TLS: add BearSSL vtls implementation

Closes #4597

7 files changed, 918 insertions, 4 deletions

diff --git a/lib/Makefile.inc b/lib/Makefile.inc
index 3a561d4d1..6c90c2675 100644
--- a/lib/Makefile.inc
+++ b/lib/Makefile.inc
@@ -30,12 +30,13 @@ LIB_VAUTH_HFILES = vauth/vauth.h vauth/digest.h vauth/ntlm.h
 LIB_VTLS_CFILES = vtls/openssl.c vtls/gtls.c vtls/vtls.c vtls/nss.c     \
   vtls/polarssl.c vtls/polarssl_threadlock.c                            \
   vtls/wolfssl.c vtls/schannel.c vtls/schannel_verify.c                 \
-  vtls/sectransp.c vtls/gskit.c vtls/mbedtls.c vtls/mesalink.c
+  vtls/sectransp.c vtls/gskit.c vtls/mbedtls.c vtls/mesalink.c          \
+  vtls/bearssl.c
 
 LIB_VTLS_HFILES = vtls/openssl.h vtls/vtls.h vtls/gtls.h                \
   vtls/nssg.h vtls/polarssl.h vtls/polarssl_threadlock.h                \
   vtls/wolfssl.h vtls/schannel.h vtls/sectransp.h vtls/gskit.h          \
-  vtls/mbedtls.h vtls/mesalink.h
+  vtls/mbedtls.h vtls/mesalink.h vtls/bearssl.h
 
 LIB_VQUIC_CFILES = vquic/ngtcp2.c vquic/quiche.c
 
diff --git a/lib/curl_config.h.cmake b/lib/curl_config.h.cmake
index e0793a7ee..60837d4f4 100644
--- a/lib/curl_config.h.cmake
+++ b/lib/curl_config.h.cmake
@@ -948,6 +948,9 @@ ${SIZEOF_TIME_T_CODE}
 /* if mbedTLS is enabled */
 #cmakedefine USE_MBEDTLS 1
 
+/* if BearSSL is enabled */
+#cmakedefine USE_BEARSSL 1
+
 /* if libSSH2 is in use */
 #cmakedefine USE_LIBSSH2 1
 
diff --git a/lib/curl_setup.h b/lib/curl_setup.h
index 13af8cdec..b4ba92931 100644
--- a/lib/curl_setup.h
+++ b/lib/curl_setup.h
@@ -644,7 +644,8 @@ int netware_init(void);
 #if defined(USE_GNUTLS) || defined(USE_OPENSSL) || defined(USE_NSS) || \
     defined(USE_MBEDTLS) || \
     defined(USE_WOLFSSL) || defined(USE_SCHANNEL) || \
-    defined(USE_SECTRANSP) || defined(USE_GSKIT) || defined(USE_MESALINK)
+    defined(USE_SECTRANSP) || defined(USE_GSKIT) || defined(USE_MESALINK) || \
+    defined(USE_BEARSSL)
 #define USE_SSL    /* SSL support has been enabled */
 #endif
 
diff --git a/lib/vtls/bearssl.c b/lib/vtls/bearssl.c
new file mode 100644
index 000000000..51694c48d
--- /dev/null
+++ b/lib/vtls/bearssl.c
@@ -0,0 +1,874 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2019, Michael Forney, <mforney@mforney.org>
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+#include "curl_setup.h"
+
+#ifdef USE_BEARSSL
+
+#include <bearssl.h>
+
+#include "bearssl.h"
+#include "urldata.h"
+#include "sendf.h"
+#include "inet_pton.h"
+#include "vtls.h"
+#include "connect.h"
+#include "select.h"
+#include "multiif.h"
+#include "curl_printf.h"
+#include "curl_memory.h"
+
+struct x509_context {
+  const br_x509_class *vtable;
+  br_x509_minimal_context minimal;
+  bool verifyhost;
+  bool verifypeer;
+};
+
+struct ssl_backend_data {
+  br_ssl_client_context ctx;
+  struct x509_context x509;
+  unsigned char buf[BR_SSL_BUFSIZE_BIDI];
+  br_x509_trust_anchor *anchors;
+  size_t anchors_len;
+  const char *protocols[2];
+  /* SSL client context is active */
+  bool active;
+};
+
+#define BACKEND connssl->backend
+
+struct cafile_parser {
+  CURLcode err;
+  bool in_cert;
+  br_x509_decoder_context xc;
+  /* array of trust anchors loaded from CAfile */
+  br_x509_trust_anchor *anchors;
+  size_t anchors_len;
+  /* buffer for DN data */
+  unsigned char dn[1024];
+  size_t dn_len;
+};
+
+static void append_dn(void *ctx, const void *buf, size_t len)
+{
+  struct cafile_parser *ca = ctx;
+
+  if(ca->err != CURLE_OK || !ca->in_cert)
+    return;
+  if(sizeof(ca->dn) - ca->dn_len < len) {
+    ca->err = CURLE_FAILED_INIT;
+    return;
+  }
+  memcpy(ca->dn + ca->dn_len, buf, len);
+  ca->dn_len += len;
+}
+
+static void x509_push(void *ctx, const void *buf, size_t len)
+{
+  struct cafile_parser *ca = ctx;
+
+  if(ca->in_cert)
