'\"
'\" Generated from file 'tls\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 1999 Matt Newman
'\" Copyright (c) 2004 Starfish Systems
'\" Copyright (c) 2024 Brian O'Hagan
'\"
.TH "tls" n 1\&.8 tls "Tcl TLS extension"
.TH "tls" n 2\&.0b1 tls "Tcl TLS extension"
.\" The -*- nroff -*- definitions below are for supplemental macros used
.\" in Tcl/Tk manual entries.
.\"
.\" .AP type name in/out ?indent?
.\"	Start paragraph describing an argument to a library procedure.
.\"	type is type of argument (int, etc.), in/out is either "in", "out",
.\"	or "in/out" to describe whether procedure reads or modifies arg,

..
.BS
.SH NAME
tls \- binding to the OpenSSL library for encrypted socket and I/O channel communications
.SH SYNOPSIS
package require \fBTcl 8\&.5-\fR
.sp
package require \fBtls 1\&.8\fR
package require \fBtls 2\&.0b1\fR
.sp
\fBtls::init\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR?
.sp
\fBtls::socket\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR? \fIhost\fR \fIport\fR
.sp
\fBtls::socket\fR \fB-server\fR \fIcommand\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR? \fIport\fR
.sp

\fBtls::version\fR
.sp
.BE
.SH DESCRIPTION
This extension provides TCL script access to secure socket communications
using the Transport Layer Security (TLS) protocol\&. It provides a generic
binding to \fIOpenSSL\fR [https://www\&.openssl\&.org/], utilizing the
\fBTcl_StackChannel\fR API in TCL 8\&.4 and higher\&.
\fBTcl_StackChannel\fR API in TCL 8\&.4 or later\&.
These sockets behave exactly the same as channels created using the built-in
\fBsocket\fR command, along with additional options for controlling
\fBsocket\fR command, but provide additional options for controlling
the SSL/TLS session\&.
.SH COMPATIBILITY
This extension is compatible with OpenSSL 1\&.1\&.1 or later\&. It requires Tcl
version 8\&.5 or later and will work with Tcl 9\&.0\&.
.SH COMMANDS
Typically one would use the \fBtls::socket\fR command to create a new encrypted
TCP socket\&. It is compatible with the native TCL \fB::socket\fR command\&.
Alternatively for an existing TCP socket, the \fBtls::import\fR command can be
used to start TLS on the connection\&.
The following are the commands provided by the TcLTLS package\&. See the
\fBExamples\fR for example usage and the "\fIdemos\fR" directory for
more example usage\&.
.TP
\fBtls::init\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR?
Optional function to set the default options used by \fBtls::socket\fR\&. If you
call \fBtls::import\fR directly, this command has no effect\&. This command
supports all of the same options as the \fBtls::socket\fR command, though you
should limit your options to only TLS related ones\&.
call \fBtls::import\fR directly, the values set by this command have no effect\&.
This command supports all of the same options as the \fBtls::socket\fR command,
though you should limit your options to only the TLS related ones\&.
.TP
\fBtls::socket\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR? \fIhost\fR \fIport\fR
This is a helper function that utilizes the underlying commands \fBsocket\fR
and \fBtls::import\fR to create the connection\&. It behaves the same as the
native TCL \fBsocket\fR command, but also supports the \fBtls:import\fR
native TCL \fBsocket\fR command, but also supports the \fBtls::import\fR
command options with one additional option\&. It returns the channel handle id
for the new socket\&.
.RS
.TP
\fB-autoservername\fR \fIbool\fR
If \fBtrue\fR, automatically set the \fB-servername\fR argument to the
\fIhost\fR argument\&. Default is \fBfalse\fR\&.
\fIhost\fR argument\&. Prior to TclTLS 2\&.0, the default is \fBfalse\fR\&.
Starting in TclTLS 2\&.0, the default is \fBtrue\fR unless \fB-servername\fR
is also specified\&.
