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# TLS (SSL)#

    Stability: 2 - Stable

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 name of an alternative curve to use, see `tls.createServer()` for more info.

### ALPN, NPN and SNI#

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

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

Note: Use of ALPN is recommended over NPN. The NPN extension has never been formally defined or documented and generally not recommended for use.

### 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. Defaults to `3`.
- `tls.CLIENT_RENEG_WINDOW` <number> Specifies the time renegotiation window in seconds. Defaults to `600` (10 minutes).

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

To test the renegotiation limits on a server, connect to it using the OpenSSL command-line client (`openssl s_client -connect address:port`) then input `R<CR>` (i.e., the letter `R` followed by a carriage return) multiple times.

## 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. 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"

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.TLSSocket`s.

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

Note: 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#

Added in: v0.3.2

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

### Event: 'newSession'#

Added in: v0.9.2

The `'newSession'` event is emitted upon creation of a new TLS session. This may be used to store sessions in external storage. The listener callback is passed three arguments when called:

- `sessionId` - The TLS session identifier
- `sessionData` - 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.

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

### Event: 'OCSPRequest'#

Added in: v0.11.13

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.

Note: 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.)

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

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

### Event: 'resumeSession'#

Added in: v0.9.2

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` - The TLS/SSL session identifier
- `callback` <Function> A callback function to be called when the prior session has been recovered.

When called, the event listener may perform a lookup in external storage using the given `sessionId` and invoke `callback(null, sessionData)` once finished. If the session cannot be resumed (i.e., doesn't exist in storage) the callback may be invoked as `callback(null, null)`. Calling `callback(err)` will terminate the incoming connection and destroy the socket.

Note: 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'#

Added in: v0.3.2

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.npnProtocol` and `tlsSocket.alpnProtocol` properties are strings that contain the selected NPN and ALPN protocols, respectively. When both NPN and ALPN extensions are received, ALPN takes precedence over NPN and the next protocol is selected by ALPN.

When ALPN has no selected protocol, `tlsSocket.alpnProtocol` returns `false`.

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

### Event: 'tlsClientError'#

Added in: v6.0.0

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)#

Added in: v0.5.3

- `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 hostname matches the supplied `hostname` (or wildcard).

### server.address()#

Added in: v0.6.0

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])#

Added in: v0.3.2

- `callback` <Function> An optional listener callback that will be registered to listen for the server instance's `'close'` event.

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#

Added in: v0.3.2 Deprecated since: v0.9.7

    Stability: 0 - Deprecated: Use server.getConnections() instead.

Returns the current number of concurrent connections on the server.

### server.getTicketKeys()#

Added in: v3.0.0

Returns a `Buffer` instance holding the keys currently used for encryption/decryption of the TLS Session Tickets

### server.listen(port[, hostname][, callback])#

Added in: v0.3.2

- `port` <number> The TCP/IP port on which to begin listening for connections. A value of `0` (zero) will assign a random port.
- `hostname` <string> The hostname, IPv4, or IPv6 address on which to begin listening for connections. If `undefined`, the server will accept connections on any IPv6 address (`::`) when IPv6 is available, or any IPv4 address (`0.0.0.0`) otherwise.
- `callback` <Function> A callback function to be invoked when the server has begun listening on the `port` and `hostname`.

The `server.listen()` methods instructs the server to begin accepting connections on the specified `port` and `hostname`.

This function operates asynchronously. If the `callback` is given, it will be called when the server has started listening.

See `net.Server` for more information.

### server.setTicketKeys(keys)#

Added in: v3.0.0

- `keys` <Buffer> The keys used for encryption/decryption of the TLS Session Tickets.

Updates the keys for encryption/decryption of the TLS Session Tickets.

Note: The key's `Buffer` should be 48 bytes long. See `ticketKeys` option in tls.createServer for more information on how it is used.

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

## Class: tls.TLSSocket#

Added in: v0.11.4

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.

