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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 = [
| `PKCS3_PEM_file of string
| `PKCS3_DER of string
| `Generate of int
]
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 = [
| `PEM_file of string
| `DER ofstring list
]
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 = [
| `PEM_file of string
| `DER ofstring list
]
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 = [
| `PEM_file of string
| `RSA of string
| `DSA of string
| `EC of string
| `PKCS8 of string
| `PKCS8_encrypted 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.
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.
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.
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.
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.
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.