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/*
* decode.c string decoding utilities
* Copyright (C) 2012-2018 Elio Blanca <eblanca76@users.sourceforge.net>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdlib.h>
#include <string.h>
/*
* This takes the command line strings starting at optind and concatenate them in order
* to build a long string. Then this string will be compared with the actual key (codename).
* Returns 0 if the strings don't match, nonzero otherwise.
*/
char validate (int argc, char **argv, int optind, int maxlen, char *codename)
{
char *source;
int avail=maxlen-1,i=0;
if (optind<argc)
{
/* `calloc' allocates and cleares the memory block before returning */
source=calloc((size_t)maxlen,sizeof(char));
if (source!=NULL) /* check allocate */
{
strncat(source,argv[optind],avail);
optind++;
avail-=strlen(source);
while ((optind<argc)&&(avail>1))
{
strncat(source," ",avail);
strncat(source,argv[optind],avail-1);
optind++;
avail=maxlen-strlen(source)-1;
}
/* command line string is now ready, now validate it */
avail=strlen(codename);
if ((int)strlen(source)==avail)
{
/* place white spaces corresponding to the white spaces in the codename
so the comparison will be easier */
/* to be extended for other critical characters */
for (i=0; i<avail; i++)
{
if (
codename[i]==' '
||
codename[i]=='\''
)
source[i]=codename[i];
}
i=!(strcasecmp(codename,source));
}
free(source);
}
}
return (char)i;
}
/*
* The scramble process itself is really trivial.
* This routine swaps the higher nibble from the first byte with the lower nibble from the last byte.
* Then it takes into account the second byte and the last but one byte and so on.
* The result is an un-readable string which can be un-scrambled using the same process
* (it is a symmetrical coding). The source data into 'scrambled.h' are calculated this way.
*/
void scramble (char *s, int len)
/* `s' is the source string to be scrambled, `len' holds its length */
{
char g1,g2;
int i,q;
if (len)
{
for (i=0, q=len-1; i<len/2; i++, q--)
{
g1=(s[i]>>4)&0x0f;
g2=(s[q]&0x0f)<<4;
s[i]=(s[i]&0x0f)|g2;
s[q]=(s[q]&0xf0)|g1;
}
if (len%2)
{
g1=(s[i]>>4)&0x0f;
g2=(s[i]&0x0f)<<4;
s[i]=g1|g2;
}
}
}
/*
* This routine works as a wrapper around the real decoding function.
*/
char *decode (char *string, int length)
{
scramble(string,length);
return string;
}
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