+    br_x509_decoder_push(&ca->xc, buf, len);
+}
+
+static CURLcode load_cafile(const char *path, br_x509_trust_anchor **anchors,
+                            size_t *anchors_len)
+{
+  struct cafile_parser ca;
+  br_pem_decoder_context pc;
+  br_x509_trust_anchor *ta;
+  size_t ta_size;
+  br_x509_trust_anchor *new_anchors;
+  size_t new_anchors_len;
+  br_x509_pkey *pkey;
+  FILE *fp;
+  unsigned char buf[BUFSIZ], *p;
+  const char *name;
+  size_t n, i, pushed;
+
+  fp = fopen(path, "rb");
+  if(!fp)
+    return CURLE_SSL_CACERT_BADFILE;
+
+  ca.err = CURLE_OK;
+  ca.in_cert = FALSE;
+  ca.anchors = NULL;
+  ca.anchors_len = 0;
+  br_pem_decoder_init(&pc);
+  br_pem_decoder_setdest(&pc, x509_push, &ca);
+  for(;;) {
+    n = fread(buf, 1, sizeof(buf), fp);
+    if(n == 0)
+      break;
+    p = buf;
+    while(n) {
+      pushed = br_pem_decoder_push(&pc, p, n);
+      if(ca.err)
+        goto fail;
+      p += pushed;
+      n -= pushed;
+
+      switch(br_pem_decoder_event(&pc)) {
+      case 0:
+        break;
+      case BR_PEM_BEGIN_OBJ:
+        name = br_pem_decoder_name(&pc);
+        if(strcmp(name, "CERTIFICATE") && strcmp(name, "X509 CERTIFICATE"))
+          break;
+        br_x509_decoder_init(&ca.xc, append_dn, &ca);
+        if(ca.anchors_len == SIZE_MAX / sizeof(ca.anchors[0])) {
+          ca.err = CURLE_OUT_OF_MEMORY;
+          goto fail;
+        }
+        new_anchors_len = ca.anchors_len + 1;
+        new_anchors = realloc(ca.anchors,
+                              new_anchors_len * sizeof(ca.anchors[0]));
+        if(!new_anchors) {
+          ca.err = CURLE_OUT_OF_MEMORY;
+          goto fail;
+        }
+        ca.anchors = new_anchors;
+        ca.anchors_len = new_anchors_len;
+        ca.in_cert = TRUE;
+        ca.dn_len = 0;
+        ta = &ca.anchors[ca.anchors_len - 1];
+        ta->dn.data = NULL;
+        break;
+      case BR_PEM_END_OBJ:
+        if(!ca.in_cert)
+          break;
+        ca.in_cert = FALSE;
+        if(br_x509_decoder_last_error(&ca.xc)) {
+          ca.err = CURLE_SSL_CACERT_BADFILE;
+          goto fail;
+        }
+        ta->flags = 0;
+        if(br_x509_decoder_isCA(&ca.xc))
+          ta->flags |= BR_X509_TA_CA;
+        pkey = br_x509_decoder_get_pkey(&ca.xc);
+        if(!pkey) {
+          ca.err = CURLE_SSL_CACERT_BADFILE;
+          goto fail;
+        }
+        ta->pkey = *pkey;
+
+        /* calculate space needed for trust anchor data */
+        ta_size = ca.dn_len;
+        switch(pkey->key_type) {
+        case BR_KEYTYPE_RSA:
+          ta_size += pkey->key.rsa.nlen + pkey->key.rsa.elen;
+          break;
+        case BR_KEYTYPE_EC:
+          ta_size += pkey->key.ec.qlen;
+          break;
+        default:
+          ca.err = CURLE_FAILED_INIT;
+          goto fail;
+        }
+
+        /* fill in trust anchor DN and public key data */
+        ta->dn.data = malloc(ta_size);
+        if(!ta->dn.data) {
+          ca.err = CURLE_OUT_OF_MEMORY;
+          goto fail;
+        }
+        memcpy(ta->dn.data, ca.dn, ca.dn_len);
+        ta->dn.len = ca.dn_len;
+        switch(pkey->key_type) {
+        case BR_KEYTYPE_RSA:
+          ta->pkey.key.rsa.n = ta->dn.data + ta->dn.len;
+          memcpy(ta->pkey.key.rsa.n, pkey->key.rsa.n, pkey->key.rsa.nlen);
+          ta->pkey.key.rsa.e = ta->pkey.key.rsa.n + ta->pkey.key.rsa.nlen;
+          memcpy(ta->pkey.key.rsa.e, pkey->key.rsa.e, pkey->key.rsa.elen);
+          break;
+        case BR_KEYTYPE_EC:
+          ta->pkey.key.ec.q = ta->dn.data + ta->dn.len;
+          memcpy(ta->pkey.key.ec.q, pkey->key.ec.q, pkey->key.ec.qlen);
+          break;
+        }
+        break;
+      default:
+        ca.err = CURLE_SSL_CACERT_BADFILE;
+        goto fail;
+      }
+    }
+  }
