ida64打开，查看伪代码
unsigned __int64 Decry()
{
char v1; // [rsp+Fh] [rbp-51h]
int v2; // [rsp+10h] [rbp-50h]
int v3; // [rsp+14h] [rbp-4Ch]
int i; // [rsp+18h] [rbp-48h]
int v5; // [rsp+1Ch] [rbp-44h]
char src[8]; // [rsp+20h] [rbp-40h]
__int64 v7; // [rsp+28h] [rbp-38h]
int v8; // [rsp+30h] [rbp-30h]
__int64 v9; // [rsp+40h] [rbp-20h]
__int64 v10; // [rsp+48h] [rbp-18h]
int v11; // [rsp+50h] [rbp-10h]
unsigned __int64 v12; // [rsp+58h] [rbp-8h]
v12 = __readfsqword(0x28u);
*(_QWORD *)src = 357761762382LL;// 数据转为16进制为‘0x534c43444e’数据在内存中是小端顺序，高位在高地址处，低位在低地址处，故实际的字符顺序应为'0x4e44434c53'转为字符为'NDCLS'
v7 = 0LL;
v8 = 0;
v9 = 512969957736LL; // 同理解出为'hadow'
v10 = 0LL;
v11 = 0;
text = (char *)join(key3, &v9); // key3='kills' ;这个join函数，就是把key3和v9两个字符串相连即'killshadow'
strcpy(key, key1);
strcat(key, src); // key1 = 'ADSFK',key = 'ADSFKNDCLS'
v2 = 0;
v3 = 0;
getchar();
v5 = strlen(key); // v5=10
for ( i = 0; i < v5; ++i )
{
if ( key[v3 % v5] > 64 && key[v3 % v5] <= 90 )// 将key的字符转为小写的算法,即key = 'adsfkndcls'
key[i] = key[v3 % v5] + 32;
++v3;
}
printf("Please input your flag:", src);
while ( 1 )
{
v1 = getchar();
if ( v1 == 10 )
break;
if ( v1 == 32 )
{
++v2;
}
else
{
if ( v1 <= 96 || v1 > 122 )
{
if ( v1 > 64 && v1 <= 90 )
str2[v2] = (v1 - 39 - key[v3++ % v5] + 97) % 26 + 97;
}
else
{
str2[v2] = (v1 - 39 - key[v3++ % v5] + 97) % 26 + 97;
}
if ( !(v3 % v5) )
putchar(32);
++v2;
}
}
if ( !strcmp(text, str2) )
puts("Congratulation!\n");
else
puts("Try again!\n");
return __readfsqword(0x28u) ^ v12;
}
先是将两个字符串拼接成keys，然后转化为小写，然后将其进行了加密，再与text进行比较
脚本
text = 'killshadow'
key = 'adsfkndcls'
#暴力字典破解
v3=0
v5=len(key)
dict1="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
flag = ""
for i in range(0,10):
n=0
for char in dict1:
x = (ord(char) - 39 - ord(key[v3%v5])+97)%26+97
if(chr(x)==text[i]):
n = n+1
if(n==1):
print(char,end="")
v3=v3+1
flag{KLDQCUDFZO}