Everchanging passphrase to avoid ECB attacksnonecb

1 files changed, 72 insertions, 0 deletions

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;
+}