From 2ccf0ff6e8cdeca63ae25e6714bc14defc4df5a2 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Tue, 17 Dec 2019 18:39:12 +0100 Subject: [PATCH] man: tweaks to the crypttab(5) man page --- man/crypttab.xml | 11 ++++++----- man/yubikey-crypttab.sh | 16 +++++++++------- 2 files changed, 15 insertions(+), 12 deletions(-) diff --git a/man/crypttab.xml b/man/crypttab.xml index d84a914a5e..9b6fffd154 100644 --- a/man/crypttab.xml +++ b/man/crypttab.xml @@ -425,10 +425,10 @@ line. This is useful for unlocking encrypted volumes through security tokens or smartcards. See below for an example how to set up this mechanism for unlocking a LUKS volume with a YubiKey security token. The specified URI can refer directly to a private RSA key stored on a token or alternatively - just to a slot or token in which case a suitable private RSA key object is automatically searched on - it. In this case if multiple suitable objects are found the token is refused. The key configured in - the third column is passed as is to RSA decryption. The resulting decrypted key is then base64 - encoded before it is used to unlock the LUKS volume. + just to a slot or token, in which case a search for a suitable private RSA key will be performed. In + this case if multiple suitable objects are found the token is refused. The key configured in the + third column is passed as is to RSA decryption. The resulting decrypted key is then base64 encoded + before it is used to unlock the LUKS volume. @@ -489,7 +489,8 @@ external /dev/sda3 keyfile:LABEL=keydev keyfile-timeout=10sYubikey-based Volume Unlocking Example The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA - decryption keys. Here's an example how to set up a Yubikey security token for this purpose: + decryption keys. Here's an example how to set up a Yubikey security token for this purpose, using + ykman from the yubikey-manager project: diff --git a/man/yubikey-crypttab.sh b/man/yubikey-crypttab.sh index b7e8ee686f..9e65bae621 100644 --- a/man/yubikey-crypttab.sh +++ b/man/yubikey-crypttab.sh @@ -7,7 +7,9 @@ ykman piv reset # Generate a new private/public key pair on the device, store the public key in 'pubkey.pem'. ykman piv generate-key -a RSA2048 9d pubkey.pem -# Create a self-signed certificate from this public key, and store it on the device. +# Create a self-signed certificate from this public key, and store it on the +# device. The "subject" should be an arbitrary string to identify the token in +# the p11tool output below. ykman piv generate-certificate --subject "Knobelei" 9d pubkey.pem # Check if the newly create key on the Yubikey shows up as token in PKCS#11. Have a look at the output, and @@ -18,16 +20,16 @@ p11tool --list-tokens dd if=/dev/urandom of=plaintext.bin bs=128 count=1 # Encode the secret key also as base64 text (with all whitespace removed) -base64 < plaintext.bin | tr -d '\n\r\t ' > plaintext.base64 +base64 < plaintext.bin | tr -d '\n\r\t ' > plaintext.base64 # Encrypt this newly generated (binary) LUKS decryption key using the public key whose private key is on the # Yubikey, store the result in /etc/encrypted-luks-key.bin, where we'll look for it during boot. -openssl rsautl -encrypt -pubin -inkey pubkey.pem -in plaintext.bin -out /etc/encrypted-luks-key.bin +sudo openssl rsautl -encrypt -pubin -inkey pubkey.pem -in plaintext.bin -out /etc/encrypted-luks-key.bin # Configure the LUKS decryption key on the LUKS device. We use very low pbkdf settings since the key already # has quite a high quality (it comes directly from /dev/urandom after all), and thus we don't need to do much -# key derivation. -cryptsetup luksAddKey /dev/sda1 plaintext.base64 --pbkdf=pbkdf2 --pbkdf-force-iterations=1000 +# key derivation. Replace /dev/sdXn by the partition to use (e.g. sda1) +sudo cryptsetup luksAddKey /dev/sdXn plaintext.base64 --pbkdf=pbkdf2 --pbkdf-force-iterations=1000 # Now securely delete the plain text LUKS key, we don't need it anymore, and since it contains secret key # material it should be removed from disk thoroughly. @@ -39,7 +41,7 @@ rm pubkey.pem # Test: Let's run systemd-cryptsetup to test if this all worked. The option string should contain the full # PKCS#11 URI we have in the clipboard, it tells the tool how to decypher the encrypted LUKS key. -systemd-cryptsetup attach mytest /dev/sda1 /etc/encrypted-luks-key.bin 'pkcs11-uri=pkcs11:…' +sudo systemd-cryptsetup attach mytest /dev/sdXn /etc/encrypted-luks-key.bin 'pkcs11-uri=pkcs11:…' # If that worked, let's now add the same line persistently to /etc/crypttab, for the future. -echo "mytest /dev/sda1 /etc/encrypted-luks-key 'pkcs11-uri=pkcs11:…' >> /etc/crypttab +sudo bash -c 'echo "mytest /dev/sdXn /etc/encrypted-luks-key \'pkcs11-uri=pkcs11:…\'" >> /etc/crypttab'