TLS (SSL)

The tls module provides an implementation of the Transport Layer Security (TLS) and Secure Socket Layer (SSL) protocols that is built on top of OpenSSL. The module can be accessed using:

const tls = require('tls');

TLS/SSL Concepts

The TLS/SSL is a public/private key infrastructure (PKI). For most common cases, each client and server must have a private key.

Private keys can be generated in multiple ways. The example below illustrates use of the OpenSSL command-line interface to generate a 2048-bit RSA private key:

openssl genrsa -out ryans-key.pem 2048

With TLS/SSL, all servers (and some clients) must have a certificate. Certificates are public keys that correspond to a private key, and that are digitally signed either by a Certificate Authority or by the owner of the private key (such certificates are referred to as "self-signed"). The first step to obtaining a certificate is to create a Certificate Signing Request (CSR) file.

The OpenSSL command-line interface can be used to generate a CSR for a private key:

openssl req -new -sha256 -key ryans-key.pem -out ryans-csr.pem

Once the CSR file is generated, it can either be sent to a Certificate Authority for signing or used to generate a self-signed certificate.

Creating a self-signed certificate using the OpenSSL command-line interface is illustrated in the example below:

openssl x509 -req -in ryans-csr.pem -signkey ryans-key.pem -out ryans-cert.pem

Once the certificate is generated, it can be used to generate a .pfx or .p12 file:

openssl pkcs12 -export -in ryans-cert.pem -inkey ryans-key.pem \
      -certfile ca-cert.pem -out ryans.pfx

Where:

• in: is the signed certificate
• inkey: is the associated private key
• certfile: is a concatenation of all Certificate Authority (CA) certs into a single file, e.g. cat ca1-cert.pem ca2-cert.pem > ca-cert.pem

Perfect Forward Secrecy

The term "Forward Secrecy" or "Perfect Forward Secrecy" describes a feature of key-agreement (i.e., key-exchange) methods. That is, the server and client keys are used to negotiate new temporary keys that are used specifically and only for the current communication session. Practically, this means that even if the server's private key is compromised, communication can only be decrypted by eavesdroppers if the attacker manages to obtain the key-pair specifically generated for the session.

Perfect Forward Secrecy is achieved by randomly generating a key pair for key-agreement on every TLS/SSL handshake (in contrast to using the same key for all sessions). Methods implementing this technique are called "ephemeral".

Currently two methods are commonly used to achieve Perfect Forward Secrecy (note the character "E" appended to the traditional abbreviations):

• DHE - An ephemeral version of the Diffie Hellman key-agreement protocol.
• ECDHE - An ephemeral version of the Elliptic Curve Diffie Hellman key-agreement protocol.

Ephemeral methods may have some performance drawbacks, because key generation is expensive.

To use Perfect Forward Secrecy using DHE with the tls module, it is required to generate Diffie-Hellman parameters and specify them with the dhparam option to tls.createSecureContext(). The following illustrates the use of the OpenSSL command-line interface to generate such parameters:

openssl dhparam -outform PEM -out dhparam.pem 2048

If using Perfect Forward Secrecy using ECDHE, Diffie-Hellman parameters are not required and a default ECDHE curve will be used. The ecdhCurve property can be used when creating a TLS Server to specify the list of names of supported curves to use, see tls.createServer() for more info.

ALPN and SNI

ALPN (Application-Layer Protocol Negotiation Extension) and SNI (Server Name Indication) are TLS handshake extensions:

• ALPN - Allows the use of one TLS server for multiple protocols (HTTP, HTTP/2)
• SNI - Allows the use of one TLS server for multiple hostnames with different SSL certificates.

Client-initiated renegotiation attack mitigation

The TLS protocol allows clients to renegotiate certain aspects of the TLS session. Unfortunately, session renegotiation requires a disproportionate amount of server-side resources, making it a potential vector for denial-of-service attacks.

To mitigate the risk, renegotiation is limited to three times every ten minutes. An 'error' event is emitted on the tls.TLSSocket instance when this threshold is exceeded. The limits are configurable:

• tls.CLIENT_RENEG_LIMIT <number> Specifies the number of renegotiation requests. Default: 3.
• tls.CLIENT_RENEG_WINDOW <number> Specifies the time renegotiation window in seconds. Default: 600 (10 minutes).

The default renegotiation limits should not be modified without a full understanding of the implications and risks.

Session Resumption

Establishing a TLS session can be relatively slow. The process can be sped up by saving and later reusing the session state. There are several mechanisms to do so, discussed here from oldest to newest (and preferred).

Session Identifiers Servers generate a unique ID for new connections and send it to the client. Clients and servers save the session state. When reconnecting, clients send the ID of their saved session state and if the server also has the state for that ID, it can agree to use it. Otherwise, the server will create a new session. See RFC 2246 for more information, page 23 and 30.

Resumption using session identifiers is supported by most web browsers when making HTTPS requests.

For Node.js, clients must call tls.TLSSocket.getSession() after the 'secureConnect' event to get the session data, and provide the data to the session option of tls.connect() to reuse the session. Servers must implement handlers for the 'newSession' and 'resumeSession' events to save and restore the session data using the session ID as the lookup key to reuse sessions. To reuse sessions across load balancers or cluster workers, servers must use a shared session cache (such as Redis) in their session handlers.

Session Tickets The servers encrypt the entire session state and send it to the client as a "ticket". When reconnecting, the state is sent to the server in the initial connection. This mechanism avoids the need for server-side session cache. If the server doesn't use the ticket, for any reason (failure to decrypt it, it's too old, etc.), it will create a new session and send a new ticket. See RFC 5077 for more information.

