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CISS.debian.live.builder/docs/MAN_CISS_ISO_BOOT_CHAIN.md
Marc S. Weidner f0ee12513f
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V8.13.416.2025.11.17 
Signed-off-by: Marc S. Weidner <msw@coresecret.dev>
2025-11-17 06:42:57 +01:00

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Table of Contents

1. CISS.debian.live.builder

Centurion Intelligence Consulting Agency Information Security Standard
Debian Live Build Generator for hardened live environment and CISS Debian Installer
Master Version: 8.13
Build: V8.13.416.2025.11.17

2. CISS.debian.live.builder – Boot & Trust Chain (Technical Documentation)

Status: 2025-11-12 Audience: CICA CISO, CISS staff, technically proficient administrators Summary: The CISS.debian Live-ISO establishes a two-stage verification chain without Microsoft-db: an early ISO-edge check (signature and FPR pin) before LUKS unlock, and a late root-FS attestation after unlock, reinforced by dm-crypt (AES-XTS) and dm-integrity (HMAC-SHA-512).

3. Overview

  • Trust anchor: Pinned fingerprint (FPR) of the signing key embedded at build time in initramfs hooks.

  • Integrity & authenticity verification:

    1. Early: Verify sha512sum.txt at the ISO edge using gpgv and FPR pin.
    2. Late: Verify an attestation hash list inside the decrypted root FS using gpgv and FPR pin.

  • Storage-level AEAD (functional): dm-crypt (AES-XTS-512) and dm-integrity (HMAC-SHA-512, 4 KiB).

  • Remotely unlock: Hardened Dropbear (modern primitives only), no passwords, no agent/forwarding.

4. Primitives & Parameters (concise)

Component Primitive / Parameter Purpose
LUKS2 aes-xts-plain64, --key-size 512, --sector-size 4096 Confidentiality (2×256-bit XTS)
dm-integrity hmac-sha512 (keyed), journal Adversary-resistant per-sector integrity/authenticity
PBKDF argon2id, --iter-time 1000 ms Key derivation, hardware-agnostic
Signatures Ed25519, RSA-4096 (FPR pinned) Public verifiability, non-repudiation
Verification gpgv --no-default-keyring No agent dependency in initramfs
Hash lists sha512sum format Deterministic content verification
Dropbear Modern KEX/AEAD (per localoptions.h) Minimal attack surface, remote unlock

5. End-to-End Boot Flow

sequenceDiagram
autonumber
participant FW as UEFI/BIOS
participant GRUB as GRUB
participant K as Kernel
participant I as initramfs + live-boot
participant D as Dropbear (optional)
participant C30 as CISS 0030 (early verify)
participant C22 as CISS 0024 (unlock)
participant LUKS as LUKS2 + dm-integrity
participant RS as RootFS (SquashFS/Overlay)
participant C42 as CISS 0042 (late attestation)

FW->>GRUB: Load kernel + initramfs
GRUB->>K: Boot kernel
K->>I: Pivot to initramfs (live-boot phases)
I->>D: (optional) Start Dropbear (remote unlock)

I->>C30: Run 0030: Verify ISO edge (gpgv, FPR pin)
alt 0030 OK
C30-->>I: Verified
else 0030 FAIL
C30-x I: Abort boot
end

I->>C24: Run 0024: LUKS open (dm-crypt + integrity), mount SquashFS
C24->>LUKS: Unlock (Argon2id PBKDF → XTS + HMAC)

I->>RS: Assemble overlay, switch_root
I->>C42: Run 0042: Verify root FS (gpgv, FPR pin) + dmsetup health
alt 0042 OK
C42-->>I: Verified
else 0045 FAIL
C42-x I: Abort boot
end

6. LUKS/dm-integrity Layering

flowchart TD


A["Plain device (/live/rootfs.crypt)"] --> B["dm-integrity (HMAC-SHA-512, 4 KiB)"];
B --> C["dm-crypt (AES-XTS-512)"];
C --> D["/dev/mapper/crypt_liveiso"];
D --> E["SquashFS mount /run/live/rootfs"];

Note: Encrypt-then-MAC at the block layer (functionally AEAD-equivalent). Any manipulation ⇒ hard I/O error.

7. Build-Time Core Step (LUKS)

cryptsetup luksFormat \
  --batch-mode \
  --cipher aes-xts-plain64 \
  --integrity hmac-sha512 \
  --iter-time 1000 \
  --key-file "/proc/$$/fd/${KEYFD}" \
  --key-size 512 \
  --label crypt_liveiso \
  --luks2-keyslots-size 16777216 \
  --luks2-metadata-size 4194304 \
  --pbkdf argon2id \
  --sector-size 4096 \
  --type luks2 \
  --use-random \
  --verbose \
  "${LUKSFS}"

Signing keys: Ed25519 and RSA-4096; FPR pinned at build time in hooks. Signing keys are additionally signed by an offline GPG Root-CA (out-of-band trust chain).

