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[原创]第六题：消失的岛屿
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发表于: 2019-6-15 21:26
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载入IDA：
通过变形的base64对输入字符串加密，与“!NGV%,$h1f4S3%2P(hkQ94==”比较，相等则成功，否则重试。
int __cdecl base64_encode(const uint8_t *bindata, char *base64, int binlength)
{
int v3; // eax
char *v4; // ebx
int v5; // eax
int v6; // ST0C_4
char *v7; // ebx
int v8; // eax
int v9; // eax
char *v10; // ebx
int v11; // eax
int v12; // eax
char *v13; // ebx
uint8_t current; // [esp+Bh] [ebp-Dh]
uint8_t currenta; // [esp+Bh] [ebp-Dh]
int j; // [esp+Ch] [ebp-Ch]
int ja; // [esp+Ch] [ebp-Ch]
int jb; // [esp+Ch] [ebp-Ch]
int i; // [esp+10h] [ebp-8h]
i = 0;
j = 0;
while ( i < binlength )
{
v3 = j;
ja = j + 1;
v4 = &base64[v3];
*v4 = charEncrypt((bindata[i] >> 2) & 0x3F);
current = 16 * bindata[i] & 0x30;
if ( i + 1 >= binlength )
{
v5 = ja;
v6 = ja + 1;
v7 = &base64[v5];
*v7 = charEncrypt(current);
base64[v6] = 61;//‘=’
v8 = v6 + 1;
j = v6 + 2;
base64[v8] = 61;//‘=’
break;
}
v9 = ja;
jb = ja + 1;
v10 = &base64[v9];
*v10 = charEncrypt((bindata[i + 1] >> 4) | current);
currenta = 4 * bindata[i + 1] & 0x3C;
if ( i + 2 >= binlength )
{
base64[jb] = charEncrypt(currenta);
v11 = jb + 1;
j = jb + 2;
base64[v11] = 61;//‘=’
break;
}
base64[jb] = charEncrypt((bindata[i + 2] >> 6) | currenta);
v12 = jb + 1;
j = jb + 2;
v13 = &base64[v12];
*v13 = charEncrypt(bindata[i + 2] & 0x3F);
i += 3;
}
base64[j] = 0;
return j;
}
int __cdecl base64_encode(const uint8_t *bindata, char *base64, int binlength)
{
int v3; // eax
char *v4; // ebx
int v5; // eax
int v6; // ST0C_4
char *v7; // ebx
int v8; // eax
int v9; // eax
char *v10; // ebx
int v11; // eax
int v12; // eax
char *v13; // ebx
uint8_t current; // [esp+Bh] [ebp-Dh]
uint8_t currenta; // [esp+Bh] [ebp-Dh]
int j; // [esp+Ch] [ebp-Ch]
int ja; // [esp+Ch] [ebp-Ch]
int jb; // [esp+Ch] [ebp-Ch]
int i; // [esp+10h] [ebp-8h]
i = 0;
j = 0;
while ( i < binlength )
{
v3 = j;
ja = j + 1;
v4 = &base64[v3];
*v4 = charEncrypt((bindata[i] >> 2) & 0x3F);
current = 16 * bindata[i] & 0x30;
if ( i + 1 >= binlength )
{
v5 = ja;
v6 = ja + 1;
v7 = &base64[v5];
*v7 = charEncrypt(current);
base64[v6] = 61;//‘=’
v8 = v6 + 1;
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