DEX file parsing --- 1, dex header parsing

A, dex file

dex file is a file type on the Android platform executable file. It file format can be summarized in the picture below:
dex File Format
DEX header is usually set to 0x70 bytes in size, comprising a flag, a version number, checksum, sha-1 signatures, and other methods, the class number and offset address information. As shown below:

Two, dex header parsing the fields

dex each file header contains the following fields:

magic: dex contains the file identifier and version starts from 0x00 8 bytes in length
checksum: dex file checksum, offset: 0x08, a length of 4 bytes.
signature: dex sha-1 signature, 0x0C offset, a length of 20 bytes
file_szie: dex file size, offset 0x20, a length of 4 bytes
header_size: dex header size, offset 0x24, a length of 4 bytes, usually 0x70
endian_ Tag: determining whether endian DEX file exchange, offset 0x28, a length of 4 bytes, is generally 0x78563412
link_size: dex file link segment size, 0 indicates statically linked, 0x2C offset, a length of 4 bytes
link_off: dex file link segment offset, offset 0x30, a length of 4 bytes
map_off: dex file map data segment offset, the offset position is 0x34, a length of 4 bytes
string_ids_size: dex file contains the number of strings, offset 0x38, a length of 4 bytes
string_ids_off: dex string file start offset, offset 0x3C, a length of 4 bytes
type_ids_size: dex number of file types, offset 0x40, a length of 4 bytes
type_ids_off: dex class file offset position, offset 0x44, a length of 4 bytes
photo_ids_size: dex file number prototype method, offset 0x48, a length of 4 bytes
photo_ids_off: dex method Prototype file offset position, offset 0x4C, a length of 4 bytes
field_ids_size: dex number fields in the file, offset 0x50, a length of 4 bytes
field_ids_off: dex file field offset position offset is 0x54, a length of 4 bytes
method_ids_size: dex file number of methods, offset 0x58, a length of 4 bytes
method_ids_off: dex file offset method, offset 0x5c, a length of 4 bytes
class_defs_size: Number dex class definition file, offset 0x60, a length of 4 bytes
class_defs_off: dex class definition file offset position, offset 0x64, a length of 4 bytes
data_size: dex segment size, offset 0x68, a length of 4 bytes
data_off: dex data segment offset, offset 0x6C, a length of 4 bytes

Three, dex header code analysis sample (Python)

dex open the open function with the binary file, then move the file pointer seek function, e.g. magic is f.seek(0x00), then read the number of bytes to the corresponding information, such as reading the version number f.seek(0x04) f.read(4), and accordingly the printing operation on the line, the more dex header simple, does not involve coding, etc. so we do not resolve it feels a belt. . . . . Specific code can be seen below or github, code running FIG attached below:
Figure code runs

Four, dex header parsing code that implements (python achieve)

import binascii

def parserHeader(f):
f.seek(0x00)
magic_mask = f.read(4)
magic_mask = binascii.b2a_hex(magic_mask)
magic_mask = str(magic_mask,encoding='utf-8')
print('文件标识符: ',end='')
print(magic_mask)  

f.seek(0x04)
magic_version = f.read(4)
magic_version = binascii.b2a_hex(magic_version)
magic_version = str(magic_version,encoding='utf-8')
print('文件版本: ',end='')
print(magic_version)

f.seek(0x08)
checksum = f.read(4)
checksum = binascii.b2a_hex(checksum)
checksum = str(checksum,encoding='utf-8')
print('校验码: ',end='')
print(checksum)

f.seek(0x0c)
signature = f.read(20)
signature = binascii.b2a_hex(signature)
signature = str(signature,encoding='utf-8')
print('SHA-1签名: ',end='')
print(signature)

f.seek(0x20)
file_size = f.read(4)
a = bytearray(file_size)
a.reverse()
file_size = bytes(a)
file_size = binascii.b2a_hex(file_size)
file_size = str(file_size,encoding='utf-8')
print('文件大小: ',end='')
print(int(file_size,16),end='')
print(' byte')

f.seek(0x24)
header_size = f.read(4)
a = bytearray(header_size)
a.reverse()
header_size = bytes(a)
header_size = binascii.b2a_hex(header_size)
header_size = str(header_size,encoding='utf-8')
print('文件头大小: ',end='')
print(int(header_size,16),end='')
print(' byte')

f.seek(0x28)
endian_tag = f.read(4)
endian_tag = binascii.b2a_hex(endian_tag)
endian_tag = str(endian_tag,encoding='utf-8')
print('字节序交换标志: ',end='')
print(endian_tag)

f.seek(0x2c)
link_size = f.read(4)
a = bytearray(link_size)
a.reverse()
link_size = bytes(a)
link_size = binascii.b2a_hex(link_size)
link_size = str(link_size,encoding='utf-8')
print('链接段大小: ',end='')
print(int(link_size,16),end='')
print(' byte')

f.seek(0x30)
link_off = f.read(4)
a = bytearray(link_off)
a.reverse()
link_off = bytes(a)
link_off = binascii.b2a_hex(link_off)
link_off = str(link_off,encoding='utf-8')
print('链接段偏移位置: ',end='')
print(hex(int(link_off,16)))

f.seek(0x34)
map_off = f.read(4)
a = bytearray(map_off)
a.reverse()
map_off = bytes(a)
map_off = binascii.b2a_hex(map_off)
map_off = str(map_off,encoding='utf-8')
print('map数据偏移位置: ',end='')
print(hex(int(map_off,16)))

