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NAME
IO::Socket::SSL::Intercept -- SSL interception (man in the middle)
SYNOPSIS
use IO::Socket::SSL::Intercept;
# create interceptor with proxy certificates
my $mitm = IO::Socket::SSL::Intercept->new(
proxy_cert_file => 'proxy_cert.pem',
proxy_key_file => 'proxy_key.pem',
...
);
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
...
}
DESCRIPTION
This module provides functionality to clone certificates and sign them
with a proxy certificate, thus making it easy to intercept SSL
connections (man in the middle). It also manages a cache of the
generated certificates.
How Intercepting SSL Works
Intercepting SSL connections is useful for analyzing encrypted traffic
for security reasons or for testing. It does not break the end-to-end
security of SSL, e.g. a properly written client will notice the
interception unless you explicitly configure the client to trust your
interceptor. Intercepting SSL works the following way:
* Create a new CA certificate, which will be used to sign the cloned
certificates. This proxy CA 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.
Using openssl such a proxy CA certificate and private key can be
created with:
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
* Configure client to connect to use intercepting proxy or somehow
redirect connections from client to the proxy (e.g. packet filter
redirects, ARP or DNS spoofing etc).
* Accept the TCP connection from the client, e.g. don't do any SSL
handshakes with the client yet.
* Establish the SSL 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 CA. This is
the step where IO::Socket::SSL::Intercept helps.
* Upgrade the TCP connection to the client to SSL using the cloned
certificate from the server. If the client trusts your proxy CA it
will accept the upgrade to SSL.
* Transfer data between client and server. While the connections to
client and server are both encrypted with SSL you will read/write
the unencrypted data in your proxy application.
METHODS
IO::Socket::SSL::Intercept helps creating the cloned certificate with
the following methods:
$mitm = IO::Socket::SSL::Intercept->new(%args)
This creates a new interceptor object. %args should be
proxy_cert X509 | proxy_cert_file filename
This is the proxy certificate. It can be either given by an
X509 object from Net::SSLeays internal representation, or
using a file in PEM format.
proxy_key EVP_PKEY | proxy_key_file filename
This is the key for the proxy certificate. It can be either
given by an EVP_PKEY object from Net::SSLeays internal
representation, or using a file in PEM format. The key
should not have a passphrase.
pubkey EVP_PKEY | pubkey_file filename
This optional argument specifies the public key used for the
cloned certificate. It can be either given by an EVP_PKEY
object from Net::SSLeays internal representation, or using a
file in PEM format. If not given it will create a new public
key on each call of "new".
serial INTEGER|CODE
This optional argument gives the starting point for the
serial numbers of the newly created certificates. If not set
the serial number will be created based on the digest of the
original certificate. If the value is code it will be called
with "serial(original_cert,CERT_asHash(original_cert))" and
should return the new serial number.
cache HASH | SUBROUTINE
This optional argument gives a way to cache created
certificates, so that they don't get recreated on future
accesses to the same host. If the argument ist not given an
internal HASH ist used.
If the argument is a hash it will store for each generated
certificate a hash reference with "cert" and "atime" in the
hash, where "atime" is the time of last access (to expire
unused entries) and "cert" is the certificate. Please note,
that the certificate is in Net::SSLeays internal X509 format
and can thus not be simply dumped and restored. The key for
the hash is an "ident" either given to "clone_cert" or
generated from the original certificate.
If the argument is a subroutine it will be called as
"$cache->(ident,sub)". This call should return either an
existing (cached) "(cert,key)" or call "sub" without
arguments to create a new "(cert,key)", store it and return
it. If called with "$cache->('type')" the function should
just return 1 to signal that it supports the current type of
cache. If it reutrns nothing instead the older cache
interface is assumed for compatibility reasons.
($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 "host:port"), 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).
$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 HASH. To work together with Storable the
"STORABLE_freeze" function is defined to call "serialize".
$mitm = IO::Socket::SSL::Intercept->unserialize($string)
This restores an Intercept object from a serialized string. To work
together with Storable the "STORABLE_thaw" function is defined to
call "unserialize".
AUTHOR
Steffen Ullrich
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