SSLproxy/sslsplit.1

.\" SSLsplit - transparent SSL/TLS interception
.\" Copyright (c) 2009-2016, Daniel Roethlisberger <daniel@roe.ch>
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.\" http://www.roe.ch/SSLsplit
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.TH SSLSPLIT 1  "1 April 2012"
.SH NAME
sslsplit \-\- transparent SSL/TLS interception
.SH SYNOPSIS
.na
.B sslsplit
[\fB-kCKwWOPZdDgGsrReumjplLSFi\fP] \fB-c\fP \fIpem\fP
\fIproxyspecs\fP [...]
.br
.B sslsplit
[\fB-kCKwWOPZdDgGsrReumjplLSFi\fP] \fB-c\fP \fIpem\fP \fB-t\fP \fIdir\fP
\fIproxyspecs\fP [...]
.br
.B sslsplit
[\fB-OPZwWdDgGsrReumjplLSFi\fP] \fB-t\fP \fIdir\fP
\fIproxyspecs\fP [...]
.br
.B sslsplit -E
.br
.B sslsplit -V
.br
.B sslsplit -h
.br
.ad
.SH DESCRIPTION
SSLsplit is a tool for man-in-the-middle attacks against SSL/TLS encrypted
network connections.  It is intended to be useful for network forensics,
application security analysis and penetration testing.
.LP
SSLsplit is designed to transparently terminate connections that are redirected
to it using a network address translation engine.  SSLsplit then terminates
SSL/TLS and initiates a new SSL/TLS connection to the original destination
address, while logging all data transmitted.
Besides NAT based operation, SSLsplit also supports static destinations and
using the server name indicated by SNI as upstream destination.
SSLsplit is purely a transparent proxy and cannot act as a HTTP or SOCKS proxy
configured in a browser.
See NAT ENGINES and PROXY SPECIFICATIONS below for specifics on the different
modes of operation.
.LP
SSLsplit supports plain TCP, plain SSL, HTTP and HTTPS connections over both
IPv4 and IPv6.
SSLsplit fully supports Server Name Indication (SNI) and is able to work with
RSA, DSA and ECDSA keys and DHE and ECDHE cipher suites.  Depending on the
version of OpenSSL, SSLsplit supports SSL 3.0, TLS 1.0, TLS 1.1 and TLS 1.2,
and optionally SSL 2.0 as well.
.LP
For SSL and HTTPS connections, SSLsplit generates and signs forged X509v3
certificates on-the-fly, mimicking the original server certificate's subject
DN, subjectAltName extension and other characteristics.
SSLsplit has the ability to use existing certificates of which the private key
is available, instead of generating forged ones.  SSLsplit supports NULL-prefix
CN certificates but otherwise does not implement exploits against specific
certificate verification vulnerabilities in SSL/TLS stacks.
.LP
SSLsplit implements a number of defences against mechanisms which would
normally prevent MitM attacks or make them more difficult.
SSLsplit can deny OCSP requests in a generic way.
For HTTP and HTTPS connections, SSLsplit removes response headers
for HPKP in order to prevent server-instructed public key pinning,
for HSTS to avoid the strict transport security restrictions,
and Alternate Protocols to prevent switching to QUIC/SPDY.
HTTP compression, encodings and keep-alive are disabled to make the logs more
readable.
.LP
As an experimental feature, SSLsplit supports STARTTLS and similar mechanisms,
where a protocol starts on a plain text TCP connection and is later upgraded to
SSL/TLS through protocol-specific means, such as the STARTTLS command in SMTP.
SSLsplit supports generic upgrading of TCP connections to SSL.
.LP
In order to maximize the chances that a connection can be successfully split,
SSLsplit does not verify upstream server certificates.  Instead, all
certificates including self-signed are accepted and if the expected hostname
signalled in SNI is missing from the server certificate, it will be added to
dynamically forged certificates.
.LP
SSLsplit does not automagically redirect any network traffic.  To actually
implement an attack, you also need to redirect the traffic to the system
running \fBsslsplit\fP.  Your options include running \fBsslsplit\fP on a
legitimate router, ARP spoofing, ND spoofing, DNS poisoning, deploying a rogue
access point (e.g. using hostap mode), physical recabling, malicious VLAN
reconfiguration or route injection, /etc/hosts modification and so on.