8. Early ISO-Edge Verification (CISS modified hook 0030, live-bottom)

Goal: Before consuming any medium content, verify:

  1. Detached signature of sha512sum.txt using gpgv against the embedded public key.
  2. FPR pinning: Parse VALIDSIG and require exact match with the build-time pinned FPR.
  3. Optional: Script self-IA – hash the executed hook and compare against the signed list (drift/bitrot detector).

Core call (initramfs):

/usr/bin/gpgv --no-default-keyring --keyring "$KEYFILE" --status-fd 1 --verify sha512sum.txt.sig sha512sum.txt
# parse [GNUPG:] VALIDSIG ... <FPR> ...

9. Late Root-FS Attestation and dmsetup Health (CISS hook 0045, live-bottom)

Goal: After LUKS unlock, validate the decrypted contents and the actual mapping topology.

  • Attestation files: /.ciss/attest/rootfs.sha512[.sig]
  • Key source: /etc/ciss/keys/*.gpg (accepted only if FPR == build-pin)
  • Health check: dmsetup table --showkeys → top crypt (AES-XTS), child integrity (HMAC-SHA-512, 4096 B)

Core calls (initramfs):

# 1) Signature and FPR pin (no agent)
/usr/bin/gpgv --no-default-keyring --keyring "$KEYFILE" --status-fd 1 --verify "$SIG" "$DATA"

# 2) Optional: Content hash verification
( cd "$ROOTMP" && /usr/bin/sha512sum -c --strict --quiet "$DATA" )

# 3) dmsetup health
dmsetup table --showkeys /dev/mapper/crypt_liveiso
dmsetup table --showkeys CHILD  # expect integrity hmac sha512 4096

10. Failure Policy (fail-closed, deterministic)

  • Abort on: missing VALIDSIG, FPR mismatch, missing key/signature, or a deviating dmsetup topology.

11. Dropbear (Hardened Remotely Unlock)

• Public-key auth only, no passwords
• Modern KEX/AEAD (e.g., curve25519, sntrup761x25519-sha512, mlkem768x25519-sha256; AES-GCM)
• No agent/X11/TCP forwarding, no SFTP
• Strict timeouts/keep-alives, restricted cipher/KEX set
• Port 42137 (per CISS convention)

Concrete selection compiled via your localoptions.h at ISO build time.

12. Integration Points & Paths

  • Hooks (build view):
    • /usr/lib/live/boot/0022-ciss-overlay-tmpfs,
    • /usr/lib/live/boot/0024-ciss-crypt-squash,
    • /usr/lib/live/boot/0026-ciss-early-sysctl,
    • /usr/lib/live/boot/0030-ciss-verify-checksums,
    • /usr/lib/live/boot/0042-ciss-post-decrypt-attest,
  • Hooks (boot view):
    • /scripts/live-premount/0022-ciss-overlay-tmpfs,
    • /scripts/live-premount/0024-ciss-crypt-squash,
    • /scripts/live-premount/0026-ciss-early-sysctl,
    • /scripts/live-bottom/0030-ciss-verify-checksums,
    • /scripts/live-bottom/0042-ciss-post-decrypt-attest
  • Key files:
    • ISO edge (for 0030): embedded public key blob (project-specific fpr)
    • Root FS (for 0042): /etc/ciss/keys/<FPR>.gpg
  • Mounts (typical): /run/live/rootfs, /run/live/overlay

13. Diagram: Trust Chain & Verification Paths

flowchart TD


A["Build time: pin EXP_FPR + embed ISO key"] --> B["ISO artifacts: sha512sum.txt + .sig"];
B --> C["Boot early (0030): gpgv verify + FPR pin"];
C -->|OK| D["LUKS open (0024)"];
D --> E["Mount RootFS"];
E --> F["Boot late (0042): gpgv verify + FPR pin (root key)"];
F --> G["dmsetup health: crypt(XTS) over integrity(HMAC-SHA-512)"];
C -- FAIL --> X["Abort"];
F -- FAIL --> X;
G -- FAIL --> X;

14. Closing Remark

This achieves a portable, self-contained trust chain without a Microsoft-db, providing strong protection against medium tampering, bitrot and active attacks both before and after decryption. The dual verification phases plus dmsetup health make the state transparent and deterministic.

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