Question

First of all the code for aes cryptographic function :

void
xorcrypto(u_int8_t *key, u_int32_t keylen,
    u_int8_t *data, u_int32_t datalen)
{

/*u_int8_t ....etc are alias for uint8_t...etc so don't bother about them*/

FILE *fp,*fq,*fr;
int i;
fp=fopen("key","wb");
fwrite((char *)key,keylen,1,fp);
fq=fopen("file.txt","wb");
fwrite((char *)data,datalen,1,fq);

fclose(fq);
fclose(fp);

system("sudo openssl enc -aes-256-cbc -salt -in file.txt
-out file.enc -pass file:key");


/* Here is the code section i need*/

}

What i need in the code section i have specified above is that it should be able to
fill/change the data (pointed by u_int8_t*data) with the contents of file file.enc

Don’t worry about the data length actually the input it is taking is from a n/w ip
packet so it has provision for data upto 1024 bytes and file contents are never going to
exceed this limit.

Here is my attempt for it (also for debugging purpose i need to mention the contents of file.enc as well as data section to stdout)

fr=fopen("file.enc","rb");
memset(data,0,sizeof(data));

i=0;

while( (ch=fgetc(fr))==EOF) {
     data[i]=ch;
     i++;
}

data[i]='\0';
i=0;
puts((char *)data);
printf("\n");
fclose(fr);

Here are some output snapshots which may help …..

udit@udit-Dabba ~/Downloads/sendip-2.5-mec-2/mec $ cat key
thisisaeskey

udit@udit-Dabba ~/Downloads/sendip-2.5-mec-2/mec $ cat file.txt
w�uP����abcd

udit@udit-Dabba ~/Downloads/sendip-2.5-mec-2/mec $ cat file.enc
Salted__����a�dR�P��l�C-<��y�O^Z��/a��3����Q

udit@udit-Dabba ~/Downloads/sendip-2.5-mec-2/mec $ hexdump -C file.enc 
00000000  53 61 6c 74 65 64 5f 5f  b6 f2 b2 d0 61 d9 64 1c  |Salted__....a.d.|
00000010  52 e0 50 96 e8 6c 0e c0  43 2d 3c c4 f6 79 1b d2  |R.P..l..C-<..y..|
00000020  4f 5e 5a b1 d6 2f 61 f8  15 f6 33 e1 88 f0 db 51  |O^Z../a...3....Q|
00000030
udit@udit-Dabba ~/Downloads/sendip-2.5-mec-2/mec $ 

The functon is unable to change the contents of pointed location (u_int8_t *data) and so was unable to write data on stdout puts(data).

Please help me on this …if any further information needed about this i will add it.

Answer 1

Try changing

while( (ch=fgetc(fr))==EOF)

into

while( (ch=fgetc(fr))!=EOF)