Python-World · chavarera · Nov 16, 2021 · Sep 17, 2021
diff --git a/projects/steganography/README.md b/projects/steganography/README.md
@@ -0,0 +1,29 @@
+# Image steganography
+
+This project contains two algorithm (LSB and DCT), which can insert some secret but invisible.
+
+**LSB** insert message into Least Significant Bit of each pixels.
+
+**DCT** insert message into Middle Frequency.
+
+## Requirement
+
+Installation:
+
+```shell
+$ pip install -r requirements.txt
+```
+
+## Usage
+
+Run LSB algorithm
+
+```shell
+$ python3 lsb.py
+```
+
+Run DCT algorithm
+
+```shell
+$ python3 dct.py
+```
diff --git a/projects/steganography/dct.py b/projects/steganography/dct.py
@@ -0,0 +1,127 @@
+#!/usr/bin/env python3
+#
+# Copyright(C) 2021 wuyaoping
+#
+# DCT algorithm has great a robust but lower capacity.
+
+import numpy as np
+import os.path as osp
+import cv2
+
+FLAG = '%'
+# Select a part location from the middle frequency
+LOC_MAX = (4, 1)
+LOC_MIN = (3, 2)
+# The difference between MAX and MIN,
+# bigger to improve robust but make picture low quality.
+ALPHA = 1
+
+# Quantizer table
+TABLE = np.array([
+    [16, 11, 10, 16, 24, 40, 51, 61],
+    [12, 12, 14, 19, 26, 58, 60, 55],
+    [14, 13, 16, 24, 40, 57, 69, 56],
+    [14, 17, 22, 29, 51, 87, 80, 62],
+    [18, 22, 37, 56, 68, 109, 103, 77],
+    [24, 35, 55, 64, 81, 104, 113, 92],
+    [49, 64, 78, 87, 103, 121, 120, 101],
+    [72, 92, 95, 98, 112, 100, 103, 99]
+])
+
+
+def insert(path, txt):
+    img = cv2.imread(path, cv2.IMREAD_ANYCOLOR)
+    txt = "{}{}{}".format(len(txt), FLAG, txt)
+    row, col = img.shape[:2]
+    max_bytes = (row // 8) * (col // 8) // 8
+    assert max_bytes >= len(
+        txt), "Message overflow the capacity:{}".format(max_bytes)
+    img = cv2.cvtColor(img, cv2.COLOR_BGR2YUV)
+    # Just use the Y plane to store message, you can use all plane
+    y, u, v = cv2.split(img)
+    y = y.astype(np.float32)
+    blocks = []
+    # Quantize blocks
+    for r_idx in range(0, 8 * (row // 8), 8):
+        for c_idx in range(0, 8 * (col // 8), 8):
+            quantized = cv2.dct(y[r_idx: r_idx+8, c_idx: c_idx+8]) / TABLE
+            blocks.append(quantized)
+    for idx in range(len(txt)):
+        encode(blocks[idx*8: (idx+1)*8], txt[idx])
+
+    idx = 0
+    # Restore Y plane
+    for r_idx in range(0, 8 * (row // 8), 8):
+        for c_idx in range(0, 8 * (col // 8), 8):
+            y[r_idx: r_idx+8, c_idx: c_idx+8] = cv2.idct(blocks[idx] * TABLE)
+            idx += 1
+    y = y.astype(np.uint8)
+    img = cv2.cvtColor(cv2.merge((y, u, v)), cv2.COLOR_YUV2BGR)
+    filename, _ = osp.splitext(path)
+    # DCT algorithm can save message even if jpg
+    filename += '_dct_embeded' + '.jpg'
+    cv2.imwrite(filename, img)
+    return filename
+
+
+# Encode a char into the blocks
+def encode(blocks, data):
+    data = ord(data)
+    for idx in range(len(blocks)):
+        bit_val = (data >> idx) & 1
+        max_val = max(blocks[idx][LOC_MAX], blocks[idx][LOC_MIN])
+        min_val = min(blocks[idx][LOC_MAX], blocks[idx][LOC_MIN])
+        if max_val - min_val <= ALPHA:
+            max_val = min_val + ALPHA + 1e-3
+        if bit_val == 1:
+            blocks[idx][LOC_MAX] = max_val
+            blocks[idx][LOC_MIN] = min_val
+        else:
+            blocks[idx][LOC_MAX] = min_val
+            blocks[idx][LOC_MIN] = max_val
+
+
+# Decode a char from the blocks
+def decode(blocks):
+    val = 0
+    for idx in range(len(blocks)):
+        if blocks[idx][LOC_MAX] > blocks[idx][LOC_MIN]:
+            val |= 1 << idx
+    return chr(val)
+
+
+def extract(path):
+    img = cv2.imread(path, cv2.IMREAD_ANYCOLOR)
+    row, col = img.shape[:2]
+    max_bytes = (row // 8) * (col // 8) // 8
+    img = cv2.cvtColor(img, cv2.COLOR_BGR2YUV)
+    y, u, v = cv2.split(img)
+    y = y.astype(np.float32)
+    blocks = []
+    for r_idx in range(0, 8 * (row // 8), 8):
+        for c_idx in range(0, 8 * (col // 8), 8):
+            quantized = cv2.dct(y[r_idx: r_idx+8, c_idx: c_idx+8]) / TABLE
+            blocks.append(quantized)
+    res = ''
+    idx = 0
+    # Extract the length of the message
+    while idx < max_bytes:
+        ch = decode(blocks[idx*8: (idx+1)*8])
+        idx += 1
+        if ch == FLAG:
+            break
+        res += ch
+    end = int(res) + idx
+    assert end <= max_bytes, "Input image isn't correct."
