nodejs/doc/api/tls.markdown

TLS (SSL)

Stability: 3 - Stable

Use require('tls') to access this module.

The tls module uses OpenSSL to provide Transport Layer Security and/or Secure Socket Layer: encrypted stream communication.

TLS/SSL is a public/private key infrastructure. Each client and each server must have a private key. A private key is created like this:

openssl genrsa -out ryans-key.pem 2048

All servers and some clients need to have a certificate. Certificates are public keys signed by a Certificate Authority or self-signed. The first step to getting a certificate is to create a "Certificate Signing Request" (CSR) file. This is done with:

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

To create a self-signed certificate with the CSR, do this:

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

Alternatively you can send the CSR to a Certificate Authority for signing.

(TODO: docs on creating a CA, for now interested users should just look at test/fixtures/keys/Makefile in the Node source code)

To create .pfx or .p12, do this:

openssl pkcs12 -export -in agent5-cert.pem -inkey agent5-key.pem \
    -certfile ca-cert.pem -out agent5.pfx

• in: certificate
• inkey: private key
• certfile: all CA certs concatenated in one file like cat ca1-cert.pem ca2-cert.pem > ca-cert.pem

Client-initiated renegotiation attack mitigation

The TLS protocol lets the client renegotiate certain aspects of the TLS session. Unfortunately, session renegotiation requires a disproportional amount of server-side resources, which makes it a potential vector for denial-of-service attacks.

To mitigate this, renegotiations are limited to three times every 10 minutes. An error is emitted on the tls.TLSSocket instance when the threshold is exceeded. The limits are configurable:

• tls.CLIENT_RENEG_LIMIT: renegotiation limit, default is 3.

• tls.CLIENT_RENEG_WINDOW: renegotiation window in seconds, default is 10 minutes.

Don't change the defaults unless you know what you are doing.

To test your server, connect to it with openssl s_client -connect address:port and tap R<CR> (that's the letter R followed by a carriage return) a few times.

NPN and SNI

NPN (Next Protocol Negotiation) and SNI (Server Name Indication) are TLS handshake extensions allowing you:

• NPN - to use one TLS server for multiple protocols (HTTP, SPDY)
• SNI - to use one TLS server for multiple hostnames with different SSL certificates.

Perfect Forward Secrecy

The term "Forward Secrecy" or "Perfect Forward Secrecy" describes a feature of key-agreement (i.e. key-exchange) methods. Practically it means that even if the private key of a (your) server is compromised, communication can only be decrypted by eavesdroppers if they manage to obtain the key-pair specifically generated for each session.

This is achieved by randomly generating a key pair for key-agreement on every handshake (in contrary to the same key for all sessions). Methods implementing this technique, thus offering Perfect Forward Secrecy, 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.

tls.getCiphers()

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

Example:

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

tls.createServer(options[, secureConnectionListener])

Creates a new tls.Server. The connectionListener argument is automatically set as a listener for the secureConnection event. The options object has these possibilities:

• pfx: A string or Buffer containing the private key, certificate and CA certs of the server in PFX or PKCS12 format. (Mutually exclusive with the key, cert and ca options.)

• key: A string or Buffer containing the private key of the server in PEM format. (Could be an array of keys). (Required)

• passphrase: A string of passphrase for the private key or pfx.

• cert: A string or Buffer containing the certificate key of the server in PEM format. (Could be an array of certs). (Required)

• ca: An array of strings or Buffers of trusted certificates in PEM format. If this is omitted several well known "root" CAs will be used, like VeriSign. These are used to authorize connections.

• crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)

• ciphers: A string describing the ciphers to use or exclude.

  To mitigate BEAST attacks it is recommended that you use this option in conjunction with the honorCipherOrder option described below to prioritize the non-CBC cipher.

  Defaults to ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:HIGH:!MD5:!aNULL. Consult the OpenSSL cipher list format documentation for details on the format.

  ECDHE-RSA-AES128-SHA256, DHE-RSA-AES128-SHA256 and AES128-GCM-SHA256 are TLS v1.2 ciphers and used when node.js is linked against OpenSSL 1.0.1 or newer, such as the bundled version of OpenSSL. Note that it is still possible for a TLS v1.2 client to negotiate a weaker cipher unless honorCipherOrder is enabled.

  RC4 is used as a fallback for clients that speak on older version of the TLS protocol. RC4 has in recent years come under suspicion and should be considered compromised for anything that is truly sensitive. It is speculated that state-level actors possess the ability to break it.

