diff --git a/tools/applypatch/bsdiff.c b/tools/applypatch/bsdiff.c
new file mode 100644
index 0000000..a2851f9
--- /dev/null
+++ b/tools/applypatch/bsdiff.c
@@ -0,0 +1,232 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// This file is a nearly line-for-line copy of bspatch.c from the
+// bsdiff-4.3 distribution; the primary differences being how the
+// input and output data are read and the error handling.  Running
+// applypatch with the -l option will display the bsdiff license
+// notice.
+
+#include <stdio.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+
+#include <bzlib.h>
+
+#include "mincrypt/sha.h"
+
+void ShowBSDiffLicense() {
+  puts("The bsdiff library used herein is:\n"
+       "\n"
+       "Copyright 2003-2005 Colin Percival\n"
+       "All rights reserved\n"
+       "\n"
+       "Redistribution and use in source and binary forms, with or without\n"
+       "modification, are permitted providing that the following conditions\n"
+       "are met:\n"
+       "1. Redistributions of source code must retain the above copyright\n"
+       "   notice, this list of conditions and the following disclaimer.\n"
+       "2. Redistributions in binary form must reproduce the above copyright\n"
+       "   notice, this list of conditions and the following disclaimer in the\n"
+       "   documentation and/or other materials provided with the distribution.\n"
+       "\n"
+       "THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR\n"
+       "IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED\n"
+       "WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE\n"
+       "ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY\n"
+       "DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL\n"
+       "DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS\n"
+       "OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)\n"
+       "HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,\n"
+       "STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING\n"
+       "IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE\n"
+       "POSSIBILITY OF SUCH DAMAGE.\n"
+       "\n------------------\n\n"
+       "This program uses Julian R Seward's \"libbzip2\" library, available\n"
+       "from http://www.bzip.org/.\n"
+       );
+}
+
+static off_t offtin(u_char *buf)
+{
+  off_t y;
+
+  y=buf[7]&0x7F;
+  y=y*256;y+=buf[6];
+  y=y*256;y+=buf[5];
+  y=y*256;y+=buf[4];
+  y=y*256;y+=buf[3];
+  y=y*256;y+=buf[2];
+  y=y*256;y+=buf[1];
+  y=y*256;y+=buf[0];
+
+  if(buf[7]&0x80) y=-y;
+
+  return y;
+}
+
+int ApplyBSDiffPatch(const unsigned char* old_data, ssize_t old_size,
+                     const char* patch_filename,
+                     FILE* output, SHA_CTX* ctx) {
+
+  FILE* f;
+  if ((f = fopen(patch_filename, "rb")) == NULL) {
+    fprintf(stderr, "failed to open patch file\n");
+    return 1;
+  }
+
+  // File format:
+  //   0       8       "BSDIFF40"
+  //   8       8       X
+  //   16      8       Y
+  //   24      8       sizeof(newfile)
+  //   32      X       bzip2(control block)
+  //   32+X    Y       bzip2(diff block)
+  //   32+X+Y  ???     bzip2(extra block)
+  // with control block a set of triples (x,y,z) meaning "add x bytes
+  // from oldfile to x bytes from the diff block; copy y bytes from the
+  // extra block; seek forwards in oldfile by z bytes".
