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.\" ========================================================================
.\"
.IX Title "IO::Socket::SSL::Intercept 3pm"
.TH IO::Socket::SSL::Intercept 3pm "2017-04-26" "perl v5.24.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
IO::Socket::SSL::Intercept \-\- SSL interception (man in the middle)
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 10
\&    use IO::Socket::SSL::Intercept;
\&    # create interceptor with proxy certificates
\&    my $mitm = IO::Socket::SSL::Intercept\->new(
\&        proxy_cert_file => \*(Aqproxy_cert.pem\*(Aq,
\&        proxy_key_file  => \*(Aqproxy_key.pem\*(Aq,
\&        ...
\&    );
\&    my $listen = IO::Socket::INET\->new( LocalAddr => .., Listen => .. );
\&    while (1) {
\&        # TCP accept new client
\&        my $client = $listen\->accept or next;
\&        # SSL connect to server
\&        my $server = IO::Socket::SSL\->new(
\&            PeerAddr => ..,
\&            SSL_verify_mode => ...,
\&            ...
\&        ) or die "ssl connect failed: $!,$SSL_ERROR";
\&        # clone server certificate
\&        my ($cert,$key) = $mitm\->clone_cert( $server\->peer_certificate );
\&        # and upgrade client side to SSL with cloned certificate
\&        IO::Socket::SSL\->start_SSL($client,
\&            SSL_server => 1,
\&            SSL_cert => $cert,
\&            SSL_key => $key
\&        ) or die "upgrade failed: $SSL_ERROR";
\&        # now transfer data between $client and $server and analyze
\&        # the unencrypted data
\&        ...
\&    }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module provides functionality to clone certificates and sign them with a
proxy certificate, thus making it easy to intercept \s-1SSL\s0 connections (man in the
middle). It also manages a cache of the generated certificates.
.SH "How Intercepting SSL Works"
.IX Header "How Intercepting SSL Works"
Intercepting \s-1SSL\s0 connections is useful for analyzing encrypted traffic for
security reasons or for testing. It does not break the end-to-end security of
\&\s-1SSL,\s0 e.g. a properly written client will notice the interception unless you
explicitly configure the client to trust your interceptor.
Intercepting \s-1SSL\s0 works the following way:
.IP "\(bu" 4
Create a new \s-1CA\s0 certificate, which will be used to sign the cloned certificates.
This proxy \s-1CA\s0 certificate should be trusted by the client, or (a properly
written client) will throw error messages or deny the connections because it
detected a man in the middle attack.
Due to the way the interception works there no support for client side
certificates is possible.
.Sp
Using openssl such a proxy \s-1CA\s0 certificate and private key can be created with:
.Sp
.Vb 4
\&  openssl genrsa \-out proxy_key.pem 1024
\&  openssl req \-new \-x509 \-extensions v3_ca \-key proxy_key.pem \-out proxy_cert.pem
\&  # export as PKCS12 for import into browser
\&  openssl pkcs12 \-export \-in proxy_cert.pem \-inkey proxy_key.pem \-out proxy_cert.p12
.Ve
.IP "\(bu" 4
Configure client to connect to use intercepting proxy or somehow redirect
connections from client to the proxy (e.g. packet filter redirects, \s-1ARP\s0 or \s-1DNS\s0
spoofing etc).
.IP "\(bu" 4
Accept the \s-1TCP\s0 connection from the client, e.g. don't do any \s-1SSL\s0 handshakes with
the client yet.
.IP "\(bu" 4
Establish the \s-1SSL\s0 connection to the server and verify the servers certificate as
usually. Then create a new certificate based on the original servers
certificate, but signed by your proxy \s-1CA.\s0
This is the step where IO::Socket::SSL::Intercept helps.
.IP "\(bu" 4
Upgrade the \s-1TCP\s0 connection to the client to \s-1SSL\s0 using the cloned certificate
from the server. If the client trusts your proxy \s-1CA\s0 it will accept the upgrade
to \s-1SSL.\s0
.IP "\(bu" 4
Transfer data between client and server. While the connections to client and
server are both encrypted with \s-1SSL\s0 you will read/write the unencrypted data in
your proxy application.
