tls: add PSK support

Add the `pskCallback` client/server option, which resolves an identity or identity hint to a pre-shared key. Add the `pskIdentityHint` server option to set the identity hint for the ServerKeyExchange message. Co-authored-by: Chris Osborn <[email protected]> Co-authored-by: stephank <[email protected]> Co-authored-by: Taylor Zane Glaeser <[email protected]> PR-URL: #23188 Reviewed-By: Sam Roberts <[email protected]> Reviewed-By: Anna Henningsen <[email protected]>
nodejs · Dec 25, 2019 · f8d7e22 · ad-m · Dec 28, 2019 · f8d7e22
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diff --git a/doc/api/errors.md b/doc/api/errors.md
@@ -1857,6 +1857,11 @@ vector for denial-of-service attacks.
 An attempt was made to issue Server Name Indication from a TLS server-side
 socket, which is only valid from a client.
 
+<a id="ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED"></a>
+### ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED
+
+Failed to set PSK identity hint. Hint may be too long.
+
 <a id="ERR_TRACE_EVENTS_CATEGORY_REQUIRED"></a>
 ### ERR_TRACE_EVENTS_CATEGORY_REQUIRED
 

diff --git a/doc/api/tls.md b/doc/api/tls.md
@@ -118,6 +118,40 @@ SNI (Server Name Indication) are TLS handshake extensions:
 * SNI: Allows the use of one TLS server for multiple hostnames with different
   SSL certificates.
 
+### Pre-shared keys
+
+<!-- type=misc -->
+
+TLS-PSK support is available as an alternative to normal certificate-based
+authentication. It uses a pre-shared key instead of certificates to
+authenticate a TLS connection, providing mutual authentication.
+TLS-PSK and public key infrastructure are not mutually exclusive. Clients and
+servers can accommodate both, choosing either of them during the normal cipher
+negotiation step.
+
+TLS-PSK is only a good choice where means exist to securely share a
+key with every connecting machine, so it does not replace PKI
+(Public Key Infrastructure) for the majority of TLS uses.
+The TLS-PSK implementation in OpenSSL has seen many security flaws in
+recent years, mostly because it is used only by a minority of applications.
+Please consider all alternative solutions before switching to PSK ciphers.
+Upon generating PSK it is of critical importance to use sufficient entropy as
+discussed in [RFC 4086][]. Deriving a shared secret from a password or other
+low-entropy sources is not secure.
+
+PSK ciphers are disabled by default, and using TLS-PSK thus requires explicitly
+specifying a cipher suite with the `ciphers` option. The list of available
+ciphers can be retrieved via `openssl ciphers -v 'PSK'`. All TLS 1.3
+ciphers are eligible for PSK but currently only those that use SHA256 digest are
+supported they can be retrieved via `openssl ciphers -v -s -tls1_3 -psk`.
+
+According to the [RFC 4279][], PSK identities up to 128 bytes in length and
+PSKs up to 64 bytes in length must be supported. As of OpenSSL 1.1.0
+maximum identity size is 128 bytes, and maximum PSK length is 256 bytes.
+
+The current implementation doesn't support asynchronous PSK callbacks due to the
+limitations of the underlying OpenSSL API.
+
 ### Client-initiated renegotiation attack mitigation
 
