'\"
'\" 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"
.\" The -*- nroff -*- definitions below are for supplemental macros used
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.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
.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::import\fR \fIchannel\fR ?\fI-option\fR? ?\fIvalue\fR? ?\fI-option value \&.\&.\&.\fR?
.sp
\fBtls::unimport\fR \fIchannel\fR
.sp
\fBtls::handshake\fR \fIchannel\fR
.sp
\fBtls::status\fR ?\fB-local\fR? \fIchannel\fR
.sp
\fBtls::connection\fR \fIchannel\fR
.sp
\fBtls::ciphers\fR ?\fIprotocol\fR? ?\fIverbose\fR? ?\fIsupported\fR?
.sp
\fBtls::protocols\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\&.
These sockets behave exactly the same as channels created using the built-in
\fBsocket\fR command, along with additional options for controlling
the SSL/TLS session\&.
.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\&.
.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\&.
.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
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\&.
.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\&.
.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\&.
.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)\&.
.TP
\fB-cipher\fR \fIstring\fR
Specifies the list of ciphers to use for TLS 1\&.2 and earlier connections\&.
String is a colon "\fB:\fR" separated list of ciphers\&.
Ciphers can be combined using the "\fB+\fR" character\&.
Prefixes can be used to permanently remove "\fB!\fR", delete "\fB-\fR", or
move to the end "\fB+\fR" a specified cipher\&.
Keywords \fB@STRENGTH\fR (sort by algorithm key length),
\fB@SECLEVEL=\fR\fIn\fR (set security level to n), and
\fBDEFAULT\fR (use default cipher list, at start only) can also be specified\&.
See the \fIOpenSSL\fR [https://docs\&.openssl\&.org/master/man1/openssl-ciphers/#options]
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\&.
.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\&.
.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\&.
.TP
\fB-post_handshake\fR \fIbool\fR
Allow post-handshake session ticket updates\&.
.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\&.
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\&.
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\&.
.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)\&.
.TP
\fB-session_id\fR \fIbinary_string\fR
Specifies the session id to resume a session\&. Not supported yet\&.
.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\&.
.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\&.
.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\&.
.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\&.
.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\&.
.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\&.
.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
\fBtls::handshake\fR \fIchannel\fR
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\&.
.TP
\fBtls::status\fR ?\fB-local\fR? \fIchannel\fR
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
\fB-local\fR option is specified, then the local certificate is used\&. Returned
values include:
.sp
SSL Status
.RS
.TP
\fBalpn\fR \fIprotocol\fR
The protocol selected after Application-Layer Protocol Negotiation (ALPN)\&.
.TP
\fBcipher\fR \fIcipher\fR
The current cipher in use for the session\&.
.TP
\fBpeername\fR \fIname\fR
The peername from the certificate\&.
.TP
\fBprotocol\fR \fIversion\fR
The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1\&.1, TLS1\&.2, TLS1\&.3, or unknown\&.
.TP
\fBsbits\fR \fIn\fR
The number of bits used for the session key\&.
.TP
\fBsignatureHashAlgorithm\fR \fIalgorithm\fR
The signature hash algorithm\&.
.TP
\fBsignatureType\fR \fItype\fR
The signature type value\&.
.TP
\fBverifyDepth\fR \fIn\fR
Maximum depth for the certificate chain verification\&. Default is -1, to check all\&.
.TP
\fBverifyMode\fR \fIlist\fR
List of certificate verification modes\&.
.TP
\fBverifyResult\fR \fIresult\fR
Certificate verification result\&.
.TP
\fBca_names\fR \fIlist\fR
List of the Certificate Authorities used to create the certificate\&.
.RE
.IP
Certificate Status
.RS
.TP
\fBall\fR \fIstring\fR
Dump of all certificate info\&.
.TP
\fBversion\fR \fIvalue\fR
The certificate version\&.
.TP
\fBserialNumber\fR \fIstring\fR
The serial number of the certificate as a hex string\&.
.TP
\fBsignature\fR \fIalgorithm\fR
Cipher algorithm used for certificate signature\&.
.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\&.
.TP
\fBsubjectUniqueID\fR \fIstring\fR
