Here is a couple of message about my phone encoding format (giving
progressively more info to a person trying to guess the format) followed
by the complete source... Use it well. (TABsize was 3.)
Okay, well without giving you the source... heres the biggest hint I can
think of...
From /etc/magic:
0 string \037\235 compressed data
Translating that to decimal and in 4 byte unsigned long we get
(\037\235\0\0 == 31,157,0,0 == 0,530,382,848
^^^^^
From the start of my posted list of phone numbers:
(503) 241-9796 ext: 09
^^^ ^
?? ?
If you know the rules for forming (valid looking) phone numbers...
Anyway, to finially give the whole thing away...
The file that is hidden starts with these 4 bytes...
1f 9d 90 54 == 0,530,419,796
Well.. I like puzzles... (as long as the answer is eventually revealed) so
I'll let you think it over for a bit, before I send you the source... ;-)
Okay well... lets assume that all valid phone numbers must be in the form
[2-9][0-1][0-9] [2-9][0-9][0-9] [0-9][0-9][0-9][0-9]
This is the form of my encoding... now if you take a sample number, like
1,234,567,890
and try encode it into a phone number, you would get
(123) 456-7890
^^
And you notice that the 1 and the two are out of range...
Well.. as it happens, for 32 bit unsigned numbers the range is 0 to
4,294,967,294... The first digit will always be 0-4, half of which are
illegal in that position, so I decided to swap the first two digits...
That doesn't fix all of the range problems, thus whenever there is an
invalid digit in position 1,2 or 4 I move it to the extension and put a
special indicator value (the higest of the legal range) in its place.
Thats the whole secret... Code will follow soon... :-)
/*
pe.c
phone encode
Written by:
Nickey MacDonald
July 7, 1993
Encode a message as a list of phone numbers... There are some tricks
used to make the phone numbers appear more realistic, and there is a
caveate... If the input file has 4 null bytes aligned of a 4 byte
boundry, then the program will think its the EOF and stop... This
could be fixed easily... I just didn't.
*/
#include
unsigned long getbytes(FILE *fp);
int main(void)
{
unsigned short i, ei; /* i=work counter, ei=ext. counter */
unsigned char pn[10], ext[4], v=0; /* Digits of phone num, ext and a */
/* pseudo random value */
unsigned long b; /* 4 bytes compress to a unsigned long */
char tpnumbuf[11]; /* a sprinft buffer for b */
/* Read until EOF or 4 properly aligned null bytes */
while((b=getbytes(stdin)) != 0)
{
ei=0;
/* Convert the unsigned long into a string */
sprintf(tpnumbuf, "%010lu", b);
/* Pick up the digits of the unsigned long */
/* Because of the distribution, swap the first two digits... */
pn[0]=tpnumbuf[1]-'0';
pn[1]=tpnumbuf[0]-'0';
for(i=2; i<10; i++)
{
pn[i]=tpnumbuf[i]-'0';
v+=pn[i];
}
/* The first digit of the area code must be [2-9] */
if (pn[0]<3)
{
ext[ei++]=pn[0];
pn[0]=2;
}
/* Currently the middle digit of area code must be 0 or 1 */
if (pn[1]>0)
{
ext[ei++]=pn[1];
pn[1]=1;
}
/* The first digit of prefix must be [2-9] */
if (pn[3]<3)
{
ext[ei++]=pn[3];
pn[3]=2;
}
/* Generate the output phone number */
fprintf(stdout, "(%d%d%d) %d%d%d-%d%d%d%d", pn[0], pn[1], pn[2],
pn[3], pn[4], pn[5],
pn[6], pn[7], pn[8], pn[9]);
/* Generate the extension if needed */
if (ei>0)
{
ext[ei++]=v%10;
fprintf(stdout, " ext: ");
for (i=0; i
void putbytes(FILE *fp, unsigned long val);
int main(void)
{
unsigned short i, ei; /* i=work counter, ei=extention work counter */
unsigned char pn[10]; /* The digits of the phone number */
unsigned long b; /* The finally decoded value from the phone num */
char pnline[30]; /* Input line buffer */
int flg=0; /* The error message is only output once */
/* Read lines until end of file */
while((fgets(pnline, 30, stdin)) != NULL)
{
/* error checking */
if ((pnline[0] != '(') ||
(pnline[4] != ')') ||
(pnline[9] != '-'))
{
if (flg==0)
{
fprintf(stderr, "Input not in correct format, output will be garbage!\n");
flg=1;
}
}
/* Extract the digits of the phone number, and convert from ASCII */
pn[0]=pnline[1]-'0';
pn[1]=pnline[2]-'0';
pn[2]=pnline[3]-'0';
pn[3]=pnline[6]-'0';
pn[4]=pnline[7]-'0';
pn[5]=pnline[8]-'0';
pn[6]=pnline[10]-'0';
pn[7]=pnline[11]-'0';
pn[8]=pnline[12]-'0';
pn[9]=pnline[13]-'0';
/* The first digit of the extension should be the 21st loc of input buf */
ei=21;
/* The first digit of an area code is always [2-9] */
if (pn[0]==2)
{
pn[0]=pnline[ei++]-'0';
}
/* Currently, the middle digit of area code is always 0 or 1 */
if (pn[1]==1)
{
pn[1]=pnline[ei++]-'0';
}
/* The first digit of a prefix is always [2-9] */
if (pn[3]==2)
{
pn[3]=pnline[ei++]-'0';
}
/* Swap first two digits */
i=pn[0];
pn[0]=pn[1];
pn[1]=i;
/* Encode the individualt digits into a unsigned long */
b=0;
for(i=0; i<10; i++)
b=b*10+pn[i];
/* output the decoded bytes */
putbytes(stdout, b);
}
return(0);
}
/* Simple encoding... 4 bytes to the longword... seperate them here */
void putbytes(FILE *fp, unsigned long val)
{
int b[4];
b[0]=(int)(val>>24 & 255);
b[1]=(int)(val>>16 & 255);
b[2]=(int)(val>> 8 & 255);
b[3]=(int)(val & 255);
fprintf(fp, "%c%c%c%c", b[0], b[1], b[2], b[3]);
}
--
Nick MacDonald | NMD on IRC
i6t4@jupiter.sun.csd.unb.ca | PGP 2.1 Public key available via finger
i6t4@unb.ca | (506) 457-1931 ^{1024/746EBB 1993/02/23}
