WiFiClientSecureBearSSL.h

/*
  WiFiClientBearSSL- SSL client/server for esp8266 using BearSSL libraries
  - Mostly compatible with Arduino WiFi shield library and standard
    WiFiClient/ServerSecure (except for certificate handling).

  Copyright (c) 2018 Earle F. Philhower, III

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/


#ifndef wificlientbearssl_h
#define wificlientbearssl_h
#include <vector>
#include "WiFiClient.h"
#include <bearssl/bearssl.h>
#include "BearSSLHelpers.h"
#include "CertStoreBearSSL.h"

namespace BearSSL {

class WiFiClientSecureCtx : public WiFiClient {
  public:
    WiFiClientSecureCtx();
    WiFiClientSecureCtx(const WiFiClientSecureCtx &rhs) = delete;
    ~WiFiClientSecureCtx() override;

    WiFiClientSecureCtx& operator=(const WiFiClientSecureCtx&) = delete;

    // TODO: usage is invalid b/c of deleted copy, but this will only trigger an error when it is actually used by something
    // TODO: don't remove just yet to avoid including the WiFiClient default implementation and unintentionally causing
    //       a 'slice' that this method tries to avoid in the first place
    std::unique_ptr<WiFiClient> clone() const override {
        return nullptr;
    }

    int connect(IPAddress ip, uint16_t port) override;
    int connect(const String& host, uint16_t port) override;
    int connect(const char* name, uint16_t port) override;

    uint8_t connected() override;
    size_t write(const uint8_t *buf, size_t size) override;
    size_t write_P(PGM_P buf, size_t size) override;
    size_t write(Stream& stream); // Note this is not virtual
    int read(uint8_t *buf, size_t size) override;
    int read(char *buf, size_t size) { return read((uint8_t*)buf, size); }
    int available() override;
    int read() override;
    int peek() override;
    size_t peekBytes(uint8_t *buffer, size_t length) override;
    bool flush(unsigned int maxWaitMs);
    bool stop(unsigned int maxWaitMs);
    void flush() override { (void)flush(0); }
    void stop() override { (void)stop(0); }

    int availableForWrite() override;

    // Allow sessions to be saved/restored automatically to a memory area
    void setSession(Session *session) { _session = session; }

    // Don't validate the chain, just accept whatever is given.  VERY INSECURE!
    void setInsecure() {
      _clearAuthenticationSettings();
      _use_insecure = true;
    }
    // Assume a given public key, don't validate or use cert info at all
    void setKnownKey(const PublicKey *pk, unsigned usages = BR_KEYTYPE_KEYX | BR_KEYTYPE_SIGN) {
      _clearAuthenticationSettings();
      _knownkey = pk;
      _knownkey_usages = usages;
    }
    // Only check SHA1 fingerprint of certificate
    bool setFingerprint(const uint8_t fingerprint[20]) {
      _clearAuthenticationSettings();
      _use_fingerprint = true;
      memcpy_P(_fingerprint, fingerprint, 20);
      return true;
    }
    bool setFingerprint(const char *fpStr);
    // Accept any certificate that's self-signed
    void allowSelfSignedCerts() {
      _clearAuthenticationSettings();
      _use_self_signed = true;
    }
    // Install certificates of trusted CAs or specific site
    void setTrustAnchors(const X509List *ta) {
      _clearAuthenticationSettings();
      _ta = ta;
    }
    // In cases when NTP is not used, app must set a time manually to check cert validity
    void setX509Time(time_t now) {
      _now = now;
    }
    // Install a client certificate for this connection, in case the server requires it (i.e. MQTT)
    void setClientRSACert(const X509List *cert, const PrivateKey *sk);
    void setClientECCert(const X509List *cert, const PrivateKey *sk,
                         unsigned allowed_usages, unsigned cert_issuer_key_type);

    // Sets the requested buffer size for transmit and receive
    void setBufferSizes(int recv, int xmit);

    // Returns whether MFLN negotiation for the above buffer sizes succeeded (after connection)
    int getMFLNStatus() {
      return connected() && br_ssl_engine_get_mfln_negotiated(_eng);
    }

    // Return an error code and possibly a text string in a passed-in buffer with last SSL failure
    int getLastSSLError(char *dest = NULL, size_t len = 0);

    // Attach a preconfigured certificate store
    void setCertStore(CertStoreBase *certStore) {
      _certStore = certStore;
    }