+  if(ferror(fp))
+    ca.err = CURLE_READ_ERROR;
+
+fail:
+  fclose(fp);
+  if(ca.err == CURLE_OK) {
+    *anchors = ca.anchors;
+    *anchors_len = ca.anchors_len;
+  }
+  else {
+    for(i = 0; i < ca.anchors_len; ++i)
+      free(ca.anchors[i].dn.data);
+    free(ca.anchors);
+  }
+
+  return ca.err;
+}
+
+static void x509_start_chain(const br_x509_class **ctx,
+                             const char *server_name)
+{
+  struct x509_context *x509 = (struct x509_context *)ctx;
+
+  if(!x509->verifyhost)
+    server_name = NULL;
+  x509->minimal.vtable->start_chain(&x509->minimal.vtable, server_name);
+}
+
+static void x509_start_cert(const br_x509_class **ctx, uint32_t length)
+{
+  struct x509_context *x509 = (struct x509_context *)ctx;
+
+  x509->minimal.vtable->start_cert(&x509->minimal.vtable, length);
+}
+
+static void x509_append(const br_x509_class **ctx, const unsigned char *buf,
+                        size_t len)
+{
+  struct x509_context *x509 = (struct x509_context *)ctx;
+
+  x509->minimal.vtable->append(&x509->minimal.vtable, buf, len);
+}
+
+static void x509_end_cert(const br_x509_class **ctx)
+{
+  struct x509_context *x509 = (struct x509_context *)ctx;
+
+  x509->minimal.vtable->end_cert(&x509->minimal.vtable);
+}
+
+static unsigned x509_end_chain(const br_x509_class **ctx)
+{
+  struct x509_context *x509 = (struct x509_context *)ctx;
+  unsigned err;
+
+  err = x509->minimal.vtable->end_chain(&x509->minimal.vtable);
+  if(err && !x509->verifypeer) {
+    /* ignore any X.509 errors */
+    err = BR_ERR_OK;
+  }
+
+  return err;
+}
+
+static const br_x509_pkey *x509_get_pkey(const br_x509_class *const *ctx,
+                                         unsigned *usages)
+{
+  struct x509_context *x509 = (struct x509_context *)ctx;
+
+  return x509->minimal.vtable->get_pkey(&x509->minimal.vtable, usages);
+}
+
+static const br_x509_class x509_vtable = {
+  sizeof(struct x509_context),
+  x509_start_chain,
+  x509_start_cert,
+  x509_append,
+  x509_end_cert,
+  x509_end_chain,
+  x509_get_pkey
+};
+
+static CURLcode bearssl_connect_step1(struct connectdata *conn, int sockindex)
+{
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  const char * const ssl_cafile = SSL_CONN_CONFIG(CAfile);
+  const char *hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
+    conn->host.name;
+  const bool verifypeer = SSL_CONN_CONFIG(verifypeer);
+  const bool verifyhost = SSL_CONN_CONFIG(verifyhost);
+  CURLcode ret;
+  unsigned version_min, version_max;
+#ifdef ENABLE_IPV6
+  struct in6_addr addr;
+#else
+  struct in_addr addr;
+#endif
+
+  switch(SSL_CONN_CONFIG(version)) {
+  case CURL_SSLVERSION_SSLv2:
+    failf(data, "BearSSL does not support SSLv2");
+    return CURLE_SSL_CONNECT_ERROR;
+  case CURL_SSLVERSION_SSLv3:
+    failf(data, "BearSSL does not support SSLv3");
+    return CURLE_SSL_CONNECT_ERROR;
+  case CURL_SSLVERSION_TLSv1_0:
+    version_min = BR_TLS10;
+    version_max = BR_TLS10;
+    break;
+  case CURL_SSLVERSION_TLSv1_1:
+    version_min = BR_TLS11;
+    version_max = BR_TLS11;
+    break;
+  case CURL_SSLVERSION_TLSv1_2:
+    version_min = BR_TLS12;
+    version_max = BR_TLS12;
+    break;
+  case CURL_SSLVERSION_DEFAULT:
+  case CURL_SSLVERSION_TLSv1:
+    version_min = BR_TLS10;
+    version_max = BR_TLS12;
+    break;
+  default:
+    failf(data, "BearSSL: unknown CURLOPT_SSLVERSION");
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  if(ssl_cafile) {
+    ret = load_cafile(ssl_cafile, &BACKEND->anchors, &BACKEND->anchors_len);
+    if(ret != CURLE_OK) {
+      if(verifypeer) {
+        failf(data, "error setting certificate verify locations:\n"
+              "  CAfile: %s\n", ssl_cafile);
+        return ret;
+      }
+      infof(data, "error setting certificate verify locations,"
