.\" $OpenBSD: tls_init.3,v 1.39 2015/09/11 13:59:20 beck Exp $
.\"
.\" Copyright (c) 2014 Ted Unangst <tedu@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.Dd $Mdocdate: September 11 2015 $
.Dt TLS_INIT 3
.Os
.Sh NAME
.Nm tls_init ,
.Nm tls_error ,
.Nm tls_config_new ,
.Nm tls_config_free ,
.Nm tls_config_parse_protocols ,
.Nm tls_config_set_ca_file ,
.Nm tls_config_set_ca_path ,
.Nm tls_config_set_ca_mem ,
.Nm tls_config_set_cert_file ,
.Nm tls_config_set_cert_mem ,
.Nm tls_config_set_ciphers ,
.Nm tls_config_set_dheparams ,
.Nm tls_config_set_ecdhecurve ,
.Nm tls_config_set_key_file ,
.Nm tls_config_set_key_mem ,
.Nm tls_config_set_protocols ,
.Nm tls_config_set_verify_depth ,
.Nm tls_config_prefer_ciphers_client ,
.Nm tls_config_prefer_ciphers_server ,
.Nm tls_config_clear_keys ,
.Nm tls_config_insecure_noverifycert ,
.Nm tls_config_insecure_noverifyname ,
.Nm tls_config_verify ,
.Nm tls_config_verify_client ,
.Nm tls_config_verify_client_optional ,
.Nm tls_load_file ,
.Nm tls_client ,
.Nm tls_server ,
.Nm tls_configure ,
.Nm tls_reset ,
.Nm tls_free ,
.Nm tls_connect ,
.Nm tls_connect_fds ,
.Nm tls_connect_servername ,
.Nm tls_connect_socket ,
.Nm tls_accept_fds ,
.Nm tls_accept_socket ,
.Nm tls_handshake ,
.Nm tls_read ,
.Nm tls_write ,
.Nm tls_close
.Nd TLS client and server API
.Sh SYNOPSIS
.In tls.h
.Ft "int"
.Fn tls_init "void"
.Ft "const char *"
.Fn tls_error "struct tls *ctx"
.Ft "struct tls_config *"
.Fn tls_config_new "void"
.Ft "void"
.Fn tls_config_free "struct tls_config *config"
.Ft "int"
.Fn tls_config_parse_protocols "uint32_t *protocols" "const char *protostr"
.Ft "int"
.Fn tls_config_set_ca_file "struct tls_config *config" "const char *ca_file"
.Ft "int"
.Fn tls_config_set_ca_path "struct tls_config *config" "const char *ca_path"
.Ft "int"
.Fn tls_config_set_ca_mem "struct tls_config *config" "const uint8_t *cert" "size_t len"
.Ft "int"
.Fn tls_config_set_cert_file "struct tls_config *config" "const char *cert_file"
.Ft "int"
.Fn tls_config_set_cert_mem  "struct tls_config *config" "const uint8_t *cert" "size_t len"
.Ft "int"
.Fn tls_config_set_ciphers "struct tls_config *config" "const char *ciphers"
.Ft "int"
.Fn tls_config_set_dheparams "struct tls_config *config" "const char *params"
.Ft "int"
.Fn tls_config_set_ecdhecurve "struct tls_config *config" "const char *name"
.Ft "int"
.Fn tls_config_set_key_file "struct tls_config *config" "const char *key_file"
.Ft "int"
.Fn tls_config_set_key_mem "struct tls_config *config" "const uint8_t *key" "size_t len"
.Ft "void"
.Fn tls_config_set_protocols "struct tls_config *config" "uint32_t protocols"
.Ft "void"
.Fn tls_config_set_verify_depth "struct tls_config *config" "int verify_depth"
.Ft "void"
.Fn tls_config_prefer_ciphers_client "struct tls_config *config"
.Ft "void"
.Fn tls_config_prefer_ciphers_server "struct tls_config *config"
.Ft "void"
.Fn tls_config_clear_keys "struct tls_config *config"
.Ft "void"
.Fn tls_config_insecure_noverifycert "struct tls_config *config"
.Ft "void"
.Fn tls_config_insecure_noverifyname "struct tls_config *config"
.Ft "void"
.Fn tls_config_verify "struct tls_config *config"
.Ft "void"
.Fn tls_config_verify_client "struct tls_config *config"
.Ft "void"
