# Module Netsys_tls

    module Netsys_tls: sig .. end

User-level TLS API

The following functions are a very thin layer on top of `Netsys_crypto_types.TLS_PROVIDER`. The provider is passed here as first-class value together with the configuration and with the endpoint (socket). In particular, we have

    module type FILE_TLS_ENDPOINT =
      sig
        module TLS : TLS_PROVIDER
        val endpoint : TLS.endpoint
        val rd_file : Unix.file_descr
        val wr_file : Unix.file_descr
      end

(see `Netsys_crypto_types`). In many cases, you can consider the packed modules as opaque values. Sometimes, however, it is useful to call functions of the provider directly. You can do this as follows, demonstrated by calling the provider function `get_peer_crt_list` for `endpoint`:

    let module Endpoint =
      (val endpoint : Netsys_crypto_types.FILE_TLS_ENDPOINT) in
    let certificates =
      Endpoint.TLS.get_peer_crt_list Endpoint.endpoint

If you do this, be aware that the inner types of the provider are meaningless outside, and you get a compiler error "type ... would escape its scope" if you try to export such typed values. Exceptions thrown by the provider should be caught and translated to `Error` with `Netsys_tls.translate_exn`.

    type dh_params = [ `Generate of int | `PKCS3_DER of string | `PKCS3_PEM_file of string ]

Diffie-Hellman parameters:

- ``PKCS3_PEM_file name`: points to a PEM-encoded PKCS3-file ("BEGIN DH PARAMETERS")
- ``PKCS3_DER data`: the parameters are in a DER-encoded PKCS3 structure
- ``Generate bits`: the parameters are generated with the passed number of bits

    type crt_list = [ `DER of string list | `PEM_file of string ]

Certificates are given either as:

- ``PEM_file name`: The certs are stored in this file, and are PEM-encoded.
- ``DER l`: The certs are given directly in their DER-encoded form

See also `Credentials.tls`.

    type crl_list = [ `DER of string list | `PEM_file of string ]

Certificate revocation lists are given either as:

- ``PEM_file name`: The CRLs are stored in this file, and are PEM-encoded.
- ``DER l`: The CRLs are given directly in their DER-encoded form

See also `Credentials.tls`.

    type private_key = [ `DSA of string
           | `EC of string
           | `PEM_file of string
           | `PKCS8 of string
           | `PKCS8_encrypted of string
           | `RSA of string ]

Private keys are given either as:

- ``PEM_file name`: The key is stored PEM-encoded in this file. The PEM header indicates the format.
- ``RSA data`: The key is a PKCS1 RSA key
- ``DSA data`: The key is a DSA key
- ``EC data`: The key is for an elliptic curve
- ``PKCS8 data`: The key is in a PKCS8 data structure
- ``PKCS8_encrypted data`: The key is in a PKCS8 data structure, and is additionally encrypted.

See also `Credentials.tls`.

    val error_message : (module Netsys_crypto_types.TLS_PROVIDER) -> string -> string

Returns the message for humans (display, log files etc.) when called with an error or warning symbol.

    val create_x509_config : ?algorithms:string ->
           ?dh_params:dh_params ->
           ?verify:((module Netsys_crypto_types.TLS_ENDPOINT) -> bool -> bool -> bool) ->
           ?system_trust:bool ->
           ?trust:crt_list list ->
           ?revoke:crl_list list ->
           ?keys:(crt_list * private_key * string option) list ->
           peer_auth:[ `None | `Optional | `Required ] ->
           (module Netsys_crypto_types.TLS_PROVIDER) ->
           (module Netsys_crypto_types.TLS_CONFIG)

The configuration includes:

- `algorithms`: a string specifying which cryptographic algorithms, protocols and protocol options are enabled, and in which priority they are used in the negotiation. (GnuTLS calls this "priority string".) The syntax is implementation-defined.
- `dh_params`: parameters for Diffie-Hellman key exchange (used for DH-based authentication, but only on the server side)
- `peer_auth`: controls whether the peer is requested to authenticate. This can be set to ``None` meaning not to request authentication and to ignore credentials, or to ``Optional` meaning not to request authentication but to check credentials if they are sent nevertheless, or to ``Required` meaning to request and check credentials. For "standard clients" you should set this to ``Required`, and for "standard servers" to ``None` or ``Required`.
- `verify` is a function called to verify the peer certificate in addition to the actions of `peer_auth`. The function must return `true` in order to be successful. The arguments of the function are the TLS endpoint, and two bools indicating the success of previous checks. The first bool says whether the certificate is trusted (based on `peer_auth`, `trust` and `system_trust`), and the second bool says whether the host name of the peer matches the name in the certificate. If not passed, `verify` defaults to `(fun _ cert_ok name_ok -> cert_ok && name_ok)`, i.e. both bools must be true.
- `system_trust`: if set, the system certificates are trusted
- `trust` specifies the CAs of peers to trust (default: empty)
- `revoke` specifies CRLs for revocation of peer certificates (default: empty)
- `keys` are our own certificates, as triples `(cert_path, private_key, password)` (default: empty)

A configuration is read-only once created, and can be used for several endpoints. In particular, it does not cache TLS sessions.

A client should set `trust` to the list of CAs it can accept on the server side. It is not required to specify a key.

A server must specify a key (but can also specify several keys). If a server requests authentication from the client, it must also set `trust`.

