set4, completed challenge 25

2 files changed, 29 insertions, 0 deletions

diff --git a/lib/lib4.c b/lib/lib4.c
new file mode 100644
index 0000000..475efe9
--- /dev/null
+++ b/lib/lib4.c
@@ -0,0 +1,22 @@
+#include "lib4.h"
+#include "lib3.h"
+#include "lib2.h"
+#include "lib.h"
+/**
+  * encrypt always with the same key, same nonce?
+  *
+  **/
+int aes_ctr_edit(char *ciphertext, int ciphertext_length, int offset, char *newtext)
+{
+	// do not allow greater ciphertexts
+	if((strlen(newtext)+offset) > ciphertext_length)
+		return 1;
+		
+	// insert newtext at offset and reencrpyt
+	char *plaintext = malloc(ciphertext_length);
+	aes_ctr(ciphertext, ciphertext_length, plaintext, key, nonce);
+	memcpy(&plaintext[offset], newtext, strlen(newtext));
+
+	aes_ctr(plaintext, ciphertext_length, ciphertext, key, nonce);
+	return 0;
+}
diff --git a/lib/lib4.h b/lib/lib4.h
new file mode 100644
index 0000000..dee52a7
--- /dev/null
+++ b/lib/lib4.h
@@ -0,0 +1,7 @@
+#ifndef __LIB_4__
+#define __LIB_4__
+
+
+int aes_ctr_edit(char *ciphertext, int ciphertext_length, int offset, char *newtext);
+
+#endif