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

SSL(3pm) User Contributed Perl Documentation SSL(3pm)

NAME
IO::Socket::SSL -- Nearly transparent SSL encapsulation for IO::Socket::INET.

SYNOPSIS
use strict;
use IO::Socket::SSL;

my $client = IO::Socket::SSL->new("www.example.com:https")
|| warn "I encountered a problem: ".IO::Socket::SSL::errstr();
$client->verify_hostname( 'www.example.com','http' )
|| die "hostname verification failed";

print $client "GET / HTTP/1.0\r\n\r\n";
print <$client>;

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.

If you are trying to use it with threads see the BUGS section.

METHODS
IO::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-insensitive) 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 dynamically or get it from a string (see
openssl PEM_read_bio_PrivateKey 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 unauthenticated 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 certificate dynamically (like in a SSL intercepting proxy)
or get it from a string (see openssl PEM_read_bio_X509 etc for getting a X509* from
a string).

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.

SSL_dh
Like SSL_dh_file, but instead of giving a file you use a preloaded 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 certificates. If you want to use that directory for
validation purposes, and that directory is not ca/, then use this option to point
IO::Socket::SSL to the right place to look.

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. See OpenSSL man page for SSL_CTX_set_verify for more
information.

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). 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_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.

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 caan 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. 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_reuse_ctx
If you have already set the above options (SSL_version through SSL_check_crl; this
does not include SSL_cipher_list yet) for a previous instance of IO::Socket::SSL,
then you can reuse the SSL context of that instance by passing it as the value for
the SSL_reuse_ctx parameter. You may also create a new instance of the
IO::Socket::SSL::SSL_Context class, using any context options that you desire
without specifying connection options, and pass that here instead.

If you use this option, all other context-related options that you pass in the same
call to new() will be ignored unless the context supplied was invalid. Note that,
contrary to versions of IO::Socket::SSL below v0.90, a global SSL context will not
be implicitly used unless you use the set_default_context() function.

SSL_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_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 wan't 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_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 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 protocol mandates that a SSL "close notify" message be sent
before the socket is closed, a shutdown() that closes the socket's write channel will
cause the close() call to hang. For a similar reason, if you try to close a copy of a
socket (as in a forking server) you will affect the original socket as well. To get
around these problems, call close with an object-oriented syntax (e.g.
$socket->close(SSL_no_shutdown => 1)) and one or more of the following parameters:

SSL_no_shutdown
If set to a true value, this option will make close() not use the SSL_shutdown()
call on the socket in question so that the close operation can complete without
problems if you have used shutdown() or are working on a copy of a socket.

SSL_fast_shutdown
If set to true only a unidirectional shutdown will be done, e.g. only the
close_notify (see SSL_shutdown(3)) will be called. Otherwise a bidrectional shutdown
will be done. If used within close() it defaults to true, if used within stop_SSL()
it defaults to false.

SSL_ctx_free
If you want to make sure that the SSL context of the socket is destroyed when you
close it, set this option to a true value.

peek(...)
This function has exactly the same syntax as sysread(), and performs nearly the same
task (reading data from the socket) but will not advance the read position so that
successive calls to peek() with the same arguments will return the same results. This
function requires OpenSSL 0.9.6a or later to work.

pending()
This function will let you know how many bytes of data are immediately ready for
reading from the socket. This is especially handy if you are doing reads on a
blocking socket or just want to know if new data has been sent over the socket.

get_cipher()
Returns the string form of the cipher that the IO::Socket::SSL object is using.

dump_peer_certificate()
Returns a parsable string with select fields from the peer SSL certificate. This
method directly returns the result of the dump_peer_certificate() method of
Net::SSLeay.

peer_certificate($field)
If a peer certificate exists, this function can retrieve values from it. If no field
is given the internal representation of certificate from Net::SSLeay is returned. The
following fields can be queried:

authority (alias issuer)
The certificate authority which signed the certificate.

owner (alias subject)
The owner of the certificate.

commonName (alias cn) - only for Net::SSLeay version >=1.30
The common name, usually the server name for SSL certificates.

subjectAltNames - only for Net::SSLeay version >=1.33
Alternative names for the subject, usually different names for the same
server, like example.org, example.com, *.example.com.

It returns a list of (typ,value) with typ GEN_DNS, GEN_IPADD etc (these
constants are exported from IO::Socket::SSL). See
Net::SSLeay::X509_get_subjectAltNames.

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 are possible, e.g. *.example.org or even
www*.example.org. Wildcards in the common name are not allowed. 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.

The scheme can be given either by specifying the name for one of the above predefined
schemes, by using a callback (see below) 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.

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').

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 suceeded and undef if failed. This might be the case for non-
blocking sockets. In this case $! is set to EAGAIN and the ssl error to SSL_WANT_READ
or SSL_WANT_WRITE. In this case the call should be retried again with the same
arguments once the socket is ready is until it succeeds.

IO::Socket::SSL->new_from_fd($fd, ...)
This will convert a socket identified via a file descriptor into an SSL socket. Note
that the argument list does not include a "MODE" argument; if you supply one, it will
be thoughtfully ignored (for compatibility with IO::Socket::INET). Instead, a mode of
'+<' is assumed, and the file descriptor passed must be able to handle such I/O
because the initial SSL handshake requires bidirectional communication.

IO::Socket::SSL::set_default_context(...)
You may use this to make IO::Socket::SSL automatically re-use a given context (unless
specifically overridden in a call to new()). It accepts one argument, which should be
either an IO::Socket::SSL object or an IO::Socket::SSL::SSL_Context object. See the
SSL_reuse_ctx option of new() for more details. Note that this sets the default
context globally, so use with caution (esp. in mod_perl scripts).