Resumption using session tickets is becoming commonly supported by many web browsers when making HTTPS requests.

For Node.js, clients use the same APIs for resumption with session identifiers as for resumption with session tickets. For debugging, if tls.TLSSocket.getTLSTicket() returns a value, the session data contains a ticket, otherwise it contains client-side session state.

Single process servers need no specific implementation to use session tickets. To use session tickets across server restarts or load balancers, servers must all have the same ticket keys. There are three 16-byte keys internally, but the tls API exposes them as a single 48-byte buffer for convenience.

Its possible to get the ticket keys by calling server.getTicketKeys() on one server instance and then distribute them, but it is more reasonable to securely generate 48 bytes of secure random data and set them with the ticketKeys option of tls.createServer(). The keys should be regularly regenerated and server's keys can be reset with server.setTicketKeys().

Session ticket keys are cryptographic keys, and they must be stored securely. With TLS 1.2 and below, if they are compromised all sessions that used tickets encrypted with them can be decrypted. They should not be stored on disk, and they should be regenerated regularly.

If clients advertise support for tickets, the server will send them. The server can disable tickets by supplying require('constants').SSL_OP_NO_TICKET in secureOptions.

Both session identifiers and session tickets timeout, causing the server to create new sessions. The timeout can be configured with the sessionTimeout option of tls.createServer().

For all the mechanisms, when resumption fails, servers will create new sessions. Since failing to resume the session does not cause TLS/HTTPS connection failures, it is easy to not notice unnecessarily poor TLS performance. The OpenSSL CLI can be used to verify that servers are resuming sessions. Use the -reconnect option to openssl s_client, for example:

$ openssl s_client -connect localhost:443 -reconnect

Read through the debug output. The first connection should say "New", for example:

New, TLSv1.2, Cipher is ECDHE-RSA-AES128-GCM-SHA256

Subsequent connections should say "Reused", for example:

Reused, TLSv1.2, Cipher is ECDHE-RSA-AES128-GCM-SHA256

Modifying the Default TLS Cipher suite

Node.js is built with a default suite of enabled and disabled TLS ciphers. Currently, the default cipher suite is:

ECDHE-RSA-AES128-GCM-SHA256:
ECDHE-ECDSA-AES128-GCM-SHA256:
ECDHE-RSA-AES256-GCM-SHA384:
ECDHE-ECDSA-AES256-GCM-SHA384:
DHE-RSA-AES128-GCM-SHA256:
ECDHE-RSA-AES128-SHA256:
DHE-RSA-AES128-SHA256:
ECDHE-RSA-AES256-SHA384:
DHE-RSA-AES256-SHA384:
ECDHE-RSA-AES256-SHA256:
DHE-RSA-AES256-SHA256:
HIGH:
!aNULL:
!eNULL:
!EXPORT:
!DES:
!RC4:
!MD5:
!PSK:
!SRP:
!CAMELLIA

This default can be replaced entirely using the --tls-cipher-list command line switch (directly, or via the NODE_OPTIONS environment variable). For instance, the following makes ECDHE-RSA-AES128-GCM-SHA256:!RC4 the default TLS cipher suite:

node --tls-cipher-list="ECDHE-RSA-AES128-GCM-SHA256:!RC4" server.js

export NODE_OPTIONS=--tls-cipher-list="ECDHE-RSA-AES128-GCM-SHA256:!RC4"
node server.js

The default can also be replaced on a per client or server basis using the ciphers option from tls.createSecureContext(), which is also available in tls.createServer(), tls.connect(), and when creating new tls.TLSSockets.

Consult OpenSSL cipher list format documentation for details on the format.

The default cipher suite included within Node.js has been carefully selected to reflect current security best practices and risk mitigation. Changing the default cipher suite can have a significant impact on the security of an application. The --tls-cipher-list switch and ciphers option should by used only if absolutely necessary.

The default cipher suite prefers GCM ciphers for Chrome's 'modern cryptography' setting and also prefers ECDHE and DHE ciphers for Perfect Forward Secrecy, while offering some backward compatibility.

128 bit AES is preferred over 192 and 256 bit AES in light of specific attacks affecting larger AES key sizes.

Old clients that rely on insecure and deprecated RC4 or DES-based ciphers (like Internet Explorer 6) cannot complete the handshaking process with the default configuration. If these clients must be supported, the TLS recommendations may offer a compatible cipher suite. For more details on the format, see the OpenSSL cipher list format documentation.

Class: tls.Server

The tls.Server class is a subclass of net.Server that accepts encrypted connections using TLS or SSL.

Event: 'keylog'

• line <Buffer> Line of ASCII text, in NSS SSLKEYLOGFILE format.
• tlsSocket <tls.TLSSocket> The tls.TLSSocket instance on which it was generated.

The keylog event is emitted when key material is generated or received by a connection to this server (typically before handshake has completed, but not necessarily). This keying material can be stored for debugging, as it allows captured TLS traffic to be decrypted. It may be emitted multiple times for each socket.

A typical use case is to append received lines to a common text file, which is later used by software (such as Wireshark) to decrypt the traffic:

const logFile = fs.createWriteStream('/tmp/ssl-keys.log', { flags: 'a' });
// ...
server.on('keylog', (line, tlsSocket) => {
  if (tlsSocket.remoteAddress !== '...')
    return; // Only log keys for a particular IP
  logFile.write(line);
});

Event: 'newSession'

The 'newSession' event is emitted upon creation of a new TLS session. This may be used to store sessions in external storage. The data should be provided to the 'resumeSession' callback.

The listener callback is passed three arguments when called:

• sessionId <Buffer> The TLS session identifier
• sessionData <Buffer> The TLS session data
• callback <Function> A callback function taking no arguments that must be invoked in order for data to be sent or received over the secure connection.