Note: 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])#

History

Version | Changes
--- | ---
v5.0.0 | ALPN options are supported now.
v0.11.4 | Added in: v0.11.4

- `socket` <net.Socket> An instance of `net.Socket`
- `options` <Object>
  - `isServer`: The SSL/TLS protocol is asymetrical, 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. Defaults to `false`.
  - `server` <net.Server> An optional `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 optionally set `requestCert` to true to request a client certificate.
  - `rejectUnauthorized`: Optional, see `tls.createServer()`
  - `NPNProtocols`: Optional, see `tls.createServer()`
  - `ALPNProtocols`: Optional, see `tls.createServer()`
  - `SNICallback`: Optional, see `tls.createServer()`
  - `session` <Buffer> An optional `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`: Optional 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()`.
  - ...: Optional `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: 'OCSPResponse'#

Added in: v0.11.13

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'#

Added in: v0.11.4

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 either ALPN or NPN was used, the `tlsSocket.alpnProtocol` or `tlsSocket.npnProtocol` properties can be checked to determine the negotiated protocol.

### tlsSocket.address()#

Added in: v0.11.4

Returns the bound address, the address family name, and port of the underlying socket as reported by the operating system. Returns an object with three properties, e.g., `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`

### tlsSocket.authorizationError#

Added in: v0.11.4

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

### tlsSocket.authorized#

Added in: v0.11.4

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

### tlsSocket.encrypted#

Added in: v0.11.4

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

### tlsSocket.getCipher()#

Added in: v0.11.4

Returns an object representing the cipher name and the SSL/TLS protocol version that first defined the cipher.

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

See `SSL_CIPHER_get_name()` and `SSL_CIPHER_get_version()` in https://www.openssl.org/docs/man1.0.2/ssl/SSL_CIPHER_get_name.html for more information.

### tlsSocket.getEphemeralKeyInfo()#

Added in: v5.0.0

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.getPeerCertificate([detailed])#

Added in: v0.11.4

- `detailed` <boolean> Include the full certificate chain if `true`, otherwise include just the peer's certificate.

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 a `issuerCertificate` property containing an object representing its issuer's certificate.

For example:

    { 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 a .issuerCertificate ... },
      raw: < 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',
      serialNumber: 'B9B0D332A1AA5635' }

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

### tlsSocket.getProtocol()#

Added in: v5.7.0

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.

Example responses include:

- `SSLv3`
- `TLSv1`
- `TLSv1.1`
- `TLSv1.2`
- `unknown`

See https://www.openssl.org/docs/man1.0.2/ssl/SSL_get_version.html for more information.

### tlsSocket.getSession()#

Added in: v0.11.4

Returns the ASN.1 encoded TLS session or `undefined` if no session was negotiated. Can be used to speed up handshake establishment when reconnecting to the server.

### tlsSocket.getTLSTicket()#

Added in: v0.11.4

Returns the TLS session ticket or `undefined` if no session was negotiated.

Note: This only works with client TLS sockets. Useful only for debugging, for session reuse provide `session` option to `tls.connect()`.

### tlsSocket.localAddress#

Added in: v0.11.4

Returns the string representation of the local IP address.

### tlsSocket.localPort#

Added in: v0.11.4

Returns the numeric representation of the local port.

### tlsSocket.remoteAddress#

Added in: v0.11.4

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

### tlsSocket.remoteFamily#

Added in: v0.11.4

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

### tlsSocket.remotePort#

Added in: v0.11.4

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

### tlsSocket.renegotiate(options, callback)#

Added in: v0.11.8

- `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. Defaults to `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`.

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

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

### tlsSocket.setMaxSendFragment(size)#

Added in: v0.11.11

- `size` <number> The maximum TLS fragment size. Defaults to `16384`. The maximum value is `16384`.

