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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 1024

All severs 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 -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 CleartextStream 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.

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. (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. (Required)

  • ca: An array of strings or Buffers of trusted certificates. 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:AES128-GCM-SHA256:RC4:HIGH:!MD5:!aNULL:!EDH. Consult the OpenSSL cipher list format documentation for details on the format.

    ECDHE-RSA-AES128-SHA256 and AES128-GCM-SHA256 are used when node.js is linked against OpenSSL 1.0.1 or newer and the client speaks TLS 1.2, RC4 is used as a secure fallback.

    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.

  • 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.

    Note that if SSLv2 is used, the server will send its list of preferences to the client, and the client chooses the cipher.

    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.

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

  • SNICallback: A function that will be called if client supports SNI TLS extension. Only one argument will be passed to it: servername. And SNICallback should return SecureContext instance. (You can use crypto.createCredentials(...).context to get proper SecureContext). If SNICallback wasn't provided - default callback with high-level API will be used (see below).

  • sessionIdContext: A string containing a 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.

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(cleartextStream) {
  console.log('server connected',
              cleartextStream.authorized ? 'authorized' : 'unauthorized');
  cleartextStream.write("welcome!\n");
  cleartextStream.setEncoding('utf8');
  cleartextStream.pipe(cleartextStream);
});
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(cleartextStream) {
  console.log('server connected',
              cleartextStream.authorized ? 'authorized' : 'unauthorized');
  cleartextStream.write("welcome!\n");
  cleartextStream.setEncoding('utf8');
  cleartextStream.pipe(cleartextStream);
});
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.

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

  • key: A string or Buffer containing the private key of the client in PEM format.

  • 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.

  • ca: An array of strings or Buffers of trusted certificates. 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. Default: true.

  • NPNProtocols: An array of string or Buffer containing supported NPN protocols. Buffer 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.

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

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

Or

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

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

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

tls.createSecurePair([credentials], [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 credentials object from crypto.createCredentials( ... )

  • 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.

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 (cleartextStream) {}

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

cleartextStream.authorized is a boolean value which indicates if the client has verified by one of the supplied certificate authorities for the server. If cleartextStream.authorized is false, then cleartextStream.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. cleartextStream.npnProtocol is a string containing selected NPN protocol. cleartextStream.servername is a string containing servername requested with SNI.

Event: 'clientError'

function (exception, securePair) { }

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

securePair is the tls.SecurePair that the error originated from.

Event: 'newSession'

function (sessionId, sessionData) { }

Emitted on creation of TLS session. May be used to store sessions in external storage.

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.

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()

Stops the server from accepting new connections. This function is asynchronous, the server is finally closed when the server emits a '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, credentials)

Add secure context that will be used if client request's SNI hostname is matching passed hostname (wildcards can be used). credentials can contain key, cert and ca.

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: tls.CleartextStream

This is a stream on top of the Encrypted stream that makes it possible to read/write an encrypted data as a cleartext data.

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

A ClearTextStream is the clear member of a SecurePair object.

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 cleartextStream.authorized to see if the server certificate was signed by one of the specified CAs. If cleartextStream.authorized === false then the error can be found in cleartextStream.authorizationError. Also if NPN was used - you can check cleartextStream.npnProtocol for negotiated protocol.

cleartextStream.authorized

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

cleartextStream.authorizationError

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

cleartextStream.getPeerCertificate()

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

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' },
  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' }

If the peer does not provide a certificate, it returns null or an empty object.

cleartextStream.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.

cleartextStream.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' }

cleartextStream.remoteAddress

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

cleartextStream.remotePort

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