Module Netmech_scram

module Netmech_scram: sig .. end

SCRAM mechanism for authentication (RFC 5802)

This implements SCRAM-SHA-1 for GSSAPI. Other profiles may be added later.

As we do not implement SASLprep, usernames and passwords are restricted to US-ASCII.

type ptype = [ `GSSAPI ]

Currently only the variant for `GSSAPI is supported

type mechanism = [ `SHA_1 ]

type profile = {

`ptype : ptype;`
`mechanism : mechanism;`	`(*`	Which mechanism	`*)`
`return_unknown_user : bool;`	`(*`	Whether servers exhibit the fact that the user is unknown	`*)`
`iteration_count_limit : int;`	`(*`	Largest supported iteration number	`*)`

}

Profile

type server_error = [ `Channel_binding_not_supported
       | `Channel_bindings_dont_match
       | `Extension of string
       | `Extensions_not_supported
       | `Invalid_encoding
       | `Invalid_