phpman > perldoc > IO::Socket::SSL::Intercept

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