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#!/bin/bash
#
# RSA private key, SSL certificate, Diffie-Hellman bits files
# -------------------------------------------
# Create an RSA private key, a self-signed SSL certificate, and some
# Diffie-Hellman cipher bits, if they have not yet been created.
#
# The RSA private key and certificate are used for:
#
# * DNSSEC DANE TLSA records
# * IMAP
# * SMTP (opportunistic TLS for port 25 and submission on ports 465/587)
# * HTTPS
#
# The certificate is created with its CN set to the PRIMARY_HOSTNAME. It is
# also used for other domains served over HTTPS until the user installs a
# better certificate for those domains.
#
# The Diffie-Hellman cipher bits are used for SMTP and HTTPS, when a
# Diffie-Hellman cipher is selected during TLS negotiation. Diffie-Hellman
# provides Perfect Forward Secrecy.
source setup/functions.sh # load our functions
source /etc/mailinabox.conf # load global vars
# Show a status line if we are going to take any action in this file.
if [ ! -f /usr/bin/openssl ] \
|| [ ! -f $STORAGE_ROOT/ssl/ssl_private_key.pem ] \
|| [ ! -f $STORAGE_ROOT/ssl/ssl_certificate.pem ] \
|| [ ! -f $STORAGE_ROOT/ssl/dh2048.pem ]; then
echo "Creating initial SSL certificate and perfect forward secrecy Diffie-Hellman parameters..."
fi
# Install openssl.
apt_install openssl
# Create a directory to store TLS-related things like "SSL" certificates.
mkdir -p $STORAGE_ROOT/ssl
# Generate a new private key.
#
# The key is only as good as the entropy available to openssl so that it
# can generate a random key. "OpenSSL’s built-in RSA key generator ....
# is seeded on first use with (on Linux) 32 bytes read from /dev/urandom,
# the process ID, user ID, and the current time in seconds. [During key
# generation OpenSSL] mixes into the entropy pool the current time in seconds,
# the process ID, and the possibly uninitialized contents of a ... buffer
# ... dozens to hundreds of times."
#
# A perfect storm of issues can cause the generated key to be not very random:
#
# * improperly seeded /dev/urandom, but see system.sh for how we mitigate this
# * the user ID of this process is always the same (we're root), so that seed is useless
# * zero'd memory (plausible on embedded systems, cloud VMs?)
# * a predictable process ID (likely on an embedded/virtualized system)
# * a system clock reset to a fixed time on boot
#
# Since we properly seed /dev/urandom in system.sh we should be fine, but I leave
# in the rest of the notes in case that ever changes.
if [ ! -f $STORAGE_ROOT/ssl/ssl_private_key.pem ]; then
# Set the umask so the key file is never world-readable.
(umask 077; hide_output \
openssl genrsa -out $STORAGE_ROOT/ssl/ssl_private_key.pem 2048)
fi
# Generate a self-signed SSL certificate because things like nginx, dovecot,
# etc. won't even start without some certificate in place, and we need nginx
# so we can offer the user a control panel to install a better certificate.
if [ ! -f $STORAGE_ROOT/ssl/ssl_certificate.pem ]; then
# Generate a certificate signing request.
CSR=/tmp/ssl_cert_sign_req-$$.csr
hide_output \
openssl req -new -key $STORAGE_ROOT/ssl/ssl_private_key.pem -out $CSR \
-sha256 -subj "/CN=$PRIMARY_HOSTNAME"
# Generate the self-signed certificate.
CERT=$STORAGE_ROOT/ssl/$PRIMARY_HOSTNAME-selfsigned-$(date --rfc-3339=date | sed s/-//g).pem
hide_output \
openssl x509 -req -days 365 \
-in $CSR -signkey $STORAGE_ROOT/ssl/ssl_private_key.pem -out $CERT
# Delete the certificate signing request because it has no other purpose.
rm -f $CSR
# Symlink the certificate into the system certificate path, so system services
# can find it.
ln -s $CERT $STORAGE_ROOT/ssl/ssl_certificate.pem
fi
# Generate some Diffie-Hellman cipher bits.
# openssl's default bit length for this is 1024 bits, but we'll create
# 2048 bits of bits per the latest recommendations.
if [ ! -f $STORAGE_ROOT/ssl/dh2048.pem ]; then
openssl dhparam -out $STORAGE_ROOT/ssl/dh2048.pem 2048
fi