Listening for this event will have an effect only on connections established after the addition of the event listener.

Event: 'OCSPRequest'

The 'OCSPRequest' event is emitted when the client sends a certificate status request. The listener callback is passed three arguments when called:

• certificate <Buffer> The server certificate
• issuer <Buffer> The issuer's certificate
• callback <Function> A callback function that must be invoked to provide the results of the OCSP request.

The server's current certificate can be parsed to obtain the OCSP URL and certificate ID; after obtaining an OCSP response, callback(null, resp) is then invoked, where resp is a Buffer instance containing the OCSP response. Both certificate and issuer are Buffer DER-representations of the primary and issuer's certificates. These can be used to obtain the OCSP certificate ID and OCSP endpoint URL.

Alternatively, callback(null, null) may be called, indicating that there was no OCSP response.

Calling callback(err) will result in a socket.destroy(err) call.

The typical flow of an OCSP Request is as follows:

1. Client connects to the server and sends an 'OCSPRequest' (via the status info extension in ClientHello).
2. Server receives the request and emits the 'OCSPRequest' event, calling the listener if registered.
3. Server extracts the OCSP URL from either the certificate or issuer and performs an OCSP request to the CA.
4. Server receives 'OCSPResponse' from the CA and sends it back to the client via the callback argument
5. Client validates the response and either destroys the socket or performs a handshake.

The issuer can be null if the certificate is either self-signed or the issuer is not in the root certificates list. (An issuer may be provided via the ca option when establishing the TLS connection.)

Listening for this event will have an effect only on connections established after the addition of the event listener.

An npm module like asn1.js may be used to parse the certificates.

Event: 'resumeSession'

The 'resumeSession' event is emitted when the client requests to resume a previous TLS session. The listener callback is passed two arguments when called:

• sessionId <Buffer> The TLS session identifier

• callback <Function> A callback function to be called when the prior session has been recovered: callback([err[, sessionData]])

  • err <Error>
  • sessionData <Buffer>

The event listener should perform a lookup in external storage for the sessionData saved by the 'newSession' event handler using the given sessionId. If found, call callback(null, sessionData) to resume the session. If not found, the session cannot be resumed. callback() must be called without sessionData so that the handshake can continue and a new session can be created. It is possible to call callback(err) to terminate the incoming connection and destroy the socket.

Listening for this event will have an effect only on connections established after the addition of the event listener.

The following illustrates resuming a TLS session:

const tlsSessionStore = {};
server.on('newSession', (id, data, cb) => {
  tlsSessionStore[id.toString('hex')] = data;
  cb();
});
server.on('resumeSession', (id, cb) => {
  cb(null, tlsSessionStore[id.toString('hex')] || null);
});

Event: 'secureConnection'

The 'secureConnection' event is emitted after the handshaking process for a new connection has successfully completed. The listener callback is passed a single argument when called:

• tlsSocket <tls.TLSSocket> The established TLS socket.

The tlsSocket.authorized property is a boolean indicating whether the client has been verified by one of the supplied Certificate Authorities for the server. If tlsSocket.authorized is false, then socket.authorizationError is set to describe how authorization failed. Note that depending on the settings of the TLS server, unauthorized connections may still be accepted.

The tlsSocket.alpnProtocol property is a string that contains the selected ALPN protocol. When ALPN has no selected protocol, tlsSocket.alpnProtocol equals false.

The tlsSocket.servername property is a string containing the server name requested via SNI.

Event: 'tlsClientError'

The 'tlsClientError' event is emitted when an error occurs before a secure connection is established. The listener callback is passed two arguments when called:

• exception <Error> The Error object describing the error
• tlsSocket <tls.TLSSocket> The tls.TLSSocket instance from which the error originated.

server.addContext(hostname, context)

• hostname <string> A SNI hostname or wildcard (e.g. '*')
• context <Object> An object containing any of the possible properties from the tls.createSecureContext() options arguments (e.g. key, cert, ca, etc).

The server.addContext() method adds a secure context that will be used if the client request's SNI name matches the supplied hostname (or wildcard).

server.address()[src]

• Returns: <Object>

Returns the bound address, the address family name, and port of the server as reported by the operating system. See net.Server.address() for more information.

server.close([callback])[src]

• callback <Function> A listener callback that will be registered to listen for the server instance's 'close' event.
• Returns: <tls.Server>

The server.close() method stops the server from accepting new connections.

This function operates asynchronously. The 'close' event will be emitted when the server has no more open connections.

server.connections

• <number>

Returns the current number of concurrent connections on the server.

server.getTicketKeys()

• Returns: <Buffer> A 48-byte buffer containing the session ticket keys.

Returns the session ticket keys.

See Session Resumption for more information.

server.listen()[src]

Starts the server listening for encrypted connections. This method is identical to server.listen() from net.Server.

server.setTicketKeys(keys)

• keys <Buffer> A 48-byte buffer containing the session ticket keys.

Sets the session ticket keys.

Changes to the ticket keys are effective only for future server connections. Existing or currently pending server connections will use the previous keys.

See Session Resumption for more information.

Class: tls.TLSSocket

The tls.TLSSocket is a subclass of net.Socket that performs transparent encryption of written data and all required TLS negotiation.

Instances of tls.TLSSocket implement the duplex Stream interface.

Methods that return TLS connection metadata (e.g. tls.TLSSocket.getPeerCertificate() will only return data while the connection is open.

new tls.TLSSocket(socket[, options])

• socket <net.Socket> | <stream.Duplex> On the server side, any Duplex stream. On the client side, any instance of net.Socket (for generic Duplex stream support on the client side, tls.connect() must be used).

