Add NAS Service Request enc/dec functions

* FGMM enc/dec library files
* Plain message encoding + logic for security protected message
* added fill_fgstmsi function
* add checks on length in 5G-S-TMSI encoder function
* encoding of NAS Service Request and relevant mandatory IEs

openair3/NAS/COMMON/IES/FGSMobileIdentity.c

@@ -38,6 +38,7 @@
 #include "FGSMobileIdentity.h"
 
 #define MIN_LEN_FGS_MOBILE_ID_IE 3 // type of identity "No identity"
+#define LEN_5G_FGS_TMSI_IE 9
 
 static int decode_guti_5gs_mobile_identity(Guti5GSMobileIdentity_t *guti, const uint8_t *buffer);
 
@@ -45,6 +46,56 @@ static int encode_guti_5gs_mobile_identity(Guti5GSMobileIdentity_t *guti, uint8_
 static int encode_suci_5gs_mobile_identity(Suci5GSMobileIdentity_t *suci, uint8_t *buffer);
 static int encode_imeisv_5gs_mobile_identity(Imeisv5GSMobileIdentity_t *imeisv, uint8_t *buffer);
 
+int encode_stmsi_5gs_mobile_identity(uint8_t *buffer, Stmsi5GSMobileIdentity_t *stmsi, uint32_t len)
+{
+  // Return if buffer is shorter than min length
+  if (len < LEN_5G_FGS_TMSI_IE)
+    return -1;
+
+  uint32_t encoded = 0;
+  // octet 4
+  *(buffer + encoded) = (DIGIT1 << 4) | ((stmsi->spare & 0x1) << 3) | (stmsi->typeofidentity & 0x7);
+  encoded++;
+  // octet 5-6
+  uint16_t temp = 0x00 | ((stmsi->amfsetid) << 6) | (stmsi->amfpointer & 0x3f);
+  IES_ENCODE_U16(buffer, encoded, temp);
+  // octet 7
+  IES_ENCODE_U32(buffer, encoded, stmsi->tmsi);
+  return encoded;
+}
+
+int decode_stmsi_5gs_mobile_identity(Stmsi5GSMobileIdentity_t *stmsi, const uint8_t *buffer, uint32_t len)
+{
+  int decoded = 0;
+  uint16_t temp;
+
+  // Return if buffer is shorter than min length
+  if (len < LEN_5G_FGS_TMSI_IE)
+    return -1;
+
+  // Octet 4: spare (bit 3) and type of identity (bits 0-2)
+  stmsi->digit1 = DIGIT1;
+  stmsi->spare = (*(buffer + decoded) >> 3) & 0x1;
+  stmsi->typeofidentity = *(buffer + decoded) & 0x7;
+
+  // Validate type of identity
+  if (stmsi->typeofidentity != FGS_MOBILE_IDENTITY_5GS_TMSI) {
+    return -1;
+  }
+
+  decoded++;
+
+  // Octet 5-6: AMF Set ID (bits 6-15) and AMF Pointer (bits 0-5)
+  IES_DECODE_U16(buffer, decoded, temp);
+  stmsi->amfsetid = (temp >> 6) & 0x03ff;
+  stmsi->amfpointer = temp & 0x3f;
+
+  // Octet 7-10: 32-bit TMSI
+  IES_DECODE_U32(buffer, decoded, stmsi->tmsi);
+
+  return decoded;
+}
+
 int decode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei, const uint8_t *buffer, uint32_t len)
 {
   int decoded_rc = TLV_DECODE_VALUE_DOESNT_MATCH;
@@ -109,6 +160,10 @@ int encode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei
                  buffer + encoded);
   }
 
+  if (fgsmobileidentity->stmsi.typeofidentity == FGS_MOBILE_IDENTITY_5GS_TMSI) {
+    encoded_rc = encode_stmsi_5gs_mobile_identity(buffer + encoded, &fgsmobileidentity->stmsi, len);
+  }
+
   if (encoded_rc < 0) {
     return encoded_rc;
   }

openair3/NAS/COMMON/IES/FGSMobileIdentity.h

@@ -37,6 +37,8 @@
 #ifndef FGS_MOBILE_IDENTITY_H_
 #define FGS_MOBILE_IDENTITY_H_
 
+// 4x 1bit according to 9.11.3.4 5GS mobile identity (type 5G-S-TMSI)
+#define DIGIT1 0xF
 
 typedef struct {
   uint8_t  spare:5;
@@ -151,5 +153,8 @@ int encode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei
 
 int decode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei, const uint8_t *buffer, uint32_t len);
 
+int encode_stmsi_5gs_mobile_identity(uint8_t *buffer, Stmsi5GSMobileIdentity_t *stmsi, uint32_t len);
+int decode_stmsi_5gs_mobile_identity(Stmsi5GSMobileIdentity_t *stmsi, const uint8_t *buffer, uint32_t len);
+
 #endif /* FGS MOBILE IDENTITY_H_ */