Sucessfully repack OTA!

2026-06-08 16:08:00 -06:00 · 2026-05-03 21:26:14 -06:00
parent 309d01bc30
commit ef1eced02d
18 changed files with 828 additions and 65 deletions
@@ -8,4 +8,5 @@ aes = "0.8.4"
 cbc = "0.1.2"
 clap = { version = "4.5.37", features = ["derive"] }
 rand = "0.8.5"
-sha2 = "0.10.9"
+rsa = "0.9.8"
+sha2 = { version = "0.10.9", features = ["oid"] }
@@ -0,0 +1,203 @@
+# OTA Unpack And Repack Guide
+
+This guide describes how to unpack and repack a Centauri Carbon 2 OTA update using
+the tools in this directory.
+
+## Build The Tool
+
+```bash
+cargo build
+```
+
+The compiled tool is:
+
+```bash
+target/debug/sig
+```
+
+## Inspect A `.sig` File
+
+Print parsed header information:
+
+```bash
+target/debug/sig info path/to/file.sig
+```
+
+Print raw unknown header bytes too:
+
+```bash
+target/debug/sig info --raw path/to/file.sig
+```
+
+Important fields:
+
+- `encrypted`: whether the payload is AES-CBC encrypted.
+- `filesize`: plaintext payload size.
+- `stored_sha256`: SHA-256 of the payload stored in the header.
+- `payload_sha256_matches`: whether the stored hash matches the actual payload.
+- `signature_valid`: whether the RSA signature at `0x100..0x200` verifies.
+
+## Unpack A Single `.sig`
+
+```bash
+target/debug/sig unpack input.sig -o output-file
+```
+
+Examples:
+
+```bash
+target/debug/sig unpack ota-package-list.json.sig -o ota-package-list.json
+target/debug/sig unpack cc2_eeb001_01.03.02.36_20260326171745.swu.sig -o update.swu
+target/debug/sig unpack release.zip.sig -o release.zip
+```
+
+`unpack` removes the 512-byte `.sig` header. If the payload is encrypted, it also
+decrypts it with the Carbon 2 AES key and trims the result to the plaintext size
+stored in the header.
+
+## Repack A Single `.sig`
+
+Use `repack` to wrap a file in a valid signed `.sig` header:
+
+```bash
+target/debug/sig repack input-file -o output.sig
+```
+
+For encrypted inner files, use a template from the original package:
+
+```bash
+target/debug/sig repack modified.swu \
+  --template original.swu.sig \
+  -o modified.swu.sig
+```
+
+```bash
+target/debug/sig repack ota-package-list.json \
+  --template original-ota-package-list.json.sig \
+  -o ota-package-list.json.sig
+```
+
+Template mode preserves metadata such as package type, version, IV, filename, and
+unknown header fields, then rewrites the size, payload hash, and RSA signature.
+
+To force encryption without a template:
+
+```bash
+target/debug/sig repack input-file --encrypt -o input-file.sig
+```
+
+Without `--encrypt` and without a template, `repack` writes a plain signed `.sig`.
+
+## Unpack A Full OTA Update
+
+The full OTA package has this structure:
+
+```text
+release.zip.sig
+└── release.zip
+    ├── cc2_...swu.sig
+    │   └── cc2_...swu
+    │       └── SWU CPIO archive contents
+    └── ota-package-list.json.sig
+        └── ota-package-list.json
+```
+
+Use the helper script:
+
+```bash
+scripts/undo-release-package.sh \
+  cc2-01.03.02.36-ee76546c665bb272b43798813f60f8dd-release-abroad.zip.sig \
+  release-unpacked
+```
+
+This creates:
+
+```text
+release-unpacked/
+├── templates/
+│   ├── release.zip.sig
+│   ├── cc2_...swu.sig
+│   └── ota-package-list.json.sig
+├── release-signed/
+│   ├── cc2_...swu.sig
+│   └── ota-package-list.json.sig
+├── release/
+│   ├── cc2_...swu
+│   └── ota-package-list.json
+├── swu/
+│   ├── .swu-manifest.json
+│   ├── sw-description
+│   ├── resource
+│   ├── uboot
+│   ├── boot0
+│   ├── kernel
+│   ├── rootfs
+│   └── cpio_item_md5
+└── repack.env
+```
+
+Edit files under `release-unpacked/swu/` to change SWU contents. For example, to
+replace the rootfs image:
+
+```bash
+cp -p test/rootfs_modified release-unpacked/swu/rootfs
+```
+
+## Repack A Full OTA Update
+
+After editing the unpacked contents, run:
+
+```bash
+scripts/redo-release-package.sh \
+  release-unpacked \
+  repacked.zip.sig
+```
+
+The script:
+
+- Rebuilds the SWU CPIO archive from `release-unpacked/swu/`.
+- Recomputes `cpio_item_md5`.
+- Re-signs the SWU `.sig` using the original SWU `.sig` as a template.
+- Updates the hash in `ota-package-list.json`.
+- Re-signs `ota-package-list.json.sig` using its original template.
