278 lines
11 KiB
C++
278 lines
11 KiB
C++
/*********************************************************************************
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* MIT License
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*
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* Copyright (c) 2020-2023 Gregg E. Berman
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*
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* https://github.com/HomeSpan/HomeSpan
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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********************************************************************************/
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#include <sodium.h>
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#include <Arduino.h>
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#include "SRP.h"
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#include "HAP.h"
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/////////////////////////////////////////////////////////////////////////////////
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/////////////////////////////////////////////////////////////////////////////////
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SRP6A::SRP6A(){
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// initialize MPI structures
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mbedtls_mpi_init(&N);
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mbedtls_mpi_init(&g);
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mbedtls_mpi_init(&s);
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mbedtls_mpi_init(&x);
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mbedtls_mpi_init(&v);
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mbedtls_mpi_init(&A);
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mbedtls_mpi_init(&b);
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mbedtls_mpi_init(&B);
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mbedtls_mpi_init(&S);
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mbedtls_mpi_init(&k);
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mbedtls_mpi_init(&u);
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mbedtls_mpi_init(&K);
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mbedtls_mpi_init(&M1);
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mbedtls_mpi_init(&M1V);
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mbedtls_mpi_init(&M2);
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mbedtls_mpi_init(&_rr);
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mbedtls_mpi_init(&t1);
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mbedtls_mpi_init(&t2);
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mbedtls_mpi_init(&t3);
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// load N and g into MPI structures
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mbedtls_mpi_read_string(&N,16,N3072);
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mbedtls_mpi_lset(&g,g3072);
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}
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//////////////////////////////////////
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SRP6A::~SRP6A(){
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mbedtls_mpi_free(&N);
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mbedtls_mpi_free(&g);
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mbedtls_mpi_free(&s);
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mbedtls_mpi_free(&x);
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mbedtls_mpi_free(&v);
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mbedtls_mpi_free(&A);
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mbedtls_mpi_free(&b);
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mbedtls_mpi_free(&B);
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mbedtls_mpi_free(&S);
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mbedtls_mpi_free(&k);
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mbedtls_mpi_free(&u);
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mbedtls_mpi_free(&K);
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mbedtls_mpi_free(&M1);
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mbedtls_mpi_free(&M1V);
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mbedtls_mpi_free(&M2);
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mbedtls_mpi_free(&_rr);
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mbedtls_mpi_free(&t1);
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mbedtls_mpi_free(&t2);
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mbedtls_mpi_free(&t3);
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}
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//////////////////////////////////////
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void SRP6A::createVerifyCode(const char *setupCode, Verification *vData){
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TempBuffer<uint8_t> tBuf(80); // temporary buffer for staging
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TempBuffer<uint8_t> tHash(64); // temporary buffer for storing SHA-512 results
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char *icp; // storage for I:P
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// generate random salt, s
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randombytes_buf(vData->salt,16); // generate 16 random bytes for salt
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// create I:P
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asprintf(&icp,"%s:%.3s-%.2s-%.3s",I,setupCode,setupCode+3,setupCode+5);
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// compute x = SHA512( s | SHA512( I | ":" | P ) )
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memcpy(tBuf,vData->salt,16); // write salt into first 16 bytes of staging buffer
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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
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mbedtls_sha512_ret(tBuf,80,tHash,0); // create second hash of salted, hashed username:password
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mbedtls_mpi_read_binary(&x,tHash,64); // load hash result into x
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// compute v = g^x %N
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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)
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mbedtls_mpi_write_binary(&v,vData->verifyCode,384); // write v into verifyCode
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free(icp);
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}
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//////////////////////////////////////
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void SRP6A::createPublicKey(const Verification *vData, uint8_t *publicKey){
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TempBuffer<uint8_t> tBuf(768); // temporary buffer for staging
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TempBuffer<uint8_t> tHash(64); // temporary buffer for storing SHA-512 results
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TempBuffer<uint8_t> privateKey(32); // temporary buffer for generating private key random numbers
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// load stored salt, s, and verification code, v
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mbedtls_mpi_read_binary(&s,vData->salt,16); // load salt into s for use in later steps
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mbedtls_mpi_read_binary(&v,vData->verifyCode,384); // load verifyCode into v for use below
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// generate random private key, b
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randombytes_buf(privateKey,32); // generate 32 random bytes for private key
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mbedtls_mpi_read_binary(&b,privateKey,32); // load private key into b
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// compute k = SHA512( N | PAD(g) )
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mbedtls_mpi_write_binary(&N,tBuf,384); // write N into first half of staging buffer
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mbedtls_mpi_write_binary(&g,tBuf+384,384); // write g into second half of staging buffer (fully padded with leading zeros)
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mbedtls_sha512_ret(tBuf,768,tHash,0); // create hash of data
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mbedtls_mpi_read_binary(&k,tHash,64); // load hash result into k
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// compute B = (kv + g^b) %N
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mbedtls_mpi_mul_mpi(&t1,&k,&v); // t1 = k*v
