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HTTPS Analysis with Raspberry PI

Since most traffic nowadays is encrypted, you can try a little trick to bypass this protection. The idea is, clients do connect to you with one of your own certificates what enables you to analyze encrypted traffic.

Objective

The aim is to analyze the HTTPS traffic from connected STA's where for example HSTS web security policy mechanism or other protections are not in use.

Precondition

You should already have read (and successful carried out) the following tutorials.

Install needed and/or optional packages

Install (or ensure they are installed) following packages.

# update system (optional)
$ sudo apt update -y && sudo apt upgrade -y

# install optional packages (optional)
$ sudo apt install -y vim tree

# install needed packages
$ sudo apt install -y iptables sslsplit

sslsplit

Note: Read this document for more information.

Configure sslsplit

Many online search results end up with a very long command line options for sslsplit, don't do that (just create your own configuration(s) file(s))!

# read configuration sample (optional)
$ sudo /usr/sslsplit/sslsplit.conf.sample

# add own sslsplit configuration
$ sudo vim /usr/sslsplit/sslsplit.conf

Add the following lines in /usr/sslsplit/sslsplit.conf configuration file (modify later for your needs).

# CA cert (equivalent to -c option)
CACert /usr/sslsplit/ca.crt

# CA key (equivalent to -k option)
CAKey /usr/sslsplit/ca.key

# Connect log (equivalent to -l)
ConnectLog /var/log/sslsplit/connect.log

# Content log (equivalent to -L option (excludes -S/-F))
ContentLog /var/log/sslsplit/content.log

# Log master keys in SSLKEYLOGFILE format (equivalent to -M option)
# MasterKeyLog /var/log/sslsplit/masterkeys.log

# Debug mode run in foreground (equivalent to -D option)
Debug yes

# Daemon mode: run in background (equivalent to -d option)
# Daemon yes

# Passthrough SSL connections (equivalent to -P option)
# Passthrough yes

# Proxy specifications (ipv4)
# ProxySpec http 192.168.0.1 8080
# ProxySpec https 192.168.0.1 8443

# Proxy specifications (ipv4)
# ProxySpec http ::ffff:c0a8:1 8080
# ProxySpec https ::ffff:c0a8:1 8443

Note: read this manual page for more information.

Generate self signed certificate

# show openssl.cnf (optional)
$ sudo cat /usr/lib/ssl/openssl.cnf

Next to all other content inside /usr/lib/ssl/openssl.cnf, ensure the following options are set.

[ req ]
distinguished_name	= req_distinguished_name

[ v3_ca ]
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid:always,issuer
basicConstraints = critical,CA:true

Generate key and certificate with OpenSSL.

# show version (optional)
$ openssl version

# show help (optional)
$ openssl help

# generate key
$ sudo openssl genrsa -out /usr/sslsplit/ca.key 4096

# generate certificate
$ sudo openssl req -new -x509 -key /usr/sslsplit/ca.key -out /usr/sslsplit/ca.crt -config /usr/lib/ssl/openssl.cnf -extensions v3_ca -subj '/O=SSLsplit Root CA/CN=SSLsplit Root CA/' -set_serial 0 -days 3650

# show content of directory (optional)
$ sudo tree /usr/sslsplit/
├── ca.crt
├── ca.key
├── sslsplit.conf
└── sslsplit.conf.sample

Add iptables rules

Route the traffic from specific ports over to sslsplit (listening on port 8443 or port 8080)

# save current iptables rules
$ iptables-save > /usr/sslsplit/rules/saved

# http/https iptables rules
$ sudo iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-ports 8080
$ sudo iptables -t nat -A PREROUTING -p tcp --dport 443 -j REDIRECT --to-ports 8443

# some other rules (optional)
$ sudo iptables -t nat -A PREROUTING -p tcp --dport 587 -j REDIRECT --to-ports 8443
$ sudo iptables -t nat -A PREROUTING -p tcp --dport 465 -j REDIRECT --to-ports 8443
$ sudo iptables -t nat -A PREROUTING -p tcp --dport 993 -j REDIRECT --to-ports 8443
$ sudo iptables -t nat -A PREROUTING -p tcp --dport 5222 -j REDIRECT --to-ports 8080

Note: You could also save the iptables-save, iptables rules, iptables clean-up and iptables-restore as bash script!

Start sslsplit

# tail all logfiles (optional)
$ sudo tail -f /var/log/sslsplit/connect.log /var/log/sslsplit/content.log /var/log/sslsplit/masterkeys.log

# start for http/https only
$ sudo sslsplit -f /usr/sslsplit/sslsplit.conf -P https 192.168.0.1 8443 http 192.168.0.1 8080

# start for ssl/tcp
$ sudo sslsplit -f /usr/sslsplit/sslsplit.conf -P ssl 0.0.0.0 8443 tcp 0.0.0.0 8080

When you are ready press CTRL + c to stop sslsplit.

Clean-up iptables rules

# clean iptables
$ iptables -F
$ iptables -X
$ iptables -t nat -F
$ iptables -t nat -X
$ iptables -t mangle -F
$ iptables -t mangle -X
$ iptables -P INPUT ACCEPT
$ iptables -P FORWARD ACCEPT
$ iptables -P OUTPUT ACCEPT

# restore iptables rules
$ iptables-restore < /usr/sslsplit/rules/saved

Start traffic analysis

# show content.log
$ sudo cat /var/log/sslsplit/content.log

# show connect.log
$ sudo cat /var/log/sslsplit/connect.log

Important

Many modern browsers protect such a kind of analysis and clients will see a warning (e.g. untrusted certificate)! For your own needs, transfer the certificate /usr/sslsplit/ca.crt from your Raspberry PI to the client device (import into a browser).

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