Merge pull request #100 from Philip-Zimmermann/main
- Fix image resize analyzer - Fixed broken stegbrute URL - Fix minor typos
This commit is contained in:
Zeecka
+1
-1
@@ -1,4 +1,4 @@
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FROM python:3.11-slim AS build
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FROM python:3.14-slim AS build
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WORKDIR /
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@@ -73,13 +73,13 @@ Here is a batch of usefull commands.
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```bash
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docker compose down -v # Remove volume containings results
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docker compose -f docker-compose-dev.yml up # Start application in developpement mode
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docker compose -f compose.dev.yml up # Start application in developpement mode
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rm -rf aperisolve/results # Remove results from developpement mode
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docker exec -it postgres psql -U aperiuser -d aperisolve # Get postgresql shell
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docker exec -it aperisolve-web bash # Get shell in running web app
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```
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> Note, if you used [docker-compose-dev.yml](docker-compose-dev.yml), you must remove "results" when switching to [production docker](docker-compose.yml).
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> Note, if you used [compose.dev.yml](compose.dev.yml), you must remove "results" when switching to [production docker](compose.yml).
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### Code quality
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@@ -94,7 +94,6 @@ GitHub CI will alert in case of failure.
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## Roadmap
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- [x] PngCheck
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- [ ] Zsteg extract / --all --> **Download `zsteg` files** such as mp3 encoded on LSB
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- [ ] Test on mobile
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- [ ] i18n
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@@ -0,0 +1,190 @@
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"""Image size bruteforcer for common PNG sizes."""
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import zlib
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import shutil
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from pathlib import Path
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from .utils import update_data
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# Full list of expected sizes
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EXPECTED_SIZES = [
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# -------------------------
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# ICONS (Square)
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# -------------------------
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(16, 16), (20, 20), (24, 24), (28, 28),
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(32, 32), (48, 48), (64, 64), (72, 72),
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(96, 96), (128, 128), (192, 192), (256, 256),
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(384, 384), (512, 512), (768, 768), (1024, 1024),
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(1536, 1536), (2048, 2048), (4096, 4096),
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# -------------------------
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# 1:1 Square (General)
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# -------------------------
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(300, 300), (500, 500), (800, 800), (1000, 1000),
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(1500, 1500), (2000, 2000), (2500, 2500), (3000, 3000),
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# -------------------------
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# 4:3 Aspect (Classic Screens)
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# -------------------------
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(320, 240), (640, 480), (800, 600), (960, 720),
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(1024, 768), (1280, 960), (1600, 1200), (2048, 1536),
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(2560, 1920), (3200, 2400), (4096, 3072),
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# -------------------------
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# 3:2 Aspect (Photography)
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# -------------------------
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(600, 400), (900, 600), (1200, 800), (1500, 1000),
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(1800, 1200), (2400, 1600), (3000, 2000), (3600, 2400),
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(4500, 3000), (6000, 4000),
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# -------------------------
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# 16:9 Aspect (Video / Web)
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# -------------------------
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(426, 240), (640, 360), (854, 480), (960, 540),
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(1280, 720), (1366, 768), (1600, 900), (1920, 1080),
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(2560, 1440), (3200, 1800), (3440, 1935), (3840, 2160),
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(5120, 2880), (7680, 4320), (10240, 5760),
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# -------------------------
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# 16:10 Aspect (Laptops)
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# -------------------------
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(1280, 800), (1440, 900), (1680, 1050),
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(1920, 1200), (2560, 1600), (2880, 1800),
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(3840, 2400), (5120, 3200),
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# -------------------------
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# Mobile Portrait (9:16)
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# -------------------------
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(720, 1280), (1080, 1920), (1440, 2560),
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(2160, 3840), (1440, 2960), (1080, 2400),
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(1170, 2532), (1284, 2778), (1290, 2796),
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# -------------------------
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# Social Media Sizes
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# -------------------------
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# Instagram
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(1080, 1080), (1080, 1350), (1080, 1920),
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# Facebook
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(1200, 628), (1200, 1200),
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# Twitter/X
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(1200, 675), (1500, 500),
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# YouTube Thumbnails
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(1280, 720), (1920, 1080),
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# -------------------------
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# Banners / Headers
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# -------------------------
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(1600, 500), (1920, 500), (2560, 700),
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(3000, 1000), (3840, 1200),
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# -------------------------
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# Print-like Digital Sizes
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# -------------------------
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(2550, 3300), # Letter @ 300 DPI
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(2480, 3508), # A4 @ 300 DPI
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(3508, 4961), # A3 @ 300 DPI
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(4961, 7016), # A2 @ 300 DPI
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(7016, 9933), # A1 @ 300 DPI
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]
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def calc_checksum(header_chunk, width_bytes, height_bytes):
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"""
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Calculates the CRC32 of the IHDR chunk with new dimensions.
