There are many reasons to start hosting an outgoing proxy. Mine was slow upstream servers. But if, for whatever reason, you wish to use an outgoing proxy, this blogpost might be helpful.

The steps are as follows: 1. Install the software (squid on Debian Linux in my case) 1. Configure the software (squid on Debian Linux) 1. Configure your various software to accept the proxy intercepting the TLS secure connections 1. Redirect all traffic through the proxy, with some exceptions if needed. (Websockets are not supported, so you will need to put some exception in for that)

Install

1. Debian doesn't include tls interception (called ssl-bump in squid) support in the default package. If you want this, you need to install squid-openssl.

apt install squid-openssl

Configure

1. Prepare the Certificate Authority (CA)

mkdir -p /etc/squid/cert/
cd /etc/squid/cert/
# This puts the private key and the self-signed certificate in the same file
openssl req -new -newkey rsa:4096 -sha256 -days 3650 -nodes -x509 -keyout myCA.pem -out myCA.pem

1. Create a config file /etc/squid/squid.conf

workers 4
acl localnet dst 0.0.0.1-0.255.255.255  # RFC 1122 "this" network (LAN)
acl localnet dst 10.0.0.0/8     # RFC 1918 local private network (LAN)
acl localnet dst 100.64.0.0/10      # RFC 6598 shared address space (CGN)
acl localnet dst 169.254.0.0/16     # RFC 3927 link-local (directly plugged) machines
acl localnet dst 172.16.0.0/12      # RFC 1918 local private network (LAN)
acl localnet dst 192.168.0.0/16     # RFC 1918 local private network (LAN)
acl localnet dst fc00::/7           # RFC 4193 local private network range
acl localnet dst fe80::/10          # RFC 4291 link-local (directly plugged) machines
acl localnet dst 2a02:a44e:5504::/56
acl tunnelips dst "/etc/squid/tunnelips.list"
acl SSL_ports port 443
acl SSL_ports port 8443
acl SSL_ports port 8843
acl SSL_ports port 5281
acl SSL_ports port 9091
acl Safe_ports port 80      # http
acl Safe_ports port 21      # ftp
acl Safe_ports port 443     # https
acl Safe_ports port 8443    # https
acl Safe_ports port 8843    # https
acl Safe_ports port 70      # gopher
acl Safe_ports port 210     # wais
acl Safe_ports port 1025-65535  # unregistered ports
acl Safe_ports port 280     # http-mgmt
acl Safe_ports port 488     # gss-http
acl Safe_ports port 591     # filemaker
acl Safe_ports port 777     # multiling http
acl Safe_ports port 9091    # transmission
acl CONNECT method CONNECT
acl step1 at_step SslBump1
acl step2 at_step SslBump2
acl step3 at_step SslBump3
acl tunnelsites ssl::server_name_regex -i "/etc/squid/tunnelsites.list"
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
http_access allow localhost manager
http_access deny manager
include /etc/squid/conf.d/*
http_access allow localnet
http_access allow localhost
http_access allow all
http_access deny all
on_unsupported_protocol tunnel all
http_port 3128 ssl-bump tls-cert=/etc/squid/cert/SQUID_CA.pem generate-host-certificates=on dynamic_cert_mem_cache_size=8MB
http_port 3129 intercept
https_port 3131 intercept ssl-bump tls-cert=/etc/squid/cert/SQUID_CA.pem generate-host-certificates=on dynamic_cert_mem_cache_size=8MB
https_port 443 intercept ssl-bump tls-cert=/etc/squid/cert/SQUID_CA.pem generate-host-certificates=on dynamic_cert_mem_cache_size=8MB
tls_outgoing_options min-version=1.2 cafile=/etc/ssl/certs/ca-certificates.crt
ssl_bump splice tunnelsites
ssl_bump splice step1 localnet
ssl_bump splice step1 tunnelips
ssl_bump peek step1
ssl_bump splice tunnelsites
ssl_bump bump
sslcrtd_program /usr/lib/squid/security_file_certgen -s /var/spool/squid/ssl_db -M 40MB
sslcrtd_children 16 startup=5 idle=3
sslproxy_cert_error deny all
server_idle_pconn_timeout 10 minutes
cache_mem 256 MB
memory_cache_mode always
maximum_object_size_in_memory 5 MB
logformat bumpsquid      %ts.%03tu %6tr %>a %Ss/%03>Hs %ssl::bump_mode %<st %rm %ru %[un %Sh/%<a %mt
access_log daemon:/var/log/squid/access.log bumpsquid
coredump_dir /var/spool/squid
refresh_pattern -i (/cgi-bin/|\?) 0 0%  0
refresh_pattern -i .(gif|png|jpg|jpeg|ico)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern -i gstatic\.com 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern -i .(iso|avi|wav|mp3|mp4|mpeg|swf|flv|x-flv)$ 43200 90% 432000 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern -i .(deb|rpm|exe|zip|tar|tgz|ram|rar|bin|ppt|doc|tiff|InRelease|Packages.gz)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern -i .(css|js)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern -i .index.(html|htm)$ 0 40% 10080 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern -i .(html|htm)$ 1440 40% 40320 override-expire ignore-no-cache ignore-no-store ignore-private ignore-auth
refresh_pattern . 0 40% 40320
shutdown_lifetime 1 seconds
global_internal_static off
dns_v4_first on
forwarded_for delete
pipeline_prefetch on
max_filedesc 204800
fqdncache_size 2048
ipcache_size 2048
ipcache_low 95
ipcache_high 98
cache_swap_low 95
cache_swap_low 98
quick_abort_min 0
quick_abort_max 0
quick_abort_pct 95
range_offset_limit -1
request_header_max_size 200 KB
reply_header_max_size 200 KB
memory_pools off
buffered_logs off
log_icp_queries off
logfile_rotate 1
icp_hit_stale on
query_icmp off
reload_into_ims on
negative_ttl 2 minutes
vary_ignore_expire on
half_closed_clients off
high_page_fault_warning 2
nonhierarchical_direct on
prefer_direct off
cachemgr_passwd none all
client_db on
forwarded_for on
via on
max_stale 1 month