• options <Object>

  • isServer: The SSL/TLS protocol is asymmetrical, TLSSockets must know if they are to behave as a server or a client. If true the TLS socket will be instantiated as a server. Default: false.
  • server <net.Server> A net.Server instance.
  • requestCert: Whether to authenticate the remote peer by requesting a certificate. Clients always request a server certificate. Servers (isServer is true) may set requestCert to true to request a client certificate.
  • rejectUnauthorized: See tls.createServer()
  • ALPNProtocols: See tls.createServer()
  • SNICallback: See tls.createServer()
  • session <Buffer> A Buffer instance containing a TLS session.
  • requestOCSP <boolean> If true, specifies that the OCSP status request extension will be added to the client hello and an 'OCSPResponse' event will be emitted on the socket before establishing a secure communication
  • secureContext: TLS context object created with tls.createSecureContext(). If a secureContext is not provided, one will be created by passing the entire options object to tls.createSecureContext().
  • ...: tls.createSecureContext() options that are used if the secureContext option is missing. Otherwise, they are ignored.

Construct a new tls.TLSSocket object from an existing TCP socket.

Event: 'keylog'

• line <Buffer> Line of ASCII text, in NSS SSLKEYLOGFILE format.

The keylog event is emitted on a client tls.TLSSocket when key material is generated or received by the socket. This keying material can be stored for debugging, as it allows captured TLS traffic to be decrypted. It may be emitted multiple times, before or after the handshake completes.

A typical use case is to append received lines to a common text file, which is later used by software (such as Wireshark) to decrypt the traffic:

const logFile = fs.createWriteStream('/tmp/ssl-keys.log', { flags: 'a' });
// ...
tlsSocket.on('keylog', (line) => logFile.write(line));

Event: 'OCSPResponse'

The 'OCSPResponse' event is emitted if the requestOCSP option was set when the tls.TLSSocket was created and an OCSP response has been received. The listener callback is passed a single argument when called:

• response <Buffer> The server's OCSP response

Typically, the response is a digitally signed object from the server's CA that contains information about server's certificate revocation status.

Event: 'secureConnect'

The 'secureConnect' event is emitted after the handshaking process for a new connection has successfully completed. The listener callback will be called regardless of whether or not the server's certificate has been authorized. It is the client's responsibility to check the tlsSocket.authorized property to determine if the server certificate was signed by one of the specified CAs. If tlsSocket.authorized === false, then the error can be found by examining the tlsSocket.authorizationError property. If ALPN was used, the tlsSocket.alpnProtocol property can be checked to determine the negotiated protocol.

tlsSocket.address()

• Returns: <Object>

Returns the bound address, the address family name, and port of the underlying socket as reported by the operating system: { port: 12346, family: 'IPv4', address: '127.0.0.1' }.

tlsSocket.authorizationError

Returns the reason why the peer's certificate was not been verified. This property is set only when tlsSocket.authorized === false.

tlsSocket.authorized

• Returns: <boolean>

Returns true if the peer certificate was signed by one of the CAs specified when creating the tls.TLSSocket instance, otherwise false.

tlsSocket.disableRenegotiation()

Disables TLS renegotiation for this TLSSocket instance. Once called, attempts to renegotiate will trigger an 'error' event on the TLSSocket.

tlsSocket.encrypted

Always returns true. This may be used to distinguish TLS sockets from regular net.Socket instances.

tlsSocket.getCipher()

• Returns: <Object>

Returns an object representing the cipher name. The version key is a legacy field which always contains the value 'TLSv1/SSLv3'.

For example: { name: 'AES256-SHA', version: 'TLSv1/SSLv3' }.

See SSL_CIPHER_get_name() in https://www.openssl.org/docs/man1.1.0/ssl/SSL_CIPHER_get_name.html for more information.

tlsSocket.getEphemeralKeyInfo()

• Returns: <Object>

Returns an object representing the type, name, and size of parameter of an ephemeral key exchange in Perfect Forward Secrecy on a client connection. It returns an empty object when the key exchange is not ephemeral. As this is only supported on a client socket; null is returned if called on a server socket. The supported types are 'DH' and 'ECDH'. The name property is available only when type is 'ECDH'.

For example: { type: 'ECDH', name: 'prime256v1', size: 256 }.

tlsSocket.getFinished()

• Returns: <Buffer> | <undefined> The latest Finished message that has been sent to the socket as part of a SSL/TLS handshake, or undefined if no Finished message has been sent yet.

As the Finished messages are message digests of the complete handshake (with a total of 192 bits for TLS 1.0 and more for SSL 3.0), they can be used for external authentication procedures when the authentication provided by SSL/TLS is not desired or is not enough.

Corresponds to the SSL_get_finished routine in OpenSSL and may be used to implement the tls-unique channel binding from RFC 5929.

tlsSocket.getPeerCertificate([detailed])

• detailed <boolean> Include the full certificate chain if true, otherwise include just the peer's certificate.
• Returns: <Object>

Returns an object representing the peer's certificate. The returned object has some properties corresponding to the fields of the certificate.

If the full certificate chain was requested, each certificate will include an issuerCertificate property containing an object representing its issuer's certificate.

