tls - binding to OpenSSL toolkit.
package require Tcl 8.4
package require tls
tls::init ?options?
tls::socket ?options? host port
tls::socket ?-server command? ?options? port
tls::status ?-local? channel
tls::connection channel
tls::handshake channel
tls::import channel ?options?
tls::unimport channel
tls::ciphers protocol ?verbose? ?supported?
tls::protocols
tls::version
This extension provides a generic binding to OpenSSL, utilizing the Tcl_StackChannel API for Tcl 8.4 and higher. The sockets behave exactly the same as channels created using Tcl's built-in socket command with additional options for controlling the SSL session.
Typically one would use the tls::socket command which provides compatibility with the native Tcl socket command. In such cases tls::import should not be used directly.
- -autoservername bool
- Automatically send the -servername as the host argument (default is false)
- -alpn list
- List of protocols to offer during Application-Layer Protocol Negotiation (ALPN). For example: h2, http/1.1, etc.
- -cadir dir
- Specify the directory containing the CA certificates. The default directory is platform specific and can be set at compile time. This can be overridden via the SSL_CERT_DIR environment variable.
- -cafile filename
- Specify the certificate authority (CA) file to use.
- -certfile filename
- Specify the filename containing the certificate to use. The default name is cert.pem. This can be overridden via the SSL_CERT_FILE environment variable.
- -cert filename
- Specify the contents of a certificate to use, as a DER encoded binary value (X.509 DER).
- -cipher string
- List of ciphers to use. String is a colon (":") separated list of ciphers or cipher suites. Cipher suites can be combined using the + character. Prefixes can be used to permanently remove ("!"), delete ("-"), or move a cypher to the end of the list ("+"). Keywords @STRENGTH (sort by algorithm key length), @SECLEVEL=n (set security level to n), and DEFAULT (use default cipher list, at start only) can also be specified. See OpenSSL documentation for the full list of valid values. (TLS 1.2 and earlier only)
- -ciphersuites string
- List of cipher suites to use. String is a colon (":") separated list of cipher suite names. (TLS 1.3 only)
- -command callback
- Callback to invoke at several points during the handshake. This is used to pass errors and tracing information, and it can allow Tcl scripts to perform their own certificate validation in place of the default validation provided by OpenSSL. See CALLBACK OPTIONS for further discussion.
- -dhparams filename
- Specify the Diffie-Hellman parameters file.
- -keyfile filename
- Specify the private key file. (default is value of -certfile)
- -key filename
- Specify the private key to use as a DER encoded value (PKCS#1 DER)
- -model channel
- Force this channel to share the same SSL_CTX structure as the specified channel, and therefore share callbacks etc.
- -password callback
- Callback to invoke when OpenSSL needs to obtain a password, typically to unlock the private key of a certificate. The callback should return a string which represents the password to be used. See CALLBACK OPTIONS for further discussion.
- -request bool
- Request a certificate from peer during SSL handshake. (default is true)
- -require bool
- Require a valid certificate from peer during SSL handshake. If this is set to true, then -request must also be set to true. (default is false)
- -securitylevel integer
- Set security level. Must be 0 to 5. The security level affects cipher suite encryption algorithms, supported ECC curves, supported signature algorithms, DH parameter sizes, certificate key sizes and signature algorithms. The default is 1. Level 3 and higher disable support for session tickets and only accept cipher suites that provide forward secrecy.
- -server bool
- Handshake as server if true, else handshake as client. (default is false)
- -servername host
- Specify server hostname. Only available if the OpenSSL library the package is linked against supports the TLS hostname extension for 'Server Name Indication' (SNI). Use to name the logical host we are talking to and expecting a certificate for.
- -session_id string
- Session id to resume session.
- -ssl2 bool
- Enable use of SSL v2. (default is false)
- -ssl3 bool
- Enable use of SSL v3. (default is false)
- -tls1 bool
- Enable use of TLS v1. (default is true)
- -tls1.1 bool
- Enable use of TLS v1.1 (default is true)
- -tls1.2 bool
- Enable use of TLS v1.2 (default is true)
- -tls1.3 bool
- Enable use of TLS v1.3 (default is true)
- issuer dn
- The distinguished name (DN) of the certificate issuer.
- subject dn
- The distinguished name (DN) of the certificate subject.
- notBefore date
- The begin date for the validity of the certificate.
- notAfter date
- The expiry date for the certificate.
- serial n
- The serial number of the certificate.
- cipher cipher
- The current cipher in use between the client and server channels.
- sbits n
- The number of bits used for the session key.
- certificate cert
- The PEM encoded certificate.
- sha1_hash hash
- The SHA1 hash of the certificate.
- sha256_hash hash
- The SHA256 hash of the certificate.
- validation result
- Certificate validation result.
- alpn protocol
- The protocol selected after Application-Layer Protocol Negotiation (ALPN).