.RE
.TP
\fBtls::socket\fR \fB-server\fR \fIcommand\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR? \fIport\fR
Same as previous, but instead creates a server socket for clients to connect to
just like the Tcl \fBsocket -server\fR command\&. It returns the channel
handle id for the new socket\&.
.TP
\fBtls::import\fR \fIchannel\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR?
Start TLS encryption on TCL channel \fIchannel\fR 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:
.RS
.TP
\fB-alpn\fR \fIlist\fR
List of protocols to offer during Application-Layer Protocol Negotiation
(ALPN)\&. For example: \fBh2\fR and \fBhttp/1\&.1\fR, but not \fBh3\fR or
\fBquic\fR\&.
\fBquic\fR\&. This option is new for TclTLS 1\&.8\&.
.TP
\fB-cadir\fR \fIdirectory\fR
Specifies the directory where the Certificate Authority (CA) certificates are
stored\&. The default is platform specific and can be set at compile time\&. The
default location can be overridden by the \fBSSL_CERT_DIR\fR environment
variable\&. See \fBCertificate Validation\fR for more details\&.
.TP
\fB-cafile\fR \fIfilename\fR
Specifies the file with the Certificate Authority (CA) certificates to use in
\fBPEM\fR file format\&. The default is "\fIcert\&.pem\fR", in the OpenSSL
directory\&. The default file can be overridden by the \fBSSL_CERT_FILE\fR environment
variable\&. See \fBCertificate Validation\fR for more details\&.
.TP
\fB-castore\fR \fIURI\fR
Specifies the Uniform Resource Identifier (URI) for the Certificate Authority
(CA) store, which may be a single container or a catalog of containers\&.
Starting with OpenSSL 3\&.2 on MS Windows, set to "\fBorg\&.openssl\&.winstore://\fR"
to use the built-in MS Windows Certificate Store\&. See
\fBCertificate Validation\fR for more details\&.
to use the built-in MS Windows Certificate Store\&.
See \fBCertificate Validation\fR for more details\&.
This option is new for TclTLS 1\&.8\&.
.TP
\fB-certfile\fR \fIfilename\fR
Specifies the name of the file with the certificate to use in PEM format
as the local (client or server) certificate\&. It also contains the public key\&.
.TP
\fB-cert\fR \fIstring\fR
Specifies the certificate to use as a DER encoded string (X\&.509 DER)\&.

documentation for the full list of valid values\&.
.TP
\fB-ciphersuites\fR \fIstring\fR
Specifies the list of cipher suites to use for TLS 1\&.3 as a colon
"\fB:\fR" separated list of cipher suite names\&. See the
\fIOpenSSL\fR [https://docs\&.openssl\&.org/master/man1/openssl-ciphers/#options]
documentation for the full list of valid values\&.
This option is new for TclTLS 1\&.8\&.
.TP
\fB-command\fR \fIcallback\fR
Specifies the callback command to be invoked at several points during the
handshake to pass errors, tracing information, and protocol messages\&.
See \fBCallback Options\fR for more info\&.
.TP
\fB-dhparams\fR \fIfilename\fR
Specifies the Diffie-Hellman (DH) parameters file\&.
.TP
\fB-keyfile\fR \fIfilename\fR
Specifies the private key file\&. The default is to use the file
specified by the \fI-certfile\fR option\&.
specified by the \fB-certfile\fR option\&.
.TP
\fB-key\fR \fIstring\fR
Specifies the private key to use as a DER encoded string (PKCS#1 DER)\&.
.TP
\fB-model\fR \fIchannel\fR
Force this channel to share the same \fISSL_CTX\fR structure as the
specified \fIchannel\fR, and therefore share config, callbacks, etc\&.
.TP
\fB-password\fR \fIcallback\fR
Specifies the callback command to invoke when OpenSSL needs to obtain a
password\&. This is typically used to unlock the private key of a certificate\&.
The callback should return a password string\&. See \fBCallback Options\fR
for more info\&.
The callback should return a password string\&. This option has changed for
TclTLS 1\&.8\&. See \fBCallback Options\fR for more info\&.
