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48 lines
2.5 KiB
Bash
48 lines
2.5 KiB
Bash
# Make sure noone can read the files we generate but us
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umask 077
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# Destroy any old key on the Yubikey (careful!)
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ykman piv reset
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# Generate a new private/public key pair on the device, store the public key in 'pubkey.pem'.
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ykman piv generate-key -a RSA2048 9d pubkey.pem
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# Create a self-signed certificate from this public key, and store it on the
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# device. The "subject" should be an arbitrary string to identify the token in
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# the p11tool output below.
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ykman piv generate-certificate --subject "Knobelei" 9d pubkey.pem
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# Check if the newly create key on the Yubikey shows up as token in PKCS#11. Have a look at the output, and
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# copy the resulting token URI to the clipboard.
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p11tool --list-tokens
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# Generate a (secret) random key to use as LUKS decryption key.
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dd if=/dev/urandom of=plaintext.bin bs=128 count=1
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# Encode the secret key also as base64 text (with all whitespace removed)
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base64 < plaintext.bin | tr -d '\n\r\t ' > plaintext.base64
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# Encrypt this newly generated (binary) LUKS decryption key using the public key whose private key is on the
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# Yubikey, store the result in /etc/encrypted-luks-key.bin, where we'll look for it during boot.
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sudo openssl rsautl -encrypt -pubin -inkey pubkey.pem -in plaintext.bin -out /etc/encrypted-luks-key.bin
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# Configure the LUKS decryption key on the LUKS device. We use very low pbkdf settings since the key already
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# has quite a high quality (it comes directly from /dev/urandom after all), and thus we don't need to do much
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# key derivation. Replace /dev/sdXn by the partition to use (e.g. sda1)
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sudo cryptsetup luksAddKey /dev/sdXn plaintext.base64 --pbkdf=pbkdf2 --pbkdf-force-iterations=1000
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# Now securely delete the plain text LUKS key, we don't need it anymore, and since it contains secret key
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# material it should be removed from disk thoroughly.
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shred -u plaintext.bin plaintext.base64
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# We don't need the public key anymore either, let's remove it too. Since this one is not security
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# sensitive we just do a regular "rm" here.
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rm pubkey.pem
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# Test: Let's run systemd-cryptsetup to test if this all worked. The option string should contain the full
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# PKCS#11 URI we have in the clipboard, it tells the tool how to decypher the encrypted LUKS key.
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sudo systemd-cryptsetup attach mytest /dev/sdXn /etc/encrypted-luks-key.bin 'pkcs11-uri=pkcs11:…'
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# If that worked, let's now add the same line persistently to /etc/crypttab, for the future.
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sudo bash -c 'echo "mytest /dev/sdXn /etc/encrypted-luks-key \'pkcs11-uri=pkcs11:…\'" >> /etc/crypttab'
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