woody-woodpacker

simple elf64 binary encryptor

building:

make

usage:

usage: ./woody_woodpacker [-d -k key] binary

-k option to specify and encryption key

-d option to decrypt an encrypted binary

logic:

• find .text section, get file offset and size
• find LOAD segment which contains the .text section
• go to end of segment and check if there are enough null bytes to insert decryptor
• if yes, encrypt .text section, insert decryptor at the end of segment, increase segment size
• save entry point, start address and size of .text section in decryptor
• change entry point in elf header to point to decryptor

encryption:

random 64 bit key from /dev/urandom

for each byte of data:

• simple xor with lower 8 bits of key,
• rotate key to the right >> by 1

sample:

root@debian:/home/user/woody-woodpacker# cat hello.c 
#include <stdio.h>
int main()
{
	puts("Hello World!");
	return 0;
}
root@debian:/home/user/woody-woodpacker# gcc hello.c -o hello
root@debian:/home/user/woody-woodpacker# ./woody_woodpacker hello
encryption key = 0x334f9db9c8c89c93
root@debian:/home/user/woody-woodpacker# ./woody
..WOODY..
Hello World!
root@debian:/home/user/woody-woodpacker# 

comparison of hexdumps: before and after encryption

intra