  NOTE: Previous revisions of this section suggested AES256-SHA as an acceptable cipher. Unfortunately, AES256-SHA is a CBC cipher and therefore susceptible to BEAST attacks. Do not use it.

• ecdhCurve: A string describing a named curve to use for ECDH key agreement or false to disable ECDH.

  Defaults to prime256v1. Consult RFC 4492 for more details.

• dhparam: DH parameter file to use for DHE key agreement. Use openssl dhparam command to create it. If the file is invalid to load, it is silently discarded.

• handshakeTimeout: Abort the connection if the SSL/TLS handshake does not finish in this many milliseconds. The default is 120 seconds.

  A 'clientError' is emitted on the tls.Server object whenever a handshake times out.

• honorCipherOrder : When choosing a cipher, use the server's preferences instead of the client preferences.

  Although, this option is disabled by default, it is recommended that you use this option in conjunction with the ciphers option to mitigate BEAST attacks.

• requestCert: If true the server will request a certificate from clients that connect and attempt to verify that certificate. Default: false.

• rejectUnauthorized: If true the server will reject any connection which is not authorized with the list of supplied CAs. This option only has an effect if requestCert is true. Default: false.

• checkServerIdentity(servername, cert): Provide an override for checking server's hostname against the certificate. Should return an error if verification fails. Return undefined if passing.

• NPNProtocols: An array or Buffer of possible NPN protocols. (Protocols should be ordered by their priority).

• SNICallback(servername, cb): A function that will be called if client supports SNI TLS extension. Two argument will be passed to it: servername, and cb. SNICallback should invoke cb(null, ctx), where ctx is a SecureContext instance. (You can use tls.createSecureContext(...) to get proper SecureContext). If SNICallback wasn't provided - default callback with high-level API will be used (see below).

• sessionTimeout: An integer specifying the seconds after which TLS session identifiers and TLS session tickets created by the server are timed out. See SSL_CTX_set_timeout for more details.

• ticketKeys: A 48-byte Buffer instance consisting of 16-byte prefix, 16-byte hmac key, 16-byte AES key. You could use it to accept tls session tickets on multiple instances of tls server.

  NOTE: Automatically shared between cluster module workers.

• sessionIdContext: A string containing an opaque identifier for session resumption. If requestCert is true, the default is MD5 hash value generated from command-line. Otherwise, the default is not provided.

• secureProtocol: The SSL method to use, e.g. SSLv3_method to force SSL version 3. The possible values depend on your installation of OpenSSL and are defined in the constant SSL_METHODS.

Here is a simple example echo server:

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

var 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') ]
};

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

Or

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

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

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

};

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

You can test this server by connecting to it with openssl s_client:

openssl s_client -connect 127.0.0.1:8000

tls.connect(options[, callback])

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

Creates a new client connection to the given port and host (old API) or options.port and options.host. (If host is omitted, it defaults to localhost.) options should be an object which specifies:

• host: Host the client should connect to

• port: Port the client should connect to

• socket: Establish secure connection on a given socket rather than creating a new socket. If this option is specified, host and port are ignored.

• path: Creates unix socket connection to path. If this option is specified, host and port are ignored.

• pfx: A string or Buffer containing the private key, certificate and CA certs of the client in PFX or PKCS12 format.

• key: A string or Buffer containing the private key of the client in PEM format. (Could be an array of keys).

• passphrase: A string of passphrase for the private key or pfx.

• cert: A string or Buffer containing the certificate key of the client in PEM format. (Could be an array of certs).

• ca: An array of strings or Buffers of trusted certificates in PEM format. If this is omitted several well known "root" CAs will be used, like VeriSign. These are used to authorize connections.

• rejectUnauthorized: If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails; err.code contains the OpenSSL error code. Default: true.

• NPNProtocols: An array of strings or Buffers containing supported NPN protocols. Buffers should have following format: 0x05hello0x05world, where first byte is next protocol name's length. (Passing array should usually be much simpler: ['hello', 'world'].)

• servername: Servername for SNI (Server Name Indication) TLS extension.

• secureProtocol: The SSL method to use, e.g. SSLv3_method to force SSL version 3. The possible values depend on your installation of OpenSSL and are defined in the constant SSL_METHODS.

• session: A Buffer instance, containing TLS session.

The callback parameter will be added as a listener for the 'secureConnect' event.