    // Select specific ciphers (i.e. optimize for speed over security)
    // These may be in PROGMEM or RAM, either will run properly
    bool setCiphers(const uint16_t *cipherAry, int cipherCount);
    bool setCiphers(const std::vector<uint16_t>& list);
    bool setCiphersLessSecure(); // Only use the limited set of RSA ciphers without EC

    // Limit the TLS versions BearSSL will connect with.  Default is
    // BR_TLS10...BR_TLS12
    bool setSSLVersion(uint32_t min = BR_TLS10, uint32_t max = BR_TLS12);

    // peek buffer API is present
    virtual bool hasPeekBufferAPI () const override { return true; }

    // return number of byte accessible by peekBuffer()
    virtual size_t peekAvailable () override { return WiFiClientSecureCtx::available(); }

    // return a pointer to available data buffer (size = peekAvailable())
    // semantic forbids any kind of read() before calling peekConsume()
    virtual const char* peekBuffer () override;

    // consume bytes after use (see peekBuffer)
    virtual void peekConsume (size_t consume) override;

  protected:
    bool _connectSSL(const char *hostName); // Do initial SSL handshake

  private:
    void _clear();
    void _clearAuthenticationSettings();
    // Only one of the following two should ever be != nullptr!
    std::shared_ptr<br_ssl_client_context> _sc;
    std::shared_ptr<br_ssl_server_context> _sc_svr;
    inline bool ctx_present() {
      return (_sc != nullptr) || (_sc_svr != nullptr);
    }
    br_ssl_engine_context *_eng; // &_sc->eng, to allow for client or server contexts
    std::shared_ptr<br_x509_minimal_context> _x509_minimal;
    std::shared_ptr<struct br_x509_insecure_context> _x509_insecure;
    std::shared_ptr<br_x509_knownkey_context> _x509_knownkey;
    std::shared_ptr<unsigned char> _iobuf_in;
    std::shared_ptr<unsigned char> _iobuf_out;
    time_t _now;
    const X509List *_ta;
    CertStoreBase *_certStore;
    int _iobuf_in_size;
    int _iobuf_out_size;
    bool _handshake_done;
    bool _oom_err;

    // Optional storage space pointer for session parameters
    // Will be used on connect and updated on close
    Session *_session;

    bool _use_insecure;
    bool _use_fingerprint;
    uint8_t _fingerprint[20];
    bool _use_self_signed;
    const PublicKey *_knownkey;
    unsigned _knownkey_usages;

    // Custom cipher list pointer or NULL if default
    std::shared_ptr<uint16_t> _cipher_list;
    uint8_t _cipher_cnt;

    // TLS ciphers allowed
    uint32_t _tls_min;
    uint32_t _tls_max;

    unsigned char *_recvapp_buf;
    size_t _recvapp_len;

    int _pollRecvBuffer(); // If there's a buffer with some pending data, return it's length
                           // If there's no buffer, poll the engine and store any received data there and return the length
                           // (which also may change the internal state, e.g. make us disconnected)

    bool _clientConnected(); // Is the underlying socket alive?
    bool _engineConnected(); // Are both socket and the bearssl engine alive?

    std::shared_ptr<unsigned char> _alloc_iobuf(size_t sz);
    void _freeSSL();
    int _run_until(unsigned target, bool blocking = true);
    size_t _write(const uint8_t *buf, size_t size, bool pmem);
    bool _wait_for_handshake(); // Sets and return the _handshake_done after connecting

    // Optional client certificate
    const X509List *_chain;
    const PrivateKey *_sk;
    unsigned _allowed_usages;
    unsigned _cert_issuer_key_type;

    // Methods for handling server.available() call which returns a client connection.
    friend class WiFiClientSecure; // access to private context constructors
    WiFiClientSecureCtx(ClientContext *client, const X509List *chain, unsigned cert_issuer_key_type,
                      const PrivateKey *sk, int iobuf_in_size, int iobuf_out_size, ServerSessions *cache,
                      const X509List *client_CA_ta, int tls_min, int tls_max);
    WiFiClientSecureCtx(ClientContext* client, const X509List *chain, const PrivateKey *sk,
                      int iobuf_in_size, int iobuf_out_size, ServerSessions *cache,
                      const X509List *client_CA_ta, int tls_min, int tls_max);

    // RSA keyed server
    bool _connectSSLServerRSA(const X509List *chain, const PrivateKey *sk,
                              ServerSessions *cache, const X509List *client_CA_ta);
    // EC keyed server
    bool _connectSSLServerEC(const X509List *chain, unsigned cert_issuer_key_type, const PrivateKey *sk,
                             ServerSessions *cache, const X509List *client_CA_ta);

