1 files changed, 67 insertions, 0 deletions
diff --git a/set4/task29.c b/set4/task29.c
new file mode 100644
index 0000000..4b6f4d0
--- /dev/null
+++ b/set4/task29.c
@@ -0,0 +1,67 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include "../lib/lib4.h"
+#include <time.h>
+
+
+int main(int argc, char **argv)
+{
+	if(argc  != 2)
+		printf("Please provide ONE key as argument!\n");
+	uint32_t *hmac;
+	uint32_t *hmac2;
+	int i;
+	unsigned char *text = "comment1=cooking%20MCs;userdata=foo;comment2=%20like%20a%20pound%20of%20bacon";
+	unsigned char *append = ";admin=true";
+	unsigned char *key = argv[1];
+	printf("Using secret key: %s\n", key);
+
+	unsigned char *padded;
+	int padding_len = md4_padding(strlen(key)+strlen(text), &padded);
+
+	printf("MD4 padding is:\n");
+	for(i=0;i<padding_len;i++)
+		printf("%02x", padded);
+
+	md4_prefix_key_mac(&hmac, text, strlen(text), key, strlen(key));
+	printf("MAC of original message:\n");
+	for(i=0;i<5;i++)
+		printf("%02x", hmac[i]);
+
+	printf("\n");
+	
+	/*
+	 * We are appending a text to the original message without knowign the
+	 * key. Actually we don't know the message here, just the hash of the orginal 
+	 * message. We have to append the right padding here, e.g. the size of the
+	 * *complete* message, not only append
+	 */
+	unsigned int new_msg_len = strlen(text)+strlen(append)+padding_len;
+	unsigned char *new_msg = malloc(new_msg_len);
+	memcpy(new_msg, text, strlen(text));
+	memcpy(&new_msg[strlen(text)], padded, padding_len);
+	memcpy(&new_msg[strlen(text)+padding_len], append, strlen(append));
+	
+	unsigned char *padding2;
+	// mesage + padding + append + padding
+	int padding2_len = md4_padding(new_msg_len+strlen(key), &padding2);
+	unsigned char *tmp2 = malloc(strlen(append)+padding2_len);
+	memcpy(tmp2, append, strlen(append));
+	memcpy(&tmp2[strlen(append)], padding2, padding2_len);
+	md4_prefix_key_forge(&hmac2, tmp2, (strlen(append)+padding2_len), hmac);
+	printf("MAC of forged message:\n");
+	for(i=0;i<5;i++)
+		printf("%02x", hmac2[i]);
+
+	printf("\n");
+	
+	/*
+	 * create the message we forged. Send this plus the hmac to the
+	 * victim. He knows the secret and test and will think that
+	 * this is a message from Alice
+	 */
+	printf("Verifying...\n");
+	if(md4_prefix_key_verify(hmac2, new_msg, new_msg_len, key, strlen(key)))
+			printf("Forged MAC got accepted!\n");
+}