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/* Provide SSL/TLS functions to ESP32 with Arduino IDE
*
* Adapted from the ssl_client1 example of mbedtls.
*
* Original Copyright (C) 2006-2015, ARM Limited, All Rights Reserved, Apache 2.0 License.
* Additions Copyright (C) 2017 Evandro Luis Copercini, Apache 2.0 License.
*/
#include "Arduino.h"
#include <esp32-hal-log.h>
#include <lwip/err.h>
#include <lwip/sockets.h>
#include <lwip/sys.h>
#include <lwip/netdb.h>
#include <mbedtls/sha256.h>
#include <mbedtls/oid.h>
#include <algorithm>
#include <string>
#include "ssl_client.h"
#include "WiFi.h"
const char *pers = "esp32-tls";
static int handle_error(int err)
{
if(err == -30848){
return err;
}
#ifdef MBEDTLS_ERROR_C
char error_buf[100];
mbedtls_strerror(err, error_buf, 100);
log_e("%s", error_buf);
#endif
log_e("MbedTLS message code: %d", err);
return err;
}
void ssl_init(sslclient_context *ssl_client)
{
mbedtls_ssl_init(&ssl_client->ssl_ctx);
mbedtls_ssl_config_init(&ssl_client->ssl_conf);
mbedtls_ctr_drbg_init(&ssl_client->drbg_ctx);
}
int start_ssl_client(sslclient_context *ssl_client, const char *host, uint32_t port, const char *rootCABuff, const char *cli_cert, const char *cli_key, const char *pskIdent, const char *psKey)
{
char buf[512];
int ret, flags, timeout;
int enable = 1;
log_v("Free internal heap before TLS %u", ESP.getFreeHeap());
log_v("Starting socket");
ssl_client->socket = -1;
ssl_client->socket = lwip_socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ssl_client->socket < 0) {
log_e("ERROR opening socket");
return ssl_client->socket;
}
IPAddress srv((uint32_t)0);
if(!WiFiGenericClass::hostByName(host, srv)){
return -1;
}
struct sockaddr_in serv_addr;
memset(&serv_addr, 0, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = srv;
serv_addr.sin_port = htons(port);
if (lwip_connect(ssl_client->socket, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) == 0) {
timeout = 30000;
lwip_setsockopt(ssl_client->socket, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
lwip_setsockopt(ssl_client->socket, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof(timeout));
lwip_setsockopt(ssl_client->socket, IPPROTO_TCP, TCP_NODELAY, &enable, sizeof(enable));
lwip_setsockopt(ssl_client->socket, SOL_SOCKET, SO_KEEPALIVE, &enable, sizeof(enable));
} else {
log_e("Connect to Server failed!");
return -1;
}
fcntl( ssl_client->socket, F_SETFL, fcntl( ssl_client->socket, F_GETFL, 0 ) | O_NONBLOCK );
log_v("Seeding the random number generator");
mbedtls_entropy_init(&ssl_client->entropy_ctx);
ret = mbedtls_ctr_drbg_seed(&ssl_client->drbg_ctx, mbedtls_entropy_func,
&ssl_client->entropy_ctx, (const unsigned char *) pers, strlen(pers));
if (ret < 0) {
return handle_error(ret);
}
log_v("Setting up the SSL/TLS structure...");
if ((ret = mbedtls_ssl_config_defaults(&ssl_client->ssl_conf,
MBEDTLS_SSL_IS_CLIENT,
MBEDTLS_SSL_TRANSPORT_STREAM,
MBEDTLS_SSL_PRESET_DEFAULT)) != 0) {
return handle_error(ret);
}
// MBEDTLS_SSL_VERIFY_REQUIRED if a CA certificate is defined on Arduino IDE and
// MBEDTLS_SSL_VERIFY_NONE if not.
