tls - binding to the OpenSSL library for encrypted socket and I/O channel communications
This extension provides TCL script access to secure socket communications using the Transport Layer Security (TLS) protocol. It provides a generic binding to OpenSSL, utilizing the Tcl_StackChannel API in TCL 8.4 and higher. These sockets behave exactly the same as channels created using the built-in socket command, along with additional options for controlling the SSL/TLS session.
Typically one would use the tls::socket command to create a new encrypted TCP socket. It is compatible with the native TCL ::socket command. Alternatively for an existing TCP socket, the tls::import command can be used to start TLS on the connection.
Optional function to set the default options used by tls::socket. If you call tls::import directly, this command has no effect. This command supports all of the same options as the tls::socket command, though you should limit your options to only TLS related ones.
This is a helper function that utilizes the underlying commands socket and tls::import to create the connection. It behaves the same as the native TCL socket command, but also supports the tls:import command options with one additional option. It returns the channel handle id for the new socket.
Same as previous, but instead creates a server socket for clients to connect to just like the Tcl socket -server command. It returns the channel handle id for the new socket.
Start TLS encryption on TCL channel channel via a stacked channel. It need not be a socket, but must provide bi-directional flow. Also sets session parameters for SSL handshake. Valid options are:
Compliment to tls::import. Used to remove the top level stacked channel from channel. This unstacks the encryption of a regular TCL channel. An error is thrown if TLS is not the top stacked channel type.
Forces the TLS negotiation handshake to take place immediately, and returns 0 if handshake is still in progress (non-blocking), or 1 if the handshake was successful. If the handshake failed, an error will be returned.
Returns the current status of an SSL channel. The result is a list of key-value pairs describing the SSL, certificate, and certificate verification status. If the SSL handshake has not yet completed, an empty list is returned. If the -local option is specified, then the local certificate is used. Returned values include:
SSL Status
The protocol selected after Application-Layer Protocol Negotiation (ALPN).
The current cipher in use for the session.
The peername from the certificate.
The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1.1, TLS1.2, TLS1.3, or unknown.
The number of bits used for the session key.
The signature hash algorithm.
The signature type value.
Maximum depth for the certificate chain verification. Default is -1, to check all.
List of certificate verification modes.
Certificate verification result.
List of the Certificate Authorities used to create the certificate.
Certificate Status
Dump of all certificate info.
The certificate version.
The serial number of the certificate as a hex string.
Cipher algorithm used for certificate signature.
The distinguished name (DN) of the certificate issuer.
The beginning date of the certificate validity.
The expiration date of the certificate validity.
The distinguished name (DN) of the certificate subject. Fields include: Common Name (CN), Organization (O), Locality or City (L), State or Province (S), and Country Name (C).
The issuer unique id.
The subject unique id.
Number of certificate extensions.
List of certificate extension names.
Authority Key Identifier (AKI) of the Issuing CA certificate that signed the SSL certificate as a hex string. This value matches the SKI value of the Intermediate CA certificate.
Subject Key Identifier (SKI) hash of the public key inside the certificate as a hex string. Used to identify certificates that contain a particular public key.
List of all of the Subject Alternative Names (SAN) including domain names, sub domains, and IP addresses that are secured by the certificate.
List of all Online Certificate Status Protocol (OCSP) URLs that can be used to check the validity of this certificate.
The PEM encoded certificate.
Cipher algorithm used for the certificate signature.
Certificate signature as a hex string.
Certificate signing digest as a hex string.
Certificate signature public key algorithm.
Certificate signature public key as a hex string.
Number of bits used for certificate signature key.
Whether the certificate signature is self signed.
The SHA1 hash of the certificate as a hex string.
The SHA256 hash of the certificate as a hex string.
Returns the current connection status of an SSL channel. The result is a list of key-value pairs describing the connection. Returned values include:
SSL Status
State of the connection.
The name of the connected to server.
The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1.1, TLS1.2, TLS1.3, or unknown.
Whether protocol renegotiation is supported or not.
The security level used for selection of ciphers, key size, etc.
Whether the session has been reused or not.
