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man: tweaks to the crypttab(5) man page
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@ -425,10 +425,10 @@
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line. This is useful for unlocking encrypted volumes through security tokens or smartcards. See below
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line. This is useful for unlocking encrypted volumes through security tokens or smartcards. See below
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for an example how to set up this mechanism for unlocking a LUKS volume with a YubiKey security
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for an example how to set up this mechanism for unlocking a LUKS volume with a YubiKey security
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token. The specified URI can refer directly to a private RSA key stored on a token or alternatively
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token. The specified URI can refer directly to a private RSA key stored on a token or alternatively
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just to a slot or token in which case a suitable private RSA key object is automatically searched on
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just to a slot or token, in which case a search for a suitable private RSA key will be performed. In
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it. In this case if multiple suitable objects are found the token is refused. The key configured in
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this case if multiple suitable objects are found the token is refused. The key configured in the
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the third column is passed as is to RSA decryption. The resulting decrypted key is then base64
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third column is passed as is to RSA decryption. The resulting decrypted key is then base64 encoded
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encoded before it is used to unlock the LUKS volume.</para></listitem>
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before it is used to unlock the LUKS volume.</para></listitem>
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</varlistentry>
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</varlistentry>
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<varlistentry>
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<varlistentry>
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@ -489,7 +489,8 @@ external /dev/sda3 keyfile:LABEL=keydev keyfile-timeout=10s</programlist
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<title>Yubikey-based Volume Unlocking Example</title>
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<title>Yubikey-based Volume Unlocking Example</title>
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<para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA
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<para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA
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decryption keys. Here's an example how to set up a Yubikey security token for this purpose:</para>
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decryption keys. Here's an example how to set up a Yubikey security token for this purpose, using
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<command>ykman</command> from the yubikey-manager project:</para>
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<programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting>
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<programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting>
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@ -7,7 +7,9 @@ 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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# 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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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 device.
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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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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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# 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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@ -18,16 +20,16 @@ p11tool --list-tokens
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dd if=/dev/urandom of=plaintext.bin bs=128 count=1
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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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# 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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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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# 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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# Yubikey, store the result in /etc/encrypted-luks-key.bin, where we'll look for it during boot.
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openssl rsautl -encrypt -pubin -inkey pubkey.pem -in plaintext.bin -out /etc/encrypted-luks-key.bin
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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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# 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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# 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.
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# key derivation. Replace /dev/sdXn by the partition to use (e.g. sda1)
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cryptsetup luksAddKey /dev/sda1 plaintext.base64 --pbkdf=pbkdf2 --pbkdf-force-iterations=1000
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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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# 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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# material it should be removed from disk thoroughly.
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@ -39,7 +41,7 @@ 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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# 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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# PKCS#11 URI we have in the clipboard, it tells the tool how to decypher the encrypted LUKS key.
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systemd-cryptsetup attach mytest /dev/sda1 /etc/encrypted-luks-key.bin 'pkcs11-uri=pkcs11:…'
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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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# If that worked, let's now add the same line persistently to /etc/crypttab, for the future.
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echo "mytest /dev/sda1 /etc/encrypted-luks-key 'pkcs11-uri=pkcs11:…' >> /etc/crypttab
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sudo bash -c 'echo "mytest /dev/sdXn /etc/encrypted-luks-key \'pkcs11-uri=pkcs11:…\'" >> /etc/crypttab'
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