.Fn tls_config_verify_client_optional "struct tls_config *config"
.Ft "int"
.Fn tls_peer_cert_provided "struct tls *ctx"
.Ft "int"
.Fn tls_peer_cert_contains_name "struct tls *ctx" "const char *name"
.Ft "int
.Fn tls_peer_cert_issuer "struct tls *ctx" "char **issuer"
.Ft "int"
.Fn tls_peer_cert_subject "struct tls *ctx" "char **subject"
.Ft "int"
.Fn tls_peer_cert_hash "struct tls *ctx" "char **hash"
.Ft "uint8_t *"
.Fn tls_load_file "const char *file" "size_t *len" "char *password"
.Ft "struct tls *"
.Fn tls_client void
.Ft "struct tls *"
.Fn tls_server void
.Ft "int"
.Fn tls_configure "struct tls *ctx" "struct tls_config *config"
.Ft "void"
.Fn tls_reset "struct tls *ctx"
.Ft "void"
.Fn tls_free "struct tls *ctx"
.Ft "int"
.Fn tls_connect "struct tls *ctx" "const char *host" "const char *port"
.Ft "int"
.Fn tls_connect_fds "struct tls *ctx" "int fd_read" "int fd_write" "const char *servername"
.Fn tls_connect_servername "struct tls *ctx" "const char *host" "const char *port" "const char *servername"
.Ft "int"
.Fn tls_connect_socket "struct tls *ctx" "int s" "const char *servername"
.Ft "int"
.Fn tls_accept_fds "struct tls *tls" "struct tls **cctx" "int fd_read" "int fd_write"
.Ft "int"
.Fn tls_accept_socket "struct tls *tls" "struct tls **cctx" "int socket"
.Ft "int"
.Fn tls_handshake "struct tls *ctx"
.Ft "ssize_t"
.Fn tls_read "struct tls *ctx" "void *buf" "size_t buflen"
.Ft "ssize_t"
.Fn tls_write "struct tls *ctx" "const void *buf" "size_t buflen"
.Ft "int"
.Fn tls_close "struct tls *ctx"
.Sh DESCRIPTION
The
.Nm tls
family of functions establishes a secure communications channel
using the TLS socket protocol.
Both clients and servers are supported.
.Pp
The
.Fn tls_init
function should be called once before any function is used.
It may be called more than once, but not concurrently.
.Pp
Before a connection is created, a configuration must be created.
The
.Fn tls_config_new
function returns a new default configuration that can be used for future
connections.
Several functions exist to change the options of the configuration; see below.
.Pp
A
.Em tls
connection is represented as a
.Em context .
A new
.Em context
is created by either the
.Fn tls_client
or
.Fn tls_server
functions.
The context can then be configured with the function
.Fn tls_configure .
The same
.Em tls_config
object can be used to configure multiple contexts.
.Pp
A client connection is initiated after configuration by calling
.Fn tls_connect .
This function will create a new socket, connect to the specified host and
port, and then establish a secure connection.
The
.Fn tls_connect_servername
function has the same behaviour, however the name to use for verification is
explicitly provided, rather than being inferred from the
.Ar host
value.
An already existing socket can be upgraded to a secure connection by calling
.Fn tls_connect_socket .
Alternatively, a secure connection can be established over a pair of existing
file descriptors by calling
.Fn tls_connect_fds .
.Pp
A server can accept a new client connection by calling
.Fn tls_accept_socket
on an already established socket connection.
Alternatively, a new client connection can be accepted over a pair of existing
file descriptors by calling
.Fn tls_accept_fds .