 <!-- type=misc -->
@@ -1207,6 +1241,9 @@ being issued by trusted CA (`options.ca`).
 <!-- YAML
 added: v0.11.3
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/23188
+    description: The `pskCallback` option is now supported.
   - version: v12.9.0
     pr-url: https://github.com/nodejs/node/pull/27836
     description: Support the `allowHalfOpen` option.
@@ -1258,6 +1295,23 @@ changes:
     verified against the list of supplied CAs. An `'error'` event is emitted if
     verification fails; `err.code` contains the OpenSSL error code. **Default:**
     `true`.
+  * `pskCallback` {Function}
+    * hint: {string} optional message sent from the server to help client
+      decide which identity to use during negotiation.
+      Always `null` if TLS 1.3 is used.
+    * Returns: {Object} in the form
+      `{ psk: <Buffer|TypedArray|DataView>, identity: <string> }`
+      or `null` to stop the negotiation process. `psk` must be
+      compatible with the selected cipher's digest.
+      `identity` must use UTF-8 encoding.
+    When negotiating TLS-PSK (pre-shared keys), this function is called
+    with optional identity `hint` provided by the server or `null`
+    in case of TLS 1.3 where `hint` was removed.
+    It will be necessary to provide a custom `tls.checkServerIdentity()`
+    for the connection as the default one will try to check hostname/IP
+    of the server against the certificate but that's not applicable for PSK
+    because there won't be a certificate present.
+    More information can be found in the [RFC 4279][].
   * `ALPNProtocols`: {string[]|Buffer[]|TypedArray[]|DataView[]|Buffer|
     TypedArray|DataView}
     An array of strings, `Buffer`s or `TypedArray`s or `DataView`s, or a
@@ -1593,8 +1647,30 @@ changes:
     provided the default callback with high-level API will be used (see below).
   * `ticketKeys`: {Buffer} 48-bytes of cryptographically strong pseudo-random
     data. See [Session Resumption][] for more information.
+  * `pskCallback` {Function}
+    * socket: {tls.TLSSocket} the server [`tls.TLSSocket`][] instance for
+      this connection.
+    * identity: {string} identity parameter sent from the client.
+    * Returns: {Buffer|TypedArray|DataView} pre-shared key that must either be
+      a buffer or `null` to stop the negotiation process. Returned PSK must be
+      compatible with the selected cipher's digest.
+    When negotiating TLS-PSK (pre-shared keys), this function is called
+    with the identity provided by the client.
+    If the return value is `null` the negotiation process will stop and an
+    "unknown_psk_identity" alert message will be sent to the other party.
+    If the server wishes to hide the fact that the PSK identity was not known,
+    the callback must provide some random data as `psk` to make the connection
+    fail with "decrypt_error" before negotiation is finished.
+    PSK ciphers are disabled by default, and using TLS-PSK thus
+    requires explicitly specifying a cipher suite with the `ciphers` option.
+    More information can be found in the [RFC 4279][].
+  * `pskIdentityHint` {string} optional hint to send to a client to help
+    with selecting the identity during TLS-PSK negotiation. Will be ignored
+    in TLS 1.3. Upon failing to set pskIdentityHint `'tlsClientError'` will be
+    emitted with `'ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED'` code.
   * ...: Any [`tls.createSecureContext()`][] option can be provided. For
-    servers, the identity options (`pfx` or `key`/`cert`) are usually required.
+    servers, the identity options (`pfx`, `key`/`cert` or `pskCallback`)
+    are usually required.
   * ...: Any [`net.createServer()`][] option can be provided.
 * `secureConnectionListener` {Function}
 * Returns: {tls.Server}
@@ -1870,3 +1946,5 @@ where `secureSocket` has the same API as `pair.cleartext`.
 [cipher list format]: https://www.openssl.org/docs/man1.1.1/man1/ciphers.html#CIPHER-LIST-FORMAT
 [modifying the default cipher suite]: #tls_modifying_the_default_tls_cipher_suite
 [specific attacks affecting larger AES key sizes]: https://www.schneier.com/blog/archives/2009/07/another_new_aes.html
+[RFC 4279]: https://tools.ietf.org/html/rfc4279
+[RFC 4086]: https://tools.ietf.org/html/rfc4086
diff --git a/lib/_tls_wrap.js b/lib/_tls_wrap.js
@@ -50,10 +50,12 @@ const { TCP, constants: TCPConstants } = internalBinding('tcp_wrap');
 const tls_wrap = internalBinding('tls_wrap');
 const { Pipe, constants: PipeConstants } = internalBinding('pipe_wrap');
 const { owner_symbol } = require('internal/async_hooks').symbols;
+const { isArrayBufferView } = require('internal/util/types');
 const { SecureContext: NativeSecureContext } = internalBinding('crypto');
 const { connResetException, codes } = require('internal/errors');
 const {
   ERR_INVALID_ARG_TYPE,
+  ERR_INVALID_ARG_VALUE,
   ERR_INVALID_CALLBACK,
   ERR_MULTIPLE_CALLBACK,
   ERR_SOCKET_CLOSED,
@@ -65,8 +67,9 @@ const {
   ERR_TLS_SESSION_ATTACK,
   ERR_TLS_SNI_FROM_SERVER
 } = codes;
+const { onpskexchange: kOnPskExchange } = internalBinding('symbols');
 const { getOptionValue } = require('internal/options');
-const { validateString } = require('internal/validators');
+const { validateString, validateBuffer } = require('internal/validators');
 const traceTls = getOptionValue('--trace-tls');
 const tlsKeylog = getOptionValue('--tls-keylog');
 const { appendFile } = require('fs');
@@ -77,6 +80,8 @@ const kHandshakeTimeout = Symbol('handshake-timeout');
 const kRes = Symbol('res');
 const kSNICallback = Symbol('snicallback');
 const kEnableTrace = Symbol('enableTrace');
+const kPskCallback = Symbol('pskcallback');
+const kPskIdentityHint = Symbol('pskidentityhint');
 
