TLS_INIT(3)

NAME
tls_init, tls_config_error, tls_error, tls_config_new, tls_config_free, tls_config_parse_protocols, tls_config_set_ca_file, tls_config_set_ca_path, tls_config_set_ca_mem, tls_config_set_cert_file, tls_config_set_cert_mem, tls_config_set_ciphers, tls_config_set_dheparams, tls_config_set_ecdhecurve, tls_config_set_key_file, tls_config_set_key_mem, tls_config_set_keypair_file, tls_config_set_keypair_mem, tls_config_set_protocols, tls_config_set_verify_depth, tls_config_prefer_ciphers_client, tls_config_prefer_ciphers_server, tls_config_clear_keys, tls_config_insecure_noverifycert, tls_config_insecure_noverifyname, tls_config_insecure_noverifytime, tls_config_verify, tls_config_verify_client, tls_config_verify_client_optional, tls_peer_cert_provided, tls_peer_cert_contains_name, tls_peer_cert_issuer, tls_peer_cert_subject, tls_peer_cert_hash, tls_peer_cert_notbefore, tls_peer_cert_notafter, tls_conn_version, tls_conn_cipher, tls_load_file, tls_client, tls_server, tls_configure, tls_reset, tls_free, tls_connect, tls_connect_fds, tls_connect_servername, tls_connect_socket, tls_accept_fds, tls_accept_socket, tls_handshake, tls_read, tls_write, tls_close - TLS client and server API

SYNOPSIS
#include <tls.h>
int
tls_init(void);
const char *
tls_config_error(struct tls_config *config);
const char *
tls_error(struct tls *ctx);
struct tls_config *
tls_config_new(void);
void
tls_config_free(struct tls_config *config);
int
tls_config_parse_protocols(uint32_t *protocols, const char *protostr);
int
tls_config_set_ca_file(struct tls_config *config, const char *ca_file);
int
tls_config_set_ca_path(struct tls_config *config, const char *ca_path);
int
tls_config_set_ca_mem(struct tls_config *config, const uint8_t *cert, size_t len);
int
tls_config_set_cert_file(struct tls_config *config, const char *cert_file);
int
tls_config_set_cert_mem(struct tls_config *config, const uint8_t *cert, size_t len);
int
tls_config_set_ciphers(struct tls_config *config, const char *ciphers);
int
tls_config_set_dheparams(struct tls_config *config, const char *params);
int
tls_config_set_ecdhecurve(struct tls_config *config, const char *name);
int
tls_config_set_key_file(struct tls_config *config, const char *key_file);
int
tls_config_set_key_mem(struct tls_config *config, const uint8_t *key, size_t len);
int
tls_config_set_keypair_file(struct tls_config *config, const char *cert_file, const char *key_file);
int
tls_config_set_keypair_mem(struct tls_config *config, const uint8_t *cert, size_t cert_len, const uint8_t *key, size_t key_len);
void
tls_config_set_protocols(struct tls_config *config, uint32_t protocols);
void
tls_config_set_verify_depth(struct tls_config *config, int verify_depth);
void
tls_config_prefer_ciphers_client(struct tls_config *config);
void
tls_config_prefer_ciphers_server(struct tls_config *config);
void
tls_config_clear_keys(struct tls_config *config);
void
tls_config_insecure_noverifycert(struct tls_config *config);
void
tls_config_insecure_noverifyname(struct tls_config *config);
void
tls_config_insecure_noverifytime(struct tls_config *config);
void
tls_config_verify(struct tls_config *config);
void
tls_config_verify_client(struct tls_config *config);
void
tls_config_verify_client_optional(struct tls_config *config);
int
tls_peer_cert_provided(struct tls *ctx);
int
tls_peer_cert_contains_name(struct tls *ctx, const char *name);
const char *
tls_peer_cert_issuer(struct tls *ctx);
const char *
tls_peer_cert_subject(struct tls *ctx);
const char *
tls_peer_cert_hash(struct tls *ctx);
time_t
tls_peer_cert_notbefore(struct tls *ctx);
time_t
tls_peer_cert_notafter(struct tls *ctx);
const char *
tls_conn_version(struct tls *ctx);
const char *
tls_conn_cipher(struct tls *ctx);
uint8_t *
tls_load_file(const char *file, size_t *len, char *password);
struct tls *
tls_client(void);
struct tls *
tls_server(void);
int
tls_configure(struct tls *ctx, struct tls_config *config);
void
tls_reset(struct tls *ctx);
void
tls_free(struct tls *ctx);
int
tls_connect(struct tls *ctx, const char *host, const char *port);
int
tls_connect_fds(struct tls *ctx, int fd_read, int fd_write, const char *servername);
int
tls_connect_servername(struct tls *ctx, const char *host, const char *port, const char *servername);
int
tls_connect_socket(struct tls *ctx, int s, const char *servername);
int
tls_accept_fds(struct tls *tls, struct tls **cctx, int fd_read, int fd_write);
int
tls_accept_socket(struct tls *tls, struct tls **cctx, int socket);
int
tls_handshake(struct tls *ctx);
ssize_t
tls_read(struct tls *ctx, void *buf, size_t buflen);
ssize_t
tls_write(struct tls *ctx, const void *buf, size_t buflen);
int
tls_close(struct tls *ctx);

