How to find the Bios Master Password for Dell 595B 2A7B A95B computers

Usually to reset the Bios' password is enough to remove the battery from the mainboard but this isn't true for all the computers.

Dell saves the bios' password in a little flash memory placed in the mainboard and so it isn't possible reset it simply removing the power to the Bios, officially the only way to remove the password from a computer that is locked with a password bios is to get in touch with the Dell Customer Assistance and provide the service tag, thanks to which it is possible generate the Bios Master Password that allows to unlock the Bios.

A russian hacker, hpgl, has found the algorithm used by Dell to generate the Master Password for the Bios 595B, 2A7B, A95B and he wrote this C code that allows to generate the password self alone:

#include <stdio.h>
#include <string.h>
#include <time.h>
#define mystr "My own utility. Copyright (C) 2007-2010 hpgl, Russia"
#define allow595B
#define allowA95B
#define allow2A7B
#define fSVCTAG 0
#define fHDDSN 1
#define fHDDold 2
#define t595B 0
#define tD35B 1
#define tA95B 2
#define t2A7B 3
#ifdef allow595B
#define f595B
#ifdef allowA95B
#define f595B
#ifdef allow2A7B
#define f595B
char bSuffix[]="595BD35BA95B2A7B";
char scancods[]="\00\0331234567890-=\010\011qwertyuiop[]\015\377asdfghjkl;'`\377\\zxcvbnm,./";
char encscans[]={0x05,0x10,0x13,0x09,0x32,0x03,0x25,0x11,0x1F,0x17,0x06,0x15, \
                 0x30,0x19,0x26,0x22,0x0A,0x02,0x2C,0x2F,0x16,0x14,0x07,0x18, \
#ifdef allow2A7B
char chartabl2A7B[72]="012345679abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ0";
unsigned int MD5magic[64]={
0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x4881d05,
0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391};
unsigned char inData[23],outData[16];
char buf1output[32], buf1input[20];
char bug4;
void calcsuffix(char bfunc, char btype, char *outbuf);
void initData(void) {
	*(int *)(&outData[0]) =0x67452301;
	*(int *)(&outData[4]) =0xEFCDAB89;
	*(int *)(&outData[8]) =0x98BADCFE;
	*(int *)(&outData[12])=0x10325476;
typedef int (encfuncT1) (int num1, int num2, int num3);
#ifdef f595B
int enc0F2(int num1, int num2, int num3) {return (((~num3 ^ num2) & num1) ^ ~num3);}
int enc0F4(int num1, int num2, int num3) {return (( ~num2 ^ num1) ^ num3); }
int enc0F5(int num1, int num2, int num3) {return (( ~num1 | ~num3) ^ num2); }
int enc1F2(int num1, int num2, int num3) {return ((( num3 ^ num2) & num1) ^ num3);}
int enc1F4(int num1, int num2, int num3) {return (( num2 ^ num1) ^ num3); }
int enc1F5(int num1, int num2, int num3) {return (( num1 | ~num3) ^ num2); }
int encF3 (int num1, int num2, int num3) {return ((( num1 ^ num2) & num3) ^ num2);}
typedef int (encfuncT2)(encfuncT1 func, int num1, int num2, int num3, int key);
int enc1F1 (encfuncT1 func, int num1, int num2, int num3, int key)
	return func(num1,num2,num3)+key;
#ifdef f595B
int enc0F1 (encfuncT1 func, int num1, int num2, int num3, int key)
	return func(num1,num2,num3)-key;
unsigned int rol(unsigned int t, int bitsrot)
	return (t >> (32-bitsrot)) | (t << bitsrot);