+- Rebuilds the release ZIP while preserving original ZIP timestamps and modes.
+- Re-signs the outer `.zip.sig` using the original outer `.sig` as a template.
+
+If no files were changed, the rebuilt package should be bit-perfect:
+
+```bash
+cmp repacked.zip.sig original.zip.sig
+```
+
+If files were changed, the rebuilt package should differ, but all `.sig` headers
+should still validate:
+
+```bash
+target/debug/sig info repacked.zip.sig
+```
+
+To validate inner signatures, unpack the release ZIP and run `info` on the inner
+`.sig` files:
+
+```bash
+target/debug/sig unpack repacked.zip.sig -o /tmp/release.zip
+unzip -q /tmp/release.zip -d /tmp/release
+target/debug/sig info /tmp/release/cc2_eeb001_01.03.02.36_20260326171745.swu.sig
+target/debug/sig info /tmp/release/ota-package-list.json.sig
+```
+
+Each should show:
+
+```text
+payload_sha256_matches: true
+signature_valid: true
+```
+
+## Notes
+
+- Inner `.sig` files are encrypted and signed.
+- The outer `.zip.sig` is plain but signed.
+- The RSA signature is stored in header bytes `0x100..0x200`.
+- The signature signs the SHA-256 digest stored at `0xE0..0x100`.
+- Reusing old signatures after modifying payloads will not work. Always use
+  `repack` or `redo-release-package.sh` so signatures are regenerated.
@@ -0,0 +1 @@
+This is a pile of badly made tooling to repack CC2 OTAs
@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ $# -lt 1 || $# -gt 2 ]]; then
+    printf 'Usage: %s input-dir [output.zip]\n' "$0" >&2
+    exit 1
+fi
+
+indir=$1
+output=${2:-release.zip}
+
+python3 - "$indir" "$output" <<'PY'
+import pathlib
+import stat
+import sys
+import zipfile
+
+
+def fail(message):
+    print(message, file=sys.stderr)
+    sys.exit(1)
+
+
+if len(sys.argv) != 3:
+    fail("Usage: build-release-zip.sh input-dir [output.zip]")
+
+root = pathlib.Path(sys.argv[1])
+output = pathlib.Path(sys.argv[2])
+
+if not root.is_dir():
+    fail(f"input directory does not exist: {root}")
+
+entries = sorted(path for path in root.iterdir() if path.is_file())
+if not entries:
+    fail(f"input directory contains no regular files: {root}")
+
+
+def zip_date_time(path):
+    modified = path.stat().st_mtime
+    return tuple(__import__("time").localtime(modified)[:6])
+
+output.parent.mkdir(parents=True, exist_ok=True)
+with zipfile.ZipFile(output, "w") as archive:
+    for src in entries:
+        mode = stat.S_IMODE(src.stat().st_mode)
+        info = zipfile.ZipInfo(src.name, date_time=zip_date_time(src))
+        info.create_system = 3
+        info.external_attr = (stat.S_IFREG | mode) << 16
+        info.compress_type = zipfile.ZIP_DEFLATED
+        archive.writestr(
+            info,
+            src.read_bytes(),
+            compress_type=zipfile.ZIP_DEFLATED,
+            compresslevel=6,
+        )
+
+print(f"wrote {output}")
+PY
@@ -0,0 +1,100 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ $# -lt 1 || $# -gt 2 ]]; then
+    printf 'Usage: %s unpacked-dir [output.zip.sig]\n' "$0" >&2
+    exit 1
+fi
+
+workdir=$1
+output=${2:-$workdir/repacked.zip.sig}
+env_file="$workdir/repack.env"
+
+if [[ ! -f "$env_file" ]]; then
+    printf 'missing repack metadata: %s\n' "$env_file" >&2
+    exit 1
+fi
+
+# shellcheck disable=SC1090
+source "$env_file"
+
+required=(
+    "$workdir/templates/release.zip.sig"
+    "$workdir/templates/$SWU_SIG_NAME"
+    "$workdir/templates/$OTA_SIG_NAME"
+    "$workdir/release-signed/$SWU_SIG_NAME"
+    "$workdir/release-signed/$OTA_SIG_NAME"
+    "$workdir/release/$OTA_NAME"
+    "$workdir/swu/.swu-manifest.json"
+)
+
+for path in "${required[@]}"; do
+    if [[ ! -e "$path" ]]; then
+        printf 'missing required repack input: %s\n' "$path" >&2
+        exit 1
+    fi
+done
+
+cargo build --quiet
+
+sig_bin=target/debug/sig
+build_dir="$workdir/build"
+release_dir="$build_dir/release"
+rebuilt_swu="$build_dir/$SWU_NAME"
+rebuilt_ota="$build_dir/$OTA_NAME"
+rebuilt_zip="$build_dir/$ZIP_NAME"
+
+rm -rf "$build_dir"
+mkdir -p "$release_dir"
+
+scripts/build-swu.sh "$workdir/swu" "$rebuilt_swu"
+"$sig_bin" repack "$rebuilt_swu" --template "$workdir/templates/$SWU_SIG_NAME" -o "$release_dir/$SWU_SIG_NAME"
+cp "$workdir/release/$OTA_NAME" "$rebuilt_ota"
+
