TLS(3)

NAME
tls_init, 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_protocols, tls_config_set_verify_depth, tls_config_clear_keys, tls_config_insecure_noverifycert, tls_config_insecure_noverifyname, tls_config_verify, tls_load_file, tls_client, tls_server, tls_configure, tls_reset, tls_close, tls_free, tls_connect, tls_connect_fds, tls_connect_servername, tls_connect_socket, tls_accept_socket, tls_read, tls_write - TLS client and server API

SYNOPSIS
#include <tls.h>
int
tls_init(void);
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);
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_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_verify(struct tls_config *config);
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);
int
tls_close(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);
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_socket(struct tls *tls, struct tls **cctx, int socket);
int
tls_read(struct tls *ctx, void *buf, size_t buflen, size_t *outlen);
int
tls_write(struct tls *ctx, const void *buf, size_t buflen, size_t *outlen);

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.

Two functions are provided for input and output, tls_read() and tls_write().

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)

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

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

•   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. (Client and server)

•   tls_config_set_key_file() sets the file from which the private key will be read. (Server)

•   tls_config_set_key_mem() directly sets the private key from memory. (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_clear_keys() clears any secret keys from memory. (Server)

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

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

•   tls_config_verify() reenables server name and certificate verification. (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_close() closes a connection after use. If the connection was established using tls_connect_fds(), only the TLS layer will be closed and it is the caller's responsibility to close the file descriptors.

•   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_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 and *cctx should be initialized to NULL.

•   tls_read() reads buflen bytes of data from the socket into buf. The amount of data read is returned in outlen.

•   tls_write() writes buflen bytes of data from buf to the socket. The amount of data written is returned in outlen.

RETURN VALUES
Functions that return int will return 0 on success and -1 on error. Functions that return a pointer will return NULL on error.

The tls_read() and tls_write() functions and the tls_connect() family of functions have two special return values.

TLS_READ_AGAIN
    A read operation is necessary to continue.
TLS_WRITE_AGAIN
    A write operation is necessary to continue.

The caller should call the appropriate function, or in the case of tls_connect(), repeat the call.

ERRORS
The tls_error() function may be used to retrieve a string containing more information about the most recent error.

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.