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.connect(options[, callback])#

History

Version | Changes
--- | ---
v8.0.0 | The `lookup` option is supported now.
v8.0.0 | The `ALPNProtocols` and `NPNProtocols` options can be `Uint8Array`s now.
v5.3.0, v4.7.0 | The `secureContext` option is supported now.
v5.0.0 | ALPN options are supported now.
v0.11.3 | Added in: v0.11.3

- `options` <Object>
  - `host` <string> Host the client should connect to, defaults to '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` <net.Socket> Establish secure connection on a given socket rather than creating a new socket. If this option is specified, `path`, `host` and `port` are ignored. 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. Defaults to `true`.
  - `NPNProtocols` <string[]> | <Buffer[]> | <Uint8Array[]> | <Buffer> | <Uint8Array> An array of strings, `Buffer`s or `Uint8Array`s, or a single `Buffer` or `Uint8Array` containing supported NPN protocols. `Buffer`s 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']`.
  - `ALPNProtocols`: <string[]> | <Buffer[]> | <Uint8Array[]> | <Buffer> | <Uint8Array> An array of strings, `Buffer`s or `Uint8Array`s, or a single `Buffer` or `Uint8Array` containing the supported ALPN protocols. `Buffer`s 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']`.
  - `servername`: <string> Server name for the SNI (Server Name Indication) TLS extension.
  - `checkServerIdentity(servername, cert)` <Function> A callback function to be used when checking the server's hostname against the certificate. This should throw 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. Defaults to `1024`.
  - `secureContext`: Optional 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. Defaults to `dns.lookup()`.
  - ...: Optional `tls.createSecureContext()` options that are used if the `secureContext` option is missing, otherwise they are ignored.
- `callback` <Function>

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

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

The following implements a simple "echo server" example:

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

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

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

    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', () => {
      server.close();
    });

Or

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

    const options = {
      pfx: fs.readFileSync('client.pfx')
    };

    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', () => {
      server.close();
    });

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

Added in: v0.11.3

- `path` <string> Default value for `options.path`.
- `options` <Object> See `tls.connect()`.
- `callback` <Function> See `tls.connect()`.

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

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

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

Added in: v0.11.3

- `port` <number> Default value for `options.port`.
- `host` <string> Optional default value for `options.host`.
- `options` <Object> See `tls.connect()`.
- `callback` <Function> See `tls.connect()`.

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

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

## tls.createSecureContext(options)#

History

Version | Changes
--- | ---
v7.3.0 | If the `key` option is an array, individual entries do not need a `passphrase` property anymore. Array entries can also just be `string`s or `Buffer`s now.
v5.2.0 | The `ca` option can now be a single string containing multiple CA certificates.
v0.11.13 | Added in: v0.11.13

- `options` <Object>
  - `pfx` <string> | <Buffer> Optional 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.
  - `key` <string> | <string[]> | <Buffer> | <Buffer[]> | <Object[]> Optional 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.
  - `passphrase` <string> Optional shared passphrase used for a single private key and/or a PFX.
  - `cert` <string> | <string[]> | <Buffer> | <Buffer[]> Optional 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.
  - `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.
  - `crl` <string> | <string[]> | <Buffer> | <Buffer[]> Optional PEM formatted CRLs (Certificate Revocation Lists).
  - `ciphers` <string> Optional cipher suite specification, replacing the default. For more information, see modifying the default cipher suite.
  - `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.
  - `ecdhCurve` <string> A string describing a named curve to use for ECDH key agreement or `false` to disable ECDH. Defaults to `tls.DEFAULT_ECDH_CURVE`. 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.
  - `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.
  - `secureProtocol` <string> Optional SSL method to use, default is `"SSLv23_method"`. The possible values are listed as SSL_METHODS, use the function names as strings. For example, `"SSLv3_method"` to force SSL version 3.
  - `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.
  - `sessionIdContext` <string> Optional opaque identifier used by servers to ensure session state is not shared between applications. Unused by clients.

Note:

- `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 http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt.

