TLS (SSL)

The node: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:

import tls from 'node:tls';

It is possible for Node.js to be built without including support for the node:crypto module. In such cases, attempting to import from tls or calling require('node:tls') will result in an error being thrown.

When using CommonJS, the error thrown can be caught using try/catch:

let tls;
try {
  tls = require('node:tls');
} catch (err) {
  console.error('tls support is disabled!');
}

When using the lexical ESM import keyword, the error can only be caught if a handler for process.on('uncaughtException') is registered before any attempt to load the module is made (using, for instance, a preload module).

When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the import() function instead of the lexical import keyword:

let tls;
try {
  tls = await import('node:tls');
} catch (err) {
  console.error('tls support is disabled!');
}

TLS/SSL is a set of protocols that rely on a public key infrastructure (PKI) to enable secure communication between a client and a server. For most common cases, each 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

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):

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

Perfect forward secrecy using ECDHE is enabled by default. The ecdhCurve option can be used when creating a TLS server to customize the list of supported ECDH curves to use. See tls.createServer() for more info.

DHE is disabled by default but can be enabled alongside ECDHE by setting the dhparam option to 'auto'. Custom DHE parameters are also supported but discouraged in favor of automatically selected, well-known parameters.

Perfect forward secrecy was optional up to TLSv1.2. As of TLSv1.3, (EC)DHE is always used (with the exception of PSK-only connections).

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 certificates.

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 the public key infrastructure (PKI) 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 and can be retrieved via openssl ciphers -v -s -tls1_3 -psk. On the client connection, a custom checkServerIdentity should be passed because the default one will fail in the absence of a certificate.

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.

To use TLS-PSK, client and server must specify the pskCallback option, a function that returns the PSK to use (which must be compatible with the selected cipher's digest).

It will be called first on the client:

• hint: <string> optional message sent from the server to help the 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.

Then on the server:

• socket: <tls.TLSSocket> the server socket instance, equivalent to this.
• identity: <string> identity parameter sent from the client.
• Returns: <Buffer> | <TypedArray> | <DataView> the PSK (or null).

A return value of null stops the negotiation process and sends an unknown_psk_identity alert message 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.

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:

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

TLSv1.3 does not support renegotiation.

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).

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 wait for the 'session' event to get the session data, and provide the data to the session option of a subsequent 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.

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 a 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.

With TLSv1.3, be aware that multiple tickets may be sent by the server, resulting in multiple 'session' events, see 'session' for more information.

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.

It's 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('node: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

Node.js is built with a default suite of enabled and disabled TLS ciphers. This default cipher list can be configured when building Node.js to allow distributions to provide their own default list.

The following command can be used to show the default cipher suite:

node -p crypto.constants.defaultCoreCipherList | tr ':' '\n'
TLS_AES_256_GCM_SHA384
TLS_CHACHA20_POLY1305_SHA256
TLS_AES_128_GCM_SHA256
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

To verify, use the following command to show the set cipher list, note the difference between defaultCoreCipherList and defaultCipherList:

node --tls-cipher-list='ECDHE-RSA-AES128-GCM-SHA256:!RC4' -p crypto.constants.defaultCipherList | tr ':' '\n'
ECDHE-RSA-AES128-GCM-SHA256
!RC4

i.e. the defaultCoreCipherList list is set at compilation time and the defaultCipherList is set at runtime.

To modify the default cipher suites from within the runtime, modify the tls.DEFAULT_CIPHERS variable, this must be performed before listening on any sockets, it will not affect sockets already opened. For example:

// Remove Obsolete CBC Ciphers and RSA Key Exchange based Ciphers as they don't provide Forward Secrecy
tls.DEFAULT_CIPHERS +=
  ':!ECDHE-RSA-AES128-SHA:!ECDHE-RSA-AES128-SHA256:!ECDHE-RSA-AES256-SHA:!ECDHE-RSA-AES256-SHA384' +
  ':!ECDHE-ECDSA-AES128-SHA:!ECDHE-ECDSA-AES128-SHA256:!ECDHE-ECDSA-AES256-SHA:!ECDHE-ECDSA-AES256-SHA384' +
  ':!kRSA';

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.