The keys must include the full certificate path `cert_path`, starting with the endpoint certificate, followed by all middle certificates, and ending with the certificate of the CA. The `private_key` is the key of the endpoint. If it is password-encrypted, the password must be given.

    val create_file_endpoint : ?resume:string ->
           role:[ `Client | `Server ] ->
           rd:Unix.file_descr ->
           wr:Unix.file_descr ->
           peer_name:string option ->
           (module Netsys_crypto_types.TLS_CONFIG) ->
           (module Netsys_crypto_types.FILE_TLS_ENDPOINT)

`create_file_endpoint ~role ~rd ~wr ~peer_name tls_config`: Creates a new TLS endpoint (encapsulated as module, together with the provider) for the case that the data flows over file descriptors. `rd` is used for reading data, and `wr` for writing (of course, both descriptors may be identical).

`peer_name` is the expected common name or DNS name of the peer. `peer_name` has an option type as it is not always required to pass it. However, keep in mind that clients normally authenticate servers (`peer_auth=`Required`). In order to do so, they need to check whether the name in the server certificate equals the DNS name of the service they are connected to. This check is done by comparing `peer_name` with the name in the certificate.

`peer_name` is also used for the SNI extension.

Servers normally need not to set `peer_name`. You can also omit it when there is no name-driven authentication at all.

`resume`: The endpoint resumes an old session whose data are passed here. This is only possible for client endpoints.

    val endpoint : (module Netsys_crypto_types.FILE_TLS_ENDPOINT) ->
           (module Netsys_crypto_types.TLS_ENDPOINT)

Coercion

    val handshake : (module Netsys_crypto_types.TLS_ENDPOINT) -> unit

Procedes the TLS protocol until payload data can be exchanged. This includes the initial handshake (if not yet done), and the verification.

    val recv : ?on_rehandshake:((module Netsys_crypto_types.TLS_ENDPOINT) -> bool) ->
           (module Netsys_crypto_types.TLS_ENDPOINT) ->
           Stdlib.Bytes.t -> int -> int -> int

`recv endpoint buffer pos len`: Receives data from `endpoint`, and puts the received bytes into `buffer` at byte position `pos`. At most `len` bytes can be received. Returns the actually received number of bytes.

If the TLS protocol is not yet at the stage where data can be received, the protocol is proceeded until this point (i.e. `handshake` is "included"). Also, renegotiation alerts are interpreted. Both phenomenons can cause that data needs to be written first.

on_rehandshake: returns whether renegotiations are allowed. Defaults to `true`. Also, this function is guaranteed to be called when a renegotiation request arrives. In this case, `recv` will raise an exception such as `Netsys_types.EAGAIN_RD` or `Netsys_types.EAGAIN_WR`, but never return normally.

If interrupted the function can be safely invoked again.

May raise `Netsys_types.EAGAIN_RD`, `Netsys_types.EAGAIN_WR`, `Unix_error(EINTR,_,_)`, and `Error`.

    val mem_recv : ?on_rehandshake:((module Netsys_crypto_types.TLS_ENDPOINT) -> bool) ->
           (module Netsys_crypto_types.TLS_ENDPOINT) ->
           Netsys_types.memory -> int -> int -> int

Same for a memory-backed buffer

    val send : (module Netsys_crypto_types.TLS_ENDPOINT) ->
           Stdlib.Bytes.t -> int -> int -> int

`send endpoint buffer pos len`: Sends data via `endpoint`, and takes the emitted bytes from `buffer` at byte position `pos`. At most `len` bytes can be sent. Returns the actually sent number of bytes.

If the TLS protocol is not yet at the stage where data can be received, the protocol is proceeded until this point (i.e. `handshake` is "included"). Also, renegotiation alerts are interpreted. Both phenomenons can cause that data needs to be received as well as sent.

If interrupted the function can be safely invoked again.

May raise `Netsys_types.EAGAIN_RD`, `Netsys_types.EAGAIN_WR`, `Unix_error(EINTR,_,_)`, and `Error`.

    val mem_send : (module Netsys_crypto_types.TLS_ENDPOINT) ->
           Netsys_types.memory -> int -> int -> int

Same for a memory-backed buffer

    val str_send : (module Netsys_crypto_types.TLS_ENDPOINT) -> string -> int -> int -> int

Same for immutable string

    val shutdown : (module Netsys_crypto_types.TLS_ENDPOINT) -> Unix.shutdown_command -> unit

Ends the TLS encapsulation of data:

- `SHUTDOWN_SEND`: The payload stream is closed for sending.
- `SHUTDOWN_ALL`: The payload stream is closed for sending and receiving.

The mode `SHUTDOWN_RECEIVE` is unsupported and silently ignored.

The function does not shut down or close the underlying file descriptors.

If interrupted the function can be safely invoked again.

May raise `Netsys_types.EAGAIN_RD`, `Netsys_types.EAGAIN_WR`, `Unix_error(EINTR,_,_)`, and `Error`.

    val at_transport_eof : (module Netsys_crypto_types.TLS_ENDPOINT) -> bool

Whether the underlying transport channel has seen the end of input. Use this after `recv` or `mem_recv` returned 0 to check whether only the TLS enf-of-input message has been read, or the underlying channel (usually the file descriptor) has indicated EOF.

    module Debug: sig .. end