+            " continuing anyway:\n");
+    }
+  }
+
+  /* initialize SSL context */
+  br_ssl_client_init_full(&BACKEND->ctx, &BACKEND->x509.minimal,
+                          BACKEND->anchors, BACKEND->anchors_len);
+  br_ssl_engine_set_versions(&BACKEND->ctx.eng, version_min, version_max);
+  br_ssl_engine_set_buffer(&BACKEND->ctx.eng, BACKEND->buf,
+                           sizeof(BACKEND->buf), 1);
+
+  /* initialize X.509 context */
+  BACKEND->x509.vtable = &x509_vtable;
+  BACKEND->x509.verifypeer = verifypeer;
+  BACKEND->x509.verifyhost = verifyhost;
+  br_ssl_engine_set_x509(&BACKEND->ctx.eng, &BACKEND->x509.vtable);
+
+  if(SSL_SET_OPTION(primary.sessionid)) {
+    void *session;
+
+    Curl_ssl_sessionid_lock(conn);
+    if(!Curl_ssl_getsessionid(conn, &session, NULL, sockindex)) {
+      br_ssl_engine_set_session_parameters(&BACKEND->ctx.eng, session);
+      infof(data, "BearSSL: re-using session ID\n");
+    }
+    Curl_ssl_sessionid_unlock(conn);
+  }
+
+  if(conn->bits.tls_enable_alpn) {
+    int cur = 0;
+
+    /* NOTE: when adding more protocols here, increase the size of the
+     * protocols array in `struct ssl_backend_data`.
+     */
+
+#ifdef USE_NGHTTP2
+    if(data->set.httpversion >= CURL_HTTP_VERSION_2 &&
+       (!SSL_IS_PROXY() || !conn->bits.tunnel_proxy)) {
+      BACKEND->protocols[cur++] = NGHTTP2_PROTO_VERSION_ID;
+      infof(data, "ALPN, offering %s\n", NGHTTP2_PROTO_VERSION_ID);
+    }
+#endif
+
+    BACKEND->protocols[cur++] = ALPN_HTTP_1_1;
+    infof(data, "ALPN, offering %s\n", ALPN_HTTP_1_1);
+
+    br_ssl_engine_set_protocol_names(&BACKEND->ctx.eng,
+                                     BACKEND->protocols, cur);
+  }
+
+  if((1 == Curl_inet_pton(AF_INET, hostname, &addr))
+#ifdef ENABLE_IPV6
+      || (1 == Curl_inet_pton(AF_INET6, hostname, &addr))
+#endif
+     ) {
+    if(verifyhost) {
+      failf(data, "BearSSL: "
+            "host verification of IP address is not supported");
+      return CURLE_PEER_FAILED_VERIFICATION;
+    }
+    hostname = NULL;
+  }
+
+  if(!br_ssl_client_reset(&BACKEND->ctx, hostname, 0))
+    return CURLE_FAILED_INIT;
+  BACKEND->active = TRUE;
+
+  connssl->connecting_state = ssl_connect_2;
+
+  return CURLE_OK;
+}
+
+static CURLcode bearssl_connect_step2(struct connectdata *conn, int sockindex)
+{
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  curl_socket_t sockfd = conn->sock[sockindex];
+  unsigned state;
+  unsigned char *buf;
+  size_t len;
+  ssize_t ret;
+  int err;
+
+  for(;;) {
+    state = br_ssl_engine_current_state(&BACKEND->ctx.eng);
+    if(state & BR_SSL_CLOSED) {
+      err = br_ssl_engine_last_error(&BACKEND->ctx.eng);
+      switch(err) {
+      case BR_ERR_X509_EXPIRED:
+        failf(data, "SSL: X.509 verification: "
+              "certificate is expired or not yet valid");
+        return CURLE_PEER_FAILED_VERIFICATION;
+      case BR_ERR_X509_BAD_SERVER_NAME:
+        failf(data, "SSL: X.509 verification: "
+              "expected server name was not found in the chain");
+        return CURLE_PEER_FAILED_VERIFICATION;
+      case BR_ERR_X509_NOT_TRUSTED:
+        failf(data, "SSL: X.509 verification: "
+              "chain could not be linked to a trust anchor");
+        return CURLE_PEER_FAILED_VERIFICATION;
+      }
+      /* X.509 errors are documented to have the range 32..63 */
+      if(err >= 32 && err < 64)
+        return CURLE_PEER_FAILED_VERIFICATION;
+      return CURLE_SSL_CONNECT_ERROR;
+    }
+    if(state & (BR_SSL_SENDAPP | BR_SSL_RECVAPP)) {
+      connssl->connecting_state = ssl_connect_3;
+      return CURLE_OK;
+    }
+    if(state & BR_SSL_SENDREC) {
+      buf = br_ssl_engine_sendrec_buf(&BACKEND->ctx.eng, &len);
+      ret = swrite(sockfd, buf, len);