.TP
\fB-post_handshake\fR \fIbool\fR
Allow post-handshake session ticket updates\&.
Allow post-handshake session ticket updates\&. This option is new for TclTLS 1\&.8\&.
.TP
\fB-request\fR \fIbool\fR
Request a certificate from the peer during the SSL handshake\&. This is needed
to do Certificate Validation\&. Starting in TclTLS 1\&.8, the default is
\fBtrue\fR\&.
\fBtrue\fR\&. Starting in TclTLS 2\&.0, if set to \fBfalse\fR and
\fB-require\fR is \fBtrue\fR, then this will be overridden to \fBtrue\fR\&.
See \fBCertificate Validation\fR for more details\&.
.TP
\fB-require\fR \fIbool\fR
Require a valid certificate from the peer during the SSL handshake\&. If this is
set to true, then \fB-request\fR must also be set to true and a either
\fB-cadir\fR, \fB-cafile\fR, \fB-castore\fR, or a platform default
must be provided in order to validate against\&. The default in TclTLS 1\&.8 and
earlier versions is \fBfalse\fR since not all platforms have certificates to
validate against in a form compatible with OpenSSL\&.
validate against in a form compatible with OpenSSL\&. Starting in TclTLS 2\&.0,
the default is \fBtrue\fR\&.
See \fBCertificate Validation\fR for more details\&.
.TP
\fB-security_level\fR \fIinteger\fR
Specifies the security level (value from 0 to 5)\&. The security level affects
the allowed cipher suite encryption algorithms, supported ECC curves,
supported signature algorithms, DH parameter sizes, certificate key sizes
and signature algorithms\&. The default is 1 prior to OpenSSL 3\&.2 and 2
thereafter\&. Level 3 and higher disable support for session tickets and
only accept cipher suites that provide forward secrecy\&.
This option is new for TclTLS 1\&.8\&.
.TP
\fB-server\fR \fIbool\fR
Specifies whether to act as a server and respond with a server handshake when a
client connects and provides a client handshake\&. The default is \fBfalse\fR\&.
.TP
\fB-servername\fR \fIhostname\fR
Specify the peer's hostname\&. This is used to set the TLS Server Name
Indication (SNI) extension\&. Set this to the expected servername in the
server's certificate or one of the Subject Alternate Names (SAN)\&.
Specify the peer's hostname\&. This is used to set the TLS Server Name Indication
(SNI) extension\&. Set this to the expected servername in the server's certificate
or one of the Subject Alternate Names (SAN)\&. Starting in TclTLS 2\&.0, this will
default to the host for the \fBtls::socket\fR command\&.
.TP
\fB-session_id\fR \fIbinary_string\fR
Specifies the session id to resume a session\&. Not supported yet\&.
This option is new for TclTLS 1\&.8\&.
.TP
\fB-ssl2\fR \fIbool\fR
Enable use of SSL v2\&. The default is \fBfalse\fR\&. Note: Recent versions of
OpenSSL no longer support SSLv2, so this may not have any effect\&. See the
\fBtls::protocols\fR command for supported protocols\&.
Enable use of SSL v2\&.The default is \fBfalse\fR\&.
OpenSSL 1\&.1+ no longer supports SSL v2, so this may not have any effect\&.
See the \fBtls::protocols\fR command for supported protocols\&.
.TP
\fB-ssl3\fR \fIbool\fR
Enable use of SSL v3\&. The default is \fBfalse\fR\&. Note: Recent versions
of OpenSSL may have this disabled at compile time, so this may not have any
effect\&. See the \fBtls::protocols\fR command for supported protocols\&.
Enable use of SSL v3\&. The default is \fBfalse\fR\&. Starting in TclTLS 1\&.8,
use of SSL v3 if only available via a compile time option\&.
See the \fBtls::protocols\fR command for supported protocols\&.
.TP
\fB-tls1\fR \fIbool\fR
Enable use of TLS v1\&. The default is \fBtrue\fR\&. Note: TLS 1\&.0 needs
SHA1 to operate, which is only available in security level 0 for Open SSL 3\&.0+\&.