{ subject:
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuer:
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuerCertificate:
   { ... another certificate, possibly with an .issuerCertificate ... },
  raw: < RAW DER buffer >,
  pubkey: < RAW DER buffer >,
  valid_from: 'Nov 11 09:52:22 2009 GMT',
  valid_to: 'Nov 6 09:52:22 2029 GMT',
  fingerprint: '2A:7A:C2:DD:E5:F9:CC:53:72:35:99:7A:02:5A:71:38:52:EC:8A:DF',
  fingerprint256: '2A:7A:C2:DD:E5:F9:CC:53:72:35:99:7A:02:5A:71:38:52:EC:8A:DF:00:11:22:33:44:55:66:77:88:99:AA:BB',
  serialNumber: 'B9B0D332A1AA5635' }

If the peer does not provide a certificate, an empty object will be returned.

tlsSocket.getPeerFinished()

• Returns: <Buffer> | <undefined> The latest Finished message that is expected or has actually been received from the socket as part of a SSL/TLS handshake, or undefined if there is no Finished message so far.

As the Finished messages are message digests of the complete handshake (with a total of 192 bits for TLS 1.0 and more for SSL 3.0), they can be used for external authentication procedures when the authentication provided by SSL/TLS is not desired or is not enough.

Corresponds to the SSL_get_peer_finished routine in OpenSSL and may be used to implement the tls-unique channel binding from RFC 5929.

tlsSocket.getProtocol()

• Returns: <string> | <null>

Returns a string containing the negotiated SSL/TLS protocol version of the current connection. The value 'unknown' will be returned for connected sockets that have not completed the handshaking process. The value null will be returned for server sockets or disconnected client sockets.

Protocol versions are:

• 'TLSv1'
• 'TLSv1.1'
• 'TLSv1.2'
• 'SSLv3'

See https://www.openssl.org/docs/man1.1.0/ssl/SSL_get_version.html for more information.

tlsSocket.getSession()

• <Buffer>

Returns the TLS session data or undefined if no session was negotiated. On the client, the data can be provided to the session option of tls.connect() to resume the connection. On the server, it may be useful for debugging.

See Session Resumption for more information.

tlsSocket.getTLSTicket()

• <Buffer>

For a client, returns the TLS session ticket if one is available, or undefined. For a server, always returns undefined.

It may be useful for debugging.

See Session Resumption for more information.

tlsSocket.isSessionReused()

• Returns: <boolean> true if the session was reused, false otherwise.

See Session Resumption for more information.

tlsSocket.localAddress

• <string>

Returns the string representation of the local IP address.

tlsSocket.localPort

• <number>

Returns the numeric representation of the local port.

tlsSocket.remoteAddress

• <string>

Returns the string representation of the remote IP address. For example, '74.125.127.100' or '2001:4860:a005::68'.

tlsSocket.remoteFamily

• <string>

Returns the string representation of the remote IP family. 'IPv4' or 'IPv6'.

tlsSocket.remotePort

• <number>

Returns the numeric representation of the remote port. For example, 443.

tlsSocket.renegotiate(options, callback)

• options <Object>

  • rejectUnauthorized <boolean> If not false, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails; err.code contains the OpenSSL error code. Default: true.
  • requestCert
• callback <Function> A function that will be called when the renegotiation request has been completed.

The tlsSocket.renegotiate() method initiates a TLS renegotiation process. Upon completion, the callback function will be passed a single argument that is either an Error (if the request failed) or null.

This method can be used to request a peer's certificate after the secure connection has been established.

When running as the server, the socket will be destroyed with an error after handshakeTimeout timeout.

tlsSocket.setMaxSendFragment(size)

• size <number> The maximum TLS fragment size. The maximum value is 16384. Default: 16384.
• Returns: <boolean>

The tlsSocket.setMaxSendFragment() method sets the maximum TLS fragment size. Returns true if setting the limit succeeded; false otherwise.

Smaller fragment sizes decrease the buffering latency on the client: larger fragments are buffered by the TLS layer until the entire fragment is received and its integrity is verified; large fragments can span multiple roundtrips and their processing can be delayed due to packet loss or reordering. However, smaller fragments add extra TLS framing bytes and CPU overhead, which may decrease overall server throughput.

tls.checkServerIdentity(hostname, cert)[src]

• hostname <string> The host name or IP address to verify the certificate against.
• cert <Object> An object representing the peer's certificate. The returned object has some properties corresponding to the fields of the certificate.
• Returns: <Error> | <undefined>

Verifies the certificate cert is issued to hostname.

Returns <Error> object, populating it with reason, host, and cert on failure. On success, returns <undefined>.

This function can be overwritten by providing alternative function as part of the options.checkServerIdentity option passed to tls.connect(). The overwriting function can call tls.checkServerIdentity() of course, to augment the checks done with additional verification.

This function is only called if the certificate passed all other checks, such as being issued by trusted CA (options.ca).

The cert object contains the parsed certificate and will have a structure similar to:

{ subject:
   { OU: [ 'Domain Control Validated', 'PositiveSSL Wildcard' ],
     CN: '*.nodejs.org' },
  issuer:
   { C: 'GB',
     ST: 'Greater Manchester',
     L: 'Salford',
     O: 'COMODO CA Limited',
     CN: 'COMODO RSA Domain Validation Secure Server CA' },
  subjectaltname: 'DNS:*.nodejs.org, DNS:nodejs.org',
  infoAccess:
   { 'CA Issuers - URI':
      [ 'http://crt.comodoca.com/COMODORSADomainValidationSecureServerCA.crt' ],
     'OCSP - URI': [ 'http://ocsp.comodoca.com' ] },
  modulus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
  exponent: '0x10001',
  pubkey: <Buffer ... >,
  valid_from: 'Aug 14 00:00:00 2017 GMT',
  valid_to: 'Nov 20 23:59:59 2019 GMT',
  fingerprint: '01:02:59:D9:C3:D2:0D:08:F7:82:4E:44:A4:B4:53:C5:E2:3A:87:4D',
  fingerprint256: '69:AE:1A:6A:D4:3D:C6:C1:1B:EA:C6:23:DE:BA:2A:14:62:62:93:5C:7A:EA:06:41:9B:0B:BC:87:CE:48:4E:02',
  ext_key_usage: [ '1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2' ],
  serialNumber: '66593D57F20CBC573E433381B5FEC280',
  raw: <Buffer ... > }

tls.connect(options[, callback])