+      if(ret == -1) {
+        if(SOCKERRNO == EAGAIN || SOCKERRNO == EWOULDBLOCK) {
+          connssl->connecting_state = ssl_connect_2_writing;
+          return CURLE_OK;
+        }
+        return CURLE_SEND_ERROR;
+      }
+      br_ssl_engine_sendrec_ack(&BACKEND->ctx.eng, ret);
+    }
+    else if(state & BR_SSL_RECVREC) {
+      buf = br_ssl_engine_recvrec_buf(&BACKEND->ctx.eng, &len);
+      ret = sread(sockfd, buf, len);
+      if(ret == -1) {
+        if(SOCKERRNO == EAGAIN || SOCKERRNO == EWOULDBLOCK) {
+          connssl->connecting_state = ssl_connect_2_reading;
+          return CURLE_OK;
+        }
+        return CURLE_READ_ERROR;
+      }
+      if(ret == 0)
+        return CURLE_SSL_CONNECT_ERROR;
+      br_ssl_engine_recvrec_ack(&BACKEND->ctx.eng, ret);
+    }
+  }
+}
+
+static CURLcode bearssl_connect_step3(struct connectdata *conn, int sockindex)
+{
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  CURLcode ret;
+
+  DEBUGASSERT(ssl_connect_3 == connssl->connecting_state);
+
+  if(conn->bits.tls_enable_alpn) {
+    const char *protocol;
+
+    protocol = br_ssl_engine_get_selected_protocol(&BACKEND->ctx.eng);
+    if(protocol) {
+      infof(data, "ALPN, server accepted to use %s\n", protocol);
+
+#ifdef USE_NGHTTP2
+      if(!strcmp(protocol, NGHTTP2_PROTO_VERSION_ID))
+        conn->negnpn = CURL_HTTP_VERSION_2;
+      else
+#endif
+      if(!strcmp(protocol, ALPN_HTTP_1_1))
+        conn->negnpn = CURL_HTTP_VERSION_1_1;
+      else
+        infof(data, "ALPN, unrecognized protocol %s\n", protocol);
+      Curl_multiuse_state(conn, conn->negnpn == CURL_HTTP_VERSION_2 ?
+                          BUNDLE_MULTIPLEX : BUNDLE_NO_MULTIUSE);
+    }
+    else
+      infof(data, "ALPN, server did not agree to a protocol\n");
+  }
+
+  if(SSL_SET_OPTION(primary.sessionid)) {
+    bool incache;
+    void *oldsession;
+    br_ssl_session_parameters *session;
+
+    session = malloc(sizeof(*session));
+    if(!session)
+      return CURLE_OUT_OF_MEMORY;
+    br_ssl_engine_get_session_parameters(&BACKEND->ctx.eng, session);
+    Curl_ssl_sessionid_lock(conn);
+    incache = !(Curl_ssl_getsessionid(conn, &oldsession, NULL, sockindex));
+    if(incache)
+      Curl_ssl_delsessionid(conn, oldsession);
+    ret = Curl_ssl_addsessionid(conn, session, 0, sockindex);
+    Curl_ssl_sessionid_unlock(conn);
+    if(ret) {
+      free(session);
+      return CURLE_OUT_OF_MEMORY;
+    }
+  }
+
+  connssl->connecting_state = ssl_connect_done;
+
+  return CURLE_OK;
+}
+
+static ssize_t bearssl_send(struct connectdata *conn, int sockindex,
+                            const void *buf, size_t len, CURLcode *err)
+{
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  unsigned state;
+  unsigned char *rec, *app;
+  size_t reclen, applen;
+  ssize_t ret;
+
+  applen = 0;
+  for(;;) {
+    state = br_ssl_engine_current_state(&BACKEND->ctx.eng);
+    if(state & BR_SSL_SENDREC) {
+      rec = br_ssl_engine_sendrec_buf(&BACKEND->ctx.eng, &reclen);
+      ret = swrite(conn->sock[sockindex], rec, reclen);
+      if(ret == -1) {
+        if(SOCKERRNO == EAGAIN || SOCKERRNO == EWOULDBLOCK)
+          *err = CURLE_AGAIN;
+        else
+          *err = CURLE_SEND_ERROR;
+        return -1;
+      }
+      br_ssl_engine_sendrec_ack(&BACKEND->ctx.eng, ret);
+    }
+    else if(state & BR_SSL_SENDAPP && applen == 0) {
+      app = br_ssl_engine_sendapp_buf(&BACKEND->ctx.eng, &applen);
+      if(applen > len)
+        applen = len;
+      memcpy(app, buf, applen);
+      br_ssl_engine_sendapp_ack(&BACKEND->ctx.eng, applen);
+      br_ssl_engine_flush(&BACKEND->ctx.eng, 0);
+    }
+    else if(state & BR_SSL_CLOSED || applen == 0) {
+      *err = CURLE_SEND_ERROR;
+      return -1;
+    }
+    else
+      break;
+  }
+
