The top level directory contains a clone file and subdirectories numbered from zero through at least the last active filter. Opening the clone file reserves a filter. The file descriptor returned from the sys-open(2) will point to the control file, ctl, of the newly allocated filter. Reading the ctl file returns a text string containing the number of the filter directory.

The filter initially cannot be used to pass messages and will not encrypt or digest messages. It is configured and controlled by writing commands to ctl.

The following commands are supported:

fd open-fd vers

Pass record messages over the communications channel open-fd. Initially, outgoing messages use version vers format records, but incoming messages of either version are accepted. Valid versions are 0x300 for SSLv3.0 and 0x301 for TLSv1.0 (which could be known as SSLv3.01.) This command must be issued before any other command and before reading or writing any messages; it may only be executed once.

version vers

Use vers format records for all future records, both outgoing and incoming. This command may only be executed once.

secret hashalg encalg isclient secretdata

Set up the digesting and encryption algorithms and secrets. Hashalg and encalg must be algorithm names returned by the corresponding files. Secretdata is the base-64 encoded (see encode(2)) secret data used for the algorithms. It must contain at least enough data to populate the secrets for digesting and encrypting. These secrets are divided into three categories: digest secrets, keys, and initialization vectors. The secrets are packed in this order, with no extra padding. Within each category, the secret for data traveling from the client to the server comes first. The incoming and outgoing secrets are automatically selected by devtls based on the isclient argument, which must be non-zero for the client of the TLS handshake, and zero for the server.
This command must be issued after version, and may be issued more than once. At least one new secret command must be issued before each changecipher command; similarly, at least one new secret command must precede each incoming changecipher message.

changecipher

Enable outgoing encryption and digesting as configured by the previous secret command. This command sends a changecipher message.

opened

Enable data messages. This command may be issued any number of times, although only the first is significant. It must follow at least one successful changecipher command.

alert alertno

Send an alert message. Alertno may be a valid alert code for either SSLv3.0 or TLSv1.0, and is mapped to an appropriate code for the protocol in use. If it is a fatal alert, the filter is set into an error state.

Application messages and handshake messages are communicated using data and hand, respectively. Only one sys-open(2) of hand is allowed at a time.

Any record layer headers and trailers are inserted and stripped automatically, and are not visible from the outside. The device tries to synchronize record boundaries with reads and writes. Each read will return data from exactly one record, and will return all of the data from the record as long as the buffer is big enough. Each write will be converted into an integral number of records, with all but potentially the last being maximal size. The maximum record length supported is 16384 bytes. This behavior is not specified in the protocols, and may not be followed by other implementations.

If a fatal alert message is received, or a fatal alert command issued, the filter is set into an error state. All further correspondence is halted, although some pending operations may not be terminated. Operations on data will fail with a 'tls error', and operations on hand will fail with a textual decoding of the alert. The current non-fatal alert messages are 'close notify', 'no renegotiation', and 'handshake canceled by user'. Receipt of one of these alerts cause the next read on hand to terminate with an error. If the alert is 'close notify', all future reads will terminate with a tls hungup error. A 'close notify' alert command will terminate all future writes or reads from data with a 'tls hungup' error.

If an error is encountered while reading or writing the underlying communications channel, the error is returned to the offending operation. If the error is not 'interrupted', the filter is set into the error state. In this case, all future operations on hand will fail with a 'channel error'.

When all file descriptors for a filter have been closed, the session is terminated and the filter reclaimed for future use. A 'close notify' alert will be sent on the underlying communications channel unless one has already been sent or the filter is in the error state.

Reading stats or status returns information about the filter. Each datum is returned on a single line of the form tag: data. Stats returns the number of bytes communicated by the data and hand channels. The four lines returned are tagged by, in order, DataIn, DataOut, HandIn, and HandOut. Status returns lines following tags: State, Version, EncIn, HashIn, NewEncIn, NewHashIn, EncOut, HashOut, NewEncOut, and NewHashOut. State's value is a string describing the status of the connection, and is one of the following: 'Handshaking', 'Established', 'RemoteClosed', 'LocalClosed', 'Alerting', 'Errored', or 'Closed'. Version's give the hexadecimal record layer version in use. The Enc and Hash fields return name of the current algorithms in use or ready to be used, if any.

Reading encalgs and hashalgs will give the space-separated list of algorithms implemented. This will always include clear, meaning no encryption or digesting. Currently implemented encryption algorithms are 'rc4_128' and '3des_ede_cbc'. Currently implemented hashing algorithms are 'md5' and 'sha1'.