libtinytac: adding tinytac_md5pad()

3 files changed, 74 insertions, 32 deletions

diff --git a/include/tinytac.h b/include/tinytac.h
index 5bf14df..ad86bb9 100644
--- a/include/tinytac.h
+++ b/include/tinytac.h
@@ -205,6 +205,19 @@
 #pragma mark - Data Types
 
 typedef struct _tinytac                   TinyTac;
+typedef struct _tinytac_packet            tinytac_pckt_t;
+
+
+struct _tinytac_packet
+{
+   uint8_t              pckt_version;  // 4 bits major and 4 bits minor
+   uint8_t              pckt_type;
+   uint8_t              pckt_seq_no;
+   uint8_t              pckt_flags;
+   uint32_t             pckt_session_id;
+   uint32_t             pckt_length;
+   uint8_t              pckt_body[];
+};
 
 
 //////////////////
@@ -245,4 +258,26 @@ tinytac_set_option(
          const void *                  invalue );
 
 
+//---------------------//
+// protocol prototypes //
+//---------------------//
+#pragma mark protocol prototypes
+
+/// generates pseudo-random pad used to obfuscate the packet body
+///
+/// @param[in]  pckt          packet used to generate psuedo-random pad
+/// @param[in]  key           shared secret key used to protect the communication
+/// @param[in]  key_len       length of shared secret key
+/// @param[in]  md5pad_prev   previously generated psuedo-random pad (must be 16 bytes)
+/// @param[out] md5pad        buffer to store generated
+///
+/// @return    Returns 0 on success or -1 on error.
+_TINYTAC_F int
+tinytac_pckt_md5pad(
+         tinytac_pckt_t *              pckt,
+         char *                        key,
+         size_t                        key_len,
+         uint8_t *                     md5pad_prev,
+         uint8_t *                     md5pad );
+
 #endif /* end of header */
diff --git a/lib/libtinytac/libtinytac.sym b/lib/libtinytac/libtinytac.sym
index 80d6b6d..ad039cd 100644
--- a/lib/libtinytac/libtinytac.sym
+++ b/lib/libtinytac/libtinytac.sym
@@ -33,4 +33,7 @@
 # memory functions
 tinytac_free
 tinytac_initialize
+#
+# protocol functions
+tinytac_pckt_md5pad
 # end of symbol export file
diff --git a/lib/libtinytac/lproto.c b/lib/libtinytac/lproto.c
index 864ecdb..8c64798 100644
--- a/lib/libtinytac/lproto.c
+++ b/lib/libtinytac/lproto.c
@@ -52,14 +52,7 @@
 #include <netinet/in.h>
 #include <netdb.h>
 #include <assert.h>
-
-
-///////////////////
-//               //
-//  Definitions  //
-//               //
-///////////////////
-#pragma mark - Definitions
+#include <openssl/evp.h>
 
 
 //////////////////
@@ -69,25 +62,6 @@
 //////////////////
 #pragma mark - Prototypes
 
-//--------------------//
-// TinyTac prototypes //
-//--------------------//
-#pragma mark TinyTac prototypes
-
-
-//-------------------//
-// object prototypes //
-//-------------------//
-#pragma mark object prototypes
-
-
-/////////////////
-//             //
-//  Variables  //
-//             //
-/////////////////
-#pragma mark - Variables
-
 
 /////////////////
 //             //
@@ -96,10 +70,40 @@
 /////////////////
 #pragma mark - Functions
 
-//-------------------//
-// TinyTac functions //
-//-------------------//
-#pragma mark TinyTac functions
-
+//------------------//
+// packet functions //
+//------------------//
+#pragma mark packet functions
+
+int
+tinytac_pckt_md5pad(
+         tinytac_pckt_t *              pckt,
+         char *                        key,
+         size_t                        key_len,
+         uint8_t *                     md5pad_prev,
+         uint8_t *                     md5pad )
+{
+   unsigned             md_len;
+   EVP_MD_CTX *         mdctx;
+
+   assert(pckt    != NULL);
+   assert(key     != NULL);
+   assert(md5pad  != NULL);
+
+   key_len = ((key)) ? key_len : 0;
+
+   mdctx = EVP_MD_CTX_new();
+   EVP_DigestInit_ex(mdctx, EVP_md5(), NULL);
+   EVP_DigestUpdate(mdctx, &pckt->pckt_session_id, 4);
+   EVP_DigestUpdate(mdctx, key, key_len);
+   EVP_DigestUpdate(mdctx, &pckt->pckt_version, 1);
+   EVP_DigestUpdate(mdctx, &pckt->pckt_seq_no, 1);
+   if ((md5pad_prev))
+      EVP_DigestUpdate(mdctx, md5pad_prev, 16);
+   EVP_DigestFinal_ex(mdctx, md5pad, &md_len);
+   EVP_MD_CTX_free(mdctx);
+
+   return(0);
+}
 
 /* end of source */