.SH OPTIONS
.TP
.B \-c \fIpemfile\fP
Use CA certificate from \fIpemfile\fP to sign certificates forged on-the-fly.
If \fIpemfile\fP also contains the matching CA private key, it is also loaded,
otherwise it must be provided with \fB-k\fP.
If \fIpemfile\fP also contains Diffie-Hellman group parameters, they are also
loaded, otherwise they can be provided with \fB-g\fP.
If \fB-t\fP is also given, SSLsplit will only forge a certificate if there is
no matching certificate in the provided certificate directory.
.TP
.B \-C \fIpemfile\fP
Use CA certificates from \fIpemfile\fP as extra certificates in the certificate
chain.  This is needed if the CA given with \fB-k\fP and \fB-c\fP is a sub-CA,
in which case any intermediate CA certificates and the root CA certificate must
be included in the certificate chain.
.TP
.B \-d
Detach from TTY and run as a daemon, logging error messages to syslog instead
of standard error.
.TP
.B \-D
Run in debug mode, log lots of debugging information to standard error.  This
also forces foreground mode and cannot be used with \fB-d\fP.
.TP
.B \-e \fIengine\fP
Use \fIengine\fP as the default NAT engine for \fIproxyspecs\fP without
explicit NAT engine, static destination address or SNI mode.
\fIengine\fP can be any of the NAT engines supported by the system, as
returned by \fB-E\fP.
.TP
.B \-E
List all supported NAT engines available on the system and exit.  See
NAT ENGINES for a list of NAT engines currently supported by SSLsplit.
.TP
.B \-F \fIlogspec\fP
Log connection content to separate log files with the given path specification
(see LOG SPECIFICATIONS below).  For each connection, a log file will be
written, which will contain both directions of data as transmitted.
Information about the connection will be contained in the filename only.
.TP
.B \-g \fIpemfile\fP
Use Diffie-Hellman group parameters from \fIpemfile\fP for Ephemereal
Diffie-Hellman (EDH/DHE) cipher suites.  If \fB-g\fP is not given, SSLsplit
first tries to load DH parameters from the PEM files given by \fB-K\fP,
\fB-k\fP or \fB-c\fP.  If no DH parameters are found in the key files, built-in
group parameters are automatically used.
The \fB-g\fP option is only available if SSLsplit was built against a version
of OpenSSL which supports Diffie-Hellman cipher suites.
.TP
.B \-G \fIcurve\fP
Use the named \fIcurve\fP for Ephemereal Elliptic Curve Diffie-Hellman (ECDHE)
cipher suites.  If \fB-G\fP is not given, a default curve (\fBprime256v1\fP) is
used automatically.
The \fB-G\fP option is only available if SSLsplit was built against a version
of OpenSSL which supports Elliptic Curve Diffie-Hellman cipher suites.
.TP
.B \-h
Display help on usage and exit.
.TP
.B \-i
For each connection, find the local process owning the connection.  This makes
process information such as pid, owner:group and executable path for
connections originating on the same system as SSLsplit available to the
connect log and enables the respective \fB-F\fP path specification directives.
\fB-i\fP is available on Mac OS X and FreeBSD; support for other platforms has
not been implemented yet.
.TP
.B \-j \fIjaildir\fP
Change the root directory to \fIjaildir\fP using chroot(2) after opening files.
Note that this has implications for \fBsni\fP \fIproxyspecs\fP.
Depending on your operating system, you will need to copy files such as
\fB/etc/resolv.conf\fP to \fIjaildir\fP in order for name resolution to work.
Using \fBsni\fP proxyspecs depends on name resolution.
Some operating systems require special device nodes such as \fB/dev/null\fP
to be present within the jail.  Check your system's documentation for details.
.TP
.B \-k \fIpemfile\fP
Use CA private key from \fIpemfile\fP to sign certificates forged on-the-fly.
If \fIpemfile\fP also contains the matching CA certificate, it is also loaded,
otherwise it must be provided with \fB-c\fP.