if (rootCABuff != NULL) {
log_v("Loading CA cert");
mbedtls_x509_crt_init(&ssl_client->ca_cert);
mbedtls_ssl_conf_authmode(&ssl_client->ssl_conf, MBEDTLS_SSL_VERIFY_REQUIRED);
ret = mbedtls_x509_crt_parse(&ssl_client->ca_cert, (const unsigned char *)rootCABuff, strlen(rootCABuff) + 1);
mbedtls_ssl_conf_ca_chain(&ssl_client->ssl_conf, &ssl_client->ca_cert, NULL);
//mbedtls_ssl_conf_verify(&ssl_client->ssl_ctx, my_verify, NULL );
if (ret < 0) {
return handle_error(ret);
}
} else if (pskIdent != NULL && psKey != NULL) {
log_v("Setting up PSK");
// convert PSK from hex to binary
if ((strlen(psKey) & 1) != 0 || strlen(psKey) > 2*MBEDTLS_PSK_MAX_LEN) {
log_e("pre-shared key not valid hex or too long");
return -1;
}
unsigned char psk[MBEDTLS_PSK_MAX_LEN];
size_t psk_len = strlen(psKey)/2;
for (int j=0; j<strlen(psKey); j+= 2) {
char c = psKey[j];
if (c >= '0' && c <= '9') c -= '0';
else if (c >= 'A' && c <= 'F') c -= 'A' - 10;
else if (c >= 'a' && c <= 'f') c -= 'a' - 10;
else return -1;
psk[j/2] = c<<4;
c = psKey[j+1];
if (c >= '0' && c <= '9') c -= '0';
else if (c >= 'A' && c <= 'F') c -= 'A' - 10;
else if (c >= 'a' && c <= 'f') c -= 'a' - 10;
else return -1;
psk[j/2] |= c;
}
// set mbedtls config
ret = mbedtls_ssl_conf_psk(&ssl_client->ssl_conf, psk, psk_len,
(const unsigned char *)pskIdent, strlen(pskIdent));
if (ret != 0) {
log_e("mbedtls_ssl_conf_psk returned %d", ret);
return handle_error(ret);
}
} else {
mbedtls_ssl_conf_authmode(&ssl_client->ssl_conf, MBEDTLS_SSL_VERIFY_NONE);
log_i("WARNING: Use certificates for a more secure communication!");
}
if (cli_cert != NULL && cli_key != NULL) {
mbedtls_x509_crt_init(&ssl_client->client_cert);
mbedtls_pk_init(&ssl_client->client_key);
log_v("Loading CRT cert");
ret = mbedtls_x509_crt_parse(&ssl_client->client_cert, (const unsigned char *)cli_cert, strlen(cli_cert) + 1);
if (ret < 0) {
return handle_error(ret);
}
log_v("Loading private key");
ret = mbedtls_pk_parse_key(&ssl_client->client_key, (const unsigned char *)cli_key, strlen(cli_key) + 1, NULL, 0);
if (ret != 0) {
return handle_error(ret);
}
mbedtls_ssl_conf_own_cert(&ssl_client->ssl_conf, &ssl_client->client_cert, &ssl_client->client_key);
}
log_v("Setting hostname for TLS session...");
// Hostname set here should match CN in server certificate
if((ret = mbedtls_ssl_set_hostname(&ssl_client->ssl_ctx, host)) != 0){
return handle_error(ret);
}
mbedtls_ssl_conf_rng(&ssl_client->ssl_conf, mbedtls_ctr_drbg_random, &ssl_client->drbg_ctx);
if ((ret = mbedtls_ssl_setup(&ssl_client->ssl_ctx, &ssl_client->ssl_conf)) != 0) {
return handle_error(ret);
}
mbedtls_ssl_set_bio(&ssl_client->ssl_ctx, &ssl_client->socket, mbedtls_net_send, mbedtls_net_recv, NULL );
log_v("Performing the SSL/TLS handshake...");
unsigned long handshake_start_time=millis();
while ((ret = mbedtls_ssl_handshake(&ssl_client->ssl_ctx)) != 0) {
if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
return handle_error(ret);
}
if((millis()-handshake_start_time)>ssl_client->handshake_timeout)
return -1;
vTaskDelay(10 / portTICK_PERIOD_MS);
}
if (cli_cert != NULL && cli_key != NULL) {
log_d("Protocol is %s Ciphersuite is %s", mbedtls_ssl_get_version(&ssl_client->ssl_ctx), mbedtls_ssl_get_ciphersuite(&ssl_client->ssl_ctx));
if ((ret = mbedtls_ssl_get_record_expansion(&ssl_client->ssl_ctx)) >= 0) {
log_d("Record expansion is %d", ret);
} else {
log_w("Record expansion is unknown (compression)");
}
}
log_v("Verifying peer X.509 certificate...");
if ((flags = mbedtls_ssl_get_verify_result(&ssl_client->ssl_ctx)) != 0) {
bzero(buf, sizeof(buf));
mbedtls_x509_crt_verify_info(buf, sizeof(buf), " ! ", flags);
log_e("Failed to verify peer certificate! verification info: %s", buf);
stop_ssl_socket(ssl_client, rootCABuff, cli_cert, cli_key); //It's not safe continue.