+    res = ''
+    while idx < end:
+        res += decode(blocks[idx*8: (idx+1)*8])
+        idx += 1
+    return res
+
+
+if __name__ == '__main__':
+    data = 'A collection of simple python mini projects to enhance your Python skills.'
+    res_path = insert('./example.png', data)
+    res = extract(res_path)
+    print(res)
diff --git a/projects/steganography/example.png b/projects/steganography/example.png
diff --git a/projects/steganography/lsb.py b/projects/steganography/lsb.py
@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+#
+# Copyright(C) 2021 wuyaoping
+#
+# LSB algorithm has a great capacity but fragile.
+
+import cv2
+import math
+import os.path as osp
+import numpy as np
+
+# Insert data in the low bit.
+# Lower make picture less loss but lower capacity.
+BITS = 2
+
+HIGH_BITS = 256 - (1 << BITS)
+LOW_BITS = (1 << BITS) - 1
+BYTES_PER_BYTE = math.ceil(8 / BITS)
+FLAG = '%'
+
+
+def insert(path, txt):
+    img = cv2.imread(path, cv2.IMREAD_ANYCOLOR)
+    # Save origin shape to restore image
+    ori_shape = img.shape
+    max_bytes = ori_shape[0] * ori_shape[1] // BYTES_PER_BYTE
+    # Encode message with length
+    txt = '{}{}{}'.format(len(txt), FLAG, txt)
+    assert max_bytes >= len(
+        txt), "Message overflow the capacity:{}".format(max_bytes)
+    data = np.reshape(img, -1)
+    for (idx, val) in enumerate(txt):
+        encode(data[idx*BYTES_PER_BYTE: (idx+1) * BYTES_PER_BYTE], val)
+
+    img = np.reshape(data, ori_shape)
+    filename, _ = osp.splitext(path)
+    # png is lossless encode that can restore message correctly
+    filename += '_lsb_embeded' + ".png"
+    cv2.imwrite(filename, img)
+    return filename
+
+
+def extract(path):
+    img = cv2.imread(path, cv2.IMREAD_ANYCOLOR)
+    data = np.reshape(img, -1)
+    total = data.shape[0]
+    res = ''
+    idx = 0
+    # Decode message length
+    while idx < total // BYTES_PER_BYTE:
+        ch = decode(data[idx*BYTES_PER_BYTE: (idx+1)*BYTES_PER_BYTE])
+        idx += 1
+        if ch == FLAG:
+            break
+        res += ch
+    end = int(res) + idx
+    assert end <= total // BYTES_PER_BYTE, "Input image isn't correct."
+
+    res = ''
+    while idx < end:
+        res += decode(data[idx*BYTES_PER_BYTE: (idx+1)*BYTES_PER_BYTE])
+        idx += 1
+    return res
+
+
+def encode(block, data):
+    data = ord(data)
+    for idx in range(len(block)):
+        block[idx] &= HIGH_BITS
+        block[idx] |= (data >> (BITS * idx)) & LOW_BITS
+
+
+def decode(block):
+    val = 0
+    for idx in range(len(block)):
+        val |= (block[idx] & LOW_BITS) << (idx * BITS)
+    return chr(val)
+
+
+if __name__ == '__main__':
+    data = 'A collection of simple python mini projects to enhance your Python skills.'
+    input_path = "./example.png"
+    res_path = insert(input_path, data)
+    res = extract(res_path)
+    print(res)
diff --git a/projects/steganography/requirements.txt b/projects/steganography/requirements.txt
@@ -0,0 +1,2 @@
+numpy==1.21.2
+opencv-python==4.5.3.56