IO::Socket::SSL::set_default_session_cache(...)
You may use this to make IO::Socket::SSL automatically re-use a given session cache
(unless specifically overridden in a call to new()). It accepts one argument, which
should be an IO::Socket::SSL::Session_Cache object or similar (e.g something which
implements get_session and add_session like IO::Socket::SSL::Session_Cache does). See
the SSL_session_cache option of new() for more details. Note that this sets the
default cache globally, so use with caution.

IO::Socket::SSL::set_ctx_defaults(%args)
With this function one can set defaults for all SSL_* parameter used for creation of
the context, like the SSL_verify* parameter.

mode - set default SSL_verify_mode
callback - set default SSL_verify_callback
scheme - set default SSL_verifycn_scheme
name - set default SSL_verifycn_name
If not given and scheme is hash reference with key callback it will be set to
'unknown'

The following methods are unsupported (not to mention futile!) and IO::Socket::SSL will
emit a large CROAK() if you are silly enough to use them:

truncate
stat
ungetc
setbuf
setvbuf
fdopen
send/recv
Note that send() and recv() cannot be reliably trapped by a tied filehandle (such as
that used by IO::Socket::SSL) and so may send unencrypted data over the socket.
Object-oriented calls to these functions will fail, telling you to use the
print/printf/syswrite and read/sysread families instead.

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::SSL qw(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 3)
to IO::Socket::SSL when calling it. The debug level will also be propagated to
Net::SSLeay::trace, see also Net::SSLeay:

use IO::Socket::SSL qw(debug0);
No debugging (default).

use IO::Socket::SSL qw(debug1);
Print out errors from IO::Socket::SSL and ciphers from Net::SSLeay.

use IO::Socket::SSL qw(debug2);
Print also information about call flow from IO::Socket::SSL and progress information
from Net::SSLeay.

use IO::Socket::SSL qw(debug3);
Print also some data dumps from IO::Socket::SSL and from Net::SSLeay.

EXAMPLES
See the 'example' directory.

BUGS
IO::Socket::SSL 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. It might probably work if you don't use SSL_verify_callback and
SSL_password_cb.

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.

LIMITATIONS
IO::Socket::SSL uses Net::SSLeay as the shiny interface to OpenSSL, which is the shiny
interface to the ugliness of SSL. As a result, you will need both Net::SSLeay and
OpenSSL on your computer before using this module.

If you have Scalar::Util (standard with Perl 5.8.0 and above) or WeakRef, IO::Socket::SSL
sockets will auto-close when they go out of scope, just like IO::Socket::INET
sockets. If you do not have one of these modules, then IO::Socket::SSL sockets will
stay open until the program ends or you explicitly close them. This is due to the fact
that a circular reference is required to make IO::Socket::SSL sockets act simultaneously
like objects and glob references.

DEPRECATIONS
The following functions are deprecated and are only retained for compatibility:

context_init()
use the SSL_reuse_ctx option if you want to re-use a context

socketToSSL() and socket_to_SSL()
use IO::Socket::SSL->start_SSL() instead

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 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.

This module is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.

Appendix: Using SSL
If you are unfamiliar with the way OpenSSL works, good references may be found in both the
book "Network Security with OpenSSL" (Oreilly & Assoc.) and the web site
<http://www.tldp.org/HOWTO/SSL-Certificates-HOWTO/>. Read on for a quick overview.

The Long of It (Detail)
The usual reason for using SSL is to keep your data safe. This means that not only do you
have to encrypt the data while it is being transported over a network, but you also have
to make sure that the right person gets the data. To accomplish this with SSL, you have
to use certificates. A certificate closely resembles a Government-issued ID (at least in
places where you can trust them). The ID contains some sort of identifying information
such as a name and address, and is usually stamped with a seal of Government Approval.
Theoretically, this means that you may trust the information on the card and do business
with the owner of the card. The same ideas apply to SSL certificates, which have some
identifying information and are "stamped" [most people refer to this as signing instead]
by someone (a Certificate Authority) who you trust will adequately verify the identifying
information. In this case, because of some clever number theory, it is extremely
difficult to falsify the stamping process. Another useful consequence of number theory
is that the certificate is linked to the encryption process, so you may encrypt data
(using information on the certificate) that only the certificate owner can decrypt.

What does this mean for you? It means that at least one person in the party has to have
an ID to get drinks :-). Seriously, it means that one of the people communicating has to
have a certificate to ensure that your data is safe. For client/server interactions, the
server must always have a certificate. If the server wants to verify that the client
is safe, then the client must also have a personal certificate. To verify that a
certificate is safe, one compares the stamped "seal" [commonly called an encrypted
digest/hash/signature] on the certificate with the official "seal" of the Certificate
Authority to make sure that they are the same. To do this, you will need the
[unfortunately named] certificate of the Certificate Authority. With all these in hand,
you can set up a SSL connection and be reasonably confident that no-one is reading your
data.

The Short of It (Summary)
For servers, you will need to generate a cryptographic private key and a certificate
request. You will need to send the certificate request to a Certificate Authority to get
a real certificate back, after which you can start serving people. For clients, you will
not need anything unless the server wants validation, in which case you will also need a
private key and a real certificate. For more information about how to get these, see
<http://www.modssl.org/docs/2.8/ssl_faq.html#ToC24>.

perl v5.10.0 2009-08-11 SSL(3pm)

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