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Add Reed-Solomon error correction to DCT steganography

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- Add reedsolo library for RS error correction (32 symbols = 16 byte correction per 223-byte chunk)
- Protect entire payload (header + data) with RS encoding
- Store 3 copies of length header with majority voting for robustness
- Handle RS chunking overhead (varies based on data size)
- Update capacity calculation to account for RS overhead (24 bytes prefix + variable RS overhead)
- Add RS to dct, web, and api optional dependencies
- Update about.html with v4.1.0 Reed-Solomon feature
- Update module docstring

This fixes DCT decode failures with certain carrier images that have
uniform areas causing unstable DCT coefficients.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
Aaron D. Lee
2026-01-04 22:28:58 -05:00
parent aac8037c04
commit d0ec99d5b5
3 changed files with 229 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
frontends/web/templates/about.html
View File

@@ -100,6 +100,7 @@
<li><strong>Output:</strong> JPEG or PNG</li>
<li><strong>Color:</strong> Color or grayscale</li>
<li><strong>Speed:</strong> ~2s</li>
<li><strong>Error Correction:</strong> Reed-Solomon <span class="badge bg-info ms-1">v4.1</span></li>
</ul>
<hr>
<div class="small">
@@ -383,11 +384,18 @@
</tr>
</thead>
<tbody>
<tr>
<td><strong>4.1.0</strong></td>
<td>
<strong>Reed-Solomon error correction</strong> for DCT mode (corrects up to 16 byte errors per 223-byte chunk),
majority voting on length headers, improved robustness with problematic carrier images
</td>
</tr>
<tr>
<td><strong>4.0.0</strong></td>
<td>
<strong>Channel keys</strong> for group/deployment isolation,
DCT default, simplified auth, passphrase replaces day_phrase,
DCT default, simplified auth, passphrase replaces day_phrase,
4-word default, JPEG fix, large image support, subprocess isolation, Python 3.10-3.12
</td>
</tr>

3
pyproject.toml
View File

@@ -48,6 +48,7 @@ dct = [
"numpy>=2.0.0",
"scipy>=1.10.0",
"jpegio>=0.2.0",
"reedsolo>=1.7.0",
]
cli = [
"click>=8.0.0",
@@ -67,6 +68,7 @@ web = [
"numpy>=2.0.0",
"scipy>=1.10.0",
"jpegio>=0.2.0",
"reedsolo>=1.7.0",
]
api = [
"fastapi>=0.100.0",
@@ -78,6 +80,7 @@ api = [
"numpy>=2.0.0",
"scipy>=1.10.0",
"jpegio>=0.2.0",
"reedsolo>=1.7.0",
]
all = [
"stegasoo[cli,web,api,dct,compression]",