+
+  unsigned char header[32];
+  if (fread(header, 1, 32, f) < 32) {
+    fprintf(stderr, "failed to read patch file header\n");
+    return 1;
+  }
+
+  if (memcmp(header, "BSDIFF40", 8) != 0) {
+    fprintf(stderr, "corrupt patch file header (magic number)\n");
+    return 1;
+  }
+
+  ssize_t ctrl_len, data_len;
+  ssize_t new_size;
+  ctrl_len = offtin(header+8);
+  data_len = offtin(header+16);
+  new_size = offtin(header+24);
+
+  if (ctrl_len < 0 || data_len < 0 || new_size < 0) {
+    fprintf(stderr, "corrupt patch file header (data lengths)\n");
+    return 1;
+  }
+
+  fclose(f);
+
+  int bzerr;
+
+#define OPEN_AT(f, bzf, offset)                                          \
+  FILE* f;                                                               \
+  BZFILE* bzf;                                                           \
+  if ((f = fopen(patch_filename, "rb")) == NULL) {                       \
+    fprintf(stderr, "failed to open patch file\n");                      \
+    return 1;                                                            \
+  }                                                                      \
+  if (fseeko(f, offset, SEEK_SET)) {                                     \
+    fprintf(stderr, "failed to seek in patch file\n");                   \
+    return 1;                                                            \
+  }                                                                      \
+  if ((bzf = BZ2_bzReadOpen(&bzerr, f, 0, 0, NULL, 0)) == NULL) {        \
+    fprintf(stderr, "failed to bzReadOpen in patch file (%d)\n", bzerr); \
+    return 1;                                                            \
+  }
+
+  OPEN_AT(cpf, cpfbz2, 32);
+  OPEN_AT(dpf, dpfbz2, 32+ctrl_len);
+  OPEN_AT(epf, epfbz2, 32+ctrl_len+data_len);
+
+#undef OPEN_AT
+
+  unsigned char* new_data = malloc(new_size);
+  if (new_data == NULL) {
+    fprintf(stderr, "failed to allocate memory for output file\n");
+    return 1;
+  }
+
+  off_t oldpos = 0, newpos = 0;
+  off_t ctrl[3];
+  off_t len_read;
+  int i;
+  unsigned char buf[8];
+  while (newpos < new_size) {
+    // Read control data
+    for (i = 0; i < 3; ++i) {
+      len_read = BZ2_bzRead(&bzerr, cpfbz2, buf, 8);
+      if (len_read < 8 || !(bzerr == BZ_OK || bzerr == BZ_STREAM_END)) {
+        fprintf(stderr, "corrupt patch (read control)\n");
+        return 1;
+      }
+      ctrl[i] = offtin(buf);
+    }
+
+    // Sanity check
+    if (newpos + ctrl[0] > new_size) {
+      fprintf(stderr, "corrupt patch (new file overrun)\n");
+      return 1;
+    }
+
+    // Read diff string
+    len_read = BZ2_bzRead(&bzerr, dpfbz2, new_data + newpos, ctrl[0]);
+    if (len_read < ctrl[0] || !(bzerr == BZ_OK || bzerr == BZ_STREAM_END)) {
+      fprintf(stderr, "corrupt patch (read diff)\n");
+      return 1;
+    }
+
+    // Add old data to diff string
+    for (i = 0; i < ctrl[0]; ++i) {
+      if ((oldpos+i >= 0) && (oldpos+i < old_size)) {
+        new_data[newpos+i] += old_data[oldpos+i];
+      }
+    }
+
+    // Adjust pointers
+    newpos += ctrl[0];
+    oldpos += ctrl[0];
+
+    // Sanity check
+    if (newpos + ctrl[1] > new_size) {
+      fprintf(stderr, "corrupt patch (new file overrun)\n");
+      return 1;
+    }
+
+    // Read extra string
+    len_read = BZ2_bzRead(&bzerr, epfbz2, new_data + newpos, ctrl[1]);
+    if (len_read < ctrl[1] || !(bzerr == BZ_OK || bzerr == BZ_STREAM_END)) {
+      fprintf(stderr, "corrupt patch (read extra)\n");
+      return 1;
+    }
+
+    // Adjust pointers
+    newpos += ctrl[1];
+    oldpos += ctrl[2];
+  }
+
+  BZ2_bzReadClose(&bzerr, cpfbz2);
+  BZ2_bzReadClose(&bzerr, dpfbz2);
+  BZ2_bzReadClose(&bzerr, epfbz2);
+  fclose(cpf);
+  fclose(dpf);
+  fclose(epf);
+
+  if (fwrite(new_data, 1, new_size, output) < new_size) {
+    fprintf(stderr, "short write of output: %d (%s)\n", errno, strerror(errno));
+    return 1;
+  }
+  SHA_update(ctx, new_data, new_size);
+  free(new_data);
+
+  return 0;
+}