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

Here is an example of a client of echo server as described previously:

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

var options = {
  // These are necessary only if using the client certificate authentication
  key: fs.readFileSync('client-key.pem'),
  cert: fs.readFileSync('client-cert.pem'),

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

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

Or

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

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

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

Class: tls.TLSSocket

Wrapper for instance of net.Socket, replaces internal socket read/write routines to perform transparent encryption/decryption of incoming/outgoing data.

new tls.TLSSocket(socket, options)

Construct a new TLSSocket object from existing TCP socket.

socket is an instance of net.Socket

options is an object that might contain following properties:

• secureContext: An optional TLS context object from tls.createSecureContext( ... )

• isServer: If true - TLS socket will be instantiated in server-mode

• server: An optional net.Server instance

• requestCert: Optional, see tls.createSecurePair

• rejectUnauthorized: Optional, see tls.createSecurePair

• NPNProtocols: Optional, see tls.createServer

• SNICallback: Optional, see tls.createServer

• session: Optional, a Buffer instance, containing TLS session

• requestOCSP: Optional, if true - OCSP status request extension would be added to client hello, and OCSPResponse event will be emitted on socket before establishing secure communication

tls.createSecureContext(details)

Creates a credentials object, with the optional details being a dictionary with keys:

• pfx : A string or buffer holding the PFX or PKCS12 encoded private key, certificate and CA certificates
• key : A string holding the PEM encoded private key
• passphrase : A string of passphrase for the private key or pfx
• cert : A string holding the PEM encoded certificate
• ca : Either a string or list of strings of PEM encoded CA certificates to trust.
• crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)
• ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.
• honorCipherOrder : When choosing a cipher, use the server's preferences instead of the client preferences. For further details see tls module documentation.

If no 'ca' details are 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.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized])

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

• credentials: A secure context object from tls.createSecureContext( ... )

• isServer: A boolean indicating whether this tls connection should be opened as a server or a client.

• requestCert: A boolean indicating whether a server should request a certificate from a connecting client. Only applies to server connections.

• rejectUnauthorized: A boolean indicating whether a server should automatically reject clients with invalid certificates. Only applies to servers with requestCert enabled.

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

NOTE: cleartext has the same APIs as tls.TLSSocket

Class: SecurePair

Returned by tls.createSecurePair.

Event: 'secure'

The event is emitted from the SecurePair once the pair has successfully established a secure connection.

Similarly to the checking for the server 'secureConnection' event, pair.cleartext.authorized should be checked to confirm whether the certificate used properly authorized.

Class: tls.Server

This class is a subclass of net.Server and has the same methods on it. Instead of accepting just raw TCP connections, this accepts encrypted connections using TLS or SSL.

Event: 'secureConnection'

function (tlsSocket) {}

This event is emitted after a new connection has been successfully handshaked. The argument is an instance of tls.TLSSocket. It has all the common stream methods and events.

socket.authorized is a boolean value which indicates if the client has verified by one of the supplied certificate authorities for the server. If socket.authorized is false, then socket.authorizationError is set to describe how authorization failed. Implied but worth mentioning: depending on the settings of the TLS server, you unauthorized connections may be accepted. socket.npnProtocol is a string containing selected NPN protocol. socket.servername is a string containing servername requested with SNI.

Event: 'clientError'

function (exception, tlsSocket) { }

When a client connection emits an 'error' event before secure connection is established - it will be forwarded here.

tlsSocket is the tls.TLSSocket that the error originated from.

Event: 'newSession'

function (sessionId, sessionData, callback) { }

Emitted on creation of TLS session. May be used to store sessions in external storage. callback must be invoked eventually, otherwise no data will be sent or received from secure connection.

NOTE: adding this event listener will have an effect only on connections established after addition of event listener.

Event: 'resumeSession'

function (sessionId, callback) { }

Emitted when client wants to resume previous TLS session. Event listener may perform lookup in external storage using given sessionId, and invoke callback(null, sessionData) once finished. If session can't be resumed (i.e. doesn't exist in storage) one may call callback(null, null). Calling callback(err) will terminate incoming connection and destroy socket.

NOTE: adding this event listener will have an effect only on connections established after addition of event listener.

Event: 'OCSPRequest'

function (certificate, issuer, callback) { }

Emitted when the client sends a certificate status request. You could parse server's current certificate to obtain OCSP url and certificate id, and after obtaining OCSP response invoke callback(null, resp), where resp is a Buffer instance. Both certificate and issuer are a Buffer DER-representations of the primary and issuer's certificates. They could be used to obtain OCSP certificate id and OCSP endpoint url.