• options <Object>

  • host <string> Host the client should connect to. Default: 'localhost'.
  • port <number> Port the client should connect to.
  • path <string> Creates unix socket connection to path. If this option is specified, host and port are ignored.
  • socket <stream.Duplex> Establish secure connection on a given socket rather than creating a new socket. Typically, this is an instance of net.Socket, but any Duplex stream is allowed. If this option is specified, path, host and port are ignored, except for certificate validation. Usually, a socket is already connected when passed to tls.connect(), but it can be connected later. Note that connection/disconnection/destruction of socket is the user's responsibility, calling tls.connect() will not cause net.connect() to be called.
  • rejectUnauthorized <boolean> If not false, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails; err.code contains the OpenSSL error code. Default: true.
  • ALPNProtocols: <string[]> | <Buffer[]> | <Uint8Array[]> | <Buffer> | <Uint8Array> An array of strings, Buffers or Uint8Arrays, or a single Buffer or Uint8Array containing the supported ALPN protocols. Buffers should have the format [len][name][len][name]... e.g. '\x08http/1.1\x08http/1.0', where the len byte is the length of the next protocol name. Passing an array is usually much simpler, e.g. ['http/1.1', 'http/1.0']. Protocols earlier in the list have higher preference than those later.
  • servername: <string> Server name for the SNI (Server Name Indication) TLS extension. It is the name of the host being connected to, and must be a host name, and not an IP address. It can be used by a multi-homed server to choose the correct certificate to present to the client, see the SNICallback option to tls.createServer().
  • checkServerIdentity(servername, cert) <Function> A callback function to be used (instead of the builtin tls.checkServerIdentity() function) when checking the server's hostname (or the provided servername when explicitly set) against the certificate. This should return an <Error> if verification fails. The method should return undefined if the servername and cert are verified.
  • session <Buffer> A Buffer instance, containing TLS session.
  • minDHSize <number> Minimum size of the DH parameter in bits to accept a TLS connection. When a server offers a DH parameter with a size less than minDHSize, the TLS connection is destroyed and an error is thrown. Default: 1024.
  • secureContext: TLS context object created with tls.createSecureContext(). If a secureContext is not provided, one will be created by passing the entire options object to tls.createSecureContext().
  • lookup: <Function> Custom lookup function. Default: dns.lookup().
  • timeout: <number> If set and if a socket is created internally, will call socket.setTimeout(timeout) after the socket is created, but before it starts the connection.
  • ...: tls.createSecureContext() options that are used if the secureContext option is missing, otherwise they are ignored.
• callback <Function>
• Returns: <tls.TLSSocket>

The callback function, if specified, will be added as a listener for the 'secureConnect' event.

tls.connect() returns a tls.TLSSocket object.

The following illustrates a client for the echo server example from tls.createServer():

// Assumes an echo server that is listening on port 8000.
const tls = require('tls');
const fs = require('fs');

const options = {
  // Necessary only if the server requires client certificate authentication.
  key: fs.readFileSync('client-key.pem'),
  cert: fs.readFileSync('client-cert.pem'),

  // Necessary only if the server uses a self-signed certificate.
  ca: [ fs.readFileSync('server-cert.pem') ],

  // Necessary only if the server's cert isn't for "localhost".
  checkServerIdentity: () => { return null; },
};

const socket = tls.connect(8000, options, () => {
  console.log('client connected',
              socket.authorized ? 'authorized' : 'unauthorized');
  process.stdin.pipe(socket);
  process.stdin.resume();
});
socket.setEncoding('utf8');
socket.on('data', (data) => {
  console.log(data);
});
socket.on('end', () => {
  console.log('server ends connection');
});

tls.connect(path[, options][, callback])

• path <string> Default value for options.path.
• options <Object> See tls.connect().
• callback <Function> See tls.connect().
• Returns: <tls.TLSSocket>

Same as tls.connect() except that path can be provided as an argument instead of an option.

A path option, if specified, will take precedence over the path argument.

tls.connect(port[, host][, options][, callback])

• port <number> Default value for options.port.
• host <string> Default value for options.host.
• options <Object> See tls.connect().
• callback <Function> See tls.connect().
• Returns: <tls.TLSSocket>

Same as tls.connect() except that port and host can be provided as arguments instead of options.

A port or host option, if specified, will take precedence over any port or host argument.

tls.createSecureContext([options])

