/* MSNMessenger的口令是经过DPAPI加密后保存在注册表中的

• 这个程序演示解码过程
  

• tombkeeper[0x40]nsfocus[0x2e]com
  

• tombkeeper[0x40]xfocus[0x2e]net
  

• 2004.08.11
  

*/

include

pragma comment(lib, "Advapi32.lib")

define FCHK(a) if (!(a)) {printf(#a " failed"); return 0;}

typedef struct _CRYPTOAPI_BLOB {

DWORD cbData;
BYTE* pbData;

} DATA_BLOB;

typedef struct _CRYPTPROTECT_PROMPTSTRUCT {

DWORD cbSize;
DWORD dwPromptFlags;
HWND hwndApp;
LPCWSTR szPrompt;

} CRYPTPROTECT_PROMPTSTRUCT, *PCRYPTPROTECT_PROMPTSTRUCT;

typedef BOOL (WINAPI *PCryptUnprotectData)(

DATA_BLOB* pDataIn,
LPWSTR* ppszDataDescr,
DATA_BLOB* pOptionalEntropy,
PVOID pvReserved,
CRYPTPROTECT_PROMPTSTRUCT* pPromptStruct,
DWORD dwFlags,
DATA_BLOB* pDataOut

);

PCryptUnprotectData CryptUnprotectData = NULL;

int main(void)

{

int ret;
HMODULE hNtdll; HKEY hKey;
DWORD dwType;
char Data[0x100] = {0};
DWORD dwSize; DATA_BLOB DataIn;
DATA_BLOB DataOut; ret = RegOpenKeyEx
(
HKEY_CURRENT_USER,
"Software\\Microsoft\\MSNMessenger",
0,
KEY_READ,
&hKey
);
if( ret != ERROR_SUCCESS ) return 1; ret = RegQueryValueEx
(
hKey,
"Password.NET Messenger Service",
NULL,
&dwType,
Data,
&dwSize
);
if( ret != ERROR_SUCCESS ) return 1; FCHK ((hNtdll = LoadLibrary ("Crypt32.dll")) != NULL);
FCHK ((CryptUnprotectData = (PCryptUnprotectData)
GetProcAddress (hNtdll, "CryptUnprotectData")) != NULL); DataIn.pbData = Data 2; //口令密文从第二位开始
DataIn.cbData = dwSize-2; CryptUnprotectData
(
&DataIn,
NULL,
NULL,
NULL,
NULL,
1,
&DataOut
); base64_decode (DataOut.pbData, Data, strlen(DataOut.pbData));
printf ( "MSN Password: %s", Data);
return 0;

}

//copied from GNU libc - libc/resolv/base64.c

int base64_decode (char const src, char target, size_t targsize)

{

static const char Base64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789 /";
static const char Pad64 = ’=’; int tarindex, state, ch;
char *pos; state = 0;
tarindex = 0; while ((ch = *src) != ’\0’)
{
if (isspace (ch)) /* Skip whitespace anywhere. */
continue; if (ch == Pad64)
break; pos = strchr (Base64, ch);
if (pos == 0) /* A non-base64 character. */
return (-1); switch (state)
{
case 0:
if (target)
{
if ((size_t) tarindex >= targsize)
return (-1);
target[tarindex] = (pos - Base64) }
state = 1;
break;
case 1:
if (target)
{
if ((size_t) tarindex 1 >= targsize)
return (-1);
target[tarindex] |= (pos - Base64) >> 4;
target[tarindex 1] = ((pos - Base64) & 0x0f) }
tarindex;
state = 2;
break;
case 2:
if (target)
{
if ((size_t) tarindex 1 >= targsize)
return (-1);
target[tarindex] |= (pos - Base64) >> 2;
target[tarindex 1] = ((pos - Base64) & 0x03) }
tarindex;
state = 3;
break;
case 3:
if (target)
{
if ((size_t) tarindex >= targsize)
return (-1);
target[tarindex] |= (pos - Base64);
}
tarindex;
state = 0;
break;
default:
abort ();
}
}

/*

• We are done decoding Base-64 chars.Let’s see if we ended
  

• on a byte boundary, and/or with erroneous trailing characters.
  

*/

if (ch == Pad64)
{ /* We got a pad char. */
ch = *src;/* Skip it, get next. */
switch (state)
{
case 0: /* Invalid = in first position */
case 1: /* Invalid = in second position */
return (-1); case 2: /* Valid, means one byte of info */
/* Skip any number of spaces. */
for ((void) NULL; ch != ’\0’; ch = *src)
if (!isspace (ch))
break;
/* Make sure there is another trailing = sign. */
if (ch != Pad64)
return (-1);
ch = *src;/* Skip the = */
/* Fall through to "single trailing =" case. */
/* FALLTHROUGH */ case 3: /* Valid, means two bytes of info */
/*
* We know this char is an =.Is there anything but
* whitespace after it?
*/
for ((void) NULL; ch != ’\0’; ch = *src)
if (!isspace (ch))
return (-1); /*
* Now make sure for cases 2 and 3 that the "extra"
* bits that slopped past the last full byte were
* zeros.If we don’t check them, they become a
* subliminal channel.
*/
if (target && target[tarindex] != 0)
return (-1);
}
}
else
{
/*
* We ended by seeing the end of the string.Make sure we
* have no partial bytes lying around.
*/
if (state != 0)
return (-1);
} return (tarindex);

}