Alternatively, callback(null, null) could be called, meaning that there is no OCSP response.

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

Typical flow:

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

NOTE: issuer could be null, if the certificate is self-signed or if the issuer is not in the root certificates list. (You could provide an issuer via ca option.)

NOTE: adding this event listener will have an effect only on connections established after addition of event listener.

NOTE: you may want to use some npm module like asn1.js to parse the certificates.

server.listen(port[, host][, callback])

Begin accepting connections on the specified port and host. If the host is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY).

This function is asynchronous. The last parameter callback will be called when the server has been bound.

See net.Server for more information.

server.close([callback])

Stops the server from accepting new connections. This function is asynchronous, the server is finally closed when the server emits a 'close' event. Optionally, you can pass a callback to listen for the 'close' event.

server.address()

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.addContext(hostname, context)

Add secure context that will be used if client request's SNI hostname is matching passed hostname (wildcards can be used). context can contain key, cert, ca and/or any other properties from tls.createSecureContext options argument.

server.maxConnections

Set this property to reject connections when the server's connection count gets high.

server.connections

The number of concurrent connections on the server.

Class: CryptoStream

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

This is an encrypted stream.

cryptoStream.bytesWritten

A proxy to the underlying socket's bytesWritten accessor, this will return the total bytes written to the socket, including the TLS overhead.

Class: tls.TLSSocket

This is a wrapped version of net.Socket that does transparent encryption of written data and all required TLS negotiation.

This instance implements a duplex Stream interfaces. It has all the common stream methods and events.

Event: 'secureConnect'

This event is emitted after a new connection has been successfully handshaked. The listener will be called no matter if the server's certificate was authorized or not. It is up to the user to test tlsSocket.authorized to see if the server certificate was signed by one of the specified CAs. If tlsSocket.authorized === false then the error can be found in tlsSocket.authorizationError. Also if NPN was used - you can check tlsSocket.npnProtocol for negotiated protocol.

Event: 'OCSPResponse'

function (response) { }

This event will be emitted if requestOCSP option was set. response is a buffer object, containing server's OCSP response.

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

tlsSocket.encrypted

Static boolean value, always true. May be used to distinguish TLS sockets from regular ones.

tlsSocket.authorized

A boolean that is true if the peer certificate was signed by one of the specified CAs, otherwise false

tlsSocket.authorizationError

The reason why the peer's certificate has not been verified. This property becomes available only when tlsSocket.authorized === false.

tlsSocket.getPeerCertificate([ detailed ])

Returns an object representing the peer's certificate. The returned object has some properties corresponding to the field of the certificate. If detailed argument is true - the full chain with issuer property will be returned, if false - only the top certificate without issuer property.

Example:

{ subject:
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuerInfo:
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuer:
   { ... another certificate ... },
  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, it returns null or an empty object.

tlsSocket.getCipher()

Returns an object representing the cipher name and the SSL/TLS protocol version of the current connection.

Example: { name: 'AES256-SHA', version: 'TLSv1/SSLv3' }

See SSL_CIPHER_get_name() and SSL_CIPHER_get_version() in http://www.openssl.org/docs/ssl/ssl.html#DEALING_WITH_CIPHERS for more information.

tlsSocket.renegotiate(options, callback)

Initiate TLS renegotiation process. The options may contain the following fields: rejectUnauthorized, requestCert (See tls.createServer for details). callback(err) will be executed with null as err, once the renegotiation is successfully completed.

NOTE: Can be used to request peer's certificate after the secure connection has been established.

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

tlsSocket.setMaxSendFragment(size)

Set maximum TLS fragment size (default and maximum value is: 16384, minimum is: 512). Returns true on success, false otherwise.

Smaller fragment size decreases buffering latency on the client: large 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.

tlsSocket.getSession()

Return ASN.1 encoded TLS session or undefined if none was negotiated. Could be used to speed up handshake establishment when reconnecting to the server.

tlsSocket.getTLSTicket()

NOTE: Works only with client TLS sockets. Useful only for debugging, for session reuse provide session option to tls.connect.

Return TLS session ticket or undefined if none was negotiated.

tlsSocket.address()

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.remoteAddress

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

tlsSocket.remoteFamily

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

tlsSocket.remotePort

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

tlsSocket.localAddress

The string representation of the local IP address.

tlsSocket.localPort

The numeric representation of the local port.