The ciphers list can contain a mixture of TLSv1.3 cipher suite names, the ones that start with 'TLS_', and specifications for TLSv1.2 and below cipher suites. The TLSv1.2 ciphers support a legacy specification format, consult the OpenSSL cipher list format documentation for details, but those specifications do not apply to TLSv1.3 ciphers. The TLSv1.3 suites can only be enabled by including their full name in the cipher list. They cannot, for example, be enabled or disabled by using the legacy TLSv1.2 'EECDH' or '!EECDH' specification.

Despite the relative order of TLSv1.3 and TLSv1.2 cipher suites, the TLSv1.3 protocol is significantly more secure than TLSv1.2, and will always be chosen over TLSv1.2 if the handshake indicates it is supported, and if any TLSv1.3 cipher suites are enabled.

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.

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.

There are only five TLSv1.3 cipher suites:

• 'TLS_AES_256_GCM_SHA384'
• 'TLS_CHACHA20_POLY1305_SHA256'
• 'TLS_AES_128_GCM_SHA256'
• 'TLS_AES_128_CCM_SHA256'
• 'TLS_AES_128_CCM_8_SHA256'

The first three are enabled by default. The two CCM-based suites are supported by TLSv1.3 because they may be more performant on constrained systems, but they are not enabled by default since they offer less security.

The OpenSSL library enforces security levels to control the minimum acceptable level of security for cryptographic operations. OpenSSL's security levels range from 0 to 5, with each level imposing stricter security requirements. The default security level is 1, which is generally suitable for most modern applications. However, some legacy features and protocols, such as TLSv1, require a lower security level (SECLEVEL=0) to function properly. For more detailed information, please refer to the OpenSSL documentation on security levels.

To adjust the security level in your Node.js application, you can include @SECLEVEL=X within a cipher string, where X is the desired security level. For example, to set the security level to 0 while using the default OpenSSL cipher list, you could use:

import { createServer, connect } from 'node:tls';
const port = 443;

createServer({ ciphers: 'DEFAULT@SECLEVEL=0', minVersion: 'TLSv1' }, function(socket) {
  console.log('Client connected with protocol:', socket.getProtocol());
  socket.end();
  this.close();
})
.listen(port, () => {
  connect(port, { ciphers: 'DEFAULT@SECLEVEL=0', maxVersion: 'TLSv1' });
});

This approach sets the security level to 0, allowing the use of legacy features while still leveraging the default OpenSSL ciphers.

You can also set the security level and ciphers from the command line using the --tls-cipher-list=DEFAULT@SECLEVEL=X as described in Modifying the default TLS cipher suite. However, it is generally discouraged to use the command line option for setting ciphers and it is preferable to configure the ciphers for individual contexts within your application code, as this approach provides finer control and reduces the risk of globally downgrading the security level.

Multiple functions can fail due to certificate errors that are reported by OpenSSL. In such a case, the function provides an <Error> via its callback that has the property code which can take one of the following values:

• 'UNABLE_TO_GET_ISSUER_CERT': Unable to get issuer certificate.
• 'UNABLE_TO_GET_CRL': Unable to get certificate CRL.
• 'UNABLE_TO_DECRYPT_CERT_SIGNATURE': Unable to decrypt certificate's signature.
• 'UNABLE_TO_DECRYPT_CRL_SIGNATURE': Unable to decrypt CRL's signature.
• 'UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY': Unable to decode issuer public key.
• 'CERT_SIGNATURE_FAILURE': Certificate signature failure.
• 'CRL_SIGNATURE_FAILURE': CRL signature failure.
• 'CERT_NOT_YET_VALID': Certificate is not yet valid.
• 'CERT_HAS_EXPIRED': Certificate has expired.
• 'CRL_NOT_YET_VALID': CRL is not yet valid.
• 'CRL_HAS_EXPIRED': CRL has expired.
• 'ERROR_IN_CERT_NOT_BEFORE_FIELD': Format error in certificate's notBefore field.
• 'ERROR_IN_CERT_NOT_AFTER_FIELD': Format error in certificate's notAfter field.
• 'ERROR_IN_CRL_LAST_UPDATE_FIELD': Format error in CRL's lastUpdate field.
• 'ERROR_IN_CRL_NEXT_UPDATE_FIELD': Format error in CRL's nextUpdate field.
• 'OUT_OF_MEM': Out of memory.
• 'DEPTH_ZERO_SELF_SIGNED_CERT': Self signed certificate.
• 'SELF_SIGNED_CERT_IN_CHAIN': Self signed certificate in certificate chain.
• 'UNABLE_TO_GET_ISSUER_CERT_LOCALLY': Unable to get local issuer certificate.
• 'UNABLE_TO_VERIFY_LEAF_SIGNATURE': Unable to verify the first certificate.
• 'CERT_CHAIN_TOO_LONG': Certificate chain too long.
• 'CERT_REVOKED': Certificate revoked.
• 'INVALID_CA': Invalid CA certificate.
• 'PATH_LENGTH_EXCEEDED': Path length constraint exceeded.
• 'INVALID_PURPOSE': Unsupported certificate purpose.
• 'CERT_UNTRUSTED': Certificate not trusted.
• 'CERT_REJECTED': Certificate rejected.
• 'HOSTNAME_MISMATCH': Hostname mismatch.

When certificate errors like UNABLE_TO_VERIFY_LEAF_SIGNATURE, DEPTH_ZERO_SELF_SIGNED_CERT, or UNABLE_TO_GET_ISSUER_CERT occur, Node.js appends a hint suggesting that if the root CA is installed locally, try running with the --use-system-ca flag to direct developers towards a secure solution, to prevent unsafe workarounds.

class tls.Server extends net.Server

Accepts encrypted connections using TLS or SSL.

This event is emitted when a new TCP stream is established, before the TLS handshake begins. socket is typically an object of type net.Socket but will not receive events unlike the socket created from the net.Server 'connection' event. Usually users will not want to access this event.

This event can also be explicitly emitted by users to inject connections into the TLS server. In that case, any Duplex stream can be passed.

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);
});

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:

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

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

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.

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

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);
});

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:

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. 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 because the client or the server did not send an ALPN extension, tlsSocket.alpnProtocol equals false.

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

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

server.addContext(hostname, context)

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).

When there are multiple matching contexts, the most recently added one is used.

server.address(): 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?): 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.getTicketKeys(): Buffer

Returns the session ticket keys.

See Session Resumption for more information.

server.listen()

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

server.setSecureContext(options)

The server.setSecureContext() method replaces the secure context of an existing server. Existing connections to the server are not interrupted.

server.setTicketKeys(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 extends net.Socket

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?)

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

The keylog event is emitted on a 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));

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:

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

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.

The 'secureConnect' event is not emitted when a <tls.TLSSocket> is created using the new tls.TLSSocket() constructor.

The 'session' event is emitted on a client tls.TLSSocket when a new session or TLS ticket is available. This may or may not be before the handshake is complete, depending on the TLS protocol version that was negotiated. The event is not emitted on the server, or if a new session was not created, for example, when the connection was resumed. For some TLS protocol versions the event may be emitted multiple times, in which case all the sessions can be used for resumption.

On the client, the session can be provided to the session option of tls.connect() to resume the connection.

See Session Resumption for more information.

For TLSv1.2 and below, tls.TLSSocket.getSession() can be called once the handshake is complete. For TLSv1.3, only ticket-based resumption is allowed by the protocol, multiple tickets are sent, and the tickets aren't sent until after the handshake completes. So it is necessary to wait for the 'session' event to get a resumable session. Applications should use the 'session' event instead of getSession() to ensure they will work for all TLS versions. Applications that only expect to get or use one session should listen for this event only once:

tlsSocket.once('session', (session) => {
  // The session can be used immediately or later.
  tls.connect({
    session: session,
    // Other connect options...
  });
});

tlsSocket.address(): 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' }.

