Problem - Kevin Tafuro

most important requirement is that padding always be unambiguous *), and there’s
no good reason to wing it.
The most widespread standard padding for block ciphers is called PKCS block padding.
The goal of PKCS block padding is that the last byte of the padded plaintext
should unambiguously describe how much padding was added to the message. PKCS
padding sets every byte of padding to the number of bytes of padding added. If the
input is block-aligned, an entire block of padding is added. For example, if four bytes
of padding were needed, the proper padding would be:
0x04040404
If you’re using a block cipher with 64-bit (8-byte) blocks, and the input is blockaligned,
the padding would be:
0x0808080808080808
Here’s an example API for adding and removing padding:
void spc_add_padding(unsigned char *pad_goes_here, int ptlen, int bl) {
int i, n = (ptlen - 1) % bl + 1;
}
for (i = 0; i < n; i++) *(pad_goes_here + i) = (unsigned char)n;
int spc_remove_padding(unsigned char *lastblock, int bl) {
unsigned char i, n = lastblock[bl - 1];
unsigned char *p = lastblock + bl;
/* In your programs you should probably throw an exception or abort instead. */
if (n > bl || n