen Ullrich.
The rewrite of this module is Copyright (C) 2002-2005 Peter Behroozi.
The original versions of this module are Copyright (C) 1999-2002 Marko
Asplund.
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-Certifi‐
cates-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 trans‐
ported over a network, but you also have to make sure that the right
person gets the data. To accomplish this with SSL, you have to use
certificates. A certificate closely resembles a Government-issued ID
(at least in places where you can trust them). The ID contains some
sort of identifying information such as a name and address, and is usu‐
ally stamped with a seal of Government Approval. Theoretically, this
means that you may trust the information on the card and do business
with the owner of the card. The same ideas apply to SSL certificates,
which have some identifying information and are "stamped" [most people
refer to this as signing instead] by someone (a Certificate Authority)
who you trust will adequately verify the identifying information. In
this case, because of some clever number theory, it is extremely diffi‐
cult to falsify the stamping process. Another useful consequence of
number theory is that the certificate is linked to the encryption
process, so you may encrypt data (using information on the certificate)
that only the certificate owner can decrypt.
What does this mean for you? It means that at least one person in the
party has to have an ID to get drinks :-). Seriously, it means that
one of the people communicating has to have a certificate to ensure
that your data is safe. For client/server interactions, the server
must always have a certificate. If the server wants to verify that the
client is safe, then the client must also have a personal certificate.
To verify that a certificate is safe, one compares the stamped "seal"
[commonly called an encrypted digest/hash/signature] on the certificate
with the official "seal" of the Certificate Authority to make sure that
they are the same. To do this, you will need the [unfortunately named]
certificate of the Certificate Authority. With all these in hand, you
can set up a SSL connection and be reasonably confident that no-one is
reading your data.
The Short of It (Summary)
For servers, you will need to generate a cryptographic private key and
a certificate request. You will need to send the certificate request
to a Certificate Authority to get a real certificate back, after which
you can start serving people. For clients, you will not need anything
unless the server wants validation, in which case you will also need a
private key and a real certificate. For more information about how to
get these, see <http://www.modssl.org/docs/2.8/ssl_faq.html#ToC24>.
perl v5.8.8 2007-08-19 SSL(3)