The subject unique id\&.
.TP
\fBnum_extensions\fR \fIn\fR
Number of certificate extensions\&.
.TP
\fBextensions\fR \fIlist\fR
List of certificate extension names\&.
.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\&.
.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\&.
.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\&.
.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\&.
.TP
\fBcertificate\fR \fIcert\fR
The PEM encoded certificate\&.
.TP
\fBsignatureAlgorithm\fR \fIalgorithm\fR
Cipher algorithm used for the certificate signature\&.
.TP
\fBsignatureValue\fR \fIstring\fR
Certificate signature as a hex string\&.
.TP
\fBsignatureDigest\fR \fIversion\fR
Certificate signing digest as a hex string\&.
.TP
\fBpublicKeyAlgorithm\fR \fIalgorithm\fR
Certificate signature public key algorithm\&.
.TP
\fBpublicKey\fR \fIstring\fR
Certificate signature public key as a hex string\&.
.TP
\fBbits\fR \fIn\fR
Number of bits used for certificate signature key\&.
.TP
\fBself_signed\fR \fIboolean\fR
Whether the certificate signature is self signed\&.
.TP
\fBsha1_hash\fR \fIhash\fR
The SHA1 hash of the certificate as a hex string\&.
.TP
\fBsha256_hash\fR \fIhash\fR
The SHA256 hash of the certificate as a hex string\&.
.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:
.sp
SSL Status
.RS
.TP
\fBstate\fR \fIstate\fR
State of the connection\&.
.TP
\fBservername\fR \fIname\fR
The name of the connected to server\&.
.TP
\fBprotocol\fR \fIversion\fR
The protocol version used for the connection: SSL2, SSL3, TLS1, TLS1\&.1, TLS1\&.2, TLS1\&.3, or unknown\&.
.TP
\fBrenegotiation_allowed\fR \fIboolean\fR
Whether protocol renegotiation is supported or not\&.
.TP
\fBsecurity_level\fR \fIlevel\fR
The security level used for selection of ciphers, key size, etc\&.
.TP
\fBsession_reused\fR \fIboolean\fR
Whether the session has been reused or not\&.
.TP
\fBis_server\fR \fIboolean\fR
Whether the connection is configured as a server (1) or client (0)\&.
.TP
\fBcompression\fR \fImode\fR
Compression method\&.
.TP
\fBexpansion\fR \fImode\fR
Expansion method\&.
.TP
\fBcaList\fR \fIlist\fR
List of Certificate Authorities (CA) for X\&.509 certificate\&.
.RE
.IP
Cipher Info
.RS
.TP
\fBcipher\fR \fIcipher\fR
The current cipher in use for the connection\&.
.TP
\fBstandard_name\fR \fIname\fR
The standard RFC name of cipher\&.
.TP
\fBalgorithm_bits\fR \fIn\fR
The number of processed bits used for cipher\&.
.TP
\fBsecret_bits\fR \fIn\fR
The number of secret bits used for cipher\&.
.TP
\fBmin_version\fR \fIversion\fR
The minimum protocol version for cipher\&.
.TP
\fBcipher_is_aead\fR \fIboolean\fR
Whether the cipher is Authenticated Encryption with Associated Data (AEAD)\&.
.TP
\fBcipher_id\fR \fIid\fR
The OpenSSL cipher id\&.
.TP
\fBdescription\fR \fIstring\fR
A text description of the cipher\&.
.TP
\fBhandshake_digest\fR \fIboolean\fR
Digest used during handshake\&.
.RE
.IP
Session Info
.RS
.TP
\fBalpn\fR \fIprotocol\fR
The protocol selected after Application-Layer Protocol Negotiation (ALPN)\&.
.TP
\fBresumable\fR \fIboolean\fR
Whether the session can be resumed or not\&.
.TP
\fBstart_time\fR \fIseconds\fR
Time since session started in seconds since epoch\&.
.TP
\fBtimeout\fR \fIseconds\fR
Max duration of session in seconds before time-out\&.
.TP
\fBlifetime\fR \fIseconds\fR
Session ticket lifetime hint in seconds\&.
.TP
\fBsession_id\fR \fIbinary_string\fR
Unique session id for use in resuming the session\&.
.TP
\fBsession_ticket\fR \fIbinary_string\fR
Unique session ticket for use in resuming the session\&.
.TP
\fBticket_app_data\fR \fIbinary_string\fR
Unique session ticket application data\&.
.TP
\fBmaster_key\fR \fIbinary_string\fR
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
\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\&.
.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\&.
.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
only they know about and a public key they can exchange with others for use in
encrypting and decrypting data\&. The process is the sender encrypts their data
using their private key and the receiver's public key\&. The data is then sent
to the receiver\&. In a similar manner, the receiver uses their private key and
the sender's public key to decrypt the data\&. This provides data integrity, to
ensure the data can't be viewed or altered during transport\&. See the
\fB-key\fR and \fB-keyfile\fR options for how to specify the private key\&.
Also see the \fB-password\fR option for how to provide the password\&.
.PP
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\&.