If \fIpemfile\fP also contains Diffie-Hellman group parameters, they are also
loaded, otherwise they can be provided with \fB-g\fP.
If \fB-t\fP is also given, SSLsplit will only forge a certificate if there is
no matching certificate in the provided certificate directory.
.TP
.B \-K \fIpemfile\fP
Use private key from \fIpemfile\fP for the leaf certificates forged on-the-fly.
If \fB-K\fP is not given, SSLsplit will generate a random 1024-bit RSA key.
.TP
.B \-l \fIlogfile\fP
Log connections to \fIlogfile\fP in a single line per connection format,
including addresses and ports and some HTTP and SSL information, if available.
SIGUSR1 will cause \fIlogfile\fP to be re-opened.
.TP
.B \-L \fIlogfile\fP
Log connection content to \fIlogfile\fP.  The content log will contain a
parsable log format with transmitted data, prepended with headers identifying
the connection and the data length of each logged segment.
SIGUSR1 will cause \fIlogfile\fP to be re-opened.
.TP
.B \-m
When dropping privileges using \fB-u\fP, override the target primary group
to be set to \fIgroup\fP.
.TP
.B \-O
Deny all Online Certificate Status Protocol (OCSP) requests on all
\fIproxyspecs\fP and for all OCSP servers with an OCSP response of
\fBtryLater\fP, causing OCSP clients to temporarily accept even revoked
certificates.
HTTP requests are being treated as OCSP requests if the method is \fBGET\fP
and the URI contains a syntactically valid OCSPRequest ASN.1 structure
parsable by OpenSSL, or if the method is \fBPOST\fP and the \fBContent-Type\fP
is \fBapplication/ocsp-request\fP.
For this to be effective, SSLsplit must be handling traffic destined to the
port used by the OCSP server.  In particular, SSLsplit must be configured to
receive traffic to all ports used by OCSP servers of targetted certificates
within the \fIcertdir\fP specified by \fB-t\fP.
.TP
.B \-p \fIpidfile\fP
Write the process ID to \fIpidfile\fP and refuse to run if the \fIpidfile\fP
is already in use by another process.
.TP
.B \-P
Passthrough SSL/TLS connections which cannot be split instead of dropping them.
Connections cannot be split if \fB-c\fP and \fB-k\fP are not given and the
site does not match any certificate loaded using \fB-t\fP, or if the connection
to the original server gives SSL/TLS errors.  Specifically, this happens if the
site requests a client certificate.
In these situations, passthrough with \fB-P\fP results in uninterrupted service
for the clients, while dropping is the more secure alternative if unmonitored
connections must be prevented.
Passthrough mode currently does not apply to SSL/TLS errors in the connection
from the client, since the connection from the client cannot easily be retried.
Specifically, \fB-P\fP does not currently work for clients that do not accept
forged certificates.
.TP
.B \-r \fIproto\fP
Force SSL/TLS protocol version on both client and server side to \fIproto\fP
by selecting the respective OpenSSL method constructor instead of the default
SSLv23_method() which supports all protocol versions.
This is useful when analyzing traffic to a server that only supports a specific
version of SSL/TLS and does not implement proper protocol negotiation.
Depending on build options and the version of OpenSSL that is used, the
following values for \fIproto\fP are accepted: \fBssl2\fP, \fBssl3\fP,
\fBtls10\fP, \fBtls11\fP and \fBtls12\fP.
Note that SSL 2.0 support is not built in by default because some servers
don't handle SSL 2.0 Client Hello messages gracefully.
.TP
.B \-R \fIproto\fP
Disable the SSL/TLS protocol version \fIproto\fP on both client and server
side by disabling the respective protocols in OpenSSL.  To disable multiple
protocol versions, \fB-R\fP can be given multiple times.  If \fI-r\fP is also
given, there will be no effect in disabling other protocol versions.
Disabling protocol versions is useful when analyzing traffic to a server that
does not handle some protocol versions well, or to test behaviour with
different protocol versions.
Depending on build options and the version of OpenSSL that is used, the
following values for \fIproto\fP are accepted: \fBssl2\fP, \fBssl3\fP,
\fBtls10\fP, \fBtls11\fP and \fBtls12\fP.
