TLS_CONFIG_SET_SESSION_ID(3) | Library Functions Manual | TLS_CONFIG_SET_SESSION_ID(3)

# NAME

`tls_config_set_session_fd`, `tls_config_set_session_id`, `tls_config_set_session_lifetime`, `tls_config_add_ticket_key` — configure resuming of TLS handshakes

# SYNOPSIS

library “libtls” libssl libcrypto
`#include <tls.h>`

int
`tls_config_set_session_fd`(struct tls_config *config, int session_fd);

int
`tls_config_set_session_id`(struct tls_config *config, const unsigned char *session_id, size_t len);

int
`tls_config_set_session_lifetime`(struct tls_config *config, int lifetime);

int
`tls_config_add_ticket_key`(struct tls_config *config, uint32_t keyrev, unsigned char *key, size_t keylen);

# DESCRIPTION

`tls_config_set_session_fd`() sets a file descriptor to be used to manage data for TLS sessions (client only). The given file descriptor must be a regular file and be owned by the current user, with permissions being restricted to only allow the owner to read and write the file (0600). If the file has a non-zero length, the client will attempt to read session data from this file and resume the previous TLS session with the server. Upon a successful handshake the file will be updated with current session data, if available. The caller is responsible for closing this file descriptor, after all TLS contexts that have been configured to use it have been freed via `tls_free`().

`tls_config_set_session_id`() sets the session identifier that will be used by the TLS server when sessions are enabled (server only). By default a random value is used.

`tls_config_set_session_lifetime`() sets the lifetime to be used for TLS sessions (server only). Session support is disabled if a lifetime of zero is specified, which is the default.

`tls_config_add_ticket_key`() adds a key used for the encryption and authentication of TLS tickets (server only). By default keys are generated and rotated automatically based on their lifetime. This function should only be used to synchronise ticket encryption key across multiple processes. Re-adding a known key will result in an error, unless it is the most recently added key.

# RETURN VALUES

These functions return 0 on success or -1 on error.

# SEE ALSO

tls_accept_socket(3), tls_config_set_protocols(3), tls_init(3), tls_load_file(3), tls_server(3)

# HISTORY

`tls_config_set_session_id`(), `tls_config_set_session_lifetime`() and `tls_config_add_ticket_key`() appeared in OpenBSD 6.1.

`tls_config_set_session_fd`() appeared in OpenBSD 6.3.

# AUTHORS

Claudio Jeker <claudio@openbsd.org>
Joel Sing <jsing@openbsd.org>

July 7, 2025 | Debian