.SH "METHODS"
.IX Header "METHODS"
IO::Socket::SSL::Intercept helps creating the cloned certificate with the
following methods:
.IP "\fB\f(CB$mitm\fB = IO::Socket::SSL::Intercept\->new(%args)\fR" 4
.IX Item "$mitm = IO::Socket::SSL::Intercept->new(%args)"
This creates a new interceptor object. \f(CW%args\fR should be
.RS 4
.IP "proxy_cert X509 | proxy_cert_file filename" 8
.IX Item "proxy_cert X509 | proxy_cert_file filename"
This is the proxy certificate.
It can be either given by an X509 object from Net::SSLeays internal
representation, or using a file in \s-1PEM\s0 format.
.IP "proxy_key \s-1EVP_PKEY\s0 | proxy_key_file filename" 8
.IX Item "proxy_key EVP_PKEY | proxy_key_file filename"
This is the key for the proxy certificate.
It can be either given by an \s-1EVP_PKEY\s0 object from Net::SSLeays internal
representation, or using a file in \s-1PEM\s0 format.
The key should not have a passphrase.
.IP "pubkey \s-1EVP_PKEY\s0 | pubkey_file filename" 8
.IX Item "pubkey EVP_PKEY | pubkey_file filename"
This optional argument specifies the public key used for the cloned certificate.
It can be either given by an \s-1EVP_PKEY\s0 object from Net::SSLeays internal
representation, or using a file in \s-1PEM\s0 format.
If not given it will create a new public key on each call of \f(CW\*(C`new\*(C'\fR.
.IP "serial \s-1INTEGER\s0" 8
.IX Item "serial INTEGER"
This optional argument gives the starting point for the serial numbers of the
newly created certificates. Default to 1.
.IP "cache \s-1HASH\s0 | \s-1SUBROUTINE\s0" 8
.IX Item "cache HASH | SUBROUTINE"
This optional argument gives a way to cache created certificates, so that they
don't get recreated on future accesses to the same host.
If the argument ist not given an internal \s-1HASH\s0 ist used.
.Sp
If the argument is a hash it will store for each generated certificate a hash
reference with \f(CW\*(C`cert\*(C'\fR and \f(CW\*(C`atime\*(C'\fR in the hash, where \f(CW\*(C`atime\*(C'\fR is the time of
last access (to expire unused entries) and \f(CW\*(C`cert\*(C'\fR is the certificate. Please
note, that the certificate is in Net::SSLeays internal X509 format and can
thus not be simply dumped and restored.
The key for the hash is an \f(CW\*(C`ident\*(C'\fR either given to \f(CW\*(C`clone_cert\*(C'\fR or generated
from the original certificate.
.Sp
If the argument is a subroutine it will be called as \f(CW\*(C`$cache\->(ident)\*(C'\fR
to get an existing (cert,key) and with \f(CW\*(C`$cache\->(ident,cert,key)\*(C'\fR to cache
the newly created certificate.
.RE
.RS 4
.RE
.IP "\fB($clone_cert,$key) = \f(CB$mitm\fB\->clone_cert($original_cert,[ \f(CB$ident\fB ])\fR" 4
.IX Item "($clone_cert,$key) = $mitm->clone_cert($original_cert,[ $ident ])"
This clones the given certificate.
An ident as the key into the cache can be given (like \f(CW\*(C`host:port\*(C'\fR), if not it
will be created from the properties of the original certificate.
It returns the cloned certificate and its key (which is the same for alle
created certificates).
.IP "\fB\f(CB$string\fB = \f(CB$mitm\fB\->serialize\fR" 4
.IX Item "$string = $mitm->serialize"
This creates a serialized version of the object (e.g. a string) which can then
be used to persistantly store created certificates over restarts of the
application. The cache will only be serialized if it is a \s-1HASH.\s0
To work together with Storable the \f(CW\*(C`STORABLE_freeze\*(C'\fR function is defined to
call \f(CW\*(C`serialize\*(C'\fR.
.IP "\fB\f(CB$mitm\fB = IO::Socket::SSL::Intercept\->unserialize($string)\fR" 4
.IX Item "$mitm = IO::Socket::SSL::Intercept->unserialize($string)"
This restores an Intercept object from a serialized string.
To work together with Storable the \f(CW\*(C`STORABLE_thaw\*(C'\fR function is defined to
call \f(CW\*(C`unserialize\*(C'\fR.
.SH "AUTHOR"
.IX Header "AUTHOR"
Steffen Ullrich