Note that SSL 2.0 support is not built in by default because some servers
don't handle SSL 2.0 Client Hello messages gracefully.
.TP
.B \-s \fIciphers\fP
Use OpenSSL \fIciphers\fP specification for both server and client SSL/TLS
connections.  If \fB-s\fP is not given, a cipher list of \fBALL:-aNULL\fP is
used.
Normally, SSL/TLS implementations choose the most secure cipher suites, not the
fastest ones.  By specifying an appropriate OpenSSL cipher list, the set of
cipher suites can be limited to fast algorithms, or \fBeNULL\fP cipher suites
can be added.  Note that for connections to be successful, the SSLsplit cipher
suites must include at least one cipher suite supported by both the client and
the server of each connection.
See ciphers(1) for details on how to construct OpenSSL cipher lists.
.TP
.B \-S \fIlogdir\fP
Log connection content to separate log files under \fIlogdir\fP.  For each
connection, a log file will be written, which will contain both directions of
data as transmitted.  Information about the connection will be contained in
the filename only.
.TP
.B \-t \fIcertdir\fP
Use private key, certificate and certificate chain from PEM files in
\fIcertdir\fP for connections to hostnames matching the respective
certificates, instead of using certificates forged on-the-fly.
A single PEM file must contain a single private key, a single certificate and
optionally intermediate and root CA certificates to use as certificate chain.
When using \fB-t\fP, SSLsplit will first attempt to use a matching certificate
loaded from \fIcertdir\fP.
If \fB-c\fP and \fB-k\fP are also given, certificates will be forged
on-the-fly for sites matching none of the common names in the certificates
loaded from \fIcertdir\fP.
Otherwise, connections matching no certificate will be dropped, or if
\fB-P\fP is given, passed through without splitting SSL/TLS.
.TP
.B \-u
Drop privileges after opening sockets and files by setting the real,
effective and stored user IDs to \fIuser\fP and loading the appropriate
primary and ancillary groups.  If \fB-u\fP is not given, SSLsplit will drop
privileges to the stored UID if EUID != UID (setuid bit scenario), or to
\fBnobody\fP if running with full \fBroot\fP privileges (EUID == UID == 0).
Due to an Apple bug, \fB-u\fP cannot be used with \fBpf\fP proxyspecs on
Mac OS X.
.TP
.B \-V
Display version and compiled features information and exit.
.TP
.B \-w \fIgendir\fP
Write generated keys and certificates to individual files in \fIgendir\fP.
For keys, the key identifier is used as filename, which consists of the SHA-1
hash of the ASN.1 bit string of the public key, as referenced by the
subjectKeyIdentifier extension in certificates.
For certificates, the SHA-1 fingerprints of the original and the used (forged)
certificate are combined to form the filename.
Note that only newly generated certificates are written to disk.
.TP
.B \-W \fIgendir\fP
Same as \fB-w\fP, but also write original certificates and certificates not
newly generated, such as those loaded from \fB-t\fP.
.TP
.B \-Z
Disable SSL/TLS compression on all connections.  This is useful if your
limiting factor is CPU, not network bandwidth.
The \fB-Z\fP option is only available if SSLsplit was built against a version
of OpenSSL which supports disabling compression.
.SH "PROXY SPECIFICATIONS"
Proxy specifications (\fIproxyspecs\fP) consist of the connection type, listen
address and static forward address or address resolution mechanism (NAT engine,
SNI DNS lookup):
.LP
.na
\fBhttps\fP \fIlistenaddr port\fP
[\fInat-engine\fP|\fIfwdaddr port\fP|\fBsni\fP \fIport\fP]
.br
\fBssl\fP   \fIlistenaddr port\fP
[\fInat-engine\fP|\fIfwdaddr port\fP|\fBsni\fP \fIport\fP]
.br
\fBhttp\fP  \fIlistenaddr port\fP
[\fInat-engine\fP|\fIfwdaddr port\fP]
.br
\fBtcp\fP   \fIlistenaddr port\fP
[\fInat-engine\fP|\fIfwdaddr port\fP]
.br
\fBautossl\fP \fIlistenaddr port\fP
[\fInat-engine\fP|\fIfwdaddr port\fP]
.ad
.TP
\fBhttps\fP
SSL/TLS interception with HTTP protocol decoding, including the removal of
HPKP, HSTS and Alternate Protocol response headers.
