From ce19147e916925945d65823543997d397af40dcb Mon Sep 17 00:00:00 2001
From: Nathan Lasseter <nathan.je.lasseter@googlemail.com>
Date: Sun, 28 Apr 2013 12:40:39 +0100
Subject: Everchanging passphrase to avoid ECB attacks

---
 Makefile  | 13 ++++++++----
 decrypt.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 encrypt.c |  4 +++-
 3 files changed, 84 insertions(+), 5 deletions(-)
 create mode 100644 decrypt.c

diff --git a/Makefile b/Makefile
index dfb3231..a7ff461 100644
--- a/Makefile
+++ b/Makefile
@@ -1,13 +1,18 @@
 CFLAGS=-Wall -Wextra
 
-encrypt:	encrypt.c
+all: encrypt decrypt
+
+%:	%.c
 	gcc ${CFLAGS} -o $@ $^
 
-install:
+install: encrypt decrypt
 	cp encrypt /usr/local/bin/encrypt
+	cp decrypt /usr/local/bin/decrypt
 
-uninstall:
+uninstall: /usr/local/bin/encrypt /usr/local/bin/decrypt
 	rm /usr/local/bin/encrypt
+	rm /usr/local/bin/decrypt
 
-clean:
+clean: encrypt decrypt
 	rm encrypt
+	rm decrypt
diff --git a/decrypt.c b/decrypt.c
new file mode 100644
index 0000000..305e1ed
--- /dev/null
+++ b/decrypt.c
@@ -0,0 +1,72 @@
+/*
+ * SimpleCrypt
+ * Non-ECB version
+ * So simple it's all one function.
+ *
+ * Nathan Lasseter (User_4574)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(int argc, char** argv) {
+
+	// We need a file to encrypt
+	if (argc != 2) {
+		fprintf(stderr, "Usage: encrypt <file>\n");
+		return EXIT_FAILURE;
+	}
+
+	// Now lets open that file
+	FILE* file = fopen(argv[1], "r");
+	if (file == NULL) {
+		fprintf(stderr, "No such file\n");
+		return EXIT_FAILURE;
+	}
+
+	// Now we need the passphrase. Get it
+	char *passphrase = malloc(256);
+	do {
+		printf("Enter Passphrase: ");
+		if (fgets(passphrase, 255, stdin) == NULL) {
+			fclose(file);
+			fprintf(stderr, "Read error or end of file\n");
+			return EXIT_FAILURE;
+		}
+	} while (strlen(passphrase) <= 0);
+
+	// And a temporary file to hold the encrypted data
+	char tpath[] = ".SimCr.XXXXXX";
+	int tempfd = mkstemp(tpath);
+	FILE* temp = fdopen(tempfd, "w");
+
+	// Now we decrypt!
+	int passlen = strlen(passphrase) - 2;
+	int c, d, j = 0;
+
+	while ((c=fgetc(file)) != EOF) {
+		d = c - passphrase[j];
+		passphrase[j] = c;
+		fputc(d, temp);
+
+		if (j == passlen) j=0;
+		else j++;
+	}
+
+	// Close the files
+	fflush(temp);
+	fclose(temp);
+	fclose(file);
+
+	// Free used memory
+	free(passphrase);
+
+	// Move the file back
+	if (rename(tpath, argv[1]) != 0) {
+		fprintf(stderr, "Your encrypted file is located in %s.", tpath);
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}
diff --git a/encrypt.c b/encrypt.c
index 90ae0dc..6f2cca8 100644
--- a/encrypt.c
+++ b/encrypt.c
@@ -1,5 +1,6 @@
 /*
  * SimpleCrypt
+ * Non-ECB version
  * So simple it's all one function.
  *
  * Nathan Lasseter (User_4574)
@@ -45,7 +46,8 @@ int main(int argc, char** argv) {
 	int c, d, j = 0;
 
 	while ((c=fgetc(file)) != EOF) {
-		d = c ^ passphrase[j];
+		d = c + passphrase[j];
+		passphrase[j] = d;
 		fputc(d, temp);
 
 		if (j == passlen) j=0;
-- 
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