+python3 - "$rebuilt_ota" "$workdir/release/$OTA_NAME" "$release_dir/$SWU_SIG_NAME" "$SWU_SIG_NAME" <<'PY'
+import hashlib
+import json
+import pathlib
+import sys
+
+ota_path = pathlib.Path(sys.argv[1])
+source_ota_path = pathlib.Path(sys.argv[2])
+swu_sig_path = pathlib.Path(sys.argv[3])
+swu_sig_name = sys.argv[4]
+
+data = json.loads(ota_path.read_text())
+digest = hashlib.sha256(swu_sig_path.read_bytes()).hexdigest()
+matched = False
+for package in data.get("packages", []):
+    if package.get("file") == swu_sig_name:
+        package["hash"] = digest
+        matched = True
+
+if not matched:
+    raise SystemExit(f"ota package list does not reference {swu_sig_name}")
+
+updated = json.dumps(data, separators=(", ", ": "))
+ota_path.write_text(updated)
+source_ota_path.write_text(updated)
+PY
+
+"$sig_bin" repack "$rebuilt_ota" --template "$workdir/templates/$OTA_SIG_NAME" -o "$release_dir/$OTA_SIG_NAME"
+
+touch -r "$workdir/release-signed/$SWU_SIG_NAME" "$release_dir/$SWU_SIG_NAME"
+touch -r "$workdir/release-signed/$OTA_SIG_NAME" "$release_dir/$OTA_SIG_NAME"
+chmod --reference="$workdir/release-signed/$SWU_SIG_NAME" "$release_dir/$SWU_SIG_NAME"
+chmod --reference="$workdir/release-signed/$OTA_SIG_NAME" "$release_dir/$OTA_SIG_NAME"
+
+scripts/build-release-zip.sh "$release_dir" "$rebuilt_zip"
+"$sig_bin" repack "$rebuilt_zip" --template "$workdir/templates/release.zip.sig" -o "$output"
+
+printf 'rebuilt %s\n' "$output"
+
+if [[ -n "${ORIGINAL_SIG:-}" && -f "$ORIGINAL_SIG" ]]; then
+    if cmp -s "$output" "$ORIGINAL_SIG"; then
+        printf 'bit-perfect match: %s\n' "$ORIGINAL_SIG"
+    else
+        printf 'warning: rebuilt output differs from %s\n' "$ORIGINAL_SIG" >&2
+        exit 2
+    fi
+fi
@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ $# -lt 1 || $# -gt 2 ]]; then
+    printf 'Usage: %s input.zip.sig [output-dir]\n' "$0" >&2
+    exit 1
+fi
+
+input=$1
+outdir=${2:-release-unpacked}
+
+if [[ ! -f "$input" ]]; then
+    printf 'input does not exist: %s\n' "$input" >&2
+    exit 1
+fi
+
+if [[ -e "$outdir" && -n "$(ls -A "$outdir")" ]]; then
+    printf 'output directory is not empty: %s\n' "$outdir" >&2
+    exit 1
+fi
+
+mkdir -p "$outdir" "$outdir/templates" "$outdir/release-signed" "$outdir/release" "$outdir/swu"
+
+cargo build --quiet
+
+sig_bin=target/debug/sig
+base=$(basename "$input")
+zip_name=${base%.sig}
+zip_path="$outdir/$zip_name"
+
+cp -p "$input" "$outdir/templates/release.zip.sig"
+"$sig_bin" unpack "$input" -o "$zip_path"
+unzip -q "$zip_path" -d "$outdir/release-signed"
+
+mapfile -t signed_files < <(python3 - "$zip_path" <<'PY'
+import sys
+import zipfile
+
+with zipfile.ZipFile(sys.argv[1]) as archive:
+    for item in archive.infolist():
+        if not item.is_dir():
+            print(item.filename)
+PY
+)
+
+swu_sig_name=''
+ota_sig_name=''
+for name in "${signed_files[@]}"; do
+    case "$name" in
+        *.swu.sig) swu_sig_name=$name ;;
+        ota-package-list.json.sig) ota_sig_name=$name ;;
+    esac
+done
+
+if [[ -z "$swu_sig_name" || -z "$ota_sig_name" ]]; then
+    printf 'release zip must contain one .swu.sig and ota-package-list.json.sig\n' >&2
+    exit 1
+fi
+
+swu_name=${swu_sig_name%.sig}
+ota_name=${ota_sig_name%.sig}
+
+cp -p "$outdir/release-signed/$swu_sig_name" "$outdir/templates/$swu_sig_name"
+cp -p "$outdir/release-signed/$ota_sig_name" "$outdir/templates/$ota_sig_name"
+
+"$sig_bin" unpack "$outdir/release-signed/$swu_sig_name" -o "$outdir/release/$swu_name"
+"$sig_bin" unpack "$outdir/release-signed/$ota_sig_name" -o "$outdir/release/$ota_name"
+scripts/extract-swu.sh "$outdir/release/$swu_name" "$outdir/swu"
+
+cat > "$outdir/repack.env" <<EOF
+ORIGINAL_SIG=$input
+ZIP_NAME=$zip_name
+SWU_SIG_NAME=$swu_sig_name
+SWU_NAME=$swu_name
+OTA_SIG_NAME=$ota_sig_name
+OTA_NAME=$ota_name
+EOF
+
+printf 'unpacked %s to %s\n' "$input" "$outdir"
@@ -29,21 +29,37 @@ pub struct Cli {
 /// repacking commands without changing the top-level parser API.
 #[derive(Subcommand)]
 pub enum Command {
-    /// Strip the .sig wrapper and write the unpacked payload.
-    Strip(StripArgs),
+    /// Unpack the .sig wrapper and write the contained payload.
+    #[command(alias = "strip")]
+    Unpack(UnpackArgs),