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

This property is 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.enableTrace()

When enabled, TLS packet trace information is written to stderr. This can be used to debug TLS connection problems.

The format of the output is identical to the output of openssl s_client -trace or openssl s_server -trace. While it is produced by OpenSSL's SSL_trace() function, the format is undocumented, can change without notice, and should not be relied on.

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

tlsSocket.exportKeyingMaterial(length, label, context?): Buffer

Keying material is used for validations to prevent different kind of attacks in network protocols, for example in the specifications of IEEE 802.1X.

Example

const keyingMaterial = tlsSocket.exportKeyingMaterial(
  128,
  'client finished');

/*
 Example return value of keyingMaterial:
 <Buffer 76 26 af 99 c5 56 8e 42 09 91 ef 9f 93 cb ad 6c 7b 65 f8 53 f1 d8 d9
    12 5a 33 b8 b5 25 df 7b 37 9f e0 e2 4f b8 67 83 a3 2f cd 5d 41 42 4c 91
    74 ef 2c ... 78 more bytes>
*/

See the OpenSSL SSL_export_keying_material documentation for more information.

tlsSocket.getCertificate(): Object

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

See tls.TLSSocket.getPeerCertificate() for an example of the certificate structure.

If there is no local certificate, an empty object will be returned. If the socket has been destroyed, null will be returned.

tlsSocket.getCipher(): Object

Returns an object containing information on the negotiated cipher suite.

For example, a TLSv1.2 protocol with AES256-SHA cipher:

{
    "name": "AES256-SHA",
    "standardName": "TLS_RSA_WITH_AES_256_CBC_SHA",
    "version": "SSLv3"
}

See SSL_CIPHER_get_name for more information.

tlsSocket.getEphemeralKeyInfo(): 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(): Buffer|undefined

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?): Object

Returns an object representing the peer's certificate. If the peer does not provide a certificate, an empty object will be returned. If the socket has been destroyed, null will be returned.

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

A certificate object has properties corresponding to the fields of the certificate.

The certificate may contain information about the public key, depending on the key type.

For RSA keys, the following properties may be defined:

For EC keys, the following properties may be defined:

Example certificate:

{ 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: 'B56CE45CB740B09A13F64AC543B712FF9EE8E4C284B542A1708A27E82A8D151CA178153E12E6DDA15BF70FFD96CB8A88618641BDFCCA03527E665B70D779C8A349A6F88FD4EF6557180BD4C98192872BCFE3AF56E863C09DDD8BC1EC58DF9D94F914F0369102B2870BECFA1348A0838C9C49BD1C20124B442477572347047506B1FCD658A80D0C44BCC16BC5C5496CFE6E4A8428EF654CD3D8972BF6E5BFAD59C93006830B5EB1056BBB38B53D1464FA6E02BFDF2FF66CD949486F0775EC43034EC2602AEFBF1703AD221DAA2A88353C3B6A688EFE8387811F645CEED7B3FE46E1F8B9F59FAD028F349B9BC14211D5830994D055EEA3D547911E07A0ADDEB8A82B9188E58720D95CD478EEC9AF1F17BE8141BE80906F1A339445A7EB5B285F68039B0F294598A7D1C0005FC22B5271B0752F58CCDEF8C8FD856FB7AE21C80B8A2CE983AE94046E53EDE4CB89F42502D31B5360771C01C80155918637490550E3F555E2EE75CC8C636DDE3633CFEDD62E91BF0F7688273694EEEBA20C2FC9F14A2A435517BC1D7373922463409AB603295CEB0BB53787A334C9CA3CA8B30005C5A62FC0715083462E00719A8FA3ED0A9828C3871360A73F8B04A4FC1E71302844E9BB9940B77E745C9D91F226D71AFCAD4B113AAF68D92B24DDB4A2136B55A1CD1ADF39605B63CB639038ED0F4C987689866743A68769CC55847E4A06D6E2E3F1',
  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',
  fingerprint512: '19:2B:3E:C3:B3:5B:32:E8:AE:BB:78:97:27:E4:BA:6C:39:C9:92:79:4F:31:46:39:E2:70:E5:5F:89:42:17:C9:E8:64:CA:FF:BB:72:56:73:6E:28:8A:92:7E:A3:2A:15:8B:C2:E0:45:CA:C3:BC:EA:40:52:EC:CA:A2:68:CB:32',
  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 ... > }