Whether the connection is configured as a server (1) or client (0).
Compression method.
Expansion method.
List of Certificate Authorities (CA) for X.509 certificate.
Cipher Info
The current cipher in use for the connection.
The standard RFC name of cipher.
The number of processed bits used for cipher.
The number of secret bits used for cipher.
The minimum protocol version for cipher.
Whether the cipher is Authenticated Encryption with Associated Data (AEAD).
The OpenSSL cipher id.
A text description of the cipher.
Digest used during handshake.
Session Info
The protocol selected after Application-Layer Protocol Negotiation (ALPN).
Whether the session can be resumed or not.
Time since session started in seconds since epoch.
Max duration of session in seconds before time-out.
Session ticket lifetime hint in seconds.
Unique session id for use in resuming the session.
Unique session ticket for use in resuming the session.
Unique session ticket application data.
Unique session master key.
Server cache mode (client, server, or both).
Without any args, returns a list of all symmetric ciphers for use with the -cipher option. With protocol, only the ciphers supported for that protocol are returned. See the tls::protocols command for the supported protocols. If verbose is specified as true then a verbose, human readable list is returned with additional information on the cipher. If supported is specified as true, then only the ciphers supported for protocol will be listed.
Returns a list of the supported SSL/TLS protocols. Valid values are: ssl2, ssl3, tls1, tls1.1, tls1.2, and tls1.3. Exact list depends on OpenSSL version and compile time flags.
Returns the OpenSSL version string.
The following options are used for peer Certificate Validation:
By default, a client TLS connection does NOT validate the server certificate chain. This limitation is due to the lack of a common cross platform database of Certificate Authority (CA) provided certificates to validate against. Many Linux systems natively support OpenSSL and thus have these certificates installed as part of the OS, but MacOS and Windows do not. In order to use the -require option, one of the following must be true:
On Linux and Unix systems with OpenSSL already installed, if the CA certificates are stored in the standard locations, or if the SSL_CERT_DIR or SSL_CERT_FILE environment variables are set, then -cadir, -cadir, and -castore aren't needed.
If OpenSSL is not installed in the default location, or when using Mac OS or Windows and OpenSSL is installed, the SSL_CERT_DIR and/or SSL_CERT_FILE environment variables or the one of the -cadir, -cadir, or -castore options must be defined.
On Windows, starting in OpenSSL 3.2, it is now possible to access the built-in Windows Certificate Store from OpenSSL. This can be achieved by setting the -castore option to "org.openssl.winstore://".
If OpenSSL is not installed, the CA certificates must be downloaded and installed with the user software. The CURL team makes them available at CA certificates extracted from Mozilla in the "cacert.pem" file. You must then either set the SSL_CERT_DIR and/or SSL_CERT_FILE environment variables or the -cadir or -cafile options to the CA cert file's install location. It is your responsibility to keep this file up to date.
As previously described, each channel can be given their own callbacks to handle intermediate processing by the OpenSSL library, using the -command, -password, and -validate_command options passed to either of tls::socket or tls::import. Unlike previous versions of TclTLS, only if the callback generates an error, will the bgerror command be invoked with the error information.
The callback for the -command option is invoked at several points during the OpenSSL handshake and during routine operations. See below for the possible arguments passed to the callback script. Values returned from the callback are ignored.
The callback for the -password option is invoked by TclTLS whenever OpenSSL needs to obtain a password. See below for the possible arguments passed to the callback script. The user provided password is expected to be returned by the callback.
The callback for the -validatecommand option is invoked during the handshake process in order for the application to validate the provided value(s). See below for the possible arguments passed to the callback script. If not specified, OpenSSL will accept all valid certificates and extensions. To reject the value and abort the connection, the callback should return 0. To accept the value and continue the connection, it should return 1. To reject the value, but continue the connection, it should return 2. This callback is new for TclTLS 1.8.
Reference implementations of these callbacks are provided in "tls.tcl" as tls::callback, tls::password, and tls::validate_command respectively. Note that these are only sample implementations. In a more realistic deployment you would specify your own callback scripts on each TLS channel using the -command, -password, and -validate_command options.