225
src/stegasoo/dct_steganography.py
View File

@@ -1,17 +1,22 @@
"""
DCT Domain Steganography Module (v3.2.0-patch2)
DCT Domain Steganography Module (v4.1.0)
Embeds data in DCT coefficients with two approaches:
1. PNG output: Scipy-based DCT transform (grayscale or color)
2. JPEG output: jpegio-based coefficient manipulation (if available)
v4.1.0 Changes:
- Reed-Solomon error correction protects against bit errors in problematic blocks
- Majority voting on length headers (3 copies) for additional robustness
- RS can correct up to 16 byte errors per 223-byte chunk
v3.2.0-patch2 Changes:
- Chunked processing for large images to avoid heap corruption
- Process image in vertical strips to limit memory per operation
- Isolated DCT operations with fresh array allocations
- Workaround for scipy.fftpack memory issues
Requires: scipy (for PNG mode), optionally jpegio (for JPEG mode)
Requires: scipy (for PNG mode), optionally jpegio (for JPEG mode), reedsolo (for error correction)
"""
import gc
@@ -102,6 +107,13 @@ JPEGIO_MAGIC = b"JPGS"
JPEGIO_MIN_COEF_MAGNITUDE = 2
JPEGIO_EMBED_CHANNEL = 0
FLAG_COLOR_MODE = 0x01
FLAG_RS_PROTECTED = 0x02 # Reed-Solomon error correction enabled
# Reed-Solomon settings - 32 symbols can correct up to 16 byte errors per 223-byte chunk
RS_NSYM = 32
RS_LENGTH_HEADER_SIZE = 8 # 8 bytes: 4 for raw_payload_length + 4 for rs_payload_length
RS_LENGTH_COPIES = 3 # Store length header 3 times for majority voting
RS_LENGTH_PREFIX_SIZE = RS_LENGTH_HEADER_SIZE * RS_LENGTH_COPIES # Total: 24 bytes
# Chunking settings for large images
MAX_CHUNK_HEIGHT = 512 # Process in 512-pixel tall strips
@@ -167,6 +179,44 @@ def has_jpegio_support() -> bool:
return HAS_JPEGIO
# ============================================================================
# REED-SOLOMON ERROR CORRECTION
# Protects against bit errors in problematic image blocks
# ============================================================================
# Check for reedsolo availability
try:
from reedsolo import RSCodec, ReedSolomonError
HAS_REEDSOLO = True
except ImportError:
HAS_REEDSOLO = False
RSCodec = None
ReedSolomonError = None
def _rs_encode(data: bytes) -> bytes:
"""Add Reed-Solomon error correction symbols to data."""
if not HAS_REEDSOLO:
return data # No protection if reedsolo not available
rs = RSCodec(RS_NSYM)
return bytes(rs.encode(data))
def _rs_decode(data: bytes) -> bytes:
"""Decode Reed-Solomon protected data, correcting errors if possible."""
if not HAS_REEDSOLO:
return data # No decoding if reedsolo not available
rs = RSCodec(RS_NSYM)
try:
decoded, _, errata_pos = rs.decode(data)
if errata_pos:
pass # Errors were corrected
return bytes(decoded)
except ReedSolomonError as e:
raise ValueError(f"Reed-Solomon decoding failed: {e}") from e
# ============================================================================
# SAFE DCT FUNCTIONS
# These create fresh arrays to avoid scipy memory corruption issues
@@ -436,7 +486,17 @@ def calculate_dct_capacity(image_data: bytes) -> DCTCapacityInfo:
bits_per_block = len(DEFAULT_EMBED_POSITIONS)
total_bits = total_blocks * bits_per_block
total_bytes = total_bits // 8
usable_bytes = max(0, total_bytes - HEADER_SIZE)
# Account for header and RS overhead
# RS format: [24-byte length prefix (3 copies)] + RS(header + data)
# RS adds RS_NSYM bytes per 223-byte chunk (255 - RS_NSYM = 223)
# Conservatively estimate RS overhead as ~15% + one chunk minimum
if HAS_REEDSOLO:
# Overhead = 24 (prefix) + 10 (header) + RS overhead
# Simplify: base overhead = 24 + 10 + 32 + 15% margin for larger data
overhead = RS_LENGTH_PREFIX_SIZE + HEADER_SIZE + RS_NSYM + 20
else:
overhead = HEADER_SIZE
usable_bytes = max(0, total_bytes - overhead)
return DCTCapacityInfo(
width=width,
@@ -538,9 +598,20 @@ def _embed_scipy_dct_safe(
flags = FLAG_COLOR_MODE if color_mode == "color" else 0
# Prepare payload bits
# Build raw payload (header + data)
header = _create_header(len(data), flags)
payload = header + data
raw_payload = header + data
# Apply Reed-Solomon error correction to entire payload if available
if HAS_REEDSOLO:
rs_payload = _rs_encode(raw_payload)
# Format: [length_header x 3 for majority voting] + [RS-encoded payload]
# Each length_header is 8 bytes: 4 for raw_payload_length + 4 for rs_payload_length
length_header = struct.pack(">II", len(raw_payload), len(rs_payload))
length_prefix = length_header * RS_LENGTH_COPIES # Repeat 3 times
payload = length_prefix + rs_payload
else:
payload = raw_payload
bits = []
for byte in payload:
for i in range(7, -1, -1):
@@ -761,8 +832,19 @@ def _embed_jpegio(
all_positions = _jpegio_get_usable_positions(coef_array)
order = _jpegio_generate_order(len(all_positions), seed)
# Build raw payload (header + data)
header = _jpegio_create_header(len(data), flags)
payload = header + data
raw_payload = header + data
# Apply Reed-Solomon error correction to entire payload if available
if HAS_REEDSOLO:
rs_payload = _rs_encode(raw_payload)
# Format: [length_header x 3 for majority voting] + [RS-encoded payload]
length_header = struct.pack(">II", len(raw_payload), len(rs_payload))
length_prefix = length_header * RS_LENGTH_COPIES
payload = length_prefix + rs_payload
else:
payload = raw_payload
bits = []
for byte in payload:
@@ -892,6 +974,69 @@ def _extract_scipy_dct_safe(stego_image: bytes, seed: bytes) -> bytes:
del padded
gc.collect()
# Try RS-protected format first (has 24-byte length prefix: 3 copies of 8-byte header)
if HAS_REEDSOLO and len(all_bits) >= RS_LENGTH_PREFIX_SIZE * 8:
# Extract length prefix (24 bytes: 3 copies of 8-byte header for majority voting)
length_prefix_bits = all_bits[: RS_LENGTH_PREFIX_SIZE * 8]
length_prefix_bytes = bytes(
[
sum(length_prefix_bits[i * 8 : (i + 1) * 8][j] << (7 - j) for j in range(8))
for i in range(RS_LENGTH_PREFIX_SIZE)
]
)
# Extract 3 copies and use majority voting
copies = []
for i in range(RS_LENGTH_COPIES):
start = i * RS_LENGTH_HEADER_SIZE
end = start + RS_LENGTH_HEADER_SIZE
copies.append(length_prefix_bytes[start:end])
# Count occurrences of each unique copy
from collections import Counter
counter = Counter(copies)
best_header, count = counter.most_common(1)[0]
# Only proceed if we have at least 2 matching copies (majority)
if count >= 2:
raw_payload_length, rs_encoded_length = struct.unpack(">II", best_header)
else:
# No majority - try first copy as fallback
raw_payload_length, rs_encoded_length = struct.unpack(">II", copies[0])
# Sanity check: both lengths should be reasonable
max_reasonable = (len(all_bits) // 8) - RS_LENGTH_PREFIX_SIZE
if (raw_payload_length > 0 and raw_payload_length <= max_reasonable and
rs_encoded_length > 0 and rs_encoded_length <= max_reasonable and
rs_encoded_length >= raw_payload_length):
# This looks like RS-protected format
total_bits_needed = (RS_LENGTH_PREFIX_SIZE + rs_encoded_length) * 8
if len(all_bits) >= total_bits_needed:
rs_bits = all_bits[RS_LENGTH_PREFIX_SIZE * 8 : total_bits_needed]
rs_encoded = bytes(
