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Signed-off-by: Marc S. Weidner <msw@coresecret.dev>
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Marc S. Weidner
2025-12-04 23:59:45 +01:00
parent c421f86d7e
commit bb56823cc4
6 changed files with 41 additions and 33 deletions
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docs/MAN_CISS_ISO_BOOT_CHAIN.md
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@@ -14,7 +14,7 @@ include_toc: true
**Status:** 2025-11-12<br>
**Audience:** CICA CISO, CISS staff, technically proficient administrators<br>
**Summary:** The CISS.debian.live.builder 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)`.<br>
**Summary:** The **CISS.debian.live.builder** 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)`.<br>
# 3. Overview
@@ -23,8 +23,9 @@ include_toc: true
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.
* **Remotely unlock:** CISS hardened and build dropbear, modern primitives only, no passwords, no agent/forwarding.
# 4. Primitives & Parameters
@@ -33,12 +34,12 @@ include_toc: true
| 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 |
| Signatures | Ed25519 or 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. Diagram: CISS Live ISO Boot Flow, complete
# 5. Diagram: CISS Live ISO Boot Flow
```mermaid
flowchart TD
subgraph Trusted HW Manufacturer
@@ -109,7 +110,7 @@ flowchart TD
0142 -- FAIL --> X;
```
# 6. Diagram: CISS Live ISO LUKS and dm-integrity layering, complete
# 6. Diagram: CISS Live ISO LUKS and dm-integrity layering
```mermaid
---
config:
@@ -127,7 +128,7 @@ flowchart TD
**Note:** Encrypt-then-MAC at the block layer (functionally AEAD-equivalent). Any manipulation ⇒ hard I/O error.
# 7. CISS Live ISO LUKS Build-Time Core Steps, complete
# 7. CISS Live ISO LUKS Build-Time Core Steps
```sh
cryptsetup luksFormat \
--batch-mode \
@@ -149,7 +150,7 @@ cryptsetup luksFormat \
**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)
# 8. Early ISO-Edge Verification (CISS modified hook 0030-ciss-verify-checksums, live-bottom)
**Goal:** Before consuming any medium content, verify:
@@ -164,13 +165,12 @@ cryptsetup luksFormat \
# parse [GNUPG:] VALIDSIG ... <FPR> ...
```
# 9. Late Root-FS Attestation and dmsetup Health (CISS hook 0045, live-bottom)
# 9. Late Root-FS Attestation and dmsetup Health (CISS hook 0042_ciss_post_decrypt_attest, called by 9990-overlay.sh)
**Goal:** After LUKS unlock, validate the **decrypted** contents and the **actual** mapping topology.
* **Attestation files:** `/root/.ciss/attest/rootfs.sha512sum.txt[.sig]`
* **Attestation files:** `/root/.ciss/attestation/<FPR>.sha512sum.txt[.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):**
@@ -180,36 +180,35 @@ cryptsetup luksFormat \
# 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.
* **Abort** on: missing `VALIDSIG`, FPR mismatch, missing key / signature.
# 11. CISS Dropbear (Hardened Remotely Unlock)
# 11. CISS hardened and built dropbear
```text
• 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)
• 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 44137 (per CISS convention)
```
*Concrete selection compiled via your `localoptions.h` at ISO build time.*
*Concrete selection compiled via [localoptions.h](../upgrades/dropbear/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`,
* [0022-ciss-overlay-tmpfs](../config/includes.chroot/usr/lib/live/boot/0022-ciss-overlay-tmpfs),
* [0024-ciss-crypt-squash](../config/includes.chroot/usr/lib/live/boot/0024-ciss-crypt-squash),
* [0026-ciss-early-sysctl](../config/includes.chroot/usr/lib/live/boot/0026-ciss-early-sysctl),
* [0030-ciss-verify-checksums](../config/includes.chroot/usr/lib/live/boot/0030-ciss-verify-checksums),
* [0042_ciss_post_decrypt_attest](../config/includes.chroot/usr/lib/live/boot/0042_ciss_post_decrypt_attest),
* [9990-main.sh](../config/includes.chroot/usr/lib/live/boot/9990-main.sh),
* [9990-networking.sh](../config/includes.chroot/usr/lib/live/boot/9990-networking.sh),
* [9990-overlay.sh](../config/includes.chroot/usr/lib/live/boot/9990-overlay.sh).
* **Hooks (boot view):**
* `/scripts/live-premount/0022-ciss-overlay-tmpfs`,
* `/scripts/live-premount/0024-ciss-crypt-squash`,
@@ -217,7 +216,7 @@ dmsetup table --showkeys CHILD # expect integrity hmac sha512 4096
* `/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)
* 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`
@@ -262,7 +261,7 @@ I -- FAIL --> X;
# 14. Closing Remarks
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.
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 make the state transparent and deterministic.
---
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