Issue
I developed an encryption algorithm which takes character by character texts from a .txt file and encrypts it, and then writes it back to another .txt file. The problem is when I read the encrypted file, a character like arrow sign acts as EOF and my loop terminates before the original EOF. Here is my code:
static void ECB_ENCRYPTION(void)
{
uint8_t i = 0, j = 0, c, buf1[16]
uint8_t plain_text[16];
// File pointers for file operations.
FILE *f, *f1;
// Encrypts the file [plaintext.txt].
f = fopen("plaintext.txt", "r");
f1 = fopen("ciphertext.txt", "w");
while(1)
{
i = 0;
while(i < 16)
{
c = getc(f);
if(feof(f))
{
break;
}
else
{
plain_text[i] = c;
++i;
}
}
if(i != 16)
{
while(i < 16)
{
plain_text[i] = ' ';
++i;
}
}
// Encrypts plain text.
AES128_ENCRYPT(plain_text, buf1);
i = 0;
while(i < 16)
{
putc(buf1[i], f1);
++i;
}
if(feof(f))
break;
}
fclose(f);
fclose(f1);
}
static void ECB_DECRYPTION(void)
{
uint8_t i = 0, j = 0, c, buf1[16];
uint8_t cipher_text[16];
// File pointers for file operations.
FILE *f, *f1;
// Encrypts the file [plaintext.txt].
f = fopen("ciphertext.txt", "r");
f1 = fopen("decryptedtext.txt", "w");
while(1)
{
i = 0;
while(i < 16)
{
c = getc(f);
if(feof(f))
{
break;
}
else
{
cipher_text[i] = c;
++i;
}
}
if(feof(f))
break;
// Decrypts cipher text.
AES128_DECRYPT(cipher_text, buf1);
i = 0;
while(i < 16)
{
putc(buf1[i], f1);
++i;
}
}
fclose(f);
fclose(f1);
}
Solution
The use of uint8_t c
rather than int c
obfuscated the true issue: opening the file in binary vs. text mode. @Klas Lindbäck
int c
would have been better. Still OP's use of uint8_t; c = getc(f); if(feof(f))
was almost correct. It fails when an read error occurs.
static void ECB_DECRYPTION(void) {
uint8_t cipher_text[16];
uint8_t buf1[16];
FILE *f = fopen("ciphertext.txt", "rb"); // add 'b'
assert(f);
FILE *f1 = fopen("decryptedtext.txt", "wb"); // add 'b'
assert(f1);
while(1)
{
int c;
for (unsigned i=0; i<16; i++) {
c = getc(f);
if (c == EOF) break;
cipher_text[i] = (uint8_t) c;
}
if(c == EOF) break; // exit loop on end-of-file or input error
AES128_DECRYPT(cipher_text, buf1);
for (unsigned i=0; i<16; i++) {
putc(buf1[i], f1);
}
}
fclose(f);
fclose(f1);
}
Answered By - chux - Reinstate Monica Answer Checked By - Dawn Plyler (PHPFixing Volunteer)
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