Seich
/
HomeSpan
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

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.
This commit is contained in:
Gregg 2021-09-23 21:12:37 -05:00
parent 0dd341faa9
commit 07da5ac924
2 changed files with 8 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
src/SRP.cpp
View File

@ -144,8 +144,8 @@ void SRP6A::createPublicKey(){
void SRP6A::getPrivateKey(){ void SRP6A::getPrivateKey(){
uint8_t privateKey[32]; uint8_t privateKey[32];
randombytes_buf(privateKey,32); // generate 32 random bytes using libsodium (which uses the ESP32 hardware-based random number generator) 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); 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 mbedtls_mpi_read_binary(&u,tHash,64); // load hash result into mpi structure u
// compute S = (Av^u)^b %N // compute S = (Av^u)^b %N
mbedtls_mpi_exp_mod(&t1,&v,&u,&N,&_rr); // t1 = v^u %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_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 ) // 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_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 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){ void SRP6A::print(mbedtls_mpi *mpi){
char sBuf[1000]; char sBuf[2000];
size_t sLen; 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((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(" "); Serial.print(" ");

2
src/src.ino
View File

@ -8,7 +8,7 @@ void setup() {
Serial.begin(115200); Serial.begin(115200);
homeSpan.setLogLevel(1); homeSpan.setLogLevel(2);
homeSpan.setStatusPin(5); homeSpan.setStatusPin(5);
homeSpan.setControlPin(33); homeSpan.setControlPin(33);