DESCRIPTION
The tls family of functions establishes a secure communications channel using the TLS socket protocol. Both clients and servers are supported.

The tls_init() function should be called once before any function is used. It may be called more than once, but not concurrently.

Before a connection is created, a configuration must be created. The 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.

A TLS connection is represented as a context. A new context is created by either the tls_client() or tls_server() functions. The context can then be configured with the function tls_configure(). The same tls_config object can be used to configure multiple contexts.

A client connection is initiated after configuration by calling tls_connect(). This function will create a new socket, connect to the specified host and port, and then establish a secure connection. The tls_connect_servername() function has the same behaviour, however the name to use for verification is explicitly provided, rather than being inferred from the host value. An already existing socket can be upgraded to a secure connection by calling tls_connect_socket(). Alternatively, a secure connection can be established over a pair of existing file descriptors by calling tls_connect_fds().

A server can accept a new client connection by calling 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 tls_accept_fds().

The TLS handshake can be completed by calling tls_handshake(). Two functions are provided for input and output, tls_read() and tls_write(). Both of these functions will result in the TLS handshake being performed if it has not already completed.

After use, a TLS context should be closed with tls_close(), and then freed by calling tls_free(). When no more contexts are to be created, the tls_config object should be freed by calling tls_config_free().

FUNCTIONS
The tls_init() function initializes global data structures. It should be called once before any other functions.

The following functions create and free configuration objects.

•   tls_config_new() allocates a new default configuration object.

•   tls_config_free() frees a configuration object.

The tls_config_parse_protocols() function parses a protocol string and returns the corresponding value via the protocols argument. This value can then be passed to the 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.

The following functions modify a configuration by setting parameters. Configuration options may apply to only clients or only servers or both.

•   tls_config_set_ca_file() sets the filename used to load a file containing the root certificates. (Client and Server)

•   tls_config_set_ca_path() sets the path (directory) which should be searched for root certificates. (Client and Server)

•   tls_config_set_ca_mem() sets the root certificates directly from memory. (Client and Server)

•   tls_config_set_cert_file() sets file from which the public certificate will be read. (Client and server)

•   tls_config_set_cert_mem() sets the public certificate directly from memory. (Client and server)

•   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:

    secure (or alias default)
    compat
    legacy
    insecure (or alias all)

    Alternatively, libssl cipher strings can be specified. See the CIPHERS section of openssl(1) for further information.

    (Client and server)

•   tls_config_set_key_file() sets the file from which the private key will be read. (Client and server)

•   tls_config_set_key_mem() directly sets the private key from memory. (Client and server)

•   tls_config_set_keypair_file() sets the files from which the public certificate and private key will be read. (Client and server)

•   tls_config_set_keypair_mem() directly sets the public certificate and private key from memory. (Client and server)

•   tls_config_set_protocols() sets which versions of the protocol may be used. Possible values are the bitwise OR of:

    TLS_PROTOCOL_TLSv1_0
    TLS_PROTOCOL_TLSv1_1
    TLS_PROTOCOL_TLSv1_2

    Additionally, the values TLS_PROTOCOL_TLSv1 (TLSv1.0, TLSv1.1 and TLSv1.2), TLS_PROTOCOLS_ALL (all supported protocols) and TLS_PROTOCOLS_DEFAULT (TLSv1.2 only) may be used. (Client and server)

•   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. (Server)

•   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. (Server)

•   tls_config_clear_keys() clears any secret keys from memory. (Server)

•   tls_config_insecure_noverifycert() disables certificate verification. Be extremely careful when using this option. (Client and server)

•   tls_config_insecure_noverifyname() disables server name verification. Be careful when using this option. (Client)

•   tls_config_insecure_noverifytime() disables validity checking of certificates. Be careful when using this option. (Client and server)

•   tls_config_verify() reenables server name and certificate verification. (Client)

•   tls_config_verify_client() enables client certificate verification, requiring the client to send a certificate. (Server)

•   tls_config_verify_client_optional() enables client certificate verification, without requiring the client to send a certificate. (Server)