.TP
\fBssl\fP
SSL/TLS interception without any lower level protocol decoding; decrypted
connection content is treated as opaque stream of bytes and not modified.
.TP
\fBhttp\fP
Plain TCP connection without SSL/TLS, with HTTP protocol decoding, including
the removal of HPKP, HSTS and Alternate Protocol response headers.
.TP
\fBtcp\fP
Plain TCP connection without SSL/TLS and without any lower level protocol
decoding; decrypted connection content is treated as opaque stream of bytes
and not modified.
.TP
\fBautossl\fP
Plain TCP connection until a Client Hello SSL/TLS message appears in the byte
stream, then automatic upgrade to SSL/TLS interception.
This is generic, protocol-independent STARTTLS support, that may erroneously
trigger on byte sequences that look like Client Hello messages even though
there was no actual STARTTLS command issued.
This is an experimental feature and may in its current state miss some Client
Hello messages depending on circumstances.  YMMV.
Testing and patches highly welcome.
.TP
.I listenaddr port
IPv4 or IPv6 address and port or service name to listen on.  This is the
address and port where the NAT engine should redirect connections to.
.TP
.I nat-engine
NAT engine to query for determining the original destination address and port
of transparently redirected connections.
If no engine is given, the default engine is used, unless overridden with
\fB-e\fP.  When using a NAT engine, \fBsslsplit\fP needs to run on the same
system as the NAT rules redirecting the traffic to \fBsslsplit\fP.
See NAT ENGINES for a list of supported NAT engines.
.TP
.I fwdaddr port
Static destination address, IPv4 or IPv6, with port or service name.  When this
is used, connections are forwarded to the given server address and port.
If \fIfwdaddr\fP is a hostname, it will be resolved to an IP address.
.TP
\fBsni\fP \fIport\fP
Use the Server Name Indication (SNI) hostname sent by the client in the
Client Hello SSL/TLS message to determine the IP address of the server to
connect to.  This only works for \fBssl\fP and \fBhttps\fP \fIproxyspecs\fP and
needs a port or service name as an argument.
Because this requires DNS lookups, it is preferrable to use NAT engine
lookups (see above), except when that is not possible, such as when there is
no supported NAT engine or when running \fBsslsplit\fP on a different system
than the NAT rules redirecting the actual connections.
Note that when using \fB-j\fP with \fBsni\fP, you may need to prepare
\fIjaildir\fP to make name resolution work from within the chroot directory.
.SH SIGNALS
A running \fBsslsplit\fP accepts SIGINT and SIGQUIT for a clean shutdown and
SIGUSR1 to re-open the long-living log files (\fB-l\fP and \fB-L\fP).
Per-connection log files (\fB-S\fP and \fB-F\fP) are not re-opened because
their filename is specific to the connection.
.SH "LOG SPECIFICATIONS"
Log specifications are composed of zero or more printf-style directives;
ordinary characters are included directly in the output path.
SSLsplit current supports the following directives:
.TP
.I %T
The initial connection time as an ISO 8601 UTC timestamp.
.TP
.I %d
The destination host and port, separated by a comma, IPv6 addresses using
underscore instead of colon.
.TP
.I %D
The destination host, IPv6 addresses using underscore instead of colon.
.TP
.I %p
The destination port.
.TP
.I %s
The source host and port, separated by a comma, IPv6 addresses using
underscore instead of colon.
.TP
.I %S
The source host, IPv6 addresses using underscore instead of colon.
.TP
.I %q
The source port.
.TP
.I %x
The name of the local process.
Requires \fB-i\fP to be used.
If process information is unavailable,
this directive will be omitted from the output path.
.TP
.I %X
The full path of the local process.
Requires \fB-i\fP to be used.
If process information is unavailable,
this directive will be omitted from the output path.
.TP
.I %u
The username or numeric uid of the local process.
Requires \fB-i\fP to be used.
If process information is unavailable,
this directive will be omitted from the output path.