.Pp
The TLS handshake can be completed by calling
.Fn tls_handshake .
Two functions are provided for input and output,
.Fn tls_read
and
.Fn tls_write .
Both of these functions will result in the TLS handshake being performed if it
has not already completed.
.Pp
After use, a tls
.Em context
should be closed with
.Fn tls_close ,
and then freed by calling
.Fn tls_free .
When no more contexts are to be created, the
.Em tls_config
object should be freed by calling
.Fn tls_config_free .
.Sh FUNCTIONS
The
.Fn tls_init
function initializes global data structures.
It should be called once before any other functions.
.Pp
The following functions create and free configuration objects.
.Bl -bullet -offset four
.It
.Fn tls_config_new
allocates a new default configuration object.
.It
.Fn tls_config_free
frees a configuration object.
.El
.Pp
The
.Fn tls_config_parse_protocols
function parses a protocol string and returns the corresponding value via the
.Ar protocols
argument.
This value can then be passed to the
.Fn tls_config_set_protocols
function.
The protocol string is a comma or colon separated list of keywords.
Valid keywords are tlsv1.0, tlsv1.1, tlsv1.2, all (all supported protocols),
default (an alias for secure), legacy (an alias for all) and secure (currently
TLSv1.2 only).
If a value has a negative prefix (in the form of a leading exclamation mark)
then it is removed from the list of available protocols, rather than being
added to it.
.Pp
The following functions modify a configuration by setting parameters.
Configuration options may apply to only clients or only servers or both.
.Bl -bullet -offset four
.It
.Fn tls_config_set_ca_file
sets the filename used to load a file
containing the root certificates.
.Em (Client)
.It
.Fn tls_config_set_ca_path
sets the path (directory) which should be searched for root
certificates.
.Em (Client)
.It
.Fn tls_config_set_ca_mem
sets the root certificates directly from memory.
.Em (Client)
.It
.Fn tls_config_set_cert_file
sets file from which the public certificate will be read.
.Em (Client and server)
.It
.Fn tls_config_set_cert_mem
sets the public certificate directly from memory.
.Em (Client and server)
.It
.Fn tls_config_set_ciphers
sets the list of ciphers that may be used.
Lists of ciphers are specified by name, and the
permitted names are: 
.Pp
.Bl -tag -width "default" -offset indent -compact
.It Dv "secure"
.It Dv "default" (an alias for secure)
.It Dv "legacy" 
.It Dv "compat" (an alias for legacy)
.El
.Pp
.Em (Client and server)
.It
.Fn tls_config_set_key_file
sets the file from which the private key will be read.
.Em (Server)
.It
.Fn tls_config_set_key_mem
directly sets the private key from memory.
.Em (Server)
.It
.Fn tls_config_set_protocols
sets which versions of the protocol may be used.
Possible values are the bitwise OR of:
.Pp
.Bl -tag -width "TLS_PROTOCOL_TLSv1_2" -offset indent -compact
.It Dv TLS_PROTOCOL_TLSv1_0
.It Dv TLS_PROTOCOL_TLSv1_1
.It Dv TLS_PROTOCOL_TLSv1_2
.El
.Pp
Additionally, the values
.Dv TLS_PROTOCOL_TLSv1
(TLSv1.0, TLSv1.1 and TLSv1.2),
.Dv TLS_PROTOCOLS_ALL
(all supported protocols) and
.Dv TLS_PROTOCOLS_DEFAULT
(TLSv1.2 only) may be used.
.Em (Client and server)
.It
.Fn tls_config_prefer_ciphers_client
prefers ciphers in the client's cipher list when selecting a cipher suite.
This is considered to be less secure than preferring the server's list.
.Em (Server)
.It
.Fn tls_config_prefer_ciphers_server
prefers ciphers in the server's cipher list when selecting a cipher suite.
This is considered to be more secure than preferring the client's list and is
the default.
.Em (Server)
.It
.Fn tls_config_clear_keys
clears any secret keys from memory.