return handle_error(ret);
} else {
log_v("Certificate verified.");
}
if (rootCABuff != NULL) {
mbedtls_x509_crt_free(&ssl_client->ca_cert);
}
if (cli_cert != NULL) {
mbedtls_x509_crt_free(&ssl_client->client_cert);
}
if (cli_key != NULL) {
mbedtls_pk_free(&ssl_client->client_key);
}
log_v("Free internal heap after TLS %u", ESP.getFreeHeap());
return ssl_client->socket;
}
void stop_ssl_socket(sslclient_context *ssl_client, const char *rootCABuff, const char *cli_cert, const char *cli_key)
{
log_v("Cleaning SSL connection.");
if (ssl_client->socket >= 0) {
close(ssl_client->socket);
ssl_client->socket = -1;
}
mbedtls_ssl_free(&ssl_client->ssl_ctx);
mbedtls_ssl_config_free(&ssl_client->ssl_conf);
mbedtls_ctr_drbg_free(&ssl_client->drbg_ctx);
mbedtls_entropy_free(&ssl_client->entropy_ctx);
}
int data_to_read(sslclient_context *ssl_client)
{
int ret, res;
ret = mbedtls_ssl_read(&ssl_client->ssl_ctx, NULL, 0);
//log_e("RET: %i",ret); //for low level debug
res = mbedtls_ssl_get_bytes_avail(&ssl_client->ssl_ctx);
//log_e("RES: %i",res); //for low level debug
if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE && ret < 0) {
return handle_error(ret);
}
return res;
}
int send_ssl_data(sslclient_context *ssl_client, const uint8_t *data, uint16_t len)
{
log_v("Writing HTTP request..."); //for low level debug
int ret = -1;
while ((ret = mbedtls_ssl_write(&ssl_client->ssl_ctx, data, len)) <= 0) {
if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
return handle_error(ret);
}
}
len = ret;
//log_v("%d bytes written", len); //for low level debug
return ret;
}
int get_ssl_receive(sslclient_context *ssl_client, uint8_t *data, int length)
{
//log_d( "Reading HTTP response..."); //for low level debug
int ret = -1;
ret = mbedtls_ssl_read(&ssl_client->ssl_ctx, data, length);
//log_v( "%d bytes read", ret); //for low level debug
return ret;
}
static bool parseHexNibble(char pb, uint8_t* res)
{
if (pb >= '0' && pb <= '9') {
*res = (uint8_t) (pb - '0'); return true;
} else if (pb >= 'a' && pb <= 'f') {
*res = (uint8_t) (pb - 'a' + 10); return true;
} else if (pb >= 'A' && pb <= 'F') {
*res = (uint8_t) (pb - 'A' + 10); return true;
}
return false;
}
// Compare a name from certificate and domain name, return true if they match
static bool matchName(const std::string& name, const std::string& domainName)
{
size_t wildcardPos = name.find('*');
if (wildcardPos == std::string::npos) {
// Not a wildcard, expect an exact match
return name == domainName;
}
size_t firstDotPos = name.find('.');
if (wildcardPos > firstDotPos) {
// Wildcard is not part of leftmost component of domain name
// Do not attempt to match (rfc6125 6.4.3.1)
return false;
}
if (wildcardPos != 0 || firstDotPos != 1) {
// Matching of wildcards such as baz*.example.com and b*z.example.com
// is optional. Maybe implement this in the future?