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
certificate unless you need to authenticate with them to login, etc\&. See the
\fB-cert\fR and \fB-certfile\fR options if you need to provide a certificate\&.
.SS "SUMMARY OF COMMAND LINE OPTIONS"
The following options are used for peer certificate validation:
.TP
\fB-cadir\fR \fIdirectory\fR
Specifies the directory where the Certificate Authority (CA) certificates are
stored\&. The default is platform specific, but is usually "\fI/etc/ssl/certs\fR" on
Linux/Unix systems\&. The default location can be overridden by the
\fBSSL_CERT_DIR\fR environment variable\&.
.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\&. On Linux/Unix systems, this is usually "\fI/etc/ssl/ca-bundle\&.pem\fR"\&.
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
\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\&. In addition, the client can manually inspect and accept or reject
each certificate using the \fI-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\&.
.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\&.
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"\&.
.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
\fB-cadir\fR or \fB-cafile\fR options to the CA cert file's install
location\&. It is your responsibility to keep this file up to date\&.
.PP
.SH "CALLBACK OPTIONS"
As previously described, each channel can be given their own callbacks
to handle intermediate processing by the OpenSSL library, using the
\fB-command\fR, \fB-password\fR, and \fB-validate_command\fR options
passed to either of \fBtls::socket\fR or \fBtls::import\fR\&.
Unlike previous versions of TclTLS, only if the callback generates an error,
will the \fBbgerror\fR command be invoked with the error information\&.
.SS "VALUES FOR COMMAND CALLBACK"
The callback for the \fB-command\fR 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\&.
.TP
\fBerror\fR \fIchannelId message\fR
This form of callback is invoked whenever an error occurs during the initial
connection, handshake, or I/O operations\&. The \fImessage\fR argument can be
from the Tcl_ErrnoMsg, OpenSSL function \fBERR_reason_error_string()\fR,
or a custom message\&. This callback is new for TclTLS 1\&.8\&.
.TP
\fBinfo\fR \fIchannelId major minor message type\fR
This form of callback is invoked by the OpenSSL function
\fBSSL_set_info_callback()\fR during the initial connection and handshake
operations\&. The arguments are:
.RS
.TP
\fImajor\fR
Major category for error\&. Valid enums are: \fBhandshake\fR, \fBalert\fR,
\fBconnect\fR, \fBaccept\fR\&.
.TP
\fIminor\fR
Minor category for error\&. Valid enums are: \fBstart\fR, \fBdone\fR, \fBread\fR,
\fBwrite\fR, \fBloop\fR, \fBexit\fR\&.
.TP
\fImessage\fR
Descriptive message string which may be generated either by
\fBSSL_state_string_long()\fR or \fBSSL_alert_desc_string_long()\fR,
depending on the context\&.
.TP
\fItype\fR
For alerts, the possible values are: \fBwarning\fR,
\fBfatal\fR, and \fBunknown\fR\&. For others, \fBinfo\fR is used\&.
This argument is new for TclTLS 1\&.8\&.
.RE
.TP
\fBmessage\fR \fIchannelId direction version content_type message\fR
This form of callback is invoked by the OpenSSL function
\fBSSL_set_msg_callback()\fR whenever a message is sent or received during the
initial connection, handshake, or I/O operations\&. It is only available when
OpenSSL is complied with the \fBenable-ssl-trace\fR option\&. This callback is
new for TclTLS 1\&.8\&. The arguments are:
.RS
.TP
\fIdirection\fR
Direction is either \fBSent\fR or \fBReceived\fR\&.
.TP
\fIversion\fR
Version is the protocol version\&.
.TP
\fIcontent_type\fR
Content type is the message content type\&.
.TP
\fImessage\fR
Message is more info from the \fBSSL_trace\fR API\&.
.RE
.TP
\fBsession\fR \fIchannelId session_id session_ticket lifetime\fR
This form of callback is invoked by the OpenSSL function
\fBSSL_CTX_sess_set_new_cb()\fR whenever a new session id is sent by the
server during the initial connection and handshake and also during the session
if the \fB-post_handshake\fR option is set to true\&. This callback is new for
TclTLS 1\&.8\&. The arguments are:
.RS
.TP
\fIsession_id\fR
Session Id is the current session identifier
.TP
\fIsession_ticket\fR
Ticket is the session ticket info
.TP
\fIlifetime\fR
Lifetime is the ticket lifetime in seconds\&.
.RE
.TP
\fBverify\fR \fIchannelId depth cert status error\fR
This callback was moved to \fB-validatecommand\fR in TclTLS 1\&.8\&.
.PP
.SS "VALUES FOR PASSWORD CALLBACK"
The callback for the \fB-password\fR 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\&.