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mbedtls_mpi_exp_mod(&t2,&g,&b,&N,&_rr); // t2 = g^b %N
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mbedtls_mpi_add_mpi(&t3,&t1,&t2); // t3 = t1 + t2
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mbedtls_mpi_mod_mpi(&B,&t3,&N); // B = t3 %N = ACCESSORY PUBLIC KEY
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mbedtls_mpi_write_binary(&B,publicKey,384); // write B into publicKey
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}
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//////////////////////////////////////
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void SRP6A::createSessionKey(const uint8_t *publicKey, size_t len){
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TempBuffer<uint8_t> tBuf(768); // temporary buffer for staging
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TempBuffer<uint8_t> tHash(64); // temporary buffer for storing SHA-512 results
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mbedtls_mpi_read_binary(&A,publicKey,len); // load client PublicKey into A
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// compute u = SHA512( PAD(A) | PAD(B) )
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mbedtls_mpi_write_binary(&A,tBuf,384); // write A into first half of staging buffer (will pad to fill 384 bytes)
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mbedtls_mpi_write_binary(&B,tBuf+384,384); // write B into second half of staging buffer (will pad to fill 384 bytes)
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mbedtls_sha512_ret(tBuf,768,tHash,0); // create hash of data
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mbedtls_mpi_read_binary(&u,tHash,64); // load hash result into mpi structure u
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// compute S = (Av^u)^b %N
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mbedtls_mpi_exp_mod(&t1,&v,&u,&N,&_rr); // t1 = v^u %N
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mbedtls_mpi_mul_mpi(&t2,&A,&t1); // t2 = A*t1
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mbedtls_mpi_mod_mpi(&t1,&t2,&N); // t1 = t2 %N (this is needed to reduce size of t2 before next calculation)
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mbedtls_mpi_exp_mod(&S,&t1,&b,&N,&_rr); // S = t1^b %N
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// compute K = SHA512( S )
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mbedtls_mpi_write_binary(&S,tBuf,384); // write S into staging buffer (only first half of buffer will be used)
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mbedtls_sha512_ret(tBuf,384,tHash,0); // create hash of data
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mbedtls_mpi_read_binary(&K,tHash,64); // load hash result into mpi structure K. This is the SRP SHARED SECRET KEY
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mbedtls_mpi_write_binary(&K,sharedSecret,64); // store SHARED SECRET in easy-to-use binary (uint8_t) format
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}
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//////////////////////////////////////
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int SRP6A::verifyClientProof(const uint8_t *proof){
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TempBuffer<uint8_t> tBuf(976); // temporary buffer for staging
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TempBuffer<uint8_t> tHash(64); // temporary buffer for storing SHA-512 results
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mbedtls_mpi_read_binary(&M1,proof,64); // load client Proof into M1
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size_t count=0; // total number of bytes for final hash
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size_t sLen;
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// compute M1V
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mbedtls_mpi_write_binary(&N,tBuf,384); // write N into staging buffer
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mbedtls_sha512_ret(tBuf,384,tHash,0); // create hash of data
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mbedtls_sha512_ret(&g3072,1,tBuf,0); // create hash of g, but place output directly into staging buffer
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for(int i=0;i<64;i++) // H(g) -> H(g) XOR H(N), with results in first 64 bytes of staging buffer
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tBuf[i]^=tHash[i];
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mbedtls_sha512_ret((uint8_t *)I,strlen(I),tBuf+64,0); // create hash of userName and concatenate result to end of staging buffer
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mbedtls_mpi_write_binary(&s,tBuf+128,16); // concatenate s to staging buffer
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sLen=mbedtls_mpi_size(&A); // get actual size of A
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mbedtls_mpi_write_binary(&A,tBuf+144,sLen); // concatenate A to staging buffer. Note A is NOT padded with leading zeros (so may be less than 384 bytes)
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count=144+sLen; // total bytes written to staging buffer so far
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sLen=mbedtls_mpi_size(&B); // get actual size of B
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mbedtls_mpi_write_binary(&B,tBuf+count,sLen); // concatenate B to staging buffer. Note B is NOT padded with leading zeros (so may be less than 384 bytes)
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count+=sLen; // increment total bytes written to staging buffer
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mbedtls_mpi_write_binary(&K,tBuf+count,64); // concatenate K to staging buffer (should always be 64 bytes since it is a hashed value)
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count+=64; // final total of bytes written to staging buffer
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mbedtls_sha512_ret(tBuf,count,tHash,0); // create hash of data
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mbedtls_mpi_read_binary(&M1V,tHash,64); // load hash result into mpi structure M1V
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// check that client Proof M1 matches M1V
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if(!mbedtls_mpi_cmp_mpi(&M1,&M1V)) // cmp_mpi uses same logic as strcmp: returns 0 if EQUAL, otherwise +/- 1
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return(1); // success - proof from HAP Client is verified
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return(0);
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}
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//////////////////////////////////////
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void SRP6A::createAccProof(uint8_t *proof){
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uint8_t tBuf[512]; // temporary buffer for staging
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// compute M2 = H( A | M1 | K )
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mbedtls_mpi_write_binary(&A,tBuf,384); // write A into staging buffer
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mbedtls_mpi_write_binary(&M1,tBuf+384,64); // concatenate M1 (now verified) to staging buffer
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mbedtls_mpi_write_binary(&K,tBuf+448,64); // concatenate K to staging buffer
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mbedtls_sha512_ret(tBuf,512,tBuf,0); // create hash of data
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mbedtls_mpi_read_binary(&M2,tBuf,64); // load hash results into mpi structure M2
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mbedtls_mpi_write_binary(&M2,proof,64); // write M2 into proof
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}
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//////////////////////////////////////
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void SRP6A::print(mbedtls_mpi *mpi){
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size_t sLen;
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mbedtls_mpi_write_string(mpi,16,NULL,0,&sLen);
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TempBuffer<char> sBuf(sLen);
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mbedtls_mpi_write_string(mpi,16,sBuf,sLen,&sLen);
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Serial.printf("%d %s\n",(sLen-1)/2,sBuf.get()); // 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)
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}
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//////////////////////////////////////
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constexpr char SRP6A::N3072[];
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constexpr char SRP6A::I[];
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const uint8_t SRP6A::g3072;
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