See the \fI-security_level\fR option\&.
Enable use of TLS v1\&. Starting in TclTLS 2\&.0, the default is \fBfalse\fR\&.
Note: TLS 1\&.0 needs SHA1 to operate, which is only available in security level
0 for Open SSL 3\&.0+\&. See the \fB-security_level\fR option\&.
.TP
\fB-tls1\&.1\fR \fIbool\fR
Enable use of TLS v1\&.1\&. The default is \fBtrue\fR\&. Note: TLS 1\&.1 needs
SHA1 to operate, which is only available in security level 0 for Open SSL 3\&.0+\&.
See the \fI-security_level\fR option\&.
Enable use of TLS v1\&.1\&. Starting in TclTLS 2\&.0, the default is \fBfalse\fR\&.
Note: TLS 1\&.1 needs SHA1 to operate, which is only available in security level
0 for Open SSL 3\&.0+\&. See the \fB-security_level\fR option\&.
.TP
\fB-tls1\&.2\fR \fIbool\fR
Enable use of TLS v1\&.2\&. The default is \fBtrue\fR\&.
.TP
\fB-tls1\&.3\fR \fIbool\fR
Enable use of TLS v1\&.3\&. The default is \fBtrue\fR\&.
Enable use of TLS v1\&.3\&. The default is \fBtrue\fR\&. This is only available
starting with OpenSSL 1\&.1\&.1 and TclTLS 1\&.7\&.
.TP
\fB-validatecommand\fR \fIcallback\fR
Specifies the callback command to invoke to validate the peer certificates
and other config info during the protocol negotiation phase\&. This can be used
by TCL scripts to perform their own Certificate Validation to supplement the
default validation provided by OpenSSL\&. The script must return a boolean true
to continue the negotiation\&. See \fBCallback Options\fR for more info\&.
This option is new for TclTLS 1\&.8\&.
.RE
.TP
\fBtls::unimport\fR \fIchannel\fR
Compliment to \fBtls::import\fR\&. Used to remove the top level stacked channel
from \fIchannel\fR\&. This unstacks the encryption of a regular TCL channel\&. An
error is thrown if TLS is not the top stacked channel type\&.
.TP

values include:
.sp
SSL Status
.RS
.TP
\fBalpn\fR \fIprotocol\fR
The protocol selected after Application-Layer Protocol Negotiation (ALPN)\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBcipher\fR \fIcipher\fR
The current cipher in use for the session\&.
.TP
\fBpeername\fR \fIname\fR
The peername from the certificate\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBprotocol\fR \fIversion\fR
The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1\&.1, TLS1\&.2, TLS1\&.3, or unknown\&.
The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1\&.1, TLS1\&.2,
TLS1\&.3, or unknown\&. This value is new for TclTLS 1\&.8\&.
.TP
\fBsbits\fR \fIn\fR
The number of bits used for the session key\&.
.TP
\fBsignatureHashAlgorithm\fR \fIalgorithm\fR
The signature hash algorithm\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsignatureType\fR \fItype\fR
The signature type value\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBverifyDepth\fR \fIn\fR
Maximum depth for the certificate chain verification\&. Default is -1, to check all\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBverifyMode\fR \fIlist\fR
List of certificate verification modes\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBverifyResult\fR \fIresult\fR
Certificate verification result\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBca_names\fR \fIlist\fR
List of the Certificate Authorities used to create the certificate\&.
This value is new for TclTLS 1\&.8\&.
.RE
.IP
Certificate Status
.RS
.TP
\fBall\fR \fIstring\fR
Dump of all certificate info\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBversion\fR \fIvalue\fR
The certificate version\&.
.TP
\fBserialNumber\fR \fIstring\fR
The serial number of the certificate as a hex string\&.
This value was changed from serial in TclTLS 1\&.8\&.
.TP
\fBsignature\fR \fIalgorithm\fR
Cipher algorithm used for certificate signature\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBissuer\fR \fIstring\fR
The distinguished name (DN) of the certificate issuer\&.