 const noop = () => {};
 
@@ -296,6 +301,67 @@ function onnewsession(sessionId, session) {
     done();
 }
 
+function onPskServerCallback(identity, maxPskLen) {
+  const owner = this[owner_symbol];
+  const ret = owner[kPskCallback](owner, identity);
+  if (ret == null)
+    return undefined;
+
+  let psk;
+  if (isArrayBufferView(ret)) {
+    psk = ret;
+  } else {
+    if (typeof ret !== 'object') {
+      throw new ERR_INVALID_ARG_TYPE(
+        'ret',
+        ['Object', 'Buffer', 'TypedArray', 'DataView'],
+        ret
+      );
+    }
+    psk = ret.psk;
+    validateBuffer(psk, 'psk');
+  }
+
+  if (psk.length > maxPskLen) {
+    throw new ERR_INVALID_ARG_VALUE(
+      'psk',
+      psk,
+      `Pre-shared key exceeds ${maxPskLen} bytes`
+    );
+  }
+
+  return psk;
+}
+
+function onPskClientCallback(hint, maxPskLen, maxIdentityLen) {
+  const owner = this[owner_symbol];
+  const ret = owner[kPskCallback](hint);
+  if (ret == null)
+    return undefined;
+
+  if (typeof ret !== 'object')
+    throw new ERR_INVALID_ARG_TYPE('ret', 'Object', ret);
+
+  validateBuffer(ret.psk, 'psk');
+  if (ret.psk.length > maxPskLen) {
+    throw new ERR_INVALID_ARG_VALUE(
+      'psk',
+      ret.psk,
+      `Pre-shared key exceeds ${maxPskLen} bytes`
+    );
+  }
+
+  validateString(ret.identity, 'identity');
+  if (Buffer.byteLength(ret.identity) > maxIdentityLen) {
+    throw new ERR_INVALID_ARG_VALUE(
+      'identity',
+      ret.identity,
+      `PSK identity exceeds ${maxIdentityLen} bytes`
+    );
+  }
+
+  return { psk: ret.psk, identity: ret.identity };
+}
 
 function onkeylogclient(line) {
   debug('client onkeylog');
@@ -694,6 +760,32 @@ TLSSocket.prototype._init = function(socket, wrap) {
     ssl.setALPNProtocols(ssl._secureContext.alpnBuffer);
   }
 