-    /// Encrypt a file and wrap it in a .sig container.
-    Encrypt(EncryptArgs),
+    /// Print parsed .sig header information.
+    Info(InfoArgs),
+
+    /// Repack a file into a signed .sig container.
+    #[command(alias = "encrypt")]
+    Repack(RepackArgs),
 }

-/// Arguments accepted by the `strip` subcommand.
+/// Arguments accepted by the `info` subcommand.
+#[derive(Args)]
+pub struct InfoArgs {
+    /// Input `.sig` file to inspect.
+    pub input: PathBuf,
+
+    /// Print exact hex bytes for unknown/reserved header regions.
+    #[arg(long)]
+    pub raw: bool,
+}
+
+/// Arguments accepted by the `unpack` subcommand.
 ///
 /// The command mirrors the browser-based unpacker at
 /// <https://docs.opencentauri.cc/extras/cc2_update_decrypt.html>: read a `.sig`
 /// file, remove the header, decrypt the payload when needed, trim it to the
 /// payload size declared in the header, then write the resulting package bytes.
 #[derive(Args)]
-pub struct StripArgs {
+pub struct UnpackArgs {
    /// Input `.sig` file.
    ///
    /// The file must begin with the Centauri/Elegoo `ELEG` magic value and must
@@ -59,20 +75,19 @@ pub struct StripArgs {
    pub output: Option<PathBuf>,
 }

-/// Arguments accepted by the `encrypt` subcommand.
+/// Arguments accepted by the `repack` subcommand.
 ///
-/// This command performs the inverse of `strip` for the subset of the format the
-/// tool understands: it encrypts a plaintext payload with the Carbon 2 AES key,
-/// writes a 512-byte `.sig` header, and appends the ciphertext. It does not yet
-/// create or verify any vendor signature material beyond the metadata needed for
-/// decryption.
+/// This command performs the inverse of `unpack`: it writes a 512-byte `.sig`
+/// header, signs the payload hash, and appends either plaintext or encrypted
+/// payload bytes. When a template is supplied, unknown header metadata and the
+/// template encryption mode are preserved by default.
 #[derive(Args)]
-pub struct EncryptArgs {
+pub struct RepackArgs {
    /// Input plaintext package file.
    ///
-    /// The bytes are copied into the encrypted payload with PKCS#7 padding. The
-    /// original unpadded length is stored in the header so `strip` can recover
-    /// the exact input bytes.
+    /// With `--encrypt`, the bytes are copied into the encrypted payload with
+    /// PKCS#7 padding. The original unpadded length is stored in the header so
+    /// `unpack` can recover the exact input bytes.
    pub input: PathBuf,

    /// Output `.sig` path.
@@ -82,9 +97,18 @@ pub struct EncryptArgs {
    #[arg(short, long)]
    pub output: Option<PathBuf>,

-    /// Filename to store inside the `.sig` header.
+    /// Encrypt the payload before writing it.
    ///
-    /// Defaults to the input file name. The `.sig` format reserves 48 bytes for
+    /// Without a template, repack writes a plain signed `.sig` unless this flag
+    /// is set. With a template, the command preserves the template encryption
+    /// mode unless this flag is set, in which case output is encrypted.
+    #[arg(long)]
+    pub encrypt: bool,
+
+    /// Override the filename stored inside the `.sig` header.
+    ///
+    /// Defaults to the template header filename when `--template` is provided,
+    /// otherwise to the input file name. The `.sig` format reserves 48 bytes for
    /// this field, so values longer than 47 bytes are rejected to preserve the
    /// trailing NUL terminator used by existing packages.
    #[arg(long)]
@@ -94,8 +118,7 @@ pub struct EncryptArgs {
    ///
    /// Use this when you need reproducible output that can match an existing
    /// encrypted package byte-for-byte. The command reuses the template IV and
-    /// opaque header metadata, then rewrites size, filename, and payload hash
-    /// fields for the new encrypted payload.
+    /// metadata, then rewrites size, filename, payload hash, and RSA signature.
    #[arg(long)]
    pub template: Option<PathBuf>,
 }
@@ -19,6 +19,11 @@ use cbc::cipher::{
    block_padding::{NoPadding, Pkcs7},
 };
 use rand::{RngCore, rngs::OsRng};
+use rsa::{
+    RsaPrivateKey, RsaPublicKey,
+    pkcs1v15::Pkcs1v15Sign,
+    pkcs8::{DecodePrivateKey, DecodePublicKey},
+};
 use sha2::{Digest, Sha256};

 /// Length of the fixed `.sig` header in bytes.
@@ -37,6 +42,47 @@ const AES_KEY: [u8; 32] = [
    0x4E, 0x16, 0x1A, 0x8B, 0xEB, 0xB8, 0xF7, 0x20, 0x73, 0x7E, 0xE6, 0x0E, 0x7F, 0x8C, 0x7E, 0x68,
 ];

+/// RSA private key used to sign the SHA-256 digest stored in `.sig` headers.
+const RSA_PRIVATE_KEY_PEM: &str = r#"-----BEGIN PRIVATE KEY-----
+MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQCgET+oNgUA1acA
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+Ca1qPNSL7+V479dcoJKM8WCq30Uehc0Gcj8BsfcCgYBTicTc3S/o2jsJLRtXzFap
+eooocDD8Q0xIFRMZplDOvAnWXq6QJ0Xyeqlx9dk41dwWvnHHJGazZPZA4wijyI0T
+orTbpLkOKpMz0hlqy9j2/k+vgf004+xfDSAywtOPop9csXxFWPB5qmdjTONv5Zpn
+bzzXqOTAU1QZvdTdOBvbUw==
+-----END PRIVATE KEY-----"#;
+
+/// RSA public key used to verify the header signature.
+const RSA_PUBLIC_KEY_PEM: &str = r#"-----BEGIN PUBLIC KEY-----
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAoBE/qDYFANWnAL8hEpzb
+E8vgHvpOkPyyzOW4eLC3xXrtE0/SmuEkGui33wyyb2qo7fvo7Adj8D72XHJR3Buc
+gtmzYpM/sdlmhwkDiNur88vKIfMfsCyO+xn1RvNplqaOoB38rudSwbwg6Gg34IUl
+C+wfZSGgg29HWwX6Y0060K9FHFBE/Ub7K4zJMiyOY3wZ3dVTU7xQ/YJ4HMAJme7O
+uVCBJCo5kGR/sSvoA2vqGQSaY8+74FxHsyFUg7mUCkBQf+BOWBK37UcDaYe654A0
+6chWI2gLw/WaDPdHsRVrUVjL47dhzbQ1Dh40SOAuV06KpvxXz8WAKa6CVD8hOnJB
+awIDAQAB
+-----END PUBLIC KEY-----"#;
+
 type Aes256CbcDec = cbc::Decryptor<Aes256>;
 type Aes256CbcEnc = cbc::Encryptor<Aes256>;