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header_chunk: The full IHDR chunk (Type + Data).
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"""
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# Reconstruct IHDR: [Type(4)] + [New Width(4)] + [New Height(4)] + [Rest of Data(5)]
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new_header = header_chunk[:4] + width_bytes + height_bytes + header_chunk[12:]
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# Calculate CRC and return as 4 bytes (Big Endian)
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return bytearray((zlib.crc32(new_header) & 0xffffffff).to_bytes(4, byteorder='big'))
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def analyze_image_resize(input_img: Path, output_dir: Path) -> None:
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"""
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Analyze an image submission using python-based resize bruteforce.
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Attempts to recover PNGs with modified resolutions but valid CRCs.
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"""
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# 1. Setup Paths
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input_img = Path(input_img)
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output_dir = Path(output_dir)
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# 3. Initialize Logs
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logs = []
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recovered_image = None
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try:
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with input_img.open("rb") as image:
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f = image.read()
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b = bytearray(f)
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# Find IHDR start
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IHDR = b.find(b'\x49\x48\x44\x52')
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if IHDR == -1:
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logs.append("Failure: PNG header (IHDR) not found.")
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update_data(output_dir, {"image_resize": {"status": "error", "error": "PNG header not found."}})
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return
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# Calculate Chunk Length (The 4 bytes BEFORE IHDR tag)
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chunk_length = int.from_bytes((b[IHDR- 4: IHDR]), byteorder="big") + 4
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# Extract Target CRC (The 4 bytes AFTER the chunk data)
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target_crc = b[IHDR + chunk_length:IHDR + chunk_length + 4]
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# Isolate the header chunk (Type + Data)
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header_chunk = b[IHDR:IHDR + chunk_length]
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logs.append(f"Target CRC found: 0x{target_crc.hex()}")
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match_found = False
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# Brute-force Loop
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for size in EXPECTED_SIZES:
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width, height = size
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# Convert dimensions to 4-byte Big Endian arrays
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width_bytes = bytearray(width.to_bytes(4, byteorder='big'))
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height_bytes = bytearray(height.to_bytes(4, byteorder='big'))
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# Check if this size matches the file's CRC
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if target_crc == calc_checksum(header_chunk, width_bytes, height_bytes):
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match_found = True
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logs.append(f"Success: Match found! Dimensions: {width}x{height}")
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# Create Output Filename
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img_name = f"recovered_{width}x{height}.png"
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# Create parent directories if they don't exist
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output_dir.mkdir(parents=True, exist_ok=True)
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output_path = output_dir / img_name
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# Splicing: [Start...IHDR+4] + [W] + [H] + [IHDR+12...End]
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full_png_data = b[:IHDR+4] + width_bytes + height_bytes + b[IHDR+12:]
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# Write the recovered file to disk
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with output_path.open("wb") as out_f:
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out_f.write(full_png_data)
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recovered_image = Path(output_dir.name) / img_name
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break # Stop looking after finding the match
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if not match_found:
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logs.append("Failure: No matching dimensions found.")