+  if (options.pskCallback && ssl.enablePskCallback) {
+    if (typeof options.pskCallback !== 'function') {
+      throw new ERR_INVALID_ARG_TYPE('pskCallback',
+                                     'function',
+                                     options.pskCallback);
+    }
+
+    ssl[kOnPskExchange] = options.isServer ?
+      onPskServerCallback : onPskClientCallback;
+
+    this[kPskCallback] = options.pskCallback;
+    ssl.enablePskCallback();
+
+    if (options.pskIdentityHint) {
+      if (typeof options.pskIdentityHint !== 'string') {
+        throw new ERR_INVALID_ARG_TYPE(
+          'options.pskIdentityHint',
+          'string',
+          options.pskIdentityHint
+        );
+      }
+      ssl.setPskIdentityHint(options.pskIdentityHint);
+    }
+  }
+
+
   if (options.handshakeTimeout > 0)
     this.setTimeout(options.handshakeTimeout, this._handleTimeout);
 
@@ -905,7 +997,7 @@ function makeSocketMethodProxy(name) {
   TLSSocket.prototype[method] = makeSocketMethodProxy(method);
 });
 
-// TODO: support anonymous (nocert) and PSK
+// TODO: support anonymous (nocert)
 
 
 function onServerSocketSecure() {
@@ -961,6 +1053,8 @@ function tlsConnectionListener(rawSocket) {
     SNICallback: this[kSNICallback] || SNICallback,
     enableTrace: this[kEnableTrace],
     pauseOnConnect: this.pauseOnConnect,
+    pskCallback: this[kPskCallback],
+    pskIdentityHint: this[kPskIdentityHint],
   });
 
   socket.on('secure', onServerSocketSecure);
@@ -1065,6 +1159,8 @@ function Server(options, listener) {
 
   this[kHandshakeTimeout] = options.handshakeTimeout || (120 * 1000);
   this[kSNICallback] = options.SNICallback;
+  this[kPskCallback] = options.pskCallback;
+  this[kPskIdentityHint] = options.pskIdentityHint;
 
   if (typeof this[kHandshakeTimeout] !== 'number') {
     throw new ERR_INVALID_ARG_TYPE(
@@ -1076,6 +1172,18 @@ function Server(options, listener) {
       'options.SNICallback', 'function', options.SNICallback);
   }
 
+  if (this[kPskCallback] && typeof this[kPskCallback] !== 'function') {
+    throw new ERR_INVALID_ARG_TYPE(
+      'options.pskCallback', 'function', options.pskCallback);
+  }
+  if (this[kPskIdentityHint] && typeof this[kPskIdentityHint] !== 'string') {
+    throw new ERR_INVALID_ARG_TYPE(
+      'options.pskIdentityHint',
+      'string',
+      options.pskIdentityHint
+    );
+  }
+
   // constructor call
   net.Server.call(this, options, tlsConnectionListener);
 
@@ -1272,6 +1380,8 @@ Server.prototype.setOptions = deprecate(function(options) {
                                   .digest('hex')
                                   .slice(0, 32);
   }
+  if (options.pskCallback) this[kPskCallback] = options.pskCallback;
+  if (options.pskIdentityHint) this[kPskIdentityHint] = options.pskIdentityHint;
 }, 'Server.prototype.setOptions() is deprecated', 'DEP0122');
 
 // SNI Contexts High-Level API
@@ -1459,7 +1569,8 @@ exports.connect = function connect(...args) {
     session: options.session,
     ALPNProtocols: options.ALPNProtocols,
     requestOCSP: options.requestOCSP,
-    enableTrace: options.enableTrace
+    enableTrace: options.enableTrace,
+    pskCallback: options.pskCallback,
   });
 
   tlssock[kConnectOptions] = options;

diff --git a/src/env.h b/src/env.h
@@ -160,11 +160,12 @@ constexpr size_t kFsStatsBufferLength =
 
