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re-rc4及其变种

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re-rc4及其变种

基本rc4

学习一个算法，最好还是编程下印象深刻些

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// re_rc4.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <Windows.h>

/*
S 状态向量
K 密钥
len 密钥长度
*/
void rc4_init(unsigned char* S, unsigned char* K, unsigned long len)
{
	char T[256] = { 0 }; //临时向量T
	unsigned char tmp = 0;
	for(int i=0; i<256; i++)
	{
		S[i] = i;
		T[i] = K[i%len];
	}
	int j = 0;
	for(int i=0; i<256; i++)
	{
		j = (j + S[i] + T[i]) % 256;
		int middle = S[i];
		S[i] = S[j];
		S[j] = middle;
	}
}

void rc4_crypt(unsigned char* S, unsigned char* Data, unsigned long len)
{
	int i = 0, j = 0, t = 0;
	unsigned long k = 0;
	unsigned char tmp;
	for(; k<len; k++)
	{
		i = (i + 1) % 256;
		j = (j + S[i]) % 256;
		tmp = S[i];
		S[i] = S[j];
		S[j] = tmp;
		t = (S[i] + S[j]) % 256;
		Data[k] ^= S[t];
	}
}
int main()
{
	unsigned char s[256] = { 0 }, s2[256] = { 0 }; // S-box
	char key[256] = { "justfortest" };
	char pData[512] = "这是一个用来加密的数据Data";
	unsigned long len = strlen(pData);
	int i;

	printf("pData=%s\n", pData);
	printf("key=%s,length=%d\n\n", key, strlen(key));
	rc4_init(s, (unsigned char*)key, strlen(key)); // 已经完成了初始化
	printf("完成对S[i]的初始化，如下：\n\n");
	for (i = 0; i < 256; i++)
	{
		printf("%02X", s[i]);
		if (i && (i + 1) % 16 == 0)putchar('\n');
	}
	printf("\n\n");
	for (i = 0; i < 256; i++) // 用s2[i]暂时保留经过初始化的s[i]，很重要的！！！
	{
		s2[i] = s[i];
	}
	printf("已经初始化，现在加密:\n\n");
	rc4_crypt(s, (unsigned char*)pData, len); // 加密
	printf("pData=%s\n\n", pData);
	printf("已经加密，现在解密:\n\n");
	rc4_crypt(s2, (unsigned char*)pData, len); // 解密
	printf("pData=%s\n\n", pData);
	getchar();
	return 0;
}

而这里，所以我们只需要截取

pData加密过后数据，key，2个变量我们就可以解密了

利用py2的Crypto库

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#coding=utf-8
from Crypto.Cipher import *
data = "7C553E5F0EB4CCB977BF6BD960E0B968FB11CED2154B0EB5F73E51EE514D5A9C01A0C53AD038"
data= data.decode("hex")
key = "SimpleCryptography"
cipher = ARC4.new(key)    #加载密钥
m = cipher.decrypt(data)   #用该密钥解密
print(m)

或者py3

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from Crypto.Cipher import ARC4
import binascii
import struct

#rc4 = ARC4.new(struct.pack("<Q", 0x6a757374666f7274657374))
rc4 = ARC4.new(b"SimpleCryptography")
data = binascii.unhexlify("7C553E5F0EB4CCB977BF6BD960E0B968FB11CED2154B0EB5F73E51EE514D5A9C01A0C53AD038")
print(rc4.decrypt(data))

为了应对变种，这里给出一份python2的rc4实现

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# -*- coding: utf-8 -*-
import random, base64

def rc4_crypt(data, key):
    """RC4 algorithm"""
    x = 0
    box = range(256)
    for i in range(256):
        x = (x + box[i] + ord(key[i % len(key)])) % 256
        temp = box[i]
        box[i] = box[x]
        box[x] = temp
    x = y = 0
    out = []
    for char in data:
        x = (x + 1) % 256
        y = (y + box[x]) % 256
        temp = box[x]
        box[x] = box[y]
        box[y] = temp
        out.append(chr(ord(char) ^ box[(box[x] + box[y]) % 256]))

    return ''.join(out)

if __name__ == '__main__':
    data="c9deea9964ca63e5b389a6ac6358a582fc4befb11334".decode("hex")
    key = "Please input the flag:\n"
    print(rc4_crypt(data,key))

python3

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# coding: utf-8
 
# import base64
import binascii
 
 
def rc4_crypt(PlainBytes:bytes, KeyBytes:bytes) -> str:
    '''[summary]
    rc4 crypt
    Arguments:
        PlainBytes {[bytes]} -- [plain bytes]
        KeyBytes {[bytes]} -- [key bytes]
    
