95 lines
4.2 KiB
Bash
Executable File
95 lines
4.2 KiB
Bash
Executable File
#!/bin/bash
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#
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# RSA private key, SSL certificate, Diffie-Hellman bits files
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# -------------------------------------------
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# Create an RSA private key, a self-signed SSL certificate, and some
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# Diffie-Hellman cipher bits, if they have not yet been created.
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#
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# The RSA private key and certificate are used for:
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#
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# * DNSSEC DANE TLSA records
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# * IMAP
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# * SMTP (opportunistic TLS for port 25 and submission on port 587)
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# * HTTPS
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#
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# The certificate is created with its CN set to the PRIMARY_HOSTNAME. It is
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# also used for other domains served over HTTPS until the user installs a
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# better certificate for those domains.
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#
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# The Diffie-Hellman cipher bits are used for SMTP and HTTPS, when a
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# Diffie-Hellman cipher is selected during TLS negotiation. Diffie-Hellman
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# provides Perfect Forward Secrecy.
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source setup/functions.sh # load our functions
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source /etc/mailinabox.conf # load global vars
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echo "Creating initial SSL certificate and perfect forward secrecy Diffie-Hellman parameters..."
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apt_install openssl
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mkdir -p $STORAGE_ROOT/ssl
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# Generate a new private key.
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#
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# The key is only as good as the entropy available to openssl so that it
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# can generate a random key. "OpenSSL’s built-in RSA key generator ....
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# is seeded on first use with (on Linux) 32 bytes read from /dev/urandom,
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# the process ID, user ID, and the current time in seconds. [During key
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# generation OpenSSL] mixes into the entropy pool the current time in seconds,
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# the process ID, and the possibly uninitialized contents of a ... buffer
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# ... dozens to hundreds of times." /dev/urandom is, in turn, seeded from
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# "the uninitialized contents of the pool buffers when the kernel starts,
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# the startup clock time in nanosecond resolution, input event and disk
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# access timings, and entropy saved across boots to a local file" as well
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# as the order of execution of concurrent accesses to /dev/urandom.
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# (Heninger et al 2012, https://factorable.net/weakkeys12.conference.pdf)
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#
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# /dev/urandom draws from the same entropy sources as /dev/random, but
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# doesn't block or issue any warnings if no entropy is actually available.
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# (http://www.2uo.de/myths-about-urandom/) Thus eventually /dev/urandom
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# can be expected to have been seeded with the "input event and disk access
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# timings", but there's no guarantee that this has even ocurred.
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#
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# Some of these seeds are obviously not helpful for us: There are no input
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# events on severs (keyboard/mouse), and the user ID of this process is
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# always the same (we're root). And the seeding of /dev/urandom with the
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# time and a seed from a previous boot is handled by *during boot* by
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# /etc/init.d/urandom, which, in principle, may not have occurred yet!
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#
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# A perfect storm of issues can cause the generated key to be not very random:
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#
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# * zero'd memory (plausible on embedded systems, cloud VMs?)
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# * a predictable process ID (likely on an embedded/virtualized system)
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# * a system clock reset to a fixed time on boot
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# * one CPU or no concurrent processes on /dev/urandom (so no concurrent accesses)
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# * no hard disk (so no disk access timings - but is this possible for us?)
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# * early run (no entry yet, boot not finished)
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# * first boot (no entropy saved from previous boot)
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#
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if [ ! -f $STORAGE_ROOT/ssl/ssl_private_key.pem ]; then
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# Set the umask so the key file is never world-readable.
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(umask 077; hide_output \
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openssl genrsa -out $STORAGE_ROOT/ssl/ssl_private_key.pem 2048)
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fi
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# Generate a certificate signing request.
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if [ ! -f $STORAGE_ROOT/ssl/ssl_cert_sign_req.csr ]; then
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hide_output \
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openssl req -new -key $STORAGE_ROOT/ssl/ssl_private_key.pem -out $STORAGE_ROOT/ssl/ssl_cert_sign_req.csr \
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-sha256 -subj "/C=$CSR_COUNTRY/ST=/L=/O=/CN=$PRIMARY_HOSTNAME"
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fi
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# Generate a SSL certificate by self-signing.
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if [ ! -f $STORAGE_ROOT/ssl/ssl_certificate.pem ]; then
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hide_output \
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openssl x509 -req -days 365 \
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-in $STORAGE_ROOT/ssl/ssl_cert_sign_req.csr -signkey $STORAGE_ROOT/ssl/ssl_private_key.pem -out $STORAGE_ROOT/ssl/ssl_certificate.pem
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fi
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# Generate some Diffie-Hellman cipher bits.
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# openssl's default bit length for this is 1024 bits, but we'll create
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# 2048 bits of bits per the latest recommendations.
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if [ ! -f $STORAGE_ROOT/ssl/dh2048.pem ]; then
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openssl dhparam -out $STORAGE_ROOT/ssl/dh2048.pem 2048
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fi
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