 // Symbols are per-isolate primitives but Environment proxies them
 // for the sake of convenience.
-#define PER_ISOLATE_SYMBOL_PROPERTIES(V)                                      \
-  V(handle_onclose_symbol, "handle_onclose")                                  \
-  V(no_message_symbol, "no_message_symbol")                                   \
-  V(oninit_symbol, "oninit")                                                  \
-  V(owner_symbol, "owner")                                                    \
+#define PER_ISOLATE_SYMBOL_PROPERTIES(V)                                       \
+  V(handle_onclose_symbol, "handle_onclose")                                   \
+  V(no_message_symbol, "no_message_symbol")                                    \
+  V(oninit_symbol, "oninit")                                                   \
+  V(owner_symbol, "owner")                                                     \
+  V(onpskexchange_symbol, "onpskexchange")                                     \
 
 // Strings are per-isolate primitives but Environment proxies them
 // for the sake of convenience.  Strings should be ASCII-only.
@@ -254,6 +255,7 @@ constexpr size_t kFsStatsBufferLength =
   V(host_string, "host")                                                       \
   V(hostmaster_string, "hostmaster")                                           \
   V(http_1_1_string, "http/1.1")                                               \
+  V(identity_string, "identity")                                               \
   V(ignore_string, "ignore")                                                   \
   V(import_string, "import")                                                   \
   V(infoaccess_string, "infoAccess")                                           \
@@ -325,6 +327,7 @@ constexpr size_t kFsStatsBufferLength =
   V(priority_string, "priority")                                               \
   V(process_string, "process")                                                 \
   V(promise_string, "promise")                                                 \
+  V(psk_string, "psk")                                                         \
   V(pubkey_string, "pubkey")                                                   \
   V(query_string, "query")                                                     \
   V(raw_string, "raw")                                                         \

diff --git a/src/node_crypto.cc b/src/node_crypto.cc
@@ -2620,6 +2620,16 @@ void SSLWrap<Base>::VerifyError(const FunctionCallbackInfo<Value>& args) {
   if (X509* peer_cert = SSL_get_peer_certificate(w->ssl_.get())) {
     X509_free(peer_cert);
     x509_verify_error = SSL_get_verify_result(w->ssl_.get());
+  } else {
+    const SSL_CIPHER* curr_cipher = SSL_get_current_cipher(w->ssl_.get());
+    const SSL_SESSION* sess = SSL_get_session(w->ssl_.get());
+    // Allow no-cert for PSK authentication in TLS1.2 and lower.
+    // In TLS1.3 check that session was reused because TLS1.3 PSK
+    // looks like session resumption. Is there a better way?
+    if (SSL_CIPHER_get_auth_nid(curr_cipher) == NID_auth_psk ||
+        (SSL_SESSION_get_protocol_version(sess) == TLS1_3_VERSION &&
+         SSL_session_reused(w->ssl_.get())))
+      return args.GetReturnValue().SetNull();
   }
 
   if (x509_verify_error == X509_V_OK)

diff --git a/src/node_errors.h b/src/node_errors.h
@@ -58,6 +58,7 @@ void PrintErrorString(const char* format, ...);
   V(ERR_STRING_TOO_LONG, Error)                                              \
   V(ERR_TLS_INVALID_PROTOCOL_METHOD, TypeError)                              \
   V(ERR_TRANSFERRING_EXTERNALIZED_SHAREDARRAYBUFFER, TypeError)              \
+  V(ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED, Error)                              \
 
 #define V(code, type)                                                         \
   inline v8::Local<v8::Value> code(v8::Isolate* isolate,                      \
@@ -101,6 +102,7 @@ void PrintErrorString(const char* format, ...);
     "Script execution was interrupted by `SIGINT`")                          \
   V(ERR_TRANSFERRING_EXTERNALIZED_SHAREDARRAYBUFFER,                         \
     "Cannot serialize externalized SharedArrayBuffer")                       \
+  V(ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED, "Failed to set PSK identity hint")  \
 
 #define V(code, message)                                                     \
   inline v8::Local<v8::Value> code(v8::Isolate* isolate) {                   \