.TP
\fBnotBefore\fR \fIdate\fR
The beginning date of the certificate validity\&.
.TP
\fBnotAfter\fR \fIdate\fR
The expiration date of the certificate validity\&.
.TP
\fBsubject\fR \fIstring\fR
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)\&.
.TP
\fBissuerUniqueID\fR \fIstring\fR
The issuer unique id\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsubjectUniqueID\fR \fIstring\fR
The subject unique id\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBnum_extensions\fR \fIn\fR
Number of certificate extensions\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBextensions\fR \fIlist\fR
List of certificate extension names\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBauthorityKeyIdentifier\fR \fIstring\fR
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\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsubjectKeyIdentifier\fR \fIstring\fR
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\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsubjectAltName\fR \fIlist\fR
List of all of the Subject Alternative Names (SAN) including domain names, sub
domains, and IP addresses that are secured by the certificate\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBocsp\fR \fIlist\fR
List of all Online Certificate Status Protocol (OCSP) URLs that can be used to
check the validity of this certificate\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBcertificate\fR \fIcert\fR
The PEM encoded certificate\&.
.TP
\fBsignatureAlgorithm\fR \fIalgorithm\fR
Cipher algorithm used for the certificate signature\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsignatureValue\fR \fIstring\fR
Certificate signature as a hex string\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsignatureDigest\fR \fIversion\fR
Certificate signing digest as a hex string\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBpublicKeyAlgorithm\fR \fIalgorithm\fR
Certificate signature public key algorithm\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBpublicKey\fR \fIstring\fR
Certificate signature public key as a hex string\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBbits\fR \fIn\fR
Number of bits used for certificate signature key\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBself_signed\fR \fIboolean\fR
Whether the certificate signature is self signed\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsha1_hash\fR \fIhash\fR
The SHA1 hash of the certificate as a hex string\&.
This value is new for TclTLS 1\&.8\&.
.TP
\fBsha256_hash\fR \fIhash\fR
The SHA256 hash of the certificate as a hex string\&.
This value is new for TclTLS 1\&.8\&.
.RE
.TP
\fBtls::connection\fR \fIchannel\fR
Returns the current connection status of an SSL channel\&. The result is a list
of key-value pairs describing the connection\&. Returned values include:
of key-value pairs describing the connection\&.
This command is new for TclTLS 1\&.8\&. Returned values include:
.sp
SSL Status
.RS
.TP
\fBstate\fR \fIstate\fR
State of the connection\&.
.TP

Unique session master key\&.
.TP
\fBsession_cache_mode\fR \fImode\fR
Server cache mode (client, server, or both)\&.
.RE
.TP
\fBtls::ciphers\fR ?\fIprotocol\fR? ?\fIverbose\fR? ?\fIsupported\fR?
Without any args, returns a list of all symmetric ciphers for use with the
Without any options, it returns a list of all symmetric ciphers for use with the
\fI-cipher\fR option\&. With \fIprotocol\fR, only the ciphers supported for that
protocol are returned\&. See the \fBtls::protocols\fR command for the supported
protocols\&. If \fIverbose\fR is specified as true then a verbose, human readable
list is returned with additional information on the cipher\&. If \fIsupported\fR
is specified as true, then only the ciphers supported for protocol will be listed\&.
The \fIsupported\fR arg is new for TclTLS 1\&.8\&.
.TP
\fBtls::protocols\fR
Returns a list of the supported SSL/TLS protocols\&. Valid values are:
\fBssl2\fR, \fBssl3\fR, \fBtls1\fR, \fBtls1\&.1\fR, \fBtls1\&.2\fR, and
\fBtls1\&.3\fR\&. Exact list depends on OpenSSL version and compile time flags\&.
This command is new for TclTLS 1\&.8\&.
.TP
\fBtls::version\fR
Returns the OpenSSL version string\&.
