From 07da5ac924c0f9cc5c39db78c9fb27b24a9f557e Mon Sep 17 00:00:00 2001
From: Gregg <homespan@icloud.com>
Date: Thu, 23 Sep 2021 21:12:37 -0500
Subject: [PATCH] Updated SRP code for 2.0.0 compatibility

Arduino-ESP32 has modified the Mbed TLS library so that it uses ESP32 hardware acceleration.  However, there is a 512-byte limit to the size of the variables used in an exponential modulo calculation.  One of the steps in the SRP code used a 768-byte variable, which cannot be handled in version 2.0.0 though it works fine in version 1.0.6.  Solution was to simply reduce the 768-byte variable by modulo N prior to performing the exponential modulo calculation.
---
 src/SRP.cpp | 13 +++++++------
 src/src.ino |  2 +-
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/SRP.cpp b/src/SRP.cpp
index 9fd0f1d..8af05eb 100644
--- a/src/SRP.cpp
+++ b/src/SRP.cpp
@@ -144,8 +144,8 @@ void SRP6A::createPublicKey(){
 void SRP6A::getPrivateKey(){
 
   uint8_t privateKey[32];
+  
   randombytes_buf(privateKey,32);                     // generate 32 random bytes using libsodium (which uses the ESP32 hardware-based random number generator)
-
   mbedtls_mpi_read_binary(&b,privateKey,32);
 }
   
@@ -164,10 +164,11 @@ void SRP6A::createSessionKey(){
   mbedtls_mpi_read_binary(&u,tHash,64);           // load hash result into mpi structure u
 
   // compute S = (Av^u)^b %N
-  
+
   mbedtls_mpi_exp_mod(&t1,&v,&u,&N,&_rr);         // t1 = v^u %N
   mbedtls_mpi_mul_mpi(&t2,&A,&t1);                // t2 = A*t1
-  mbedtls_mpi_exp_mod(&S,&t2,&b,&N,&_rr);         // S = t2^b %N
+  mbedtls_mpi_mod_mpi(&t1,&t2,&N);                // t1 = t2 %N  (this is needed to reduce size of t2 before next calculation)
+  mbedtls_mpi_exp_mod(&S,&t1,&b,&N,&_rr);         // S = t1^b %N
 
   // compute K = SHA512( S )
   
@@ -176,7 +177,7 @@ void SRP6A::createSessionKey(){
   mbedtls_mpi_read_binary(&K,tHash,64);           // load hash result into mpi structure K.  This is the SRP SHARED SECRET KEY
 
   mbedtls_mpi_write_binary(&K,sharedSecret,64);   // store SHARED SECRET in easy-to-use binary (uint8_t) format
-    
+  
 }
 
 //////////////////////////////////////
@@ -267,10 +268,10 @@ int SRP6A::writeTLV(kTLVType tag, mbedtls_mpi *mpi){
 
 void SRP6A::print(mbedtls_mpi *mpi){
   
-  char sBuf[1000];
+  char sBuf[2000];
   size_t sLen;
 
-  mbedtls_mpi_write_string(mpi,16,sBuf,1000,&sLen);
+  mbedtls_mpi_write_string(mpi,16,sBuf,2000,&sLen);
   
   Serial.print((sLen-1)/2);         // subtract 1 for null-terminator, and then divide by 2 to get number of bytes (e.g. 4F = 2 characters, but represents just one mpi byte)
   Serial.print(" ");
diff --git a/src/src.ino b/src/src.ino
index 4e2fd9f..d294292 100644
--- a/src/src.ino
+++ b/src/src.ino
@@ -8,7 +8,7 @@ void setup() {
  
   Serial.begin(115200);
  
-  homeSpan.setLogLevel(1);
+  homeSpan.setLogLevel(2);
   homeSpan.setStatusPin(5);
   homeSpan.setControlPin(33);