Save work on AES and RC4.

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.
+//
+
+void
+_pdfioCryptoRC4Crypt(
+    _pdfio_rc4_t  *ctx,			// I - Context
+    uint8_t       *buffer,		// I - Buffer
+    size_t        len)			// I - Size of buffers
+{
+  uint8_t	tmp,			// Swap variable
+		i, j,			// Looping vars
+		t;			// Current S box
+
+
+  // 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...
+    *buffer++ ^= ctx->sbox[t];
+    len --;
+  }
+
+  // Copy current S box indices back to context...
+  ctx->i = i;
+  ctx->j = j;
+}