.Em (Server)
.It
.Fn tls_config_insecure_noverifycert
disables certificate verification.
Be extremely careful when using this option.
.Em (Client and server)
.It
.Fn tls_config_insecure_noverifyname
disables server name verification.
Be careful when using this option.
.Em (Client)
.It
.Fn tls_config_verify
reenables server name and certificate verification.
.Em (Client)
.It
.Fn tls_config_verify_client
enables client certificate verification, requiring the client to send
a certificate.
.Em (Server)
.It
.Fn tls_peer_cert_provided
checks if the peer of 
.Ar ctx 
has provided a certificate.
.Fn tls_peer_cert_provided
can only succeed after the handshake is complete. 
.Em (Server and client)
.It
.Fn tls_peer_cert_constains_name
checks if the peer of a tls 
.Ar ctx
 has povided a certificate that contains a 
SAN or CN that matches
.Ar name
.Fn tls_peer_cert_contains_name
can only succeed after the handshake is complete. 
.Em (Server and client)
.It
.Fn tls_peer_cert_subject
returns a string in
.Ar subject
corresponding to the subject of the peer certificate from
.Ar ctx .
.Fn tls_peer_cert_subject
will only succeed after the handshake is complete. 
Callers must free the string returned in 
.Ar subject .
.Em (Server and client)
.It
.Fn tls_peer_cert_issuer
returns a string in 
.Ar subject
corresponding to the issuer of the peer certificate from
.Ar ctx .
.Fn tls_peer_cert_issuer
will only succeed after the handshake is complete. 
Callers must free the string returned in 
.Ar issuer .
.Em (Server and client)
.It
.Fn tls_peer_cert_hash
returns a string
in
.Ar hash
corresponding to a hash of the raw peer certificate from
.Ar ctx
prefixed by a hash name followed by a colon. 
The hash currently used is SHA256, however this
can change in the future. The hash string for a certificate
in file
.Ar mycert.crt
can be generated using the commands:
.Bd -literal -offset indent
h=$(openssl x509 -outform der -in mycert.crt | sha256)
printf "SHA256:${h}\\n"
.Ed
.Pp
.Fn tls_peer_cert_subject
will only succeed after the handshake is complete. 
Callers must free the string returned in 
.Ar hash .
.Em (Server and client)
.It
.Fn tls_config_verify_client_opional
enables client certificate verification, without requiring the client
to send a certificate.
.Em (Server)
.It
.Fn tls_load_file
loads a certificate or key from disk into memory to be loaded with
.Fn tls_config_set_ca_mem ,
.Fn tls_config_set_cert_mem
or
.Fn tls_config_set_key_mem .
A private key will be decrypted if the optional
.Ar password
argument is specified.
.Em (Client and server)
.El
.Pp
The following functions create, prepare, and free a connection context.
.Bl -bullet -offset four
.It
.Fn tls_client
creates a new tls context for client connections.
.It
.Fn tls_server
creates a new tls context for server connections.
.It
.Fn tls_configure
readies a tls context for use by applying the configuration
options.
.It
.Fn tls_free
frees a tls context after use.
.El
.Pp
The following functions initiate a connection and perform input and output
operations.
.Bl -bullet -offset four
.It
.Fn tls_connect
connects a client context to the server named by
.Fa host .
The
.Fa port
may be numeric or a service name.
If it is NULL then a host of the format "hostname:port" is permitted.
.It
.Fn tls_connect_fds
connects a client context to a pair of existing file descriptors.
.It
.Fn tls_connect_socket
connects a client context to an already established socket connection.
.It
.Fn tls_accept_fds
creates a new context suitable for reading and writing on an existing pair of
file descriptors and returns it in
.Fa *cctx .
A configured server context should be passed in
.Fa ctx .
.It
.Fn tls_accept_socket
creates a new context suitable for reading and writing on an already
established socket connection and returns it in
.Fa *cctx .
A configured server context should be passed in
.Fa ctx .