    // X.509 validators differ from server to client
    bool _installClientX509Validator(); // Set up X509 validator for a client conn.
    bool _installServerX509Validator(const X509List *client_CA_ta); // Setup X509 client cert validation, if supplied

    uint8_t *_streamLoad(Stream& stream, size_t size);
}; // class WiFiClientSecureCtx


class WiFiClientSecure : public WiFiClient {

  // WiFiClient's "ClientContext* _client" is always nullptr in this class.
  // Instead, all virtual functions call their counterpart in "WiFiClientecureCtx* _ctx"
  //          which also derives from WiFiClient (this parent is the one which is eventually used)

  // TODO: notice that this complicates the implementation by having two distinct ways the client connection is managed, consider:
  // - implementing the secure connection details in the ClientContext
  //   (i.e. delegate the write & read functions there)
  // - simplify the inheritance chain by implementing base wificlient class and inherit the original wificlient and wificlientsecure from it
  // - abstract internals so it's possible to seamlessly =default copy and move with the instance *without* resorting to manual copy and initialization of each member

  // TODO: prefer implementing virtual overrides in the .cpp (or, at least one of them)

  public:

    WiFiClientSecure():_ctx(new WiFiClientSecureCtx()) { _owned = _ctx.get(); }
    WiFiClientSecure(const WiFiClientSecure &rhs): WiFiClient(), _ctx(rhs._ctx) { if (_ctx) _owned = _ctx.get(); }
    ~WiFiClientSecure() override { _ctx = nullptr; }

    WiFiClientSecure& operator=(const WiFiClientSecure&) = default;

    std::unique_ptr<WiFiClient> clone() const override { return std::unique_ptr<WiFiClient>(new WiFiClientSecure(*this)); }

    uint8_t status() override { return _ctx->status(); }
    int connect(IPAddress ip, uint16_t port) override { return _ctx->connect(ip, port); }
    int connect(const String& host, uint16_t port) override { return _ctx->connect(host, port); }
    int connect(const char* name, uint16_t port) override { return _ctx->connect(name, port); }

    uint8_t connected() override { return _ctx->connected(); }
    size_t write(const uint8_t *buf, size_t size) override { return _ctx->write(buf, size); }
    size_t write_P(PGM_P buf, size_t size) override { return _ctx->write_P(buf, size); }
    size_t write(const char *buf) { return write((const uint8_t*)buf, strlen(buf)); }
    size_t write_P(const char *buf) { return write_P((PGM_P)buf, strlen_P(buf)); }
    size_t write(Stream& stream) /* Note this is not virtual */ { return _ctx->write(stream); }
    int read(uint8_t *buf, size_t size) override { return _ctx->read(buf, size); }
    int available() override { return _ctx->available(); }
    int availableForWrite() override { return _ctx->availableForWrite(); }
    int read() override { return _ctx->read(); }
    int peek() override { return _ctx->peek(); }
    size_t peekBytes(uint8_t *buffer, size_t length) override { return _ctx->peekBytes(buffer, length); }
    bool flush(unsigned int maxWaitMs) { return _ctx->flush(maxWaitMs); }
    bool stop(unsigned int maxWaitMs) { return _ctx->stop(maxWaitMs); }
    void flush() override { (void)flush(0); }
    void stop() override { (void)stop(0); }

    IPAddress remoteIP() override { return _ctx->remoteIP(); }
    uint16_t  remotePort() override { return _ctx->remotePort(); }
    IPAddress localIP() override { return _ctx->localIP(); }
    uint16_t  localPort() override { return _ctx->localPort(); }

    // Allow sessions to be saved/restored automatically to a memory area
    void setSession(Session *session) { _ctx->setSession(session); }

    // Don't validate the chain, just accept whatever is given.  VERY INSECURE!
    void setInsecure() { _ctx->setInsecure(); }

    // Assume a given public key, don't validate or use cert info at all
    void setKnownKey(const PublicKey *pk, unsigned usages = BR_KEYTYPE_KEYX | BR_KEYTYPE_SIGN) {
      _ctx->setKnownKey(pk, usages);
    }
    // Only check SHA1 fingerprint of certificate
    bool setFingerprint(const uint8_t fingerprint[20]) {
      return _ctx->setFingerprint(fingerprint);
    }
    bool setFingerprint(const char *fpStr) { return _ctx->setFingerprint(fpStr); }
    // Accept any certificate that's self-signed
    void allowSelfSignedCerts() { _ctx->allowSelfSignedCerts(); }