@@ -59,6 +105,72 @@ struct Header {
    iv: [u8; 16],
 }

+/// Human-readable view of every known `.sig` header field.
+///
+/// The format still has unknown regions. Those are exposed as non-zero counts
+/// and SHA-256 digests so different files can be compared without dumping large
+/// binary blobs to the terminal.
+#[derive(Debug)]
+pub struct HeaderInfo {
+    /// Total input file length.
+    pub total_len: usize,
+    /// Number of bytes after the fixed 512-byte header.
+    pub payload_len: usize,
+    /// Big-endian magic as raw bytes.
+    pub magic: [u8; 4],
+    /// Raw package type byte at `0x04`.
+    pub package_type_raw: u8,
+    /// Low seven bits of the package type byte.
+    pub package_type: u8,
+    /// Whether the high bit of the package type byte is set.
+    pub is_encrypted: bool,
+    /// Header version major byte at `0x05`.
+    pub version_major: u8,
+    /// Header version minor byte at `0x06`.
+    pub version_minor: u8,
+    /// Currently unknown byte at `0x07`.
+    pub byte_07: u8,
+    /// Plaintext payload size from `0x08..0x10`.
+    pub filesize: u64,
+    /// NUL-terminated header filename from `0x10..0x40`.
+    pub filename: String,
+    /// Unknown/reserved bytes from `0x40..0x90`.
+    pub reserved_40_90: RegionInfo,
+    /// Encryption offset from `0x90..0x98`.
+    pub encrypt_offset: u64,
+    /// Encrypted payload length from `0x98..0xA0`.
+    pub encrypt_length: u64,
+    /// AES-CBC IV from `0xA0..0xB0`.
+    pub iv_hex: String,
+    /// Encrypted payload length/size mirror from `0xB0..0xB8`.
+    pub encrypt_filesize: u64,
+    /// Unknown/reserved bytes from `0xB8..0xE0`.
+    pub reserved_b8_e0: RegionInfo,
+    /// Stored SHA-256 digest from `0xE0..0x100`.
+    pub stored_sha256_hex: String,
+    /// SHA-256 of the actual bytes after the header.
+    pub payload_sha256_hex: String,
+    /// Whether `stored_sha256_hex` matches `payload_sha256_hex`.
+    pub payload_sha256_matches: bool,
+    /// Whether the RSA signature at `0x100..0x200` verifies the stored SHA-256.
+    pub signature_valid: bool,
+    /// Opaque 256-byte region from `0x100..0x200`.
+    pub opaque_100_200: RegionInfo,
+}
+
+/// Summary for an unknown or reserved header byte range.
+#[derive(Debug)]
+pub struct RegionInfo {
+    /// Number of bytes in the region.
+    pub len: usize,
+    /// Number of non-zero bytes in the region.
+    pub nonzero_count: usize,
+    /// SHA-256 digest of the region.
+    pub sha256_hex: String,
+    /// Exact region bytes as lowercase hexadecimal.
+    pub bytes_hex: String,
+}
+
 /// Unpack a complete `.sig` file held in memory.
 ///
 /// The input must include both the 512-byte header and the wrapped payload. The
@@ -84,13 +196,101 @@ pub fn unpack_sig(raw: &[u8]) -> Result<Vec<u8>, Box<dyn Error>> {
    }
 }

