Created SRP6A:createVerifyCode()

This generates an SRP verification code from a setupCode and randomly-generated salt.  Function creates the salt internally and returns both the resulting verification code and salt that was used.  These are stored in NVS permanently.

Next Step: create SRP6A:loadVerifycode()

src/HAP.cpp

@@ -13,6 +13,34 @@ void HAPClient::init(){
 
   Serial.print("\n");
 
+  nvs_handle srpHandle;
+  
+  struct {                                      // temporary structure to hold SRP verification code and salt stored in NVS
+    uint8_t salt[16];
+    uint8_t verifyCode[384];
+  } verifyData;
+  
+  nvs_open("SRP",NVS_READWRITE,&srpHandle);     // open SRP data namespace in NVS
+  
+  if(!nvs_get_blob(srpHandle,"VERIFYDATA",NULL,&len)){                   // if found verification code data in NVS
+    nvs_get_blob(srpHandle,"VERIFYDATA",&verifyData,&len);               // retrieve data
+//    Serial.print("Found SRP Verification Data\n\n");
+//    hexPrintRow(verifyData.salt,16); Serial.print("\n");
+//    hexPrintRow(verifyData.verifyCode,384); Serial.print("\n");   
+  } else {
+    char c[128];
+    sprintf(c,"Generating SRP verification data for default Setup Code: %.3s-%.2s-%.3s\n\n",homeSpan.defaultSetupCode,homeSpan.defaultSetupCode+3,homeSpan.defaultSetupCode+5);
+    Serial.print(c);
+    srp.createVerifyCode(homeSpan.defaultSetupCode,verifyData.verifyCode,verifyData.salt);         // create verification code from default Setup Code and random salt
+    nvs_set_blob(srpHandle,"VERIFYDATA",&verifyData,sizeof(verifyData));                           // update data
+    nvs_commit(srpHandle);                                                                         // commit to NVS
+    
+//    hexPrintRow(verifyData.salt,16); Serial.print("\n");
+//    hexPrintRow(verifyData.verifyCode,384); Serial.print("\n");   
+  }
+
+  nvs_close(srpHandle);
+
   nvs_open("HAP",NVS_READWRITE,&nvsHandle);     // open HAP data namespace in NVS
   
   if(!nvs_get_blob(nvsHandle,"ACCESSORY",NULL,&len)){                    // if found long-term Accessory data in NVS
@@ -52,7 +80,7 @@ void HAPClient::init(){
 
   printControllers();                                                         
 
-  tlv8.create(kTLVType_State,1,"STATE");                 // define each the actual TLV records needed for the implementation of HAP; one for each kTLVType needed (HAP Table 5-6)
+  tlv8.create(kTLVType_State,1,"STATE");                 // define the actual TLV records needed for the implementation of HAP; one for each kTLVType needed (HAP Table 5-6)
   tlv8.create(kTLVType_PublicKey,384,"PUBKEY");
   tlv8.create(kTLVType_Method,1,"METHOD");
   tlv8.create(kTLVType_Salt,16,"SALT");
@@ -384,8 +412,8 @@ int HAPClient::postPairSetupURL(){
       tlv8.clear();
       tlv8.val(kTLVType_State,pairState_M2);            // set State=<M2>
       srp.createPublicKey();                          // create accessory public key from random Pair-Setup code (displayed to user)
-      srp.loadTLV(kTLVType_PublicKey,&srp.B);         // load server public key, B (MUST MAKE THIS A LIVE CALCULATION TO GENERATE RANDOM SET-UP CODE)
+      srp.loadTLV(kTLVType_PublicKey,&srp.B);         // load server public key, B
-      srp.loadTLV(kTLVType_Salt,&srp.s);              // load salt, s (MUST MAKE THIS RANDOM AS WELL)
+      srp.loadTLV(kTLVType_Salt,&srp.s);              // load salt, s
       tlvRespond();                                   // send response to client
 