.PP
.SH "CERTIFICATE VALIDATION"
.SS "PKI AND CERTIFICATES"
Using the Public Key Infrastructure (PKI), each user creates a private key that

In order to provide authentication, i\&.e\&. ensuring someone is who they say they
are, the public key and user identification info is stored in a X\&.509
certificate and that certificate is authenticated (i\&.e\&. signed) by a Certificate
Authority (CA)\&. Users can then exchange these certificates during the TLS
initialization process and check them against the root CA certificates to ensure
they are valid\&. This is handled by OpenSSL via the \fB-request\fR and
\fB-require\fR options\&. See the \fB-cadir\fR, \fB-cadir\fR, and
\fB-castore\fR options for how tp specify where to find the CA certificates\&.
\fB-castore\fR options for how to specify where to find the CA certificates\&.
Optionally, in a future release, they can also be checked against the Certificate
Revocation List (CRL) of revoked certificates\&. Certificates can also be
self-signed, but they are by default not trusted unless you add them to your
certificate store\&.
.PP
Typically when visiting web sites, only the client needs to check the server's
certificate to ensure it is valid\&. The server doesn't need to check the client

The default file can be overridden by the \fBSSL_CERT_FILE\fR environment
variable\&.
.TP
\fB-castore\fR \fIURI\fR
Specifies the Uniform Resource Identifier (URI) for the Certificate Authority
(CA) store, which may be a single container or a catalog of containers\&.
Starting with OpenSSL 3\&.2 on MS Windows, set to "\fBorg\&.openssl\&.winstore://\fR"
to use the built-in MS Windows Certificate Store\&.
This store only supports root certificate stores\&. See
to use the built-in MS Windows Certificate Store\&. Starting in TclTLS 2\&.0, this
is the default if \fB-cadir\fR, \fB-cadir\fR, and \fB-castore\fR are
not specified\&. This store only supports root certificate stores\&.
\fBCertificate Validation\fR for more details\&.
.TP
\fB-request\fR \fIbool\fR
Request a certificate from the peer during the SSL handshake\&. This is needed
to do Certificate Validation\&. Starting in TclTLS 1\&.8, the default is
\fBtrue\fR\&. Starting in TclTLS 2\&.0, if set to \fBfalse\fR and
\fB-require\fR is \fBtrue\fR, then this will be overridden to \fBtrue\fR\&.
\fBtrue\fR\&. In addition, the client can manually inspect and accept or reject
each certificate using the \fI-validatecommand\fR option\&.
In addition, the client can manually inspect and accept or reject
each certificate using the \fB-validatecommand\fR option\&.
.TP
\fB-require\fR \fIbool\fR
Require a valid certificate from the peer during the SSL handshake\&. If this is
set to true, then \fB-request\fR must also be set to true and a either
\fB-cadir\fR, \fB-cafile\fR, \fB-castore\fR, or a platform default
must be provided in order to validate against\&. The default in TclTLS 1\&.8 and
earlier versions is \fBfalse\fR since not all platforms have certificates to
validate against in a form compatible with OpenSSL\&.
validate against in a form compatible with OpenSSL\&. Starting in TclTLS 2\&.0,
the default is \fBtrue\fR\&.
.PP
.SS "WHEN ARE COMMAND LINE OPTIONS NEEDED?"
In TclTLS 1\&.8 and earlier versions, certificate validation is
\fINOT\fR enabled by default\&. 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 MS Windows do not\&.
Staring in TclTLS 2\&.0, this has been changed to require certificate validation
In order to use the \fB-require\fR option, one of the following
by default\&. In order to use the \fB-require\fR option, one of the following
must be true:
.IP \(bu
On Linux and Unix systems with OpenSSL already installed or if the CA
certificates are available in PEM format, and if they are stored in the
standard locations, or if the \fBSSL_CERT_DIR\fR or \fBSSL_CERT_FILE\fR
environment variables are set, then \fB-cadir\fR, \fB-cadir\fR,
and \fB-castore\fR aren't needed\&.