## tls.createServer([options][, secureConnectionListener])#

History

Version | Changes
--- | ---
v8.0.0 | The `ALPNProtocols` and `NPNProtocols` options can be `Uint8Array`s now.
v5.0.0 | ALPN options are supported now.
v0.3.2 | Added in: v0.3.2

- `options` <Object>
  - `handshakeTimeout` <number> Abort the connection if the SSL/TLS handshake does not finish in the specified number of milliseconds. Defaults to `120` seconds. A `'tlsClientError'` is emitted on the `tls.Server` object whenever a handshake times out.
  - `requestCert` <boolean> If `true` the server will request a certificate from clients that connect and attempt to verify that certificate. Defaults to `false`.
  - `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`. Defaults to `true`.
  - `NPNProtocols` <string[]> | <Buffer[]> | <Uint8Array[]> | <Buffer> | <Uint8Array> An array of strings, `Buffer`s or `Uint8Array`s, or a single `Buffer` or `Uint8Array` containing supported NPN protocols. `Buffer`s 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.)
  - `ALPNProtocols`: <string[]> | <Buffer[]> | <Uint8Array[]> | <Buffer> | <Uint8Array> An array of strings, `Buffer`s or `Uint8Array`s, or a single `Buffer` or `Uint8Array` containing the supported ALPN protocols. `Buffer`s 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.) When the server receives both NPN and ALPN extensions from the client, ALPN takes precedence over NPN and the server does not send an NPN extension to the client.
  - `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).
  - `sessionTimeout` <number> An integer specifying the number of seconds after which the TLS session identifiers and TLS session tickets created by the server will time out. See SSL_CTX_set_timeout for more details.
  - `ticketKeys`: A 48-byte `Buffer` instance consisting of a 16-byte prefix, a 16-byte HMAC key, and a 16-byte AES key. This can be used to accept TLS session tickets on multiple instances of the TLS server.
  - ...: Any `tls.createSecureContext()` options can be provided. For servers, the identity options (`pfx` or `key`/`cert`) are usually required.
- `secureConnectionListener` <Function>

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

Note: 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 the client certificate authentication.
      requestCert: true,

      // This is necessary only if the client uses the 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');
    });

Or

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

    const options = {
      pfx: fs.readFileSync('server.pfx'),

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

    };

    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');
    });

This server can be tested by connecting to it using `openssl s_client`:

    openssl s_client -connect 127.0.0.1:8000

## tls.getCiphers()#

Added in: v0.10.2

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

For example:

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

## tls.DEFAULT_ECDH_CURVE#

Added in: v0.11.13

The default curve name to use for ECDH key agreement in a tls server. The default value is `'prime256v1'` (NIST P-256). Consult RFC 4492 and FIPS.186-4 for more details.

## Deprecated APIs#

### Class: CryptoStream#

Added in: v0.3.4 Deprecated since: v0.11.3

    Stability: 0 - Deprecated: Use tls.TLSSocket instead.

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

#### cryptoStream.bytesWritten#

Added in: v0.3.4 Deprecated since: v0.11.3

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#

Added in: v0.3.2 Deprecated since: v0.11.3

    Stability: 0 - Deprecated: Use tls.TLSSocket instead.

Returned by `tls.createSecurePair()`.

#### Event: 'secure'#

Added in: v0.3.2 Deprecated since: v0.11.3

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])#

History

Version | Changes
--- | ---
v5.0.0 | ALPN options are supported now.
v0.11.3 | Deprecated since: v0.11.3
v0.3.2 | Added in: v0.3.2

    Stability: 0 - Deprecated: Use tls.TLSSocket instead.

- `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`: An optional TLS context object from `tls.createSecureContext()`
  - `isServer`: If `true` the TLS socket will be instantiated in server-mode. Defaults to `false`.
  - `server` <net.Server> An optional `net.Server` instance
  - `requestCert`: Optional, see `tls.createServer()`
  - `rejectUnauthorized`: Optional, see `tls.createServer()`
  - `NPNProtocols`: Optional, see `tls.createServer()`
  - `ALPNProtocols`: Optional, see `tls.createServer()`
  - `SNICallback`: Optional, see `tls.createServer()`
  - `session` <Buffer> An optional `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.

Note: `cleartext` has the same API as `tls.TLSSocket`.

Note: 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:

    secure_socket = tls.TLSSocket(socket, options);

where `secure_socket` has the same API as `pair.cleartext`.