.TP
\fBpassword\fR \fIrwflag size\fR
Invoked when loading or storing an encrypted PEM certificate\&. The arguments are:
.RS
.TP
\fIrwflag\fR
The read/write flag is 0 for reading/decryption or 1 for writing/encryption\&.
The latter can be used to determine when to prompt the user to confirm\&.
This argument is new for TclTLS 1\&.8\&.
.TP
\fIsize\fR
The size is the maximum length of the password in bytes\&.
This argument is new for TclTLS 1\&.8\&.
.RE
.PP
.SS "VALUES FOR VALIDATE COMMAND CALLBACK"
The callback for the \fB-validatecommand\fR 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\&.
.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\&.
.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
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
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
\fB-command\fR in TclTLS 1\&.8\&. The arguments are:
.RS
.TP
\fIdepth\fR
The depth is the integer depth of the certificate in the certificate chain,
where 0 is the peer certificate and higher values going up to the Certificate
Authority (CA)\&.
.TP
\fIcert\fR
The cert argument is a list of key-value pairs similar to those returned by
\fBtls::status\fR\&.
.TP
\fIstatus\fR
The status argument is the boolean validity of the current certificate where 0
is invalid and 1 is valid\&.
.TP
\fIerror\fR
The error argument is the error message, if any, generated by
\fBX509_STORE_CTX_get_error()\fR\&.
.RE
.PP
Reference implementations of these callbacks are provided in "\fItls\&.tcl\fR"
as \fBtls::callback\fR, \fBtls::password\fR, and \fBtls::validate_command\fR
respectively\&. Note that these are only \fIsample\fR implementations\&. In a more
realistic deployment you would specify your own callback scripts on each TLS
channel using the \fB-command\fR, \fB-password\fR, and
\fB-validate_command\fR options\&.
.PP
The default behavior when the \fB-command\fR and \fB-validate_command\fR
options are not specified, is for TclTLS to process the associated library
callbacks internally\&. The default behavior when the \fB-password\fR option
is not specified is for TclTLS to process the associated library callbacks by
attempting to call \fBtls::password\fR\&. The difference between these two
behaviors is a consequence of maintaining compatibility with earlier
implementations\&.
.PP
\fIThe use of the reference callbacks \fBtls::callback\fR, \fBtls::password\fR,
and \fBtls::validate_command\fR is not recommended\&. They may be removed from future releases\&.\fR
.SH DEBUG
For most debugging needs, the \fB-callback\fR 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
\fB--enable-debug\fR can be used to get detailed execution flow status\&.
.PP
TLS key logging can be enabled by setting the environment variable
\fBSSLKEYLOGFILE\fR 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\&.
.PP
The \fBtls::debug\fR variable provides some additional control over the
debug logging in the \fBtls::callback\fR, \fBtls::password\fR, and
\fBtls::validate_command\fR default handlers in "\fItls\&.tcl\fR"\&.
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"
The following are example scripts to download a webpage and file using the
http package\&. See \fBCertificate Validation\fR for whether the
\fB-cadir\fR, \fB-cafile\fR, and \fB-castore\fR options are also
needed\&. See the demos directory for more example scripts\&.
.PP
Example #1: Download a web page
.CS



package require http
package require tls

set url "https://www\&.tcl\&.tk/"
http::register https 443 [list ::tls::socket -autoservername 1 -require 1]

# Get URL
set token [http::geturl $url]

# Check for error
if {[http::status $token] ne "ok"} {
    puts [format "Error %s" [http::status $token]]
}

# Save web page to file
set ch [open example\&.html wb]
puts $ch [http::data $token]
close $ch

# Cleanup
::http::cleanup $token

.CE
Example #2: Download a file
.CS



package require http
package require tls

set url "https://wiki\&.tcl-lang\&.org/sitemap\&.xml"
http::register https 443 [list ::tls::socket -autoservername 1 -require 1]

# Open output file
set filename [file tail $url]
set ch [open $filename wb]

# Get file
set token [::http::geturl $url -blocksize 65536 -channel $ch]

# Check for error
if {[http::status $token] ne "ok"} {
    puts [format "Error %s" [http::status $token]]
}

# Cleanup
close $ch
::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
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
.SH COPYRIGHT
.nf
Copyright (c) 1999 Matt Newman
Copyright (c) 2004 Starfish Systems
Copyright (c) 2024 Brian O'Hagan

.fi