From 30c2e6bdbeef4bd4dbabf06cf359bd8578af4628 Mon Sep 17 00:00:00 2001
From: Jeff Connelly <shellreef+git@gmail.com>
Date: Tue, 10 Jun 2008 22:50:42 -0700
Subject: [PATCH] Add pad rewriting, in otp_replace.

---
 SecureMail.py |  5 +++--
 cotp.c        | 28 +++++++++++++++++++++-------
 libotp.c      | 39 ++++++++++++++++++++++++++++++++++++++-
 libotp.h      |  1 +
 4 files changed, 63 insertions(+), 10 deletions(-)

diff --git a/SecureMail.py b/SecureMail.py
index 06721c7..04d4938 100644
--- a/SecureMail.py
+++ b/SecureMail.py
@@ -15,7 +15,8 @@ import time
 
 # Every X seconds, send a message, and queue messages to be sent at in this
 # interval. 
-FILL_INTERVAL = 10
+#FILL_INTERVAL = 10
+FILL_INTERVAL = None
 
 # Real subject used for all encrypted messages
 # Note: make a Gmail filter that filters (Secure Message) into the Secure tag
@@ -178,7 +179,7 @@ class SecureMail(threading.Thread):
         if channel filling is disabled."""
         if FILL_INTERVAL is None:
             print "Sending %s bytes now" % (len(body,))
-            return self.send(to, subject, body)
+            return self.send_now(to, subject, body)
         else:
             self.sendq.put((to, subject, body))
             print "Enqueued to send at next interval, pending: %s" % (self.sendq.qsize(),)
diff --git a/cotp.c b/cotp.c
index 3c5b3b7..0213020 100644
--- a/cotp.c
+++ b/cotp.c
@@ -56,10 +56,11 @@ void test()
     free_pads();
 }
 
-/* Operation mode - trinary :) */
+/* Operation mode */
 #define ENCRYPT -1
 #define AUTO     0
 #define DECRYPT 1
+#define REPLACE 2
 
 void usage()
 {
@@ -67,7 +68,8 @@ void usage()
             "\n"
             "Mode selection:\n"
             "-e     Encrypt\n"
-            "-d     Decrypt with <pad_name>\n"
+            "-d     Decrypt\n"
+            "-r     Replace what an existing encrypted message decrypts to\n"
             "Default is automatic.\n"
             "\n"
             "-t     Specify pad name to encrypt with. Default: first pad.\n");
@@ -114,14 +116,14 @@ char *read_input(unsigned int *size)
 
 int main(int argc, char **argv)
 {
-    int ch, mode;
+    int ch, mode, i;
     unsigned int length, output_length;
     char *to, *input, *output;
 
     mode = AUTO;
     to = NULL;
 
-    while((ch = getopt(argc, argv, "edt:")) != -1) {
+    while((ch = getopt(argc, argv, "erdt:")) != -1) {
         switch(ch)
         {
         case 'e': 
@@ -133,6 +135,9 @@ int main(int argc, char **argv)
         case 't':
             to = optarg;
             break;
+        case 'r':
+            mode = REPLACE;
+            break;
         case '?':
         default:
             usage();
@@ -141,8 +146,6 @@ int main(int argc, char **argv)
     argc -= optind;
     argv += optind;
 
-    input = read_input(&length);
-
     /* Automatic mode - guess based on magic markers.
      * Explicit modes still allowed so can encrypt data with
      * magic markers in it (if you ever want to). */
@@ -155,13 +158,24 @@ int main(int argc, char **argv)
 
     load_config("otp.conf");
 
+    input = read_input(&length);
+
     if (mode == ENCRYPT) {
         output = otp_encrypt(input, length, to, &output_length);
     } else if (mode == DECRYPT) {
         output_length = otp_decrypt(input, &output);
+    } else if (mode == REPLACE) {
+        if (!strstr(input, MARKER_END)) {
+            fprintf(stderr, "need encrypted pad, trailed by new message\n");
+            exit(EXIT_FAILURE);
+        }
+
+        otp_replace(input, strstr(input, MARKER_END) + strlen(MARKER_END) + 1);
+        output_length = 0;
     }
 
-    printf("%s", output);
+    for (i = 0; i < output_length; ++i)
+        putchar(output[i]); 
 
     free(output);
     free_pads();
diff --git a/libotp.c b/libotp.c
index f7f63e3..defe403 100644
--- a/libotp.c
+++ b/libotp.c
@@ -114,7 +114,7 @@ void load_pad(char *local_filename, char *pad_name)
     FILE *fp;
     PAD *new_pad;
 
-    fp = fopen("/Volumes/Not Backed Up/otp/otp-dazzlement", "rb");
+    fp = fopen(local_filename, "rb+");
     if (!fp) {
         perror("fopen");
         exit(EXIT_FAILURE);
@@ -459,6 +459,43 @@ unsigned int otp_decrypt(char *input, char **out)
     return length;
 }
 
+/** Replace part of the pad corresponding to an encrypted message 
+ * so that it encrypts to something else.
+ *
+ * @param input A packaged, encrypted message.
+ * @param with What to make 'input' decrypt to by changing the pad.
+ */
+unsigned int otp_replace(char *input, char *with)
+{
+    unsigned int length;
+    int i;
+    char c;
+
+    MESSAGE *msg;
+    msg = unpackage(input);
+
+    if (fseek(msg->pad->fp, msg->offset, SEEK_SET) < 0) {
+        perror("fseek");
+        exit(EXIT_FAILURE);
+    }
+
+    for (i = 0; i < msg->length; ++i) {
+        char with_c;
+
+        /* What to make the message decrypt to. */
+        if (i < strlen(with))
+            with_c = with[i];
+        else
+            with_c = '\0';
+
+        c = msg->cipher_text[i] ^ with_c;
+
+        fputc(c, msg->pad->fp);
+    }
+
+    return length;
+}
+
 /** Package up a message for transport.
  *
  * @return Packaged message. Caller frees.
diff --git a/libotp.h b/libotp.h
index 86d64a3..89a0b92 100644
--- a/libotp.h
+++ b/libotp.h
@@ -53,4 +53,5 @@ MESSAGE *unpackage(char *input);
 void free_message(MESSAGE *);
 char *otp_encrypt(char *input, unsigned int length, char *to, unsigned int *out_length);
 unsigned int otp_decrypt(char *input, char **out);
+unsigned int otp_replace(char *input, char *with);
 
-- 
2.11.4.GIT