1. Create the certificate database by issuing

/usr/lib/squid/security_file_certgen -c -s /var/spool/squid/ssl_db -M 4MB

and correct access rights with

chmod -R proxy:proxy  /var/spool/squid/ssl_db

1. Restart squid with systemctl restart squid

Configure client software

1. Prepare the CA certificate for use by browsers.

# This can be added to browsers
openssl x509 -in /etc/squid/cert/myCA.pem -outform DER -out /tmp/myCA.der

1. Add the squid CA to the system wide ca-certificates

# Copy the CA to the ca-certificates directory
sudo openssl x509 -in /etc/squid/cert/myCA.pem -out /usr/share/ca-certificates/myCA.crt

1. Add the line myCA.crt to /etc/ca-certificates.conf and run sudo update-ca-certificates
2. For firefox (this is what I use), open the settings, find security devices and add /usr/lib/x86_64-linux-gnu/pkcs11/p11-kit-trust.so as a security device. This means Firefox will also trust the system wide CAs.
3. For other browsers, you can import the /tmp/myCA.der as a Certificate Authority.

Force all traffic through the proxy

1. Install packages for firewall management if not already installed: sudo apt install netfilter-persistent iptables-persistent
2. Configure the firewall rules

sudo iptables -t nat -A OUTPUT -p tcp -m tcp --dport 80 -m owner --uid-owner root -j RETURN
sudo iptables -t nat -A OUTPUT -p tcp -m tcp --dport 80 -m owner --uid-owner proxy -j RETURN
sudo iptables -t nat -A OUTPUT -p tcp -m tcp --dport 443 -m owner --uid-owner root -j RETURN
sudo iptables -t nat -A OUTPUT -p tcp -m tcp --dport 443 -m owner --uid-owner proxy -j RETURN
sudo iptables -t nat -A OUTPUT -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 3129
sudo iptables -t nat -A OUTPUT -p tcp -m tcp --dport 443 -j REDIRECT --to-ports 3131

1. Save the rules: sudo netfilter-persistent save

Have a cup of tea

Because you're done. You might need to relogin/reboot for the p11-kit stuff to take effect.