.It
.Fn tls_handshake
performs the TLS handshake.
It is only necessary to call this function if you need to guarantee that the
handshake has completed, as both
.Fn tls_read
and
.Fn tls_write
will perform the TLS handshake if necessary.
.It
.Fn tls_read
reads
.Fa buflen
bytes of data from the socket into
.Fa buf .
The amount of data read is returned in
.Fa outlen .
.It
.Fn tls_write
writes
.Fa buflen
bytes of data from
.Fa buf
to the socket.
The amount of data written is returned in
.Fa outlen .
.It
.Fn tls_close
closes a connection after use.
Only the TLS layer will be shut down and the caller is responsible for closing
the file descriptors, unless the connection was established using
.Fn tls_connect
or
.Fn tls_connect_servername .
.El
.Sh RETURN VALUES
The 
.Fn tls_peer_cert_provided
and
.Fn tls_peer_cert_contain_name
functions return 1 if the check succeeds, and 0 if it does not. 
All other functions that return
.Vt int
or
.Vt ssize_t
will return 0 on success and -1 on error.
Functions that return a pointer will return NULL on error, which indicates an
out of memory condition.
.Pp
The
.Fn tls_handshake ,
.Fn tls_read ,
.Fn tls_write ,
and
.Fn tls_close
functions have two special return values:
.Pp
.Bl -tag -width "TLS_WANT_POLLOUT" -offset indent -compact
.It Dv TLS_WANT_POLLIN
The underlying read file descriptor needs to be readable in order to continue.
.It Dv TLS_WANT_POLLOUT
The underlying write file descriptor needs to be writeable in order to continue.
.El
.Pp
In the case of blocking file descriptors, the same function call should be
repeated immediately.
In the case of non-blocking file descriptors, the same function call should be
repeated when the required condition has been met.
.Pp
Callers of these functions cannot rely on the value of the global
.Ar errno .
To prevent mishandling of error conditions,
.Fn tls_handshake ,
.Fn tls_read ,
.Fn tls_write ,
and
.Fn tls_close
all explicitly clear
.Ar errno .
.Sh EXAMPLES
The following example demonstrates how to handle TLS writes on a blocking
file descriptor:
.Bd -literal -offset indent
\&...
while (len > 0) {
	ssize_t ret;

	ret = tls_write(ctx, buf, len);
	if (ret == TLS_WANT_POLLIN || ret == TLS_WANT_POLLOUT)
		continue;
        if (ret < 0)
		err(1, "tls_write: %s", tls_error(ctx));
	buf += ret;
	len -= ret;
}
\&...
.Ed
.Bd -literal -offset indent
.Pp
The following example demonstrates how to handle TLS writes on a
non-blocking file descriptor using
.Xr poll 2 :
.Bd -literal -offset indent
\&...
pfd[0].fd = fd;
pfd[0].events = POLLIN|POLLOUT;
while (len > 0) {
	nready = poll(pfd, 1, 0);
	if (nready == -1)
		err(1, "poll");
	if ((pfd[0].revents & (POLLERR|POLLNVAL)))
		errx(1, "bad fd %d", pfd[0].fd);
	if ((pfd[0].revents & (pfd[0].events|POLLHUP))) {
		ssize_t ret;

		ret = tls_write(ctx, buf, len);
		if (ret == TLS_WANT_POLLIN)
			pfd[0].events = POLLIN;
		else if (ret == TLS_WANT_POLLOUT)
			pfd[0].events = POLLOUT;
		else if (ret < 0)
			err(1, "tls_write: %s", tls_error(ctx));
		else {
			buf += ret;
			len -= ret;
		}
        }
}
\&...
.Ed
.Sh ERRORS
The
.Fn tls_error
function may be used to retrieve a string containing more information
about the most recent error.
.\" .Sh SEE ALSO
.Sh HISTORY
The
.Nm tls
API first appeared in
.Ox 5.6
as a response to the unnecessary challenges other APIs present in
order to use them safely.