[
sum(rs_bits[i * 8 : (i + 1) * 8][j] << (7 - j) for j in range(8))
for i in range(rs_encoded_length)
]
)
try:
# RS decode to get header + data
raw_payload = _rs_decode(rs_encoded)
# Parse header from decoded payload
_, flags, data_length = _parse_header(
[((raw_payload[i // 8] >> (7 - i % 8)) & 1) for i in range(HEADER_SIZE * 8)]
)
# Extract data
data = raw_payload[HEADER_SIZE : HEADER_SIZE + data_length]
return data
except (ValueError, struct.error):
pass # Fall through to legacy format
# Legacy format: header not protected by RS
_, flags, data_length = _parse_header(all_bits)
data_bits = all_bits[HEADER_SIZE * 8 : (HEADER_SIZE + data_length) * 8]
@@ -922,6 +1067,72 @@ def _extract_jpegio(stego_image: bytes, seed: bytes) -> bytes:
all_positions = _jpegio_get_usable_positions(coef_array)
order = _jpegio_generate_order(len(all_positions), seed)
# Try RS-protected format first (has 24-byte length prefix: 3 copies for majority voting)
if HAS_REEDSOLO and len(all_positions) >= RS_LENGTH_PREFIX_SIZE * 8:
# Extract length prefix (24 bytes: 3 copies of 8-byte header)
length_prefix_bits = []
for pos_idx in order[: RS_LENGTH_PREFIX_SIZE * 8]:
row, col = all_positions[pos_idx]
coef = coef_array[row, col]
length_prefix_bits.append(coef & 1)
length_prefix_bytes = bytes(
[
sum(length_prefix_bits[i * 8 : (i + 1) * 8][j] << (7 - j) for j in range(8))
for i in range(RS_LENGTH_PREFIX_SIZE)
]
)
# Extract 3 copies and use majority voting
from collections import Counter
copies = []
for i in range(RS_LENGTH_COPIES):
start = i * RS_LENGTH_HEADER_SIZE
end = start + RS_LENGTH_HEADER_SIZE
copies.append(length_prefix_bytes[start:end])
counter = Counter(copies)
best_header, count = counter.most_common(1)[0]
if count >= 2:
raw_payload_length, rs_encoded_length = struct.unpack(">II", best_header)
else:
raw_payload_length, rs_encoded_length = struct.unpack(">II", copies[0])
# Sanity check
max_reasonable = (len(all_positions) // 8) - RS_LENGTH_PREFIX_SIZE
if (raw_payload_length > 0 and raw_payload_length <= max_reasonable and
rs_encoded_length > 0 and rs_encoded_length <= max_reasonable and
rs_encoded_length >= raw_payload_length):
total_bits_needed = (RS_LENGTH_PREFIX_SIZE + rs_encoded_length) * 8
if len(all_positions) >= total_bits_needed:
# Extract RS-encoded data
all_bits = []
for bit_idx, pos_idx in enumerate(order):
if bit_idx >= total_bits_needed:
break
row, col = all_positions[pos_idx]
coef = coef_array[row, col]
all_bits.append(coef & 1)
rs_bits = all_bits[RS_LENGTH_PREFIX_SIZE * 8 :]
rs_encoded = bytes(
[
sum(rs_bits[i * 8 : (i + 1) * 8][j] << (7 - j) for j in range(8))
for i in range(rs_encoded_length)
]
)
try:
raw_payload = _rs_decode(rs_encoded)
_, flags, data_length = _jpegio_parse_header(raw_payload[:HEADER_SIZE])
data = raw_payload[HEADER_SIZE : HEADER_SIZE + data_length]
return data
except (ValueError, struct.error):
pass # Fall through to legacy format
# Legacy format: header not protected by RS
header_bits = []
for pos_idx in order[: HEADER_SIZE * 8]:
row, col = all_positions[pos_idx]
@@ -936,7 +1147,6 @@ def _extract_jpegio(stego_image: bytes, seed: bytes) -> bytes:
)
_, flags, data_length = _jpegio_parse_header(header_bytes)
total_bits_needed = (HEADER_SIZE + data_length) * 8
all_bits = []
@@ -948,7 +1158,6 @@ def _extract_jpegio(stego_image: bytes, seed: bytes) -> bytes:
all_bits.append(coef & 1)
data_bits = all_bits[HEADER_SIZE * 8 :]
data = bytes(
[
sum(data_bits[i * 8 : (i + 1) * 8][j] << (7 - j) for j in range(8))