+  return applen;
+}
+
+static ssize_t bearssl_recv(struct connectdata *conn, int sockindex,
+                            char *buf, size_t len, CURLcode *err)
+{
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  unsigned state;
+  unsigned char *rec, *app;
+  size_t reclen, applen;
+  ssize_t ret;
+
+  for(;;) {
+    state = br_ssl_engine_current_state(&BACKEND->ctx.eng);
+    if(state & BR_SSL_RECVREC) {
+      rec = br_ssl_engine_recvrec_buf(&BACKEND->ctx.eng, &reclen);
+      ret = sread(conn->sock[sockindex], rec, reclen);
+      if(ret == -1 && (SOCKERRNO == EAGAIN || SOCKERRNO == EWOULDBLOCK)) {
+        *err = CURLE_AGAIN;
+        return -1;
+      }
+      if(ret <= 0) {
+        *err = CURLE_RECV_ERROR;
+        return -1;
+      }
+      br_ssl_engine_recvrec_ack(&BACKEND->ctx.eng, ret);
+    }
+    else if(state & BR_SSL_RECVAPP) {
+      app = br_ssl_engine_recvapp_buf(&BACKEND->ctx.eng, &applen);
+      if(applen > len)
+        applen = len;
+      memcpy(buf, app, applen);
+      br_ssl_engine_recvapp_ack(&BACKEND->ctx.eng, applen);
+      break;
+    }
+    else {
+      *err = CURLE_RECV_ERROR;
+      return -1;
+    }
+  }
+
+  return applen;
+}
+
+static CURLcode bearssl_connect_common(struct connectdata *conn,
+                                       int sockindex,
+                                       bool nonblocking,
+                                       bool *done)
+{
+  CURLcode ret;
+  struct Curl_easy *data = conn->data;
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  curl_socket_t sockfd = conn->sock[sockindex];
+  time_t timeout_ms;
+  int what;
+
+  /* check if the connection has already been established */
+  if(ssl_connection_complete == connssl->state) {
+    *done = TRUE;
+    return CURLE_OK;
+  }
+
+  if(ssl_connect_1 == connssl->connecting_state) {
+    ret = bearssl_connect_step1(conn, sockindex);
+    if(ret)
+      return ret;
+  }
+
+  while(ssl_connect_2 == connssl->connecting_state ||
+        ssl_connect_2_reading == connssl->connecting_state ||
+        ssl_connect_2_writing == connssl->connecting_state) {
+    /* check allowed time left */
+    timeout_ms = Curl_timeleft(data, NULL, TRUE);
+
+    if(timeout_ms < 0) {
+      /* no need to continue if time already is up */
+      failf(data, "SSL connection timeout");
+      return CURLE_OPERATION_TIMEDOUT;
+    }
+
+    /* if ssl is expecting something, check if it's available. */
+    if(ssl_connect_2_reading == connssl->connecting_state ||
+       ssl_connect_2_writing == connssl->connecting_state) {
+
+      curl_socket_t writefd = ssl_connect_2_writing ==
+        connssl->connecting_state?sockfd:CURL_SOCKET_BAD;
+      curl_socket_t readfd = ssl_connect_2_reading ==
+        connssl->connecting_state?sockfd:CURL_SOCKET_BAD;
+
+      what = Curl_socket_check(readfd, CURL_SOCKET_BAD, writefd,
+                               nonblocking?0:timeout_ms);
+      if(what < 0) {
+        /* fatal error */
+        failf(data, "select/poll on SSL socket, errno: %d", SOCKERRNO);
+        return CURLE_SSL_CONNECT_ERROR;
+      }
+      else if(0 == what) {
+        if(nonblocking) {
+          *done = FALSE;
+          return CURLE_OK;
+        }
+        else {
+          /* timeout */
+          failf(data, "SSL connection timeout");
+          return CURLE_OPERATION_TIMEDOUT;
+        }
+      }
+      /* socket is readable or writable */
+    }
+
+    /* Run transaction, and return to the caller if it failed or if this
+     * connection is done nonblocking and this loop would execute again. This
+     * permits the owner of a multi handle to abort a connection attempt
+     * before step2 has completed while ensuring that a client using select()
+     * or epoll() will always have a valid fdset to wait on.