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# 4. Final Data Update
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output_data = {
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"image_resize": { # Key name must match your module name in AperiSolve
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"status": "ok",
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"output": logs
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}
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}
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if recovered_image:
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output_data["image_resize"]["image"] = "/image/" + str(recovered_image)
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update_data(output_dir, output_data)
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except Exception as e:
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update_data(output_dir, {"image_resize": {"status": "error", "error": str(e)}})
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return None
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@@ -3,6 +3,6 @@
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from pathlib import Path
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IMAGE_EXTENSIONS = [".png", ".jpg", ".jpeg", ".gif", ".bmp", ".webp", ".tiff"]
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WORKER_FILES = ["binwalk", "foremost", "steghide", "zsteg"]
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WORKER_FILES = ["binwalk", "foremost", "steghide", "zsteg", "image_resize"]
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RESULT_FOLDER = Path(__file__).parent.resolve() / "results"
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@@ -8,6 +8,7 @@ const TOOL_ORDER = [
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"steghide",
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"zsteg",
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"strings",
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"image_resize",
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];
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function escapeHtml(text) {
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@@ -248,7 +249,7 @@ function parseResult(result) {
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analyzer.className = `analyzer a-${escapeHtml(tool)}`;
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resultDiv.appendChild(analyzer);
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analyzer.innerHTML += `<h2>${capitalize(tool)}</h2>`;
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analyzer.innerHTML += `<h2>${capitalize(tool.replace("_"," "))}</h2>`;
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if (result[tool]["status"] === "ok") {
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if ("images" in result[tool]) {
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@@ -270,8 +271,17 @@ function parseResult(result) {
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}
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}
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}
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if ("image" in result[tool]) {
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// Parse image output
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analyzer.innerHTML += `<div class='results_img'><img src='${escapeHtml(
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result[tool]["image"]
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)}'/></div>`;
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}
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// Parse text output
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if (typeof result[tool]["output"] === "string") {
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analyzer.innerHTML += `<pre>${escapeHtml(
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result[tool]["output"]
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@@ -6,8 +6,8 @@
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<div>
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<div>
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This cheatsheet is intended to guide CTF players in their research. This cheatsheet is not representative of
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modern steganography/seganalysis techniques, and its content does not match with the creation of an interesting
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challenges 😉.
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modern steganography/steganalysis techniques, and its content does not match with the creation of an interesting
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challenge 😉.
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</div>
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</div>
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<h2>Check file type / metadata</h2>
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@@ -48,7 +48,7 @@
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<ul class="fa-ul">
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<li>Verify the checksums of the file. These are usually CRC32, some tools like <a
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href='http://www.libpng.org/pub/png/apps/pngcheck.html' target='_blank' class='highlight'>PngCheck</a> or <a
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href='https://github.com/sherlly/PCRT' target='_blank' class='highlight'>PCRT</a> are usefull to verify and
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href='https://github.com/sherlly/PCRT' target='_blank' class='highlight'>PCRT</a> are useful to verify and
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correct these checksums.</li>
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</ul>
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<div class="command">
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@@ -13,6 +13,7 @@ from .analyzers.steghide import analyze_steghide
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from .analyzers.strings import analyze_strings
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from .analyzers.zsteg import analyze_zsteg
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from .analyzers.pngcheck import analyze_pngcheck
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from .analyzers.image_resize import analyze_image_resize
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from .app import app, db
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from .config import RESULT_FOLDER
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from .models import Image, Submission
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@@ -53,6 +54,7 @@ def analyze_image(submission_hash: str) -> None:
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(analyze_pngcheck, img_path, result_path),
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(analyze_steghide, img_path, result_path, submission.password),
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(analyze_zsteg, img_path, result_path),
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(analyze_image_resize, img_path, result_path),
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]
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# Deep analysis only
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