The default behavior when the -command and -validate_command options are not specified, is for TclTLS to process the associated library callbacks internally. The default behavior when the -password option is not specified is for TclTLS to process the associated library callbacks by attempting to call tls::password. The difference between these two behaviors is a consequence of maintaining compatibility with earlier implementations.
The use of the reference callbacks tls::callback, tls::password, and tls::validate_command is not recommended. They may be removed from future releases.
For most debugging needs, the -callback option can be used to provide sufficient insight and information on the TLS handshake and progress. If further troubleshooting insight is needed, the compile time option --enable-debug can be used to get detailed execution flow status.
TLS key logging can be enabled by setting the environment variable SSLKEYLOGFILE to the name of the file to log to. Then whenever TLS key material is generated or received it will be logged to the file. This is useful for logging key data for network logging tools to use to decrypt the data.
The tls::debug variable provides some additional control over these reference callbacks. Its value is zero by default. Higher values produce more diagnostic output, and will also force the verify method in tls::callback to accept the certificate, even when it is invalid if the -validatecommand option is set to tls::validate_command.
The use of the variable tls::debug is not recommended. It may be removed from future releases.
These examples use the default Unix platform SSL certificates. For standard installations, -cadir and -cafile should not be needed. If your certificates are in non-standard locations, update -cadir or use -cafile as needed.
Example #1: Use HTTP package
package require http
package require tls
set url "https://www.tcl.tk/"
http::register https 443 [list ::tls::socket -autoservername true -require true -cadir /etc/ssl/certs -command ::tls::callback -password ::tls::password -validatecommand ::tls::validate_command]
# Check for error
set token [http::geturl $url]
if {[http::status $token] ne "ok"} {
puts [format "Error %s" [http::status $token]]
}
# Get web page
set data [http::data $token]
puts [string length $data]
# Cleanup
::http::cleanup $token
Example #2: Use raw socket
package require tls
set url "www.tcl-lang.org"
set port 443
set ch [tls::socket -autoservername 1 -servername $url -request 1 -require 1 -alpn {http/1.1} -cadir /etc/ssl/certs -command ::tls::callback -password ::tls::password -validatecommand ::tls::validate_command $url $port]
chan configure $ch -buffersize 65536
tls::handshake $ch
puts $ch "GET / HTTP/1.1"
flush $ch
after 500
set data [read $ch]
array set status [tls::status $ch]
array set conn [tls::connection $ch]
array set chan [chan configure $ch]
close $ch
parray status
parray conn
parray chan
These examples use the default Unix platform SSL certificates. For standard installations, -cadir and -cafile should not be needed. If your certificates are in non-standard locations, set -cadir or use -cafile as needed.
Example #3: Get web page
package require http
package require tls
set url "https://www.tcl.tk/"
http::register https 443 [list ::tls::socket -autoservername true -require true -cadir /etc/ssl/certs]
# Check for error
set token [http::geturl $url]
if {[http::status $token] ne "ok"} {
puts [format "Error %s" [http::status $token]]
}
# Get web page
set data [http::data $token]
puts $data
# Cleanup
::http::cleanup $token
Example #4: Download file
package require http package require tls set url "https://wiki.tcl-lang.org/sitemap.xml" set filename [file tail $url] http::register https 443 [list ::tls::socket -autoservername true -require true -cadir /etc/ssl/certs] # Get file set ch [open $filename wb] set token [::http::geturl $url -blocksize 65536 -channel $ch] # Cleanup close $ch ::http::cleanup $token
The capabilities of this package can vary enormously based upon how the linked to OpenSSL library was configured and built. New versions may obsolete older protocol versions, add or remove ciphers, change default values, etc. Use the tls::protocols commands to obtain the supported protocol versions.
I/O, IP Address, OpenSSL, SSL, TCP, TLS, TclTLS, asynchronous I/O, bind, certificate, channel, connection, domain name, host, https, network, network address, socket, tls
tls
Copyright © 1999 Matt Newman
Copyright © 2004 Starfish Systems
Copyright © 2024 Brian O'Hagan