.IP \(bu
If OpenSSL is not installed in the default location, or when using Mac OS
or MS Windows and OpenSSL is installed, the \fBSSL_CERT_DIR\fR and/or
\fBSSL_CERT_FILE\fR environment variables or the one of the \fB-cadir\fR,
\fB-cadir\fR, or \fB-castore\fR options must be defined\&.
.IP \(bu
On MS Windows, starting in OpenSSL 3\&.2, it is now possible to access the
built-in Windows Certificate Store from OpenSSL\&. This can utilized by
setting the \fB-castore\fR option to "\fBorg\&.openssl\&.winstore://\fR"\&.
In TclTLS 2\&.0, this is the default value if \fB-cadir\fR,
\fB-cadir\fR, and \fB-castore\fR are not specified\&.
.IP \(bu
If OpenSSL is not installed or the CA certificates are not available in PEM
format, the CA certificates must be downloaded and installed with the user
software\&. The CURL team makes them available at
\fICA certificates extracted
from Mozilla\fR [https://curl\&.se/docs/caextract\&.html] in the "\fIcacert\&.pem\fR" file\&. You must then either set the
\fBSSL_CERT_DIR\fR and/or \fBSSL_CERT_FILE\fR environment variables or the

continue the connection, it should return 2\&. This callback is new for TclTLS 1\&.8\&.
.TP
\fBalpn\fR \fIchannelId protocol match\fR
For servers, this form of callback is invoked when the client ALPN extension is
received\&. If \fImatch\fR is true, then \fIprotocol\fR is the first
\fB-alpn\fR protocol option in common to both the client and server\&.
If not, the first client specified protocol is used\&. This callback is called
after the Hello and ALPN callbacks\&.
after the Hello and SNI callbacks\&.
.TP
\fBhello\fR \fIchannelId servername\fR
For servers, this form of callback is invoked during client hello message
processing\&. The purpose is so the server can select the appropriate certificate
to present to the client, and to make other configuration adjustments relevant
to that server name and its configuration\&. It is called before the SNI and ALPN
callbacks\&.
.TP
\fBsni\fR \fIchannelId servername\fR
For servers, this form of callback is invoked when the Server Name Indication
(SNI) extension is received\&. The \fIservername\fR argument is the client
provided server name specified in the \fB-servername</b>\fR option\&. The
provided server name specified in the \fB-servername\fR option\&. The
purpose is so when a server supports multiple names, the right certificate
can be used\&. It is called after the hello callback but before the ALPN
can be used\&. It is called after the Hello callback but before the ALPN
callback\&.
.TP
\fBverify\fR \fIchannelId depth cert status error\fR
This form of callback is invoked by OpenSSL when a new certificate is received
from the peer\&. It allows the client to check the certificate verification
results and choose whether to continue or not\&. It is called for each
certificate in the certificate chain\&. This callback was moved from

The default value is 0 with higher values producing more diagnostic output,
and will also force the verify method in \fBtls::callback\fR to accept the
certificate, even if it is invalid when the \fB-validatecommand\fR
option is set to \fBtls::validate_command\fR\&.
.PP
\fIThe use of the variable \fBtls::debug\fR is not recommended\&.
It may be removed from future releases\&.\fR
.SH "HTTP PACKAGE EXAMPLES"
.SH EXAMPLES
The following are example scripts to download a webpage and file using the
http package\&. See \fBCertificate Validation\fR for whether the
http package\&. See \fBCertificate Validation\fR for when the
\fB-cadir\fR, \fB-cafile\fR, and \fB-castore\fR options are also
needed\&. See the demos directory for more example scripts\&.
needed\&. See the "\fIdemos\fR" directory for more example scripts\&.
.PP
Example #1: Download a web page
.CS



package require http

::http::cleanup $token

.CE
.SH "SPECIAL CONSIDERATIONS"
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 \fBtls::protocols\fR commands to obtain the supported
Use the \fBtls::protocols\fR command to obtain the supported
protocol versions\&.
.SH "SEE ALSO"
\fIOpenSSL\fR [https://www\&.openssl\&.org/], http, socket
.SH KEYWORDS
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
.SH CATEGORY
tls