set4, completed challend 28

2 files changed, 43 insertions, 2 deletions

diff --git a/lib/lib4.c b/lib/lib4.c
index 5b7ec7d..1b25ef9 100644
--- a/lib/lib4.c
+++ b/lib/lib4.c
@@ -21,8 +21,9 @@ int aes_ctr_edit(char *ciphertext, int ciphertext_length, int offset, char *newt
 	return 0;
 }
 
-void sha1_hmac(unsigned int *mac, unsigned char *message, unsigned int msg_len, unsigned char *key,
-		unsigned int key_len)
+
+void sha1_hmac(unsigned int *mac, unsigned char *message, unsigned int msg_len,
+		unsigned char *key, unsigned int key_len)
 {
 	char *res = malloc(msg_len + key_len);
 
@@ -32,6 +33,7 @@ void sha1_hmac(unsigned int *mac, unsigned char *message, unsigned int msg_len,
 	SHA1Context sh;
 
 	SHA1Reset(&sh);
+
 	SHA1Input(&sh, res, (msg_len + key_len));
 	SHA1Result(&sh);
 
@@ -48,3 +50,39 @@ int sha1_hmac_verify(unsigned int *mac, unsigned char *msg, unsigned int msg_len
 	return !memcmp(com_mac, mac, 20);
 
 }
+
+int sha1_padding(unsigned long msg_len, char **result)
+{
+	int i;
+	unsigned int padding_len = 64 - (msg_len % 64);
+	// enough sapce for the length of the message?
+	padding_len = padding_len < 9 ? padding_len+64 : padding_len;
+
+	(*result) = malloc(padding_len);
+
+	memset((*result), 0x00, padding_len);
+	// append 1
+	memset(&(*result)[0], 0x80, 1);
+	//(*result)[0] = 0x80;
+
+	// write the 8 byte msg_len at the end bytewise
+	for(i=0;i<8;i++) {
+		(*result)[padding_len-i-1] = (msg_len*8 >> (i*8)) & 0xFF;
+	}
+
+	return padding_len;
+}
+
+void sha1_hmac_forge(unsigned int *mac, unsigned char *text, unsigned int text_len,
+		unsigned int *sha1_registers)
+{
+	SHA1Context sh;
+	SHA1Reset(&sh);
+
+	sha1_set_magic_nr(&sh, sha1_registers);
+
+	SHA1Input(&sh, text, text_len);
+	SHA1Result(&sh);
+
+	memcpy(mac, &(sh.Message_Digest), 20);
+}
diff --git a/lib/lib4.h b/lib/lib4.h
index 1d7bd36..08ecbcc 100644
--- a/lib/lib4.h
+++ b/lib/lib4.h
@@ -10,4 +10,7 @@ void sha1_hmac(unsigned int *mac, unsigned char *message, unsigned int msg_len,
 		unsigned int key_len);
 int sha1_hmac_verify(unsigned int *mac, unsigned char *msg, unsigned int msg_len,
 		unsigned char *key, unsigned int key_len);
+int sha1_padding(unsigned long msg_len, char **result);
+void sha1_hmac_forge(unsigned int *mac, unsigned char *text, unsigned int text_len,
+		unsigned int *sha1_registers);
 #endif