+     */
+    ret = bearssl_connect_step2(conn, sockindex);
+    if(ret || (nonblocking &&
+               (ssl_connect_2 == connssl->connecting_state ||
+                ssl_connect_2_reading == connssl->connecting_state ||
+                ssl_connect_2_writing == connssl->connecting_state)))
+      return ret;
+  }
+
+  if(ssl_connect_3 == connssl->connecting_state) {
+    ret = bearssl_connect_step3(conn, sockindex);
+    if(ret)
+      return ret;
+  }
+
+  if(ssl_connect_done == connssl->connecting_state) {
+    connssl->state = ssl_connection_complete;
+    conn->recv[sockindex] = bearssl_recv;
+    conn->send[sockindex] = bearssl_send;
+    *done = TRUE;
+  }
+  else
+    *done = FALSE;
+
+  /* Reset our connect state machine */
+  connssl->connecting_state = ssl_connect_1;
+
+  return CURLE_OK;
+}
+
+static size_t Curl_bearssl_version(char *buffer, size_t size)
+{
+  return msnprintf(buffer, size, "BearSSL");
+}
+
+static bool Curl_bearssl_data_pending(const struct connectdata *conn,
+                                      int connindex)
+{
+  const struct ssl_connect_data *connssl = &conn->ssl[connindex];
+
+  return br_ssl_engine_current_state(&BACKEND->ctx.eng) & BR_SSL_RECVAPP;
+}
+
+static CURLcode Curl_bearssl_random(struct Curl_easy *data UNUSED_PARAM,
+                                    unsigned char *entropy, size_t length)
+{
+  static br_hmac_drbg_context ctx;
+  static bool seeded = FALSE;
+
+  if(!seeded) {
+    br_prng_seeder seeder;
+
+    br_hmac_drbg_init(&ctx, &br_sha256_vtable, NULL, 0);
+    seeder = br_prng_seeder_system(NULL);
+    if(!seeder || !seeder(&ctx.vtable))
+      return CURLE_FAILED_INIT;
+    seeded = TRUE;
+  }
+  br_hmac_drbg_generate(&ctx, entropy, length);
+
+  return CURLE_OK;
+}
+
+static CURLcode Curl_bearssl_connect(struct connectdata *conn, int sockindex)
+{
+  CURLcode ret;
+  bool done = FALSE;
+
+  ret = bearssl_connect_common(conn, sockindex, FALSE, &done);
+  if(ret)
+    return ret;
+
+  DEBUGASSERT(done);
+
+  return CURLE_OK;
+}
+
+static CURLcode Curl_bearssl_connect_nonblocking(struct connectdata *conn,
+                                                 int sockindex, bool *done)
+{
+  return bearssl_connect_common(conn, sockindex, TRUE, done);
+}
+
+static void *Curl_bearssl_get_internals(struct ssl_connect_data *connssl,
+                                        CURLINFO info UNUSED_PARAM)
+{
+  return &BACKEND->ctx;
+}
+
+static void Curl_bearssl_close(struct connectdata *conn, int sockindex)
+{
+  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
+  unsigned char *buf;
+  size_t len, i;
+  ssize_t ret;
+
+  if(BACKEND->active) {
+    br_ssl_engine_close(&BACKEND->ctx.eng);
+    while(br_ssl_engine_current_state(&BACKEND->ctx.eng) & BR_SSL_SENDREC) {
+      buf = br_ssl_engine_sendrec_buf(&BACKEND->ctx.eng, &len);
+      ret = swrite(conn->sock[sockindex], buf, len);
+      if(ret < 0)
+        break;
+      br_ssl_engine_sendrec_ack(&BACKEND->ctx.eng, ret);
+    }
+  }
+  for(i = 0; i < BACKEND->anchors_len; ++i)
+    free(BACKEND->anchors[i].dn.data);
+  free(BACKEND->anchors);
+}
+
+static void Curl_bearssl_session_free(void *ptr)
+{
+  free(ptr);
+}
+
+static CURLcode Curl_bearssl_md5sum(unsigned char *input,
+                                    size_t inputlen,
