pdfio/pdfio-rc4.c

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//
// RC4 functions for PDFio.
//
// Copyright © 2021 by Michael R Sweet.
//
// Original code by Tim Martin
// Copyright © 1999 by Carnegie Mellon University, All Rights Reserved
//
// Permission to use, copy, modify, and distribute this software and its
// documentation for any purpose and without fee is hereby granted,
// provided that the above copyright notice appear in all copies and that
// both that copyright notice and this permission notice appear in
// supporting documentation, and that the name of Carnegie Mellon
// University not be used in advertising or publicity pertaining to
// distribution of the software without specific, written prior
// permission.
//
// CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
// THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE FOR
// ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
// OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//
#include "pdfio-private.h"
//
// '_pdfioCryptoRC4Init()' - Initialize an RC4 context with the specified key.
//
void
_pdfioCryptoRC4Init(
_pdfio_rc4_t *ctx, // IO - Context
const uint8_t *key, // I - Key
size_t keylen) // I - Length of key
{
size_t i; // Looping var
uint8_t j, // S box counter
tmp; // Temporary variable
// Fill in linearly s0=0, s1=1, ...
for (i = 0; i < 256; i ++)
ctx->sbox[i] = (uint8_t)i;
for (i = 0, j = 0; i < 256; i ++)
{
// j = (j + Si + Ki) mod 256
j += ctx->sbox[i] + key[i % keylen];
// Swap Si and Sj...
tmp = ctx->sbox[i];
ctx->sbox[i] = ctx->sbox[j];
ctx->sbox[j] = tmp;
}
// Initialize counters to 0 and return...
ctx->i = 0;
ctx->j = 0;
}
//
// '_pdfioCryptoRC4Crypt()' - De/encrypt the given buffer.
//
// "inbuffer" and "outbuffer" can point to the same memory.
//
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size_t // O - Number of output bytes
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_pdfioCryptoRC4Crypt(
_pdfio_rc4_t *ctx, // I - Context
uint8_t *outbuffer, // I - Output buffer
const uint8_t *inbuffer, // I - Input buffer
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size_t len) // I - Size of buffers
{
uint8_t tmp, // Swap variable
i, j, // Looping vars
t; // Current S box
size_t outbytes = len; // Number of output bytes
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// Loop through the entire buffer...
i = ctx->i;
j = ctx->j;
while (len > 0)
{
// Get the next S box indices...
i ++;
j += ctx->sbox[i];
// Swap Si and Sj...
tmp = ctx->sbox[i];
ctx->sbox[i] = ctx->sbox[j];
ctx->sbox[j] = tmp;
// Get the S box index for this byte...
t = ctx->sbox[i] + ctx->sbox[j];
// Encrypt using the S box...
*outbuffer++ = *inbuffer++ ^ ctx->sbox[t];
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len --;
}
// Copy current S box indices back to context...
ctx->i = i;
ctx->j = j;
return (outbytes);
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}