tlsSocket.getPeerFinished(): Buffer|undefined

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.getPeerX509Certificate(): X509Certificate

Returns the peer certificate as an <X509Certificate> object.

If there is no peer certificate, or the socket has been destroyed, undefined will be returned.

tlsSocket.getProtocol(): 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:

• 'SSLv3'
• 'TLSv1'
• 'TLSv1.1'
• 'TLSv1.2'
• 'TLSv1.3'

See the OpenSSL SSL_get_version documentation for more information.

tlsSocket.getSession()

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.

Note: getSession() works only for TLSv1.2 and below. For TLSv1.3, applications must use the 'session' event (it also works for TLSv1.2 and below).

tlsSocket.getSharedSigalgs(): Array

See SSL_get_shared_sigalgs for more information.

tlsSocket.getTLSTicket()

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.getX509Certificate(): X509Certificate

Returns the local certificate as an <X509Certificate> object.

If there is no local certificate, or the socket has been destroyed, undefined will be returned.

tlsSocket.isSessionReused(): boolean

See Session Resumption for more information.

Returns the string representation of the local IP address.

Returns the numeric representation of the local port.

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

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

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

tlsSocket.renegotiate(options, callback): boolean

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.

For TLSv1.3, renegotiation cannot be initiated, it is not supported by the protocol.

tlsSocket.setKeyCert(context)

The tlsSocket.setKeyCert() method sets the private key and certificate to use for the socket. This is mainly useful if you wish to select a server certificate from a TLS server's ALPNCallback.

tlsSocket.setMaxSendFragment(size?): 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): 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 is intended to be used in combination with the checkServerIdentity option that can be passed to tls.connect() and as such operates on a certificate object. For other purposes, consider using x509.checkHost() instead.

This function can be overwritten by providing an alternative function as the options.checkServerIdentity option that is 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).

Earlier versions of Node.js incorrectly accepted certificates for a given hostname if a matching uniformResourceIdentifier subject alternative name was present (see CVE-2021-44531). Applications that wish to accept uniformResourceIdentifier subject alternative names can use a custom options.checkServerIdentity function that implements the desired behavior.

tls.connect(options?, callback?): tls.TLSSocket

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

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

Unlike the https API, tls.connect() does not enable the SNI (Server Name Indication) extension by default, which may cause some servers to return an incorrect certificate or reject the connection altogether. To enable SNI, set the servername option in addition to host.

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

// Assumes an echo server that is listening on port 8000.
import { connect } from 'node:tls';
import { readFileSync } from 'node:fs';
import { stdin } from 'node:process';

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

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

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

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

To generate the certificate and key for this example, run:

openssl req -x509 -newkey rsa:2048 -nodes -sha256 -subj '/CN=localhost' \
  -keyout client-key.pem -out client-cert.pem

Then, to generate the server-cert.pem certificate for this example, run:

openssl pkcs12 -certpbe AES-256-CBC -export -out server-cert.pem \
  -inkey client-key.pem -in client-cert.pem

tls.connect(path, options?, callback?): 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?): 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?)

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 SecureContext object. It is usable as an argument to several tls APIs, such as server.addContext(), but has no public methods. The tls.Server constructor and the tls.createServer() method do not support the secureContext option.