+                                    unsigned char *md5sum,
+                                    size_t md5len UNUSED_PARAM)
+{
+  br_md5_context ctx;
+
+  br_md5_init(&ctx);
+  br_md5_update(&ctx, input, inputlen);
+  br_md5_out(&ctx, md5sum);
+  return CURLE_OK;
+}
+
+static CURLcode Curl_bearssl_sha256sum(const unsigned char *input,
+                                       size_t inputlen,
+                                       unsigned char *sha256sum,
+                                       size_t sha256len UNUSED_PARAM)
+{
+  br_sha256_context ctx;
+
+  br_sha256_init(&ctx);
+  br_sha256_update(&ctx, input, inputlen);
+  br_sha256_out(&ctx, sha256sum);
+  return CURLE_OK;
+}
+
+const struct Curl_ssl Curl_ssl_bearssl = {
+  { CURLSSLBACKEND_BEARSSL, "bearssl" },
+
+  0,
+
+  sizeof(struct ssl_backend_data),
+
+  Curl_none_init,
+  Curl_none_cleanup,
+  Curl_bearssl_version,
+  Curl_none_check_cxn,
+  Curl_none_shutdown,
+  Curl_bearssl_data_pending,
+  Curl_bearssl_random,
+  Curl_none_cert_status_request,
+  Curl_bearssl_connect,
+  Curl_bearssl_connect_nonblocking,
+  Curl_bearssl_get_internals,
+  Curl_bearssl_close,
+  Curl_none_close_all,
+  Curl_bearssl_session_free,
+  Curl_none_set_engine,
+  Curl_none_set_engine_default,
+  Curl_none_engines_list,
+  Curl_none_false_start,
+  Curl_bearssl_md5sum,
+  Curl_bearssl_sha256sum
+};
+
+#endif /* USE_BEARSSL */
diff --git a/lib/vtls/bearssl.h b/lib/vtls/bearssl.h
new file mode 100644
index 000000000..5f94922b9
--- /dev/null
+++ b/lib/vtls/bearssl.h
@@ -0,0 +1,32 @@
+#ifndef HEADER_CURL_BEARSSL_H
+#define HEADER_CURL_BEARSSL_H
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2019, Michael Forney, <mforney@mforney.org>
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "curl_setup.h"
+
+#ifdef USE_BEARSSL
+
+extern const struct Curl_ssl Curl_ssl_bearssl;
+
+#endif /* USE_BEARSSL */
+#endif /* HEADER_CURL_BEARSSL_H */
diff --git a/lib/vtls/vtls.c b/lib/vtls/vtls.c
index e6d756225..894fd8a43 100644
--- a/lib/vtls/vtls.c
+++ b/lib/vtls/vtls.c
@@ -517,7 +517,7 @@ void Curl_ssl_close_all(struct Curl_easy *data)
 
 #if defined(USE_OPENSSL) || defined(USE_GNUTLS) || defined(USE_SCHANNEL) || \
   defined(USE_SECTRANSP) || defined(USE_POLARSSL) || defined(USE_NSS) || \
-  defined(USE_MBEDTLS) || defined(USE_WOLFSSL)
+  defined(USE_MBEDTLS) || defined(USE_WOLFSSL) || defined(USE_BEARSSL)
 int Curl_ssl_getsock(struct connectdata *conn, curl_socket_t *socks)
 {
   struct ssl_connect_data *connssl = &conn->ssl[FIRSTSOCKET];
@@ -1189,6 +1189,8 @@ const struct Curl_ssl *Curl_ssl =
   &Curl_ssl_schannel;
 #elif defined(USE_MESALINK)
   &Curl_ssl_mesalink;
+#elif defined(USE_BEARSSL)
+  &Curl_ssl_bearssl;
 #else
 #error "Missing struct Curl_ssl for selected SSL backend"
 #endif
diff --git a/lib/vtls/vtls.h b/lib/vtls/vtls.h
index 61d8416c2..976cc4360 100644
--- a/lib/vtls/vtls.h
+++ b/lib/vtls/vtls.h
@@ -108,6 +108,7 @@ CURLcode Curl_none_md5sum(unsigned char *input, size_t inputlen,
 #include "sectransp.h"      /* SecureTransport (Darwin) version */
 #include "mbedtls.h"        /* mbedTLS versions */
 #include "mesalink.h"       /* MesaLink versions */
+#include "bearssl.h"        /* BearSSL versions */
 
 #ifndef MAX_PINNED_PUBKEY_SIZE
 #define MAX_PINNED_PUBKEY_SIZE 1048576 /* 1MB */