Add doco to our SMB signing code.

This should make it clearer what magic numbers refer to the magic numbers
in the CIFS spec, and what bits and peices are being appended into the MD5
calculation where.

Andrew Bartlett
(This used to be commit 7f1c271cfb04f621e36f1acf60979652e82dc6f4)

1 files changed, 32 insertions, 5 deletions

diff --git a/source3/libsmb/smb_signing.c b/source3/libsmb/smb_signing.c
index 4e9b895a1b..76e3eb8988 100644
--- a/source3/libsmb/smb_signing.c
+++ b/source3/libsmb/smb_signing.c
@@ -21,6 +21,15 @@
 
 #include "includes.h"
 
+/* the SNIA Technical Reference tells us that this is '40 or 44' bytes
+   long, but NTLM only uses 40, and we don't know what value to use for
+   NTLMv2 */
+
+/* my guess is 64, and other evidence indicates we don't setup the
+   session key correctly, so that's why it's failing */
+
+#define SIMPLE_SMB_SIGNING_MAC_KEY_LEN 64
+
 struct smb_basic_signing_context {
 	DATA_BLOB mac_key;
 	uint32 send_seq_num;
@@ -111,6 +120,9 @@ static void cli_simple_sign_outgoing_message(struct cli_state *cli)
 	/*
 	 * Firstly put the sequence number into the first 4 bytes.
 	 * and zero out the next 4 bytes.
+	 *
+	 * We put the sequence into the packet, becouse we are going
+	 * to copy over it anyway.
 	 */
 	SIVAL(cli->outbuf, smb_ss_field, 
 	      data->send_seq_num);
@@ -132,7 +144,7 @@ static void cli_simple_sign_outgoing_message(struct cli_state *cli)
 	memcpy(&cli->outbuf[smb_ss_field], calc_md5_mac, 8);
 
 /*	cli->outbuf[smb_ss_field+2]=0; 
-	Uncomment this to test if the remote server actually verifies signitures...*/
+	Uncomment this to test if the remote server actually verifies signatures...*/
 	data->send_seq_num++;
 	data->reply_seq_num = data->send_seq_num;
 	data->send_seq_num++;
@@ -155,6 +167,8 @@ static BOOL cli_simple_check_incoming_message(struct cli_state *cli)
 	/*
 	 * Firstly put the sequence number into the first 4 bytes.
 	 * and zero out the next 4 bytes.
+	 *
+	 * We do this here, to avoid modifying the packet.
 	 */
 
 	SIVAL(sequence_buf, 0, data->reply_seq_num);
@@ -163,15 +177,28 @@ static BOOL cli_simple_check_incoming_message(struct cli_state *cli)
 	/* get a copy of the server-sent mac */
 	memcpy(server_sent_mac, &cli->inbuf[smb_ss_field], sizeof(server_sent_mac));
 	
-	/* Calculate the 16 byte MAC and place first 8 bytes into the field. */
+	/* Calculate the 16 byte MAC - but don't alter the data in the
+	   incoming packet.
+	   
+	   This makes for a bit for fussing about, but it's not too bad.
+	*/
 	MD5Init(&md5_ctx);
+
+	/* intialise with the key */
 	MD5Update(&md5_ctx, data->mac_key.data, 
 		  data->mac_key.length); 
+
+	/* copy in the first bit of the SMB header */
 	MD5Update(&md5_ctx, cli->inbuf + 4, smb_ss_field - 4);
+
+	/* copy in the sequence number, instead of the signature */
 	MD5Update(&md5_ctx, sequence_buf, sizeof(sequence_buf));
-	
+
+	/* copy in the rest of the packet in, skipping the signature */
 	MD5Update(&md5_ctx, cli->inbuf + offset_end_of_sig, 
 		  smb_len(cli->inbuf) - (offset_end_of_sig - 4));
+
+	/* caclulate the MD5 sig */ 
 	MD5Final(calc_md5_mac, &md5_ctx);
 
 	good = (memcmp(server_sent_mac, calc_md5_mac, 8) == 0);
@@ -219,10 +246,10 @@ BOOL cli_simple_set_signing(struct cli_state *cli, const uchar user_session_key[
 	data = smb_xmalloc(sizeof(*data));
 	cli->sign_info.signing_context = data;
 	
-	data->mac_key = data_blob(NULL, MIN(response.length + 16, 40));
+	data->mac_key = data_blob(NULL, MIN(response.length + 16, SIMPLE_SMB_SIGNING_MAC_KEY_LEN));
 
 	memcpy(&data->mac_key.data[0], user_session_key, 16);
-	memcpy(&data->mac_key.data[16],response.data, MIN(response.length, 40 - 16));
+	memcpy(&data->mac_key.data[16],response.data, MIN(response.length, SIMPLE_SMB_SIGNING_MAC_KEY_LEN - 16));
 
 	/* Initialise the sequence number */
 	data->send_seq_num = 0;