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

If the ca option is not given, then Node.js will default to using Mozilla's publicly trusted list of CAs.

Custom DHE parameters are discouraged in favor of the new dhparam: 'auto' option. When set to 'auto', well-known DHE parameters of sufficient strength will be selected automatically. Otherwise, if necessary, openssl dhparam can be used to create custom parameters. The key length must be greater than or equal to 1024 bits or else an error will be thrown. Although 1024 bits is permissible, use 2048 bits or larger for stronger security.

tls.createServer(options?, secureConnectionListener?): 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 node:cluster module workers.

The following illustrates a simple echo server:

import { createServer } from 'node:tls';
import { readFileSync } from 'node:fs';

const options = {
  key: readFileSync('server-key.pem'),
  cert: 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: [ readFileSync('client-cert.pem') ],
};

const server = 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');
});

To generate the certificate and key for this example, run:

openssl req -x509 -newkey rsa:2048 -nodes -sha256 -subj '/CN=localhost' \
  -keyout server-key.pem -out server-cert.pem

Then, to generate the client-cert.pem certificate for this example, run:

openssl pkcs12 -certpbe AES-256-CBC -export -out client-cert.pem \
  -inkey server-key.pem -in server-cert.pem

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

tls.setDefaultCACertificates(certs)

Sets the default CA certificates used by Node.js TLS clients. If the provided certificates are parsed successfully, they will become the default CA certificate list returned by tls.getCACertificates() and used by subsequent TLS connections that don't specify their own CA certificates. The certificates will be deduplicated before being set as the default.

This function only affects the current Node.js thread. Previous sessions cached by the HTTPS agent won't be affected by this change, so this method should be called before any unwanted cachable TLS connections are made.

To use system CA certificates as the default:

const tls = require('node:tls');
tls.setDefaultCACertificates(tls.getCACertificates('system'));

This function completely replaces the default CA certificate list. To add additional certificates to the existing defaults, get the current certificates and append to them:

const tls = require('node:tls');
const currentCerts = tls.getCACertificates('default');
const additionalCerts = ['-----BEGIN CERTIFICATE-----\n...'];
tls.setDefaultCACertificates([...currentCerts, ...additionalCerts]);

tls.getCACertificates(type?): string[]

Returns an array containing the CA certificates from various sources, depending on type:

• "default": return the CA certificates that will be used by the Node.js TLS clients by default.
  • When --use-bundled-ca is enabled (default), or --use-openssl-ca is not enabled, this would include CA certificates from the bundled Mozilla CA store.
  • When --use-system-ca is enabled, this would also include certificates from the system's trusted store.
  • When NODE_EXTRA_CA_CERTS is used, this would also include certificates loaded from the specified file.
• "system": return the CA certificates that are loaded from the system's trusted store, according to rules set by --use-system-ca. This can be used to get the certificates from the system when --use-system-ca is not enabled.
• "bundled": return the CA certificates from the bundled Mozilla CA store. This would be the same as tls.rootCertificates.
• "extra": return the CA certificates loaded from NODE_EXTRA_CA_CERTS. It's an empty array if NODE_EXTRA_CA_CERTS is not set.

tls.getCiphers(): string[]

Returns an array with the names of the supported TLS ciphers. The names are lower-case for historical reasons, but must be uppercased to be used in the ciphers option of tls.createSecureContext().

Not all supported ciphers are enabled by default. See Modifying the default TLS cipher suite.

Cipher names that start with 'tls_' are for TLSv1.3, all the others are for TLSv1.2 and below.

console.log(tls.getCiphers()); // ['aes128-gcm-sha256', 'aes128-sha', ...]

An immutable array of strings representing the root certificates (in PEM format) from the bundled Mozilla CA store as supplied by the current Node.js version.

The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.

To get the actual CA certificates used by the current Node.js instance, which may include certificates loaded from the system store (if --use-system-ca is used) or loaded from a file indicated by NODE_EXTRA_CA_CERTS, use tls.getCACertificates().

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.