void blockEncodeF(int *outdata, int *encblock, encfuncT2 func1,
                  encfuncT1 func2, encfuncT1 func3, encfuncT1 func4, encfuncT1 func5 )
	char S[4][4] = {{ 7, 12, 17, 22 },{ 5, 9, 14, 20 },{ 4, 11, 16, 23 },{ 6, 10, 15, 21 }};
	int A,B,C,D,t,i;
	for (i=0;i<64;i++) { 		t=MD5magic[i]; 		switch (i>>4) {
			case 0: t=A+func1(func2,B,C,D, t+encblock[(i) & 15]); break;
			case 1: t=A+func1(func3,B,C,D, t+encblock[(i*5+1) & 15]); break;
			case 2: t=A+func1(func4,B,C,D, t+encblock[(i*3+5) & 15]); break;
			case 3: t=A+func1(func5,B,C,D, t+encblock[(i*7) & 15]); break;
		A=D; D=C; C=B; B+=rol(t,S[i>>4][i&3]);
void blockEncode(char *outdata, int *encblock, char btype) {
	if (btype==tD35B)
		blockEncodeF((int *)outdata,encblock,enc1F1,enc1F2,encF3,enc1F4,enc1F5);
#ifdef f595B
		blockEncodeF((int *)outdata,encblock,enc0F1,enc0F2,encF3,enc0F4,enc0F5);
void encode(char *inbuf,int cnt,char btype) {
	int encBlock[16];
	char *ptr;
	ptr=&((char *)encBlock)[cnt];
	encBlock[16-2]=((unsigned int)cnt << 3);
void psw(char bfunc, char btype, char *outbuf) {
	int cnt,i,lenpsw,r;
	if (bfunc==fHDDold) {
//		calcsuffix(bfunc,btype,outbuf);
		for (cnt=0;cnt<8;cnt++) 			outbuf[cnt]= scancods[ outbuf[cnt] ]; 	} else { 		memset(inData,0,sizeof(inData)); 		if (bfunc==fSVCTAG) cnt=7; 		else cnt=11; 		if ((bfunc==fHDDSN) && (btype==tA95B)) 			memcpy(inData,&buf1input[3],cnt-3); 		else 			memcpy(inData,buf1input,cnt); 		if (btype==t595B) memcpy(&inData[cnt],&bSuffix[0],4); else 		if (btype==tD35B) memcpy(&inData[cnt],&bSuffix[4],4); else 		if (btype==tA95B) memcpy(&inData[cnt],&bSuffix[0],4); else 		if (btype==t2A7B) memcpy(&inData[cnt],&bSuffix[12],4); 		cnt += 4; 		inData[cnt] = inData[4] & 0x1F; 		inData[cnt+1] = ((inData[4] >> 5) | (((inData[3] >> 5) | (inData[3] << 3)) & 0xF1) & 0x1F); 		inData[cnt+2] = ((inData[3] >> 2) & 0x1F);
		inData[cnt+3] = (inData[3] >> 7) | ((inData[2] << 1) & 0x1F); 		inData[cnt+4] = (inData[2] >> 4) | ((inData[1] << 4) & 0x1F); 		inData[cnt+5] = (inData[1] >> 1) & 0x1F;
		inData[cnt+6] = (inData[1] >> 6) | ((inData[0] << 2) & 0x1F); 		inData[cnt+7] = (inData[0] >> 3) & 0x1F;
		for (i=cnt;i<8+cnt;i++) {
			r = 0xAA;
			if (inData[i] & 1)
				r ^= inData[4];
			if (inData[i] & 2)
				r ^= inData[3];
			if (inData[i] & 4)
				r ^= inData[2];
			if (inData[i] & 8)
				r ^= inData[1];
			if (inData[i] & 16)
				r ^= inData[0];
			inData[i] = encscans[r % sizeof(encscans)];
		cnt = 23;
		r = outData[0] % 9;
		lenpsw = 0;
		for (cnt=0;cnt<16;cnt++) {
			if ((r <= cnt) && (lenpsw<8)) { 				buf1output[lenpsw++] = scancods[encscans[outData[cnt] % sizeof(encscans)]]; 			} 		} 	} } int main(int argc, char *argv[]) { 	unsigned char len,len1,bfunc,eol=1,echo=0, *minus,s2[20]; 	signed char btype; int argn=0; 	if (argc>1)
	if (!echo)
		fputs("" mystr "\n" \
		  "Short service tag should be right padded with '*' up to length 7 chars\n" \
		  "HDD serial number is right 11 chars from real HDDSerNum left padded with '*'\n" \
		  "Some BIOSes has left pad HDD serial number with spaces instead '*'\n",stdout);
	while (!feof(stdin)) {
		if ((argc<=1) && argn) break; 		fputs("Input: #",stdout); 		if (argc>1) {
