The option --disable-luks2-reencryption completely disable
LUKS2 reencryption code.
When used, the libcryptsetup library can read metadata with
reencryption code, but all reencryption API calls and cryptsetup
reencrypt commands are disabled.
Devices with online reencryption in progress cannot be activated.
This option can cause some incompatibilities. Please use with care.
Fix possible attacks against data confidentiality through LUKS2 online
reencryption extension crash recovery.
An attacker can modify on-disk metadata to simulate decryption in
progress with crashed (unfinished) reencryption step and persistently
decrypt part of the LUKS device.
This attack requires repeated physical access to the LUKS device but
no knowledge of user passphrases.
The decryption step is performed after a valid user activates
the device with a correct passphrase and modified metadata.
There are no visible warnings for the user that such recovery happened
(except using the luksDump command). The attack can also be reversed
afterward (simulating crashed encryption from a plaintext) with
possible modification of revealed plaintext.
The problem was caused by reusing a mechanism designed for actual
reencryption operation without reassessing the security impact for new
encryption and decryption operations. While the reencryption requires
calculating and verifying both key digests, no digest was needed to
initiate decryption recovery if the destination is plaintext (no
encryption key). Also, some metadata (like encryption cipher) is not
protected, and an attacker could change it. Note that LUKS2 protects
visible metadata only when a random change occurs. It does not protect
against intentional modification but such modification must not cause
a violation of data confidentiality.
The fix introduces additional digest protection of reencryption
metadata. The digest is calculated from known keys and critical
reencryption metadata. Now an attacker cannot create correct metadata
digest without knowledge of a passphrase for used keyslots.
For more details, see LUKS2 On-Disk Format Specification version 1.1.0.
This bug enabled to create LUKS2 keyslots encrypted by
cipher_null when explicitely requested by user. LUKS2
was never meant to allow keyslot encryption with
cipher_null. cipher_null is meant for debug purposes
only as a segment cipher.
We missed keyslot json validation when unlocking all keys necessary
for reencryption. Also assign appropriate verified digest id to
keys in volume key structure.
In fact we need only stored key size in examined keyslot. It's valid for
default segment volume keys and in case of non-default segment
keys it always returns -1 and fallbacks to stored key size query
instead.
This patch makes available LUKS2 per-keyslot encryption settings to user.
In LUKS2, keyslot can use different encryption that data.
We can use new crypt_keyslot_get_encryption and crypt_keyslot_set_encryption
API calls to set/get this encryption.
For cryptsetup new --keyslot-cipher and --keyslot-key-size options are added.
The default keyslot encryption algorithm (if cannot be derived from data encryption)
is now available as configure options (default is aes-xts-plain64 with 512-bits key).
NOTE: default was increased from 256-bits.
- do not run general LUKS2 format validation from inside the specific one
- validate luks2 json object only
- temporary move digests count restrictions, going to be fixed in next
commit
This patch fixes several problems:
- pbkdf benchmark should be run with keyslot encryption key length
instead volume key length
- run LUKS2 keyslot validation on final keyslot json object instead
temporary stub created in keyslot_alloc
- replace whole json kdf object during keyslot update. We left behind
old parameters from old pbkdf during transition to differnt type
A keyslot not bound to any segment can store any key for any purpose.
To easily check slot status, new enum value is introduced.
This status is valid only for LUKS2, so the functions are backward compatible
with LUKS1.
Some ciphers and key sizes created on-disk metadata that cannot be used.
Use the same test for length-preserving cipher as LUKS1.
Also check if key for integrity algorithm is not too small.
Fixes#373.