•   tls_peer_cert_provided() checks if the peer of ctx has provided a certificate. tls_peer_cert_provided() can only succeed after the handshake is complete. (Server and client)

•   tls_peer_cert_contains_name() checks if the peer of a TLS ctx has provided a certificate that contains a SAN or CN that matches name. tls_peer_cert_contains_name() can only succeed after the handshake is complete. (Server and client)

•   tls_peer_cert_subject() returns a string corresponding to the subject of the peer certificate from ctx. tls_peer_cert_subject() will only succeed after the handshake is complete. (Server and client)

•   tls_peer_cert_issuer() returns a string corresponding to the issuer of the peer certificate from ctx. tls_peer_cert_issuer() will only succeed after the handshake is complete. (Server and client)

•   tls_peer_cert_hash() returns a string corresponding to a hash of the raw peer certificate from ctx prefixed by a hash name followed by a colon. The hash currently used is SHA256, though this could change in the future. The hash string for a certificate in file mycert.crt can be generated using the commands:

        h=$(openssl x509 -outform der -in mycert.crt | sha256)
        printf "SHA256:${h}\n"

•   tls_peer_cert_notbefore() returns the time corresponding to the start of the validity period of the peer certificate from ctx. tls_peer_cert_notbefore() will only succeed after the handshake is complete. (Server and client)

•   tls_peer_cert_notafter() returns the time corresponding to the end of the validity period of the peer certificate from ctx. tls_peer_cert_notafter() will only succeed after the handshake is complete. (Server and client)

•   tls_conn_version() returns a string corresponding to a TLS version negotiated with the peer connected to ctx. tls_conn_version() will only succeed after the handshake is complete.

•   tls_conn_cipher() returns a string corresponding to the cipher suite negotiated with the peer connected to ctx. tls_conn_cipher() will only succeed after the handshake is complete. (Server and client)

•   tls_load_file() loads a certificate or key from disk into memory to be loaded with tls_config_set_ca_mem(), tls_config_set_cert_mem() or tls_config_set_key_mem(). A private key will be decrypted if the optional password argument is specified. (Client and server)

The following functions create, prepare, and free a connection context.

•   tls_client() creates a new TLS context for client connections.

•   tls_server() creates a new TLS context for server connections.

•   tls_configure() readies a TLS context for use by applying the configuration options.

•   tls_free() frees a TLS context after use.

The following functions initiate a connection and perform input and output operations.

•   tls_connect() connects a client context to the server named by host. The port may be numeric or a service name. If it is NULL then a host of the format "hostname:port" is permitted.

•   tls_connect_fds() connects a client context to a pair of existing file descriptors.

•   tls_connect_socket() connects a client context to an already established socket connection.

•   tls_accept_fds() creates a new context suitable for reading and writing on an existing pair of file descriptors and returns it in *cctx. A configured server context should be passed in ctx.

•   tls_accept_socket() creates a new context suitable for reading and writing on an already established socket connection and returns it in *cctx. A configured server context should be passed in ctx.

•   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 tls_read() and tls_write() will perform the TLS handshake if necessary.

•   tls_read() reads buflen bytes of data from the socket into buf. It returns the amount of data read.

•   tls_write() writes buflen bytes of data from buf to the socket. It returns the amount of data written.

•   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 tls_connect() or tls_connect_servername().

RETURN VALUES
The tls_peer_cert_provided() and tls_peer_cert_contains_name() functions return 1 if the check succeeds, and 0 if it does not. Functions that return a time_t will return a time in epoch-seconds on success, and -1 on error. Functions that return a ssize_t will return a size on success, and -1 on error. All other functions that return int 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.

The tls_handshake(), tls_read(), tls_write(), and tls_close() functions have two special return values:

TLS_WANT_POLLIN
    The underlying read file descriptor needs to be readable in order to continue.
TLS_WANT_POLLOUT
    The underlying write file descriptor needs to be writeable in order to continue.

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.

Callers of these functions cannot rely on the value of the global errno. To prevent mishandling of error conditions, tls_handshake(), tls_read(), tls_write(), and tls_close() all explicitly clear errno.

EXAMPLES
The following example demonstrates how to handle TLS writes on a blocking file descriptor:

    ...
    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;
    }
    ...

The following example demonstrates how to handle TLS writes on a non-blocking file descriptor using poll(2):

    ...
    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;
    		}
    	}
    }
    ...

ERRORS
The tls_config_error() and tls_error() functions may be used to retrieve a string containing more information about the most recent error relating to a configuration or context.

HISTORY
The tls API first appeared in OpenBSD 5.6 as a response to the unnecessary challenges other APIs present in order to use them safely.