DEX文件解析---1、dex文件头解析

DEX文件解析---1、dex文件头解析

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一、dex文件

    dex文件是Android平台上可执行文件的一种文件类型。它的文件格式可以下面这张图概括：



    dex文件头一般固定为0x70个字节大小，包含标志、版本号、校验码、sha-1签名以及其他一些方法、类的数量和偏移地址等信息。如下图所示：

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二、dex文件头各字段解析

    dex文件头包含以下各个字段：

1. magic:包含了dex文件标识符以及版本，从0x00开始，长度为8个字节
2. checksum:dex文件校验码，偏移量为:0x08，长度为4个字节。
3. signature:dex sha-1签名，偏移量为0x0c,长度为20个字节
4. file_szie:dex文件大小，偏移量为0x20，长度为4个字节
5. header_size:dex文件头大小，偏移量为0x24，长度为4个字节，一般为0x70
6. endian_tag:dex文件判断字节序是否交换，偏移量为0x28，长度为4个字节，一般情况下为0x78563412
7. link_size:dex文件链接段大小，为0则表示为静态链接，偏移量为0x2c，长度为4个字节
8. link_off:dex文件链接段偏移位置，偏移量为0x30，长度为4个字节
9. map_off:dex文件中map数据段偏移位置，偏移位置为0x34，长度为4个字节
10. string_ids_size:dex文件包含的字符串数量，偏移量为0x38，长度为4个字节
11. string_ids_off:dex文件字符串开始偏移位置，偏移量为0x3c，长度为4个字节
12. type_ids_size:dex文件类数量，偏移量为0x40，长度为4个字节
13. type_ids_off:dex文件类偏移位置，偏移量为0x44，长度为4个字节
14. photo_ids_size:dex文件中方法原型数量，偏移量为0x48，长度为4个字节
15. photo_ids_off:dex文件中方法原型偏移位置，偏移量为0x4c，长度为4个字节
16. field_ids_size:dex文件中字段数量，偏移量为0x50，长度为4个字节
17. field_ids_off:dex文件中字段偏移位置，偏移量为0x54，长度为4个字节
18. method_ids_size:dex文件中方法数量，偏移量为0x58，长度为4个字节
19. method_ids_off:dex文件中方法偏移位置，偏移量为0x5c，长度为4个字节
20. class_defs_size:dex文件中类定义数量，偏移量为0x60，长度为4个字节
21. class_defs_off:dex文件中类定义偏移位置，偏移量为0x64，长度为4个字节
22. data_size:dex数据段大小，偏移量为0x68，长度为4个字节
23. data_off:dex数据段偏移位置，偏移量为0x6c，长度为4个字节

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三、dex文件头代码解析示例(python)

    dex使用open函数以二进制打开文件，然后使用seek函数移动文件指针，例如magic就是f.seek(0x00)，然后读取相应信息的字节数即可，例如读取版本号f.seek(0x04) f.read(4)，然后做相应打印操作就行，dex文件头较简单，不涉及编码等，所以解析起来感觉脑子都不用带。。。。。具体代码可以看下面或者github，下面附上代码运行图：

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四、dex文件头解析实现代码(python实现)

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()

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五、相关链接

  参考链接

• https://blog.csdn.net/tabactivity/article/details/78950379
• https://blog.csdn.net/sinat_18268881/article/details/55832757

  某作者github链接(相关附件下载)：https://github.com/windy-purple/parserDex

  PS:部分图片来自于网络，侵删