		else {
			if (!eol) while (!feof(stdin) && (fgetc(stdin)!='\n')); eol=0;
			if (fgets(buf1input,16+1+1,stdin)==NULL) {
				if (echo) fputs("\n",stdout);
		if (len && (buf1input[len-1]=='\n')) {len--;eol=1;buf1input[len]=0;}
		if (echo) {fputs(buf1input,stdout);fputs("\n",stdout);}
		if (len==11) {
			if (minus!=NULL) {
				fputs("- Incorrect input\n",stdout);
			fputs("By HDD serial number for older BIOS: ",stdout);
		} else {
			if (len==0) break;
			if (minus==NULL) {
				fputs("- No BIOS type found in input string, must be followed by -595B and other registered\n",stdout);
			len1=minus-(unsigned char*)buf1input;
#ifdef allow595B
			if (strncmp(&buf1input[len1+1],&bSuffix[0],4)==0) btype=t595B;
			if (strncmp(&buf1input[len1+1],&bSuffix[4],4)==0) btype=tD35B;
#ifdef allowA95B
			if (strncmp(&buf1input[len1+1],&bSuffix[8],4)==0) btype=tA95B;
#ifdef allow2A7B
			if (strncmp(&buf1input[len1+1],&bSuffix[12],4)==0) btype=t2A7B;
			if (btype<0) {
				fputs("- Invalid service tag in input string, allowed only -D35B and other registered\n",stdout);
			struct tm *time1; time_t timer1=time(NULL);
			strftime(s2,sizeof(s2),"%d.%m.%Y %H:%M",time1);
			fputs(" DELL ",stdout);
			if (len1==7) {
				fputs("service tag: ",stdout);
			} else
			if (len1==11) {
				fputs("HDD serial number: ",stdout);
			else {
				fputs("- Incorrect input, must be 7 chars service tag or 11 chars HDD serial number\n",stdout);
		fputs(" password: ",stdout);
		if (bug4) fputs(" !bug4 warning - password may not work!",stdout);
		if (btype==t595B) if (bfunc==fSVCTAG) { //to check if A95B bug
			char mpw1[20];
			if (strcmp(mpw1,buf1output)!=0) {
				fputs(" passwordA95B: ",stdout);
	return 0;

The code and the Windows bin can be downloaded from this article in the Dogbert's blog and from which I here report the how-to:

  1. Download the archive of the keygen from the link above. It contains two files: a C file (source code) and an executable. If you are on Windows, just unpack and double-click the executable. If you are on Mac/Linux/BSD, compile the C file:
    gcc -o dell dell.c 
  2. You are asked to enter the serial number of your device. Use ONLY CAPITALS for the serial number.
  3. Press Enter and you'll get the password. Keep in mind that the passwords are encoded for a QWERTY-type keyboard layout (US-EN). Also, some models require you to press Ctrl+Enter after entering the password.

In this Dogbert's blog article there are others usefull informations about the BIOS Password Backdoors and there is more code wrote in python by the same blog's author to find the Bios Master Password for notebooks of various brands as Fujitsu-Siemens, HP, Sony, Samsung and for the generic Bios as Insyde H20 and Phoenix.

Вячеслав Бачериков converted in javascript the code by hpgl and di Dogbert and has created an online tool available at this address (sources).

These are the softwares used by the usual unscrupulous users who use the work of others to sell on the web the Bios Master Password at absurd prices and that Dogbert has repeatedly denounced on his blog(*).