- version value
- The protocol version used for the connection: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, or unknown
- state state
- State of the connection: initializing, handshake, established
- servername name
- The name of the connected to server.
- protocol version
- The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1.1, TLS1.2, TLS1.3, or unknown.
- renegotiation state
- Whether protocol renegotiation is allowed or disallowed.
- alpn protocol
- The protocol selected after Application-Layer Protocol Negotiation (ALPN).
- securitylevel level
- The security level used for selection of ciphers, key size, etc.
- cipher cipher
- The current cipher in use for the connection.
- standard_name name
- The standard RFC name of cipher.
- bits n
- The number of processed bits used for cipher.
- secret_bits n
- The number of secret bits used for cipher.
- min_version version
- The minimum protocol version for cipher.
- description string
- A text description of the cipher.
- session_reused boolean
- Whether the session has been reused or not.
- session_id string
- Unique session id for use in resuming the session.
- session_ticket string
- Unique session ticket for use in resuming the session.
- resumable boolean
- Can the session be resumed or not.
- start_time seconds
- Time since session started in seconds since epoch.
- timeout seconds
- Max duration of session in seconds before time-out.
- compression mode
- Compression method.
- expansion mode
- Expansion method.
- session_cache_mode mode
- Server cache mode (client, server, or both).
As indicated above, individual channels can be given their own callbacks to handle intermediate processing by the OpenSSL library, using the -command and -password options passed to either of tls::socket or tls::import.
- -command callback
- Invokes the specified callback script at several points during the OpenSSL handshake. Except as indicated below, values returned from the callback are ignored. Arguments appended to the script upon callback take one of the following forms:
- alpn protocol
- This form of callback is invoked when server selects the first -alpn specified protocol common to the client and server. If none, first client one is used.
- hello
- This form of callback is invoked during client hello message processing.
- info channel major minor message
- This form of callback is invoked by the OpenSSL function
SSL_CTX_set_info_callback().
The major and minor arguments are used to represent the state information bitmask.The message argument is a descriptive string which may be generated either by
- Possible values for major are:
handshake, alert, connect, accept.- Possible values for minor are:
start, done, read, write, loop, exit.SSL_state_string_long()or bySSL_alert_desc_string_long(), depending on context.
- session session_id ticket lifetime
- This form of callback is invoked by the OpenSSL function
SSL_CTX_sess_set_new_cb(). Where session_id is the current session identifier, ticket is the session ticket info, and lifetime is the the ticket lifetime in seconds.
- sni servername
- This form of callback is invoked when the server receives the SNI header from the client where servername is the client specified servername. Used to allow multiple names for same server so the right certificate can be used.
- verify channel depth cert status error
- This form of callback is invoked by the OpenSSL function
SSL_set_verify().
The depth argument is an integer representing the current depth on the certificate chain, with0as the subject certificate and higher values denoting progressively more indirect issuer certificates.
The cert argument is a list of key-value pairs similar to those returned by tls::status.
The status argument is an integer representing the current validity of the certificate. A value of0means the certificate is deemed invalid. A value of1means the certificate is deemed valid.
The error argument supplies the message, if any, generated byX509_STORE_CTX_get_error().
The callback may override normal validation processing by explicitly returning one of the above status values.
- -password callback
- Invokes the specified callback script when OpenSSL needs to obtain a password. The callback should return a string which represents the password to be used. No arguments are appended to the script upon callback.
Reference implementations of these callbacks are provided in the distribution as tls::callback and tls::password respectively. Note that these are sample implementations only. In a more realistic deployment you would specify your own callback scripts on each TLS channel using the -command and -password options.
The default behavior when the -command option is not specified is for TLS to process the associated library callbacks internally. The default behavior when the -password option is not specified is for TLS 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 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.
The use of the reference callbacks tls::callback and tls::password is not recommended. They may be removed from future releases.
The use of the variable tls::debug is not recommended. It may be removed from future releases.
This example uses a sample server.pem provided with the TLS release, courtesy of the OpenSSL project.
package require http
package require tls
http::register https 443 [list ::tls::socket -autoservername true -require true -cadir /etc/ssl/certs]
set tok [http::geturl https://www.tcl.tk/]
The capabilities of this package can vary enormously based upon how your OpenSSL library was configured and built. At the most macro-level OpenSSL supports a "no patents" build, which disables RSA, IDEA, RC(2,4,5) and SSL2 - if your OpenSSL is configured this way then you will need to build TLS with the -DNO_PATENTS option - and the resultant module will function correctly and also support ADH certificate-less encryption, however you will be unable to utilize this to speak to normal Web Servers, which typically require RSA support. Please see http://www.openssl.org/ for more information on the whole issue of patents and US export restrictions.
socket, fileevent, OpenSSL
Copyright © 1999 Matt Newman. Copyright © 2004 Starfish Systems.