update NEWS

NEWS

@@ -44,36 +44,43 @@ CHANGES WITH 252 in spe:
           systemd-stub is booted. This is useful for implementing TPM2 policies
           for LUKS encrypted volumes and encrypted system/service credentials,
           that robustly bind to kernels carrying appropriate PCR signature
-          information. The signed expected PCR information may be embedded
+          information. The signed expected PCR information, and the public key
-          inside UKI images for this purpose so that it is automatically
+          used for the signature may be embedded inside UKIs for this purpose,
-          available in userspace, once the UKI is booted.
+          so that it is automatically available in userspace, once the UKI is
+          booted.
 
           systemd-cryptsetup, systemd-cryptenroll and systemd-creds have been
           updated to make use of this information if available in the booted
-          kernel.
+          kernel: when locking an encrypted volume/credential to the TPM
-
+          systemd-cryptenroll/systemd-creds will use the public key embedded in
-          Net effect: if you boot a properly prepared kernel, TPM-bound disk
+          the booted UKI to bind the volume/credential to the kernel (and
-          encryption now defaults to be locked to kernels which carry PCR
+          future versions thereof, as long as it carries PCR information signed
-          signatures from the same signature key pair. Example: if a
+          by the same key pair). When unlocking such an encrypted
-          hypothetical distro FooOS prepares its UKI kernels like this,
+          volume/credential systemd-cryptsetup/systemd-creds will use the
-          TPM-based disk encryption is now – by default – bound to only FooOS
+          signature embedded in the booted UKI to gain access.
-          kernels, and encrypted volumes bound to the TPM cannot be unlocked on
-          other kernels from other sources. (But do note this behaviour
-          requires preparation/enabling in the UKI, and of course users can
-          always enroll non-TPM ways to unlock the volume.)
 
           Binding TPM-based disk encryption to public keys/signatures of PCR
           values — instead of literal PCR values — addresses the inherent
           "brittleness" of traditional PCR-bound TPM disk encryption schemes:
-          disks remain accessible even if the UKI image is updated, without any
+          disks remain accessible even if the UKI is updated, without any TPM
-          prepartion during the update scheme — as long as each UKI carries the
+          specific preparation during the OS update — as long as each UKI
-          necessary PCR signature information.
+          carries the necessary PCR signature information.
+
+          Net effect: if you boot a properly prepared kernel, TPM-bound disk
+          encryption now defaults to be locked to kernels which carry PCR
+          signatures from the same signature key pair. Example: if a
+          hypothetical distro FooOS prepares its UKIs like this, TPM-based disk
+          encryption is now – by default – bound to only FooOS kernels, and
+          encrypted volumes bound to the TPM cannot be unlocked on other
+          kernels from other sources. (But do note this behaviour requires
+          preparation/enabling in the UKI, and of course users can always
+          enroll non-TPM ways to unlock the volume.)
 
         * systemd-pcrphase is a new tool that is invoked at 4 places during
           system runtime, and measures additional words into TPM2 PCR 11, to
           mark milestones of the boot process. This allows binding access to
           specific TPM2-encrypted secrets to specific phases of the boot
-          process. (Think: LUKS2 disk encryption key only accessible in the
+          process. (Example: LUKS2 disk encryption key only accessible in the
           initrd, but not later.)
 
         Changes in systemd itself, i.e. the manager and units