.TP
.I %g
The group name or numeric gid of the local process.
Requires \fB-i\fP to be used.
If process information is unavailable,
this directive will be omitted from the output path.
.TP
.I %%
A literal '%' character.
.LP
.SH "NAT ENGINES"
SSLsplit currently supports the following NAT engines:
.TP
.B pf
OpenBSD packet filter (pf) \fBrdr\fP/\fBrdr-to\fP NAT redirects, also available
on FreeBSD, NetBSD and Mac OS X.
Fully supported, including IPv6.
Note that SSLsplit needs permission to open \fB/dev/pf\fP for reading, which by
default means that it needs to run under \fBroot\fP privileges.
Assuming inbound interface \fBem0\fP, first in old (FreeBSD, Mac OS X),
then in new (OpenBSD 4.7+) syntax:
.LP
.RS
.nf
\fBrdr pass on em0 proto tcp from 2001:db8::/64 to any port  80 \\
         ->       ::1 port 10080\fP
\fBrdr pass on em0 proto tcp from 2001:db8::/64 to any port 443 \\
         ->       ::1 port 10443\fP
\fBrdr pass on em0 proto tcp from  192.0.2.0/24 to any port  80 \\
         -> 127.0.0.1 port 10080\fP
\fBrdr pass on em0 proto tcp from  192.0.2.0/24 to any port 443 \\
         -> 127.0.0.1 port 10443\fP
.fi
.RE
.LP
.RS
.nf
\fBpass in quick on em0 proto tcp from 2001:db8::/64 to any \\
         port  80 rdr-to       ::1 port 10080\fP
\fBpass in quick on em0 proto tcp from 2001:db8::/64 to any \\
         port 443 rdr-to       ::1 port 10443\fP
\fBpass in quick on em0 proto tcp from  192.0.2.0/24 to any \\
         port  80 rdr-to 127.0.0.1 port 10080\fP
\fBpass in quick on em0 proto tcp from  192.0.2.0/24 to any \\
         port 443 rdr-to 127.0.0.1 port 10443\fP
.fi
.RE
.TP
.B ipfw
FreeBSD IP firewall (IPFW) divert sockets, also available on Mac OS X.
Available on FreeBSD and OpenBSD using pf \fBdivert-to\fP.
Fully supported on FreeBSD and OpenBSD, including IPv6.
Only supports IPv4 on Mac OS X due to the ancient version of IPFW included.
First in IPFW, then in pf \fBdivert-to\fP syntax:
.LP
.RS
.nf
\fBipfw add fwd       ::1,10080 tcp from 2001:db8::/64 to any  80\fP
\fBipfw add fwd       ::1,10443 tcp from 2001:db8::/64 to any 443\fP
\fBipfw add fwd 127.0.0.1,10080 tcp from 192.0.2.0/24  to any  80\fP
\fBipfw add fwd 127.0.0.1,10443 tcp from 192.0.2.0/24  to any 443\fP
.fi
.RE
.LP
.RS
.nf
\fBpass in quick on em0 proto tcp from 2001:db8::/64 to any \\
         port  80 divert-to       ::1 port 10080\fP
\fBpass in quick on em0 proto tcp from 2001:db8::/64 to any \\
         port 443 divert-to       ::1 port 10443\fP
\fBpass in quick on em0 proto tcp from  192.0.2.0/24 to any \\
         port  80 divert-to 127.0.0.1 port 10080\fP
\fBpass in quick on em0 proto tcp from  192.0.2.0/24 to any \\
         port 443 divert-to 127.0.0.1 port 10443\fP
.fi
.RE
.TP
.B ipfilter
IPFilter (ipfilter, ipf), available on many systems, including FreeBSD, NetBSD,
Linux and Solaris.
Note that SSLsplit needs permission to open \fB/dev/ipnat\fP for reading, which
by default means that it needs to run under \fBroot\fP privileges.
Only supports IPv4 due to limitations in the SIOCGNATL ioctl(2) interface.