    // Install certificates of trusted CAs or specific site
    void setTrustAnchors(const X509List *ta) { _ctx->setTrustAnchors(ta); }
    // In cases when NTP is not used, app must set a time manually to check cert validity
    void setX509Time(time_t now) { _ctx->setX509Time(now); }
    // Install a client certificate for this connection, in case the server requires it (i.e. MQTT)
    void setClientRSACert(const X509List *cert, const PrivateKey *sk) { _ctx->setClientRSACert(cert, sk); }
    void setClientECCert(const X509List *cert, const PrivateKey *sk,
                         unsigned allowed_usages, unsigned cert_issuer_key_type) {
      _ctx->setClientECCert(cert, sk, allowed_usages, cert_issuer_key_type);
    }

    // Sets the requested buffer size for transmit and receive
    void setBufferSizes(int recv, int xmit) { _ctx->setBufferSizes(recv, xmit); }

    // Returns whether MFLN negotiation for the above buffer sizes succeeded (after connection)
    int getMFLNStatus() { return _ctx->getMFLNStatus(); }

    // Return an error code and possibly a text string in a passed-in buffer with last SSL failure
    int getLastSSLError(char *dest = NULL, size_t len = 0) { return _ctx->getLastSSLError(dest, len); }

    // Attach a preconfigured certificate store
    void setCertStore(CertStoreBase *certStore) { _ctx->setCertStore(certStore); }

    // Select specific ciphers (i.e. optimize for speed over security)
    // These may be in PROGMEM or RAM, either will run properly
    bool setCiphers(const uint16_t *cipherAry, int cipherCount) { return _ctx->setCiphers(cipherAry, cipherCount); }
    bool setCiphers(const std::vector<uint16_t> list) { return _ctx->setCiphers(list); }
    bool setCiphersLessSecure() { return _ctx->setCiphersLessSecure(); } // Only use the limited set of RSA ciphers without EC

    // Limit the TLS versions BearSSL will connect with.  Default is
    // BR_TLS10...BR_TLS12. Allowed values are: BR_TLS10, BR_TLS11, BR_TLS12
    bool setSSLVersion(uint32_t min = BR_TLS10, uint32_t max = BR_TLS12) { return _ctx->setSSLVersion(min, max); };

    // Check for Maximum Fragment Length support for given len before connection (possibly insecure)
    static bool probeMaxFragmentLength(IPAddress ip, uint16_t port, uint16_t len);
    static bool probeMaxFragmentLength(const char *hostname, uint16_t port, uint16_t len);
    static bool probeMaxFragmentLength(const String& host, uint16_t port, uint16_t len);

    // peek buffer API is present
    virtual bool hasPeekBufferAPI () const override { return true; }

    // return number of byte accessible by peekBuffer()
    virtual size_t peekAvailable () override { return _ctx->available(); }

    // return a pointer to available data buffer (size = peekAvailable())
    // semantic forbids any kind of read() before calling peekConsume()
    virtual const char* peekBuffer () override { return _ctx->peekBuffer(); }

    // consume bytes after use (see peekBuffer)
    virtual void peekConsume (size_t consume) override { return _ctx->peekConsume(consume); }

  private:
    std::shared_ptr<WiFiClientSecureCtx> _ctx;

    // Methods for handling server.available() call which returns a client connection.
    friend class WiFiServerSecure; // Server needs to access these constructors
    WiFiClientSecure(ClientContext *client, const X509List *chain, unsigned cert_issuer_key_type,
                      const PrivateKey *sk, int iobuf_in_size, int iobuf_out_size, ServerSessions *cache,
                      const X509List *client_CA_ta, int tls_min, int tls_max):
      _ctx(new WiFiClientSecureCtx(client, chain, cert_issuer_key_type, sk, iobuf_in_size, iobuf_out_size, cache, client_CA_ta, tls_min, tls_max)) {
    }

    WiFiClientSecure(ClientContext* client, const X509List *chain, const PrivateKey *sk,
                      int iobuf_in_size, int iobuf_out_size, ServerSessions *cache,
                      const X509List *client_CA_ta, int tls_min, int tls_max):
      _ctx(new WiFiClientSecureCtx(client, chain, sk, iobuf_in_size, iobuf_out_size, cache, client_CA_ta, tls_min, tls_max)) {
    }

}; // class WiFiClientSecure

}; // namespace BearSSL

#endif