return false;
}
size_t domainNameFirstDotPos = domainName.find('.');
if (domainNameFirstDotPos == std::string::npos) {
return false;
}
return domainName.substr(domainNameFirstDotPos) == name.substr(firstDotPos);
}
// Verifies certificate provided by the peer to match specified SHA256 fingerprint
bool verify_ssl_fingerprint(sslclient_context *ssl_client, const char* fp, const char* domain_name)
{
// Convert hex string to byte array
uint8_t fingerprint_local[32];
int len = strlen(fp);
int pos = 0;
for (size_t i = 0; i < sizeof(fingerprint_local); ++i) {
while (pos < len && ((fp[pos] == ' ') || (fp[pos] == ':'))) {
++pos;
}
if (pos > len - 2) {
log_d("pos:%d len:%d fingerprint too short", pos, len);
return false;
}
uint8_t high, low;
if (!parseHexNibble(fp[pos], &high) || !parseHexNibble(fp[pos+1], &low)) {
log_d("pos:%d len:%d invalid hex sequence: %c%c", pos, len, fp[pos], fp[pos+1]);
return false;
}
pos += 2;
fingerprint_local[i] = low | (high << 4);
}
// Get certificate provided by the peer
const mbedtls_x509_crt* crt = mbedtls_ssl_get_peer_cert(&ssl_client->ssl_ctx);
if (!crt)
{
log_d("could not fetch peer certificate");
return false;
}
// Calculate certificate's SHA256 fingerprint
uint8_t fingerprint_remote[32];
mbedtls_sha256_context sha256_ctx;
mbedtls_sha256_init(&sha256_ctx);
mbedtls_sha256_starts(&sha256_ctx, false);
mbedtls_sha256_update(&sha256_ctx, crt->raw.p, crt->raw.len);
mbedtls_sha256_finish(&sha256_ctx, fingerprint_remote);
// Check if fingerprints match
if (memcmp(fingerprint_local, fingerprint_remote, 32))
{
log_d("fingerprint doesn't match");
return false;
}
// Additionally check if certificate has domain name if provided
if (domain_name)
return verify_ssl_dn(ssl_client, domain_name);
else
return true;
}
// Checks if peer certificate has specified domain in CN or SANs
bool verify_ssl_dn(sslclient_context *ssl_client, const char* domain_name)
{
log_d("domain name: '%s'", (domain_name)?domain_name:"(null)");
std::string domain_name_str(domain_name);
std::transform(domain_name_str.begin(), domain_name_str.end(), domain_name_str.begin(), ::tolower);
// Get certificate provided by the peer
const mbedtls_x509_crt* crt = mbedtls_ssl_get_peer_cert(&ssl_client->ssl_ctx);
// Check for domain name in SANs
const mbedtls_x509_sequence* san = &crt->subject_alt_names;
while (san != nullptr)
{
std::string san_str((const char*)san->buf.p, san->buf.len);
std::transform(san_str.begin(), san_str.end(), san_str.begin(), ::tolower);
if (matchName(san_str, domain_name_str))
return true;
log_d("SAN '%s': no match", san_str.c_str());
// Fetch next SAN
san = san->next;
}
// Check for domain name in CN
const mbedtls_asn1_named_data* common_name = &crt->subject;
while (common_name != nullptr)
{
// While iterating through DN objects, check for CN object
if (!MBEDTLS_OID_CMP(MBEDTLS_OID_AT_CN, &common_name->oid))
{
std::string common_name_str((const char*)common_name->val.p, common_name->val.len);
if (matchName(common_name_str, domain_name_str))
return true;
log_d("CN '%s': not match", common_name_str.c_str());
}
// Fetch next DN object
common_name = common_name->next;
}
return false;
}