f.seek(0x38)
stringidsSize = f.read(4)
a = bytearray(stringidsSize)
a.reverse()
stringidsSize = bytes(a)
stringidsSize = binascii.b2a_hex(stringidsSize)
stringidsSize = str(stringidsSize,encoding='utf-8')
print('字符串数量: ',end='')
print(int(stringidsSize,16),end='')
print('(',end='')
print(hex(int(stringidsSize,16)),end='')
print(')')

f.seek(0x3c)
string_ids_off = f.read(4)
a = bytearray(string_ids_off)
a.reverse()
string_ids_off = bytes(a)
string_ids_off = binascii.b2a_hex(string_ids_off)
string_ids_off = str(string_ids_off,encoding='utf-8')
print('字符串偏移位置: ',end='')
print(hex(int(string_ids_off,16)))

f.seek(0x40)
type_ids_size = f.read(4)
a = bytearray(type_ids_size)
a.reverse()
type_ids_size = bytes(a)
type_ids_size = binascii.b2a_hex(type_ids_size)
type_ids_size = str(type_ids_size,encoding='utf-8')
print('类数量: ',end='')
print(int(type_ids_size,16),end='')
print('(',end='')
print(hex(int(type_ids_size,16)),end='')
print(')')

f.seek(0x44)
type_ids_off = f.read(4)
a = bytearray(type_ids_off)
a.reverse()
type_ids_off = bytes(a)
type_ids_off = binascii.b2a_hex(type_ids_off)
type_ids_off = str(type_ids_off,encoding='utf-8')
print('类偏移位置: ',end='')
print(hex(int(type_ids_off,16)))

f.seek(0x48)
photo_ids_size = f.read(4)
a = bytearray(photo_ids_size)
a.reverse()
photo_ids_size = bytes(a)
photo_ids_size = binascii.b2a_hex(photo_ids_size)
photo_ids_size = str(photo_ids_size,encoding='utf-8')
print('方法原型数量: ',end='')
print(int(photo_ids_size,16),end='')
print('(',end='')
print(hex(int(photo_ids_size,16)),end='')
print(')')

f.seek(0x4c)
photo_ids_off = f.read(4)
a = bytearray(photo_ids_off)
a.reverse()
photo_ids_off = bytes(a)
photo_ids_off = binascii.b2a_hex(photo_ids_off)
photo_ids_off = str(photo_ids_off,encoding='utf-8')
print('方法原型偏移位置: ',end='')
print(hex(int(photo_ids_off,16)))

f.seek(0x50)
field_ids_size = f.read(4)
a = bytearray(field_ids_size)
a.reverse()
field_ids_size = bytes(a)
field_ids_size = binascii.b2a_hex(field_ids_size)
field_ids_size = str(field_ids_size,encoding='utf-8')
print('字段数量: ',end='')
print(int(field_ids_size,16),end='')
print('(',end='')
print(hex(int(field_ids_size,16)),end='')
print(')')

f.seek(0x54)
field_ids_off = f.read(4)
a = bytearray(field_ids_off)
a.reverse()
field_ids_off = bytes(a)
field_ids_off = binascii.b2a_hex(field_ids_off)
field_ids_off = str(field_ids_off,encoding='utf-8')
print('字段偏移位置: ',end='')
print(hex(int(field_ids_off,16)))

f.seek(0x58)
method_ids_size = f.read(4)
a = bytearray(method_ids_size)
a.reverse()
method_ids_size = bytes(a)
method_ids_size = binascii.b2a_hex(method_ids_size)
method_ids_size = str(method_ids_size,encoding='utf-8')
print('方法数量: ',end='')
print(int(method_ids_size,16),end='')
print('(',end='')
print(hex(int(method_ids_size,16)),end='')
print(')')

f.seek(0x5c)
method_ids_off = f.read(4)
a = bytearray(method_ids_off)
a.reverse()
method_ids_off = bytes(a)
method_ids_off = binascii.b2a_hex(method_ids_off)
method_ids_off = str(method_ids_off,encoding='utf-8')
print('方法偏移位置: ',end='')
print(hex(int(method_ids_off,16)))

f.seek(0x60)
class_defs_size = f.read(4)
a = bytearray(class_defs_size)
a.reverse()
class_defs_size = bytes(a)
class_defs_size = binascii.b2a_hex(class_defs_size)
class_defs_size = str(class_defs_size,encoding='utf-8')
print('类定义数量: ',end='')
print(int(class_defs_size,16),end='')
print('(',end='')
print(hex(int(class_defs_size,16)),end='')
print(')')

f.seek(0x64)
class_defs_off = f.read(4)
a = bytearray(class_defs_off)
a.reverse()
class_defs_off = bytes(a)
class_defs_off = binascii.b2a_hex(class_defs_off)
class_defs_off = str(class_defs_off,encoding='utf-8')
print('类定义偏移位置: ',end='')
print(hex(int(class_defs_off,16)))

f.seek(0x68)
data_size = f.read(4)
a = bytearray(data_size)
a.reverse()
data_size = bytes(a)
data_size = binascii.b2a_hex(data_size)
data_size = str(data_size,encoding='utf-8')
print('数据段大小: ',end='')
print(int(data_size,16),end='')
print('(',end='')
print(hex(int(data_size,16)),end='')
print(')')

f.seek(0x6c)
data_off = f.read(4)
a = bytearray(data_off)
a.reverse()
data_off = bytes(a)
data_off = binascii.b2a_hex(data_off)
data_off = str(data_off,encoding='utf-8')
print('数据段偏移位置: ',end='')
print(hex(int(data_off,16)))

if __name__ == '__main__':
f = open("C:\\Users\\admin\\Desktop\\android_nx\\classes.dex", 'rb', True)
parserHeader(f)
f.close()

V. Related Links

Reference links

An author github link (related accessories download): https://github.com/windy-purple/parserDex

PS: Some pictures from the network, intrusion deleted