From e8701195e66f2d27ffe17fb514eae8173795aaf7 Mon Sep 17 00:00:00 2001
From: Georgiy Bondarenko <69736697+nehilo@users.noreply.github.com>
Date: Thu, 4 Mar 2021 22:54:23 +0500
Subject: Initial commit

---
 buildroot/share/PlatformIO/scripts/chitu_crypt.py | 127 ++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 buildroot/share/PlatformIO/scripts/chitu_crypt.py

(limited to 'buildroot/share/PlatformIO/scripts/chitu_crypt.py')

diff --git a/buildroot/share/PlatformIO/scripts/chitu_crypt.py b/buildroot/share/PlatformIO/scripts/chitu_crypt.py
new file mode 100644
index 0000000..aa67587
--- /dev/null
+++ b/buildroot/share/PlatformIO/scripts/chitu_crypt.py
@@ -0,0 +1,127 @@
+Import("env")
+import os
+import random
+import struct
+import uuid
+
+# Relocate firmware from 0x08000000 to 0x08008800
+env['CPPDEFINES'].remove(("VECT_TAB_ADDR", "0x8000000"))
+env['CPPDEFINES'].append(("VECT_TAB_ADDR", "0x08008800"))
+
+custom_ld_script = os.path.abspath("buildroot/share/PlatformIO/ldscripts/chitu_f103.ld")
+for i, flag in enumerate(env["LINKFLAGS"]):
+    if "-Wl,-T" in flag:
+        env["LINKFLAGS"][i] = "-Wl,-T" + custom_ld_script
+    elif flag == "-T":
+        env["LINKFLAGS"][i + 1] = custom_ld_script
+
+
+def calculate_crc(contents, seed):
+    accumulating_xor_value = seed;
+
+    for i in range(0, len(contents), 4):
+        value = struct.unpack('<I', contents[ i : i + 4])[0]
+        accumulating_xor_value = accumulating_xor_value ^ value
+    return accumulating_xor_value
+
+def xor_block(r0, r1, block_number, block_size, file_key):
+    # This is the loop counter
+    loop_counter = 0x0
+
+    # This is the key length
+    key_length = 0x18
+
+    # This is an initial seed
+    xor_seed = 0x4BAD
+
+    # This is the block counter
+    block_number = xor_seed * block_number
+
+    #load the xor key from the file
+    r7 =  file_key
+
+    for loop_counter in range(0, block_size):
+        # meant to make sure different bits of the key are used.
+        xor_seed = int(loop_counter/key_length)
+
+        # IP is a scratch register / R12
+        ip = loop_counter - (key_length * xor_seed)
+
+        # xor_seed = (loop_counter * loop_counter) + block_number
+        xor_seed = (loop_counter * loop_counter) + block_number
+
+        # shift the xor_seed left by the bits in IP.
+        xor_seed = xor_seed >> ip
+
+        # load a byte into IP
+        ip = r0[loop_counter]
+
+        # XOR the seed with r7
+        xor_seed = xor_seed ^ r7
+
+        # and then with IP
+        xor_seed = xor_seed ^ ip
+
+        #Now store the byte back
+        r1[loop_counter] = xor_seed & 0xFF
+
+        #increment the loop_counter
+        loop_counter = loop_counter + 1
+
+
+def encrypt_file(input, output_file, file_length):
+    input_file = bytearray(input.read())
+    block_size = 0x800
+    key_length = 0x18
+
+    uid_value = uuid.uuid4()
+    file_key = int(uid_value.hex[0:8], 16)
+
+    xor_crc = 0xEF3D4323;
+
+    # the input file is exepcted to be in chunks of 0x800
+    # so round the size
+    while len(input_file) % block_size != 0:
+        input_file.extend(b'0x0')
+
+    # write the file header
+    output_file.write(struct.pack(">I", 0x443D2D3F))
+    # encrypt the contents using a known file header key
+
+    # write the file_key
+    output_file.write(struct.pack("<I", file_key))
+
+    #TODO - how to enforce that the firmware aligns to block boundaries?
+    block_count = int(len(input_file) / block_size)
+    print ("Block Count is ", block_count)
+    for block_number in range(0, block_count):
+        block_offset = (block_number * block_size)
+        block_end = block_offset + block_size
+        block_array = bytearray(input_file[block_offset: block_end])
+        xor_block(block_array, block_array, block_number, block_size, file_key)
+        for n in range (0, block_size):
+            input_file[block_offset + n] = block_array[n]
+
+        # update the expected CRC value.
+        xor_crc = calculate_crc(block_array, xor_crc)
+
+    # write CRC
+    output_file.write(struct.pack("<I", xor_crc))
+
+    # finally, append the encrypted results.
+    output_file.write(input_file)
+    return
+
+
+# Encrypt ${PROGNAME}.bin and save it as 'update.cbd'
+def encrypt(source, target, env):
+    firmware = open(target[0].path, "rb")
+    update = open(target[0].dir.path +'/update.cbd', "wb")
+    length = os.path.getsize(target[0].path)
+
+    encrypt_file(firmware, update, length)
+
+    firmware.close()
+    update.close()
+
+env.AddPostAction("$BUILD_DIR/${PROGNAME}.bin", encrypt);
-- 
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