• options <Object>

  • ca <string> | <string[]> | <Buffer> | <Buffer[]> Optionally override the trusted CA certificates. Default is to trust the well-known CAs curated by Mozilla. Mozilla's CAs are completely replaced when CAs are explicitly specified using this option. The value can be a string or Buffer, or an Array of strings and/or Buffers. Any string or Buffer can contain multiple PEM CAs concatenated together. The peer's certificate must be chainable to a CA trusted by the server for the connection to be authenticated. When using certificates that are not chainable to a well-known CA, the certificate's CA must be explicitly specified as a trusted or the connection will fail to authenticate. If the peer uses a certificate that doesn't match or chain to one of the default CAs, use the ca option to provide a CA certificate that the peer's certificate can match or chain to. For self-signed certificates, the certificate is its own CA, and must be provided. For PEM encoded certificates, supported types are "X509 CERTIFICATE", and "CERTIFICATE".
  • cert <string> | <string[]> | <Buffer> | <Buffer[]> Cert chains in PEM format. One cert chain should be provided per private key. Each cert chain should consist of the PEM formatted certificate for a provided private key, followed by the PEM formatted intermediate certificates (if any), in order, and not including the root CA (the root CA must be pre-known to the peer, see ca). When providing multiple cert chains, they do not have to be in the same order as their private keys in key. If the intermediate certificates are not provided, the peer will not be able to validate the certificate, and the handshake will fail.
  • ciphers <string> Cipher suite specification, replacing the default. For more information, see modifying the default cipher suite.
  • clientCertEngine <string> Name of an OpenSSL engine which can provide the client certificate.
  • crl <string> | <string[]> | <Buffer> | <Buffer[]> PEM formatted CRLs (Certificate Revocation Lists).
  • dhparam <string> | <Buffer> Diffie Hellman parameters, required for Perfect Forward Secrecy. Use openssl dhparam to create the parameters. The key length must be greater than or equal to 1024 bits, otherwise an error will be thrown. It is strongly recommended to use 2048 bits or larger for stronger security. If omitted or invalid, the parameters are silently discarded and DHE ciphers will not be available.
  • ecdhCurve <string> A string describing a named curve or a colon separated list of curve NIDs or names, for example P-521:P-384:P-256, to use for ECDH key agreement. Set to auto to select the curve automatically. Use crypto.getCurves() to obtain a list of available curve names. On recent releases, openssl ecparam -list_curves will also display the name and description of each available elliptic curve. Default: tls.DEFAULT_ECDH_CURVE.
  • honorCipherOrder <boolean> Attempt to use the server's cipher suite preferences instead of the client's. When true, causes SSL_OP_CIPHER_SERVER_PREFERENCE to be set in secureOptions, see OpenSSL Options for more information.
  • key <string> | <string[]> | <Buffer> | <Buffer[]> | <Object[]> Private keys in PEM format. PEM allows the option of private keys being encrypted. Encrypted keys will be decrypted with options.passphrase. Multiple keys using different algorithms can be provided either as an array of unencrypted key strings or buffers, or an array of objects in the form {pem: <string|buffer>[, passphrase: <string>]}. The object form can only occur in an array. object.passphrase is optional. Encrypted keys will be decrypted with object.passphrase if provided, or options.passphrase if it is not.
  • maxVersion <string> Optionally set the maximum TLS version to allow. One of TLSv1.2', 'TLSv1.1', or 'TLSv1'. Cannot be specified along with the secureProtocol option, use one or the other. Default: tls.DEFAULT_MAX_VERSION.
  • minVersion <string> Optionally set the minimum TLS version to allow. One of TLSv1.2', 'TLSv1.1', or 'TLSv1'. Cannot be specified along with the secureProtocol option, use one or the other. It is not recommended to use less than TLSv1.2, but it may be required for interoperability. Default: tls.DEFAULT_MIN_VERSION.
  • passphrase <string> Shared passphrase used for a single private key and/or a PFX.
  • pfx <string> | <string[]> | <Buffer> | <Buffer[]> | <Object[]> PFX or PKCS12 encoded private key and certificate chain. pfx is an alternative to providing key and cert individually. PFX is usually encrypted, if it is, passphrase will be used to decrypt it. Multiple PFX can be provided either as an array of unencrypted PFX buffers, or an array of objects in the form {buf: <string|buffer>[, passphrase: <string>]}. The object form can only occur in an array. object.passphrase is optional. Encrypted PFX will be decrypted with object.passphrase if provided, or options.passphrase if it is not.
  • secureOptions <number> Optionally affect the OpenSSL protocol behavior, which is not usually necessary. This should be used carefully if at all! Value is a numeric bitmask of the SSL_OP_* options from OpenSSL Options.
  • secureProtocol <string> The TLS protocol version to use. The possible values are listed as SSL_METHODS, use the function names as strings. For example, use 'TLSv1_1_method' to force TLS version 1.1, or 'TLS_method' to allow any TLS protocol version. It is not recommended to use TLS versions less than 1.2, but it may be required for interoperability. Default: none, see minVersion.
  • sessionIdContext <string> Opaque identifier used by servers to ensure session state is not shared between applications. Unused by clients.

tls.createServer() sets the default value of the honorCipherOrder option to true, other APIs that create secure contexts leave it unset.

tls.createServer() uses a 128 bit truncated SHA1 hash value generated from process.argv as the default value of the sessionIdContext option, other APIs that create secure contexts have no default value.

The tls.createSecureContext() method creates a credentials object.

A key is required for ciphers that make use of certificates. Either key or pfx can be used to provide it.

If the 'ca' option is not given, then Node.js will use the default publicly trusted list of CAs as given in https://hg.mozilla.org/mozilla-central/raw-file/tip/security/nss/lib/ckfw/builtins/certdata.txt.

tls.createServer([options][, secureconnectionlistener])