Assuming inbound interface \fBbge0\fP:
.LP
.RS
.nf
\fBrdr bge0 0.0.0.0/0 port  80 -> 127.0.0.1 port 10080\fP
\fBrdr bge0 0.0.0.0/0 port 443 -> 127.0.0.1 port 10443\fP
.fi
.RE
.TP
.B netfilter
Linux netfilter using the iptables REDIRECT target.
Only supports IPv4 due to limitations in the SO_ORIGINAL_DST getsockopt(2)
interface.
.LP
.RS
.nf
\fBiptables -t nat -A PREROUTING -s 192.0.2.0/24 \\
         -p tcp --dport  80 \\
         -j REDIRECT --to-ports 10080\fP
\fBiptables -t nat -A PREROUTING -s 192.0.2.0/24 \\
         -p tcp --dport 443 \\
         -j REDIRECT --to-ports 10443\fP
.fi
.LP
Note that SSLsplit is only able to accept incoming connections if it binds
to the correct IP address (e.g. 192.0.2.1) or on all interfaces (0.0.0.0).
REDIRECT uses the local interface address of the incoming interface as
target IP address, or 127.0.0.1 for locally generated packets.
.RE
.TP
.B tproxy
Linux netfilter using the iptables TPROXY target together with routing
table magic to allow non-local traffic to originate on local sockets.
Fully supported, including IPv6.
.LP
.RS
.nf
\fBip -f inet6 rule add fwmark 1 lookup 100\fP
\fBip -f inet6 route add local default dev lo table 100\fP
\fBip6tables -t mangle -N DIVERT\fP
\fBip6tables -t mangle -A DIVERT -j MARK --set-mark 1\fP
\fBip6tables -t mangle -A DIVERT -j ACCEPT\fP
\fBip6tables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT\fP
\fBip6tables -t mangle -A PREROUTING -s 2001:db8::/64 \\
          -p tcp --dport 80 \\
          -j TPROXY --tproxy-mark 0x1/0x1 --on-port 10080\fP
\fBip6tables -t mangle -A PREROUTING -s 2001:db8::/64 \\
          -p tcp --dport 443 \\
          -j TPROXY --tproxy-mark 0x1/0x1 --on-port 10443\fP
\fBip -f inet rule add fwmark 1 lookup 100\fP
\fBip -f inet route add local default dev lo table 100\fP
\fBiptables -t mangle -N DIVERT\fP
\fBiptables -t mangle -A DIVERT -j MARK --set-mark 1\fP
\fBiptables -t mangle -A DIVERT -j ACCEPT\fP
\fBiptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT\fP
\fBiptables -t mangle -A PREROUTING -s 192.0.2.0/24 \\
         -p tcp --dport 80 \\
         -j TPROXY --tproxy-mark 0x1/0x1 --on-port 10080\fP
\fBiptables -t mangle -A PREROUTING -s 192.0.2.0/24 \\
         -p tcp --dport 443 \\
         -j TPROXY --tproxy-mark 0x1/0x1 --on-port 10443\fP
.fi
.LP
Note that return path filtering (rp_filter) also needs to be disabled on
interfaces which handle TPROXY redirected traffic.
.RE
.SH EXAMPLES
Matching the above NAT engine configuration samples, intercept HTTP and HTTPS
over IPv4 and IPv6 using forged certificates with CA private key \fBca.key\fP
and certificate \fBca.crt\fP, logging connections to \fBconnect.log\fP and
connection data into separate files under \fB/tmp\fP (add \fB-e\fP
\fInat-engine\fP to select the appropriate engine if multiple engines are
available on your system):
.LP
.nf
\fBsslsplit -k ca.key -c ca.crt -l connect.log -L /tmp \\
         https ::1 10443  https 127.0.0.1 10443 \\
         http  ::1 10080  http  127.0.0.1 10080\fP
.fi
.LP
If the Linux netfilter engine is used with the iptables REDIRECT target, it is
important to listen to the correct IP address (e.g. 192.0.2.1) or on all
interfaces (0.0.0.0), otherwise SSLsplit is not able to accept incoming
connections.