-/// Pack plaintext bytes into an encrypted `.sig` container.
+/// Return the NUL-terminated filename stored in a `.sig` header.
+pub fn header_filename(raw: &[u8]) -> Result<String, Box<dyn Error>> {
+    if raw.len() < HEADER_LEN {
+        return Err("input is too small to contain a .sig header".into());
+    }
+
+    let header = &raw[..HEADER_LEN];
+    let magic = u32::from_be_bytes(header[0..4].try_into()?);
+    if magic != MAGIC {
+        return Err(format!("invalid .sig magic: 0x{magic:08x}").into());
+    }
+
+    let filename = &header[0x10..0x40];
+    let end = filename
+        .iter()
+        .position(|byte| *byte == 0)
+        .unwrap_or(filename.len());
+
+    Ok(std::str::from_utf8(&filename[..end])?.to_owned())
+}
+
+/// Parse and summarize all known `.sig` header fields.
+pub fn header_info(raw: &[u8]) -> Result<HeaderInfo, Box<dyn Error>> {
+    if raw.len() < HEADER_LEN {
+        return Err("input is too small to contain a .sig header".into());
+    }
+
+    let header = &raw[..HEADER_LEN];
+    let magic = header[0..4].try_into()?;
+    if u32::from_be_bytes(magic) != MAGIC {
+        return Err(format!("invalid .sig magic: 0x{:08x}", u32::from_be_bytes(magic)).into());
+    }
+
+    let package_type_raw = header[0x04];
+    let payload = &raw[HEADER_LEN..];
+    let stored_sha256_hex = bytes_to_hex(&header[0xE0..0x100]);
+    let payload_sha256_hex = bytes_to_hex(&Sha256::digest(payload));
+    let payload_sha256_matches = stored_sha256_hex == payload_sha256_hex;
+
+    Ok(HeaderInfo {
+        total_len: raw.len(),
+        payload_len: payload.len(),
+        magic,
+        package_type_raw,
+        package_type: package_type_raw & 0x7F,
+        is_encrypted: package_type_raw & 0x80 != 0,
+        version_major: header[0x05],
+        version_minor: header[0x06],
+        byte_07: header[0x07],
+        filesize: u64::from_le_bytes(header[0x08..0x10].try_into()?),
+        filename: header_filename(raw)?,
+        reserved_40_90: region_info(&header[0x40..0x90]),
+        encrypt_offset: u64::from_le_bytes(header[0x90..0x98].try_into()?),
+        encrypt_length: u64::from_le_bytes(header[0x98..0xA0].try_into()?),
+        iv_hex: bytes_to_hex(&header[0xA0..0xB0]),
+        encrypt_filesize: u64::from_le_bytes(header[0xB0..0xB8].try_into()?),
+        reserved_b8_e0: region_info(&header[0xB8..0xE0]),
+        stored_sha256_hex,
+        payload_sha256_hex,
+        payload_sha256_matches,
+        signature_valid: verify_payload_signature(&header[0xE0..0x100], &header[0x100..0x200]),
+        opaque_100_200: region_info(&header[0x100..0x200]),
+    })
+}
+
+fn region_info(bytes: &[u8]) -> RegionInfo {
+    RegionInfo {
+        len: bytes.len(),
+        nonzero_count: bytes.iter().filter(|byte| **byte != 0).count(),
+        sha256_hex: bytes_to_hex(&Sha256::digest(bytes)),
+        bytes_hex: bytes_to_hex(bytes),
+    }
+}
+
+fn bytes_to_hex(bytes: &[u8]) -> String {
+    const HEX: &[u8; 16] = b"0123456789abcdef";
+    let mut out = String::with_capacity(bytes.len() * 2);
+    for byte in bytes {
+        out.push(HEX[(byte >> 4) as usize] as char);
+        out.push(HEX[(byte & 0x0F) as usize] as char);
+    }
+    out
+}
+
+/// Pack plaintext bytes into a plain signed `.sig` container.
 ///
 /// The generated file is intentionally conservative: it writes the fields needed
 /// by the known Carbon 2 unpacker and by [`unpack_sig`], but it does not claim to
-/// recreate every vendor metadata field. The payload is encrypted with the fixed
-/// Carbon 2 AES-256 key and a fresh random IV stored in the header.
+/// recreate every vendor metadata field.
 pub fn pack_sig(payload: &[u8], filename: &str) -> Result<Vec<u8>, Box<dyn Error>> {
+    pack_sig_inner(payload, filename, None, None, false)
+}
+
+/// Pack plaintext bytes into an encrypted signed `.sig` container.
+pub fn pack_sig_encrypted(payload: &[u8], filename: &str) -> Result<Vec<u8>, Box<dyn Error>> {
    let mut iv = [0u8; 16];
    OsRng.fill_bytes(&mut iv);

@@ -107,7 +307,7 @@ pub fn pack_sig_with_iv(
    filename: &str,
    iv: [u8; 16],
 ) -> Result<Vec<u8>, Box<dyn Error>> {
-    pack_sig_inner(payload, filename, iv, None)
+    pack_sig_inner(payload, filename, Some(iv), None, true)
 }

 /// Pack plaintext bytes using the IV and opaque metadata from an existing `.sig` header.
@@ -122,38 +322,53 @@ pub fn pack_sig_with_template(
    payload: &[u8],
    filename: &str,
    template: &[u8],
+    encrypt: Option<bool>,
 ) -> Result<Vec<u8>, Box<dyn Error>> {
    if template.len() < HEADER_LEN {
        return Err("template is too small to contain a .sig header".into());
    }

-    let iv = template[0xA0..0xB0].try_into()?;
-    pack_sig_inner(payload, filename, iv, Some(&template[..HEADER_LEN]))
+    let template_header = &template[..HEADER_LEN];
+    let template_is_encrypted = template_header[0x04] & 0x80 != 0;
+    let encrypt = encrypt.unwrap_or(template_is_encrypted);
+    let iv = if encrypt {
+        Some(template_header[0xA0..0xB0].try_into()?)
+    } else {
+        None
+    };
+    pack_sig_inner(payload, filename, iv, Some(template_header), encrypt)
 }

 fn pack_sig_inner(
    payload: &[u8],
    filename: &str,
-    iv: [u8; 16],
+    iv: Option<[u8; 16]>,
    header_template: Option<&[u8]>,
+    encrypt: bool,
 ) -> Result<Vec<u8>, Box<dyn Error>> {
    let filename_bytes = filename.as_bytes();
    if filename_bytes.len() >= 48 {
        return Err("header filename must be 47 bytes or shorter".into());
    }