    Returns:
        [string] -- [hex string]
    '''
 
    keystreamList = []
    cipherList = []
 
    keyLen = len(KeyBytes)
    plainLen = len(PlainBytes)
    S = list(range(256))
 
    j = 0
    for i in range(256):
        j = (j + S[i] + KeyBytes[i % keyLen]) % 256
        temp = S[i]
        S[i] = S[j]
        S[j] = S[i]
        #S[i], S[j] = S[j], S[i]
 
    i = 0
    j = 0
    for m in range(plainLen):
        i = (i + 1) % 256
        j = (j + S[i]) % 256
        S[i], S[j] = S[j], S[i]
        k = S[(S[i] + S[j]) % 256]
        cipherList.append(k ^ PlainBytes[m])
 
    result_hexstr = ''.join(['%02x' % i for i in cipherList])
    return result_hexstr.upper()
 
 
if __name__ == "__main__":
    data = '43C8B53E236C4756B8FF24E5AA08A549'
    key = '3C381919191918181818181817111111'
    rc4_result = 'BC9CD0200AB174B467956B4CAE2178BE'
    print(f'data:{data}\nkey:{key}\nrc4_original:{rc4_result}')
    print("rc4 result:", rc4_crypt(binascii.a2b_hex(data), binascii.a2b_hex(key.upper())))

这样对着代码稍作改动就可以解密

变种rc4–写错的rc4

稍微做了点改动的rc4，你能看出来吗

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// re_rc4.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <Windows.h>

/*
S 状态向量
K 密钥
len 密钥长度
*/
void rc4_init(unsigned char* S, unsigned char* K, unsigned long len)
{
	char T[256] = { 0 }; //临时向量T
	unsigned char tmp = 0;
	for(int i=0; i<256; i++)
	{
		S[i] = i;
		T[i] = K[i%len];
	}
	int j = 0;
	for(int i=0; i<256; i++)
	{
		j = (j + S[i] + T[i]) % 256;
		int middle = S[i];
		S[i] = S[j];
		S[j] = middle;
	}
}

void rc4_crypt(unsigned char* S, unsigned char* Data, unsigned long len)
{
	int i = 0, j = 0, t = 0;
	unsigned long k = 0;
	unsigned char tmp;
	for(; k<len; k++)
	{
		i = (i + 1) % 256;
		j = (j + S[i]) % 256;
		tmp = S[i];
		S[i] = S[j];
		S[j] = tmp;
		t = (S[i] + S[j]) % 256;
		Data[k] ^= S[t];
	}
}
int main()
{
	unsigned char s[256] = { 0 }, s2[256] = { 0 }; // S-box
	char key[256] = { "justfortest" };
	char pData[512] = "这是一个用来加密的数据Data";
	unsigned long len = strlen(pData);
	int i;
	rc4_init(s, (unsigned char*)key, strlen(key)); // 已经完成了初始化
	for (i = 0; i < 256; i++) // 用s2[i]暂时保留经过初始化的s[i]，很重要的！！！
	{
		s2[i] = s[i];
	}
	rc4_crypt(s, (unsigned char*)pData, len); // 加密
	rc4_crypt(s2, (unsigned char*)pData, len); // 解密
	return 0;
}

解密算法

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# coding: utf-8
 
# import base64
import binascii
 
 
def rc4_crypt(PlainBytes:bytes, KeyBytes:bytes) -> str:
    '''[summary]
    rc4 crypt
    Arguments:
        PlainBytes {[bytes]} -- [plain bytes]
        KeyBytes {[bytes]} -- [key bytes]
    