.LP
Intercepting IMAP/IMAPS using the same settings:
.LP
.nf
\fBsslsplit -k ca.key -c ca.crt -l connect.log -L /tmp \\
         ssl ::1 10993  ssl 127.0.0.1 10993 \\
         tcp ::1 10143  tcp 127.0.0.1 10143\fP
.fi
.LP
A more targetted setup, HTTPS only, using certificate/chain/key files from
\fB/path/to/cert.d\fP and statically redirecting to \fBwww.example.org\fP
instead of querying a NAT engine:
.LP
.nf
\fBsslsplit -t /path/to/cert.d -l connect.log -L /tmp \\
         https ::1       10443 www.example.org 443 \\
         https 127.0.0.1 10443 www.example.org 443\fP
.fi
.LP
The original example, but using SSL options optimized for speed by disabling
compression and selecting only fast cipher cipher suites and using a
precomputed private key \fBleaf.key\fP for the forged certificates.  Most
significant speed increase is gained by choosing fast algorithms and small
keysizes for the CA and leaf private keys.  Check \fBopenssl speed\fP for
algorithm performance on your system.  Note that clients may not support all
algorithms and key sizes.  Also, some clients warn their users about cipher
suites they consider weak.
.LP
.nf
\fBsslsplit -Z -s NULL:RC4:AES128:-DHE -K leaf.key \\
         -k ca.key -c ca.crt -l connect.log -L /tmp \\
         https ::1 10443  https 127.0.0.1 10443 \\
         http  ::1 10080  http  127.0.0.1 10080\fP
.fi
.LP
The original example, but running as a daemon under user \fBsslsplit\fP and
writing a PID file:
.LP
.nf
\fBsslsplit -d -p /var/run/sslsplit.pid -u sslsplit \\
         -k ca.key -c ca.crt -l connect.log -L /tmp \\
         https ::1 10443  https 127.0.0.1 10443 \\
         http  ::1 10080  http  127.0.0.1 10080\fP
.fi
.LP
To generate a CA private key \fBca.key\fP  and certificate \fBca.crt\fP using
OpenSSL:
.LP
.nf
\fBcat >x509v3ca.cnf <<'EOF'\fP
[ req ]
distinguished_name = reqdn

[ reqdn ]

[ v3_ca ]
basicConstraints        = CA:TRUE
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid:always,issuer:always
\fBEOF\fP

\fBopenssl genrsa -out ca.key 2048\fP
\fBopenssl req -new -nodes -x509 -sha256 -out ca.crt -key ca.key \\
        -config x509v3ca.cnf -extensions v3_ca \\
        -subj '/O=SSLsplit Root CA/CN=SSLsplit Root CA/' \\
        -set_serial 0 -days 3650\fP
.fi
.SH NOTES
SSLsplit is able to handle a relatively high number of listeners and
connections due to a multithreaded, event based architecture based on libevent,
taking advantage of platform specific select() replacements such as kqueue.
The main thread handles the listeners and signalling, while a number of worker
threads equal to twice the number of CPU cores is used for handling the actual
connections in separate event bases, including the CPU-intensive SSL/TLS
handling.
.LP
Care has been taken to choose well-performing data structures for caching
certificates and SSL sessions.  Logging is implemented in separate disk writer
threads to ensure that socket event handling threads don't have to block on
disk I/O.
DNS lookups are performed asynchroniously.
SSLsplit uses SSL session caching on both ends to minimize the amount of full
SSL handshakes, but even then, the limiting factor in handling SSL connections
are the actual bignum computations.
.SH "SEE ALSO"
openssl(1), ciphers(1), speed(1),
pf(4), ipfw(8), iptables(8), ip6tables(8), ip(8),
hostapd(8), arpspoof(8), parasite6(8), yersinia(8),
.I https://www.roe.ch/SSLsplit
.SH AUTHORS
SSLsplit was written by Daniel Roethlisberger <daniel@roe.ch>.

The following individuals have contributed code or documentation, in
chronological order of their first contribution:
Steve Wills, Landon Fuller, Wayne Jensen, Rory McNamara, Alexander Neumann,
Adam Jacob Muller, Richard Poole, Maciej Kotowicz, Eun Soo Park and Christian
Groschupp.
.SH BUGS
Use Github for submission of bug reports or patches:
.LP
.RS
.I https://github.com/droe/sslsplit
.RE
.LP