• options <Object>

  • ALPNProtocols: <string[]> | <Buffer[]> | <Uint8Array[]> | <Buffer> | <Uint8Array> An array of strings, Buffers or Uint8Arrays, or a single Buffer or Uint8Array containing the supported ALPN protocols. Buffers should have the format [len][name][len][name]... e.g. 0x05hello0x05world, where the first byte is the length of the next protocol name. Passing an array is usually much simpler, e.g. ['hello', 'world']. (Protocols should be ordered by their priority.)
  • clientCertEngine <string> Name of an OpenSSL engine which can provide the client certificate.
  • handshakeTimeout <number> Abort the connection if the SSL/TLS handshake does not finish in the specified number of milliseconds. A 'tlsClientError' is emitted on the tls.Server object whenever a handshake times out. Default: 120000 (120 seconds).
  • rejectUnauthorized <boolean> If not false the server will reject any connection which is not authorized with the list of supplied CAs. This option only has an effect if requestCert is true. Default: true.
  • requestCert <boolean> If true the server will request a certificate from clients that connect and attempt to verify that certificate. Default: false.
  • sessionTimeout <number> The number of seconds after which a TLS session created by the server will no longer be resumable. See Session Resumption for more information. Default: 300.
  • SNICallback(servername, cb) <Function> A function that will be called if the client supports SNI TLS extension. Two arguments will be passed when called: servername and cb. SNICallback should invoke cb(null, ctx), where ctx is a SecureContext instance. (tls.createSecureContext(...) can be used to get a proper SecureContext.) If SNICallback wasn't 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.
  • ...: Any tls.createSecureContext() option can be provided. For servers, the identity options (pfx or key/cert) are usually required.
• secureConnectionListener <Function>
• Returns: <tls.Server>

Creates a new tls.Server. The secureConnectionListener, if provided, is automatically set as a listener for the 'secureConnection' event.

The ticketKeys options is automatically shared between cluster module workers.

The following illustrates a simple echo server:

const tls = require('tls');
const fs = require('fs');

const options = {
  key: fs.readFileSync('server-key.pem'),
  cert: fs.readFileSync('server-cert.pem'),

  // This is necessary only if using client certificate authentication.
  requestCert: true,

  // This is necessary only if the client uses a self-signed certificate.
  ca: [ fs.readFileSync('client-cert.pem') ]
};

const server = tls.createServer(options, (socket) => {
  console.log('server connected',
              socket.authorized ? 'authorized' : 'unauthorized');
  socket.write('welcome!\n');
  socket.setEncoding('utf8');
  socket.pipe(socket);
});
server.listen(8000, () => {
  console.log('server bound');
});

The server can be tested by connecting to it using the example client from tls.connect().

tls.getCiphers()

• Returns: <string[]>

Returns an array with the names of the supported SSL ciphers.

console.log(tls.getCiphers()); // ['AES128-SHA', 'AES256-SHA', ...]

tls.DEFAULT_ECDH_CURVE

The default curve name to use for ECDH key agreement in a tls server. The default value is 'auto'. See tls.createSecureContext() for further information.

tls.DEFAULT_MAX_VERSION

• <string> The default value of the maxVersion option of tls.createSecureContext(). It can be assigned any of the supported TLS protocol versions, 'TLSv1.2', 'TLSv1.1', or 'TLSv1'. Default: 'TLSv1.2'.

tls.DEFAULT_MIN_VERSION

• <string> The default value of the minVersion option of tls.createSecureContext(). It can be assigned any of the supported TLS protocol versions, 'TLSv1.2', 'TLSv1.1', or 'TLSv1'. Default: 'TLSv1', unless changed using CLI options. Using --tls-min-v1.0 sets the default to 'TLSv1'. Using --tls-min-v1.1 sets the default to 'TLSv1.1'. Using --tls-min-v1.2 sets the default to 'TLSv1.2'. If multiple of the options are provided, the lowest minimum is used.

Deprecated APIs

Class: CryptoStream

The tls.CryptoStream class represents a stream of encrypted data. This class is deprecated and should no longer be used.

cryptoStream.bytesWritten

The cryptoStream.bytesWritten property returns the total number of bytes written to the underlying socket including the bytes required for the implementation of the TLS protocol.

Class: SecurePair

Returned by tls.createSecurePair().

Event: 'secure'

The 'secure' event is emitted by the SecurePair object once a secure connection has been established.

As with checking for the server 'secureConnection' event, pair.cleartext.authorized should be inspected to confirm whether the certificate used is properly authorized.

tls.createSecurePair([context][, isserver][, requestCert][, rejectunauthorized][, options])

• context <Object> A secure context object as returned by tls.createSecureContext()
• isServer <boolean> true to specify that this TLS connection should be opened as a server.
• requestCert <boolean> true to specify whether a server should request a certificate from a connecting client. Only applies when isServer is true.
• rejectUnauthorized <boolean> If not false a server automatically reject clients with invalid certificates. Only applies when isServer is true.

• options

  • secureContext: A TLS context object from tls.createSecureContext()
  • isServer: If true the TLS socket will be instantiated in server-mode. Default: false.
  • server <net.Server> A net.Server instance
  • requestCert: See tls.createServer()
  • rejectUnauthorized: See tls.createServer()
  • ALPNProtocols: See tls.createServer()
  • SNICallback: See tls.createServer()
  • session <Buffer> A Buffer instance containing a TLS session.
  • requestOCSP <boolean> If true, specifies that the OCSP status request extension will be added to the client hello and an 'OCSPResponse' event will be emitted on the socket before establishing a secure communication.

Creates a new secure pair object with two streams, one of which reads and writes the encrypted data and the other of which reads and writes the cleartext data. Generally, the encrypted stream is piped to/from an incoming encrypted data stream and the cleartext one is used as a replacement for the initial encrypted stream.

tls.createSecurePair() returns a tls.SecurePair object with cleartext and encrypted stream properties.

Using cleartext has the same API as tls.TLSSocket.

The tls.createSecurePair() method is now deprecated in favor of tls.TLSSocket(). For example, the code:

pair = tls.createSecurePair(/* ... */);
pair.encrypted.pipe(socket);
socket.pipe(pair.encrypted);

can be replaced by:

secureSocket = tls.TLSSocket(socket, options);

where secureSocket has the same API as pair.cleartext.