-    let ciphertext = encrypt_payload(payload, &iv)?;
-    let encrypted_sha256 = Sha256::digest(&ciphertext).into();
-    let mut output = Vec::with_capacity(HEADER_LEN + ciphertext.len());
+    let payload_out = if encrypt {
+        let iv = iv.ok_or("encrypted repack requires an IV")?;
+        encrypt_payload(payload, &iv)?
+    } else {
+        payload.to_vec()
+    };
+    let payload_sha256 = Sha256::digest(&payload_out).into();
+    let mut output = Vec::with_capacity(HEADER_LEN + payload_out.len());
    output.extend_from_slice(&build_header(
        filename_bytes,
        payload.len(),
-        ciphertext.len(),
-        &iv,
-        encrypted_sha256,
+        payload_out.len(),
+        iv,
+        payload_sha256,
        header_template,
+        encrypt,
    )?);
-    output.extend_from_slice(&ciphertext);
+    output.extend_from_slice(&payload_out);

    Ok(output)
 }
@@ -169,14 +384,15 @@ fn pack_sig_inner(
 fn build_header(
    filename: &[u8],
    payload_len: usize,
-    encrypted_len: usize,
-    iv: &[u8; 16],
-    encrypted_sha256: [u8; 32],
+    output_payload_len: usize,
+    iv: Option<[u8; 16]>,
+    payload_sha256: [u8; 32],
    template: Option<&[u8]>,
+    encrypt: bool,
 ) -> Result<[u8; HEADER_LEN], Box<dyn Error>> {
    let payload_len = u64::try_from(payload_len).map_err(|_| "payload is too large")?;
-    let encrypted_len =
-        u64::try_from(encrypted_len).map_err(|_| "encrypted payload is too large")?;
+    let output_payload_len =
+        u64::try_from(output_payload_len).map_err(|_| "output payload is too large")?;

    let mut header = [0u8; HEADER_LEN];
    if let Some(template) = template {
@@ -184,20 +400,44 @@ fn build_header(
    }

    header[0..4].copy_from_slice(&MAGIC.to_be_bytes());
-    header[0x04] = 0x83;
-    header[0x05] = 0x01;
-    header[0x06] = 0x02;
+    if template.is_none() || (header[0x04] & 0x80 != 0) != encrypt {
+        header[0x04] = if encrypt { 0x83 } else { 0x04 };
+        header[0x05] = 0x01;
+        header[0x06] = 0x02;
+    }
    header[0x08..0x10].copy_from_slice(&payload_len.to_le_bytes());
    header[0x10..0x40].fill(0);
    header[0x10..0x10 + filename.len()].copy_from_slice(filename);
-    header[0x98..0xA0].copy_from_slice(&encrypted_len.to_le_bytes());
-    header[0xA0..0xB0].copy_from_slice(iv);
-    header[0xB0..0xB8].copy_from_slice(&encrypted_len.to_le_bytes());
-    header[0xE0..0x100].copy_from_slice(&encrypted_sha256);
+    if encrypt {
+        let iv = iv.ok_or("encrypted header requires an IV")?;
+        header[0x98..0xA0].copy_from_slice(&output_payload_len.to_le_bytes());
+        header[0xA0..0xB0].copy_from_slice(&iv);
+        header[0xB0..0xB8].copy_from_slice(&output_payload_len.to_le_bytes());
+    } else {
+        header[0x98..0xA0].fill(0);
+        header[0xA0..0xB0].fill(0);
+        header[0xB0..0xB8].copy_from_slice(&payload_len.to_le_bytes());
+    }
+    header[0xE0..0x100].copy_from_slice(&payload_sha256);
+    let signature = sign_payload_hash(&payload_sha256)?;
+    header[0x100..0x200].copy_from_slice(&signature);

    Ok(header)
 }

+fn sign_payload_hash(payload_sha256: &[u8; 32]) -> Result<Vec<u8>, Box<dyn Error>> {
+    let key = RsaPrivateKey::from_pkcs8_pem(RSA_PRIVATE_KEY_PEM)?;
+    Ok(key.sign(Pkcs1v15Sign::new::<Sha256>(), payload_sha256)?)
+}
+
+fn verify_payload_signature(payload_sha256: &[u8], signature: &[u8]) -> bool {
+    let Ok(key) = RsaPublicKey::from_public_key_pem(RSA_PUBLIC_KEY_PEM) else {
+        return false;
+    };
+    key.verify(Pkcs1v15Sign::new::<Sha256>(), payload_sha256, signature)
+        .is_ok()
+}
+
 /// Parse the fixed-width `.sig` header.
 ///
 /// Offsets are based on the browser implementation:
@@ -22,31 +22,86 @@ fn main() -> Result<(), Box<dyn Error>> {
    let cli = Cli::parse();

    match cli.command {
-        Command::Strip(args) => strip(args)?,
-        Command::Encrypt(args) => encrypt(args)?,
+        Command::Unpack(args) => unpack(args)?,
+        Command::Info(args) => info(args)?,
+        Command::Repack(args) => repack(args)?,
    }

    Ok(())
 }

-/// Execute the `encrypt` subcommand.
-///
-/// The command reads a plaintext payload, wraps it with a fresh-IV encrypted
-/// `.sig` header via [`crypto::pack_sig`], and writes the resulting container.
-fn encrypt(args: cli::EncryptArgs) -> Result<(), Box<dyn Error>> {
+/// Execute the `info` subcommand.
+fn info(args: cli::InfoArgs) -> Result<(), Box<dyn Error>> {
    let raw = fs::read(&args.input)?;
-    let filename = match args.filename {
-        Some(filename) => filename,
-        None => args
+    let info = crypto::header_info(&raw)?;
+
+    println!("file: {}", args.input.display());
+    println!("total_len: {}", info.total_len);
+    println!("header_len: {}", crypto::HEADER_LEN);
+    println!("payload_len: {}", info.payload_len);
+    println!(
+        "magic: {}",
+        std::str::from_utf8(&info.magic).unwrap_or("<non-ascii>")
+    );
+    println!("package_type_raw: 0x{:02x}", info.package_type_raw);
+    println!("package_type: {}", info.package_type);
+    println!("encrypted: {}", info.is_encrypted);
+    println!("version: {}.{}", info.version_major, info.version_minor);
+    println!("byte_07: 0x{:02x}", info.byte_07);
+    println!("filesize: {}", info.filesize);
+    println!("filename: {}", info.filename);
+    print_region("reserved_40_90", &info.reserved_40_90, args.raw);
+    println!("encrypt_offset: {}", info.encrypt_offset);
+    println!("encrypt_length: {}", info.encrypt_length);
+    println!("iv: {}", info.iv_hex);
+    println!("encrypt_filesize: {}", info.encrypt_filesize);
+    print_region("reserved_b8_e0", &info.reserved_b8_e0, args.raw);
+    println!("stored_sha256: {}", info.stored_sha256_hex);
+    println!("payload_sha256: {}", info.payload_sha256_hex);
+    println!("payload_sha256_matches: {}", info.payload_sha256_matches);
+    println!("signature_valid: {}", info.signature_valid);
+    print_region("opaque_100_200", &info.opaque_100_200, args.raw);
+
+    Ok(())
+}
+
+fn print_region(name: &str, region: &crypto::RegionInfo, raw: bool) {
+    println!("{name}_len: {}", region.len);
+    println!("{name}_nonzero_count: {}", region.nonzero_count);
+    println!("{name}_sha256: {}", region.sha256_hex);
+    if raw {
+        println!("{name}_bytes_hex:");
+        for chunk in region.bytes_hex.as_bytes().chunks(64) {
+            println!("  {}", std::str::from_utf8(chunk).unwrap_or(""));
+        }
+    }
+}
+
+/// Execute the `repack` subcommand.
+///
+/// The command reads a plaintext payload, wraps it in a signed `.sig` header,
+/// and optionally encrypts the payload.
+fn repack(args: cli::RepackArgs) -> Result<(), Box<dyn Error>> {
+    let raw = fs::read(&args.input)?;
+    let template = match args.template {
+        Some(template) => Some(fs::read(template)?),
+        None => None,
+    };
+    let filename = match (args.filename, template.as_deref()) {
+        (Some(filename), _) => filename,
+        (None, Some(template)) => crypto::header_filename(template)?,
+        (None, None) => args
            .input
            .file_name()
            .ok_or("input path does not have a file name")?
            .to_string_lossy()
            .into_owned(),
    };
-    let packed = if let Some(template) = args.template {
-        let template = fs::read(template)?;
-        crypto::pack_sig_with_template(&raw, &filename, &template)?
+    let packed = if let Some(template) = template {
+        let encrypt = if args.encrypt { Some(true) } else { None };
+        crypto::pack_sig_with_template(&raw, &filename, &template, encrypt)?
+    } else if args.encrypt {
+        crypto::pack_sig_encrypted(&raw, &filename)?
    } else {
        crypto::pack_sig(&raw, &filename)?
    };
@@ -58,19 +113,21 @@ fn encrypt(args: cli::EncryptArgs) -> Result<(), Box<dyn Error>> {
    Ok(())
 }

-/// Execute the `strip` subcommand.
+/// Execute the `unpack` subcommand.
 ///
-/// `strip` removes the 512-byte `.sig` wrapper and writes the contained package
+/// `unpack` removes the 512-byte `.sig` wrapper and writes the contained package
 /// bytes. For encrypted packages, [`crypto::unpack_sig`] performs the AES-CBC
 /// decryption before returning the payload.
-fn strip(args: cli::StripArgs) -> Result<(), Box<dyn Error>> {
+fn unpack(args: cli::UnpackArgs) -> Result<(), Box<dyn Error>> {
    let raw = fs::read(&args.input)?;
+    let filename = crypto::header_filename(&raw)?;
    let unpacked = crypto::unpack_sig(&raw)?;
    let output_path = args
        .output
        .unwrap_or_else(|| default_output_path(&args.input));

    fs::write(&output_path, unpacked)?;
+    println!("header filename: {filename}");
    println!("wrote {}", output_path.display());

    Ok(())
@@ -83,6 +83,7 @@ fn encrypts_ota_package_list_fixture() {
        EXPECTED_OTA_PACKAGE_LIST,
        "ota-package-list.json",
        ENCRYPTED_OTA_PACKAGE_LIST,
+        None,
    )
    .expect("failed to pack embedded plaintext fixture");

@@ -1 +0,0 @@
-{"packages": [{"file": "cc2_eeb001_01.03.02.36_20260326171745.swu.sig", "hash": "46aa459b61340a84ff52e2865347d42a568351919441fb9db6e185424220b192"}], "version": "01.03.02.36"}
				`@@ -0,0 +1 @@`
				`This is a pile of badly made tooling to repack CC2 OTAs`
				`@@ -1 +0,0 @@`
				`{"packages": [{"file": "cc2_eeb001_01.03.02.36_20260326171745.swu.sig", "hash": "46aa459b61340a84ff52e2865347d42a568351919441fb9db6e185424220b192"}], "version": "01.03.02.36"}`