    Returns:
        [string] -- [hex string]
    '''
 
    keystreamList = []
    cipherList = []
 
    keyLen = len(KeyBytes)
    plainLen = len(PlainBytes)
    S = list(range(256))
 
    j = 0
    for i in range(256):
        j = (j + S[i] + KeyBytes[i % keyLen]) % 256
        temp = S[i]
        S[i] = S[j]
        S[j] = S[i]
        #S[i], S[j] = S[j], S[i]
 
    i = 0
    j = 0
    for m in range(plainLen):
        i = (i + 1) % 256
        j = (j + S[i]) % 256
        S[i], S[j] = S[j], S[i]
        k = S[(S[i] + S[j]) % 256]
        cipherList.append(k ^ PlainBytes[m])
 
    result_hexstr = ''.join(['%02x' % i for i in cipherList])
    return result_hexstr.upper()
 
 
if __name__ == "__main__":
    data = '43C8B53E236C4756B8FF24E5AA08A549'
    key = '3C381919191918181818181817111111'
    rc4_result = 'BC9CD0200AB174B467956B4CAE2178BE'
    print('data:',data , 'key', key, 'rc4_result:',rc4_result)
    print("rc4 result:", rc4_crypt(binascii.a2b_hex(data), binascii.a2b_hex(key.upper())))

变种rc4–带偏移的rc4

rc4_init这里还是很明显的

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bool __fastcall sub_401760(__int64 a1, __int64 a2, __int64 a3, _DWORD *a4, int a5)
{
  bool result; // al
  int v6; // ST04_4
  signed __int64 v7; // [rsp+8h] [rbp-18h]
  int v8; // [rsp+14h] [rbp-Ch]
  int v9; // [rsp+18h] [rbp-8h]
  signed int i; // [rsp+1Ch] [rbp-4h]
  signed int j; // [rsp+1Ch] [rbp-4h]

  *a4 = 0;
  a4[1] = 0;
  v7 = (a4 + 2);
  for ( i = 0; i <= 255; ++i )
    *(v7 + 4LL * i) = i;
  v8 = 0;
  result = 0;
  LOBYTE(v9) = 0;
  for ( j = 0; j <= 255; ++j )
  {
    v6 = *(4LL * j + v7);
    v9 = (v9 + v6 + *(v8 + a3));
    *(v7 + 4LL * j) = *(4LL * v9 + v7);
    *(v7 + 4LL * v9) = v6;
    result = ++v8 >= a5;
    if ( v8 >= a5 )
      v8 = 0;
  }
  return result;
}

这里做了点变化

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_DWORD *__fastcall sub_40188D(__int64 a1, __int64 a2, __int64 a3, _DWORD *a4, int a5)
{
  int v5; // ST04_4
  int v6; // ST00_4
  _DWORD *result; // rax
  signed __int64 v8; // [rsp+8h] [rbp-18h]
  int v9; // [rsp+14h] [rbp-Ch]
  int v10; // [rsp+18h] [rbp-8h]
  int i; // [rsp+1Ch] [rbp-4h]

  v10 = *a4;
  v9 = a4[1];
  v8 = (a4 + 2);
  for ( i = 0; i < a5; ++i )
  {
    v10 = (v10 + 1);
    v5 = *(4LL * v10 + v8);
    v9 = (v9 + v5);
    v6 = *(4LL * v9 + v8);
    *(v8 + 4LL * v10) = v6;
    *(v8 + 4LL * v9) = v5;
    *(i + a3) ^= *(4LL * (v5 + v6 + 24) + v8); //重点 24
  }
  *a4 = v10;
  result = a4;
  a4[1] = v9;
  return result;
}

这里加了偏移,24

变种的解密

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# -*- coding: utf-8 -*-
import random, base64

def rc4_crypt(data, key):
    """RC4 algorithm"""
    x = 0
    box = range(256)
    for i in range(256):
        x = (x + box[i] + ord(key[i % len(key)])) % 256
        box[i], box[x] = box[x], box[i]
    x = y = 0
    out = []
    for char in data:
        x = (x + 1) % 256
        y = (y + box[x]) % 256
        box[x], box[y] = box[y], box[x]
        out.append(chr(ord(char) ^ box[(box[x] + box[y]+24) % 256]))

    return ''.join(out)

if __name__ == '__main__':
    data="c9deea9964ca63e5b389a6ac6358a582fc4befb11334".decode("hex")
    key = "Please input the flag:\n"
    print(rc4_crypt(data,key))

本文作者：NoOne
本文地址： https://noonegroup.xyz/posts/95c19a10/
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