       pairStatus=pairState_M3;                        // set next expected pair-state request from client

src/HomeSpan.cpp

@@ -53,7 +53,7 @@ void Span::begin(Category catID, char *displayName, char *hostNameBase, char *mo
 
   if(!digitalRead(resetPin)){                       // factory reset pin is low upon start-up
     nvs_flash_erase();                              // erase NVS storage
-    Serial.print("** FACTORY RESET PIN LOW!  ALL STORED DATA ERASED **\n");
+    Serial.print("** FACTORY RESET PIN LOW!  ALL STORED DATA ERASED **\n\n");
     statusLED.start(100);
     delay(5000);
     Serial.print("Re-starting...\n\n");

src/HomeSpan.h

@@ -48,6 +48,7 @@ struct Span{
   char *modelName;                              // model name of this device - broadcast as Bonjour field "md" 
   char category[3]="";                          // category ID of primary accessory - broadcast as Bonjour field "ci" (HAP Section 13)
   unsigned long snapTime;                       // current time (in millis) snapped before entering Service loops() or updates()
+  char *defaultSetupCode="46637726";            // default Setup Code upon factory reset; user will change to desired code when configuring network
 
   int resetPin=21;                              // drive this pin low to "factory" reset NVS data on start-up
   int resetPressed=0;                           // tracks pressing of reset button

src/SRP.cpp

@@ -62,6 +62,33 @@ SRP6A::SRP6A(){
 
 //////////////////////////////////////
 
+void SRP6A::createVerifyCode(const char *setupCode, uint8_t *verifyCode, uint8_t *salt){
+
+  uint8_t tBuf[80];     // temporary buffer for staging 
+  uint8_t tHash[64];    // temporary buffer for storing SHA-512 results 
+  char icp[22];         // storage for I:P
+
+  randombytes_buf(salt,16);                 // generate 16 random bytes using libsodium (which uses the ESP32 hardware-based random number generator)    
+  mbedtls_mpi_read_binary(&s,salt,16);
+
+  sprintf(icp,"Pair-Setup:%.3s-%.2s-%.3s",setupCode,setupCode+3,setupCode+5);
+
+  // compute x = SHA512( s | SHA512( I | ":" | P ) )
+
+  mbedtls_mpi_write_binary(&s,tBuf,16);                          // write s into first 16 bytes of staging buffer            
+  mbedtls_sha512_ret((uint8_t *)icp,strlen(icp),tBuf+16,0);      // create hash of username:password and write into last 64 bytes of staging buffer
+  mbedtls_sha512_ret(tBuf,80,tHash,0);                           // create second hash of salted, hashed username:password 
+  mbedtls_mpi_read_binary(&x,tHash,64);                          // load hash result into mpi structure x
+
+  // compute v = g^x % N
+  
+  mbedtls_mpi_exp_mod(&v,&g,&x,&N,&_rr);                         // create verifier, v (_rr is an internal "helper" structure that mbedtls uses to speed up subsequent exponential calculations)
+  mbedtls_mpi_write_binary(&v,verifyCode,384);                   // write v into verifyCode
+  
+}
+
+//////////////////////////////////////
+
 void SRP6A::createPublicKey(){
 
   uint8_t tBuf[80];     // temporary buffer for staging 

src/SRP.h

@@ -40,6 +40,9 @@ struct SRP6A {
   uint8_t sharedSecret[64];                        // permanent storage for binary version of SHARED SECRET KEY for ease of use upstream
 
   SRP6A();                                         // initializes N, G, and computes k
+  
+  void createVerifyCode(const char *setupCode, uint8_t *verifyCode, uint8_t *salt);
+  
   void getSalt();                                  // generates and stores random 16-byte salt, s
   void getPrivateKey();                            // generates and stores random 32-byte private key, b
   void getSetupCode(char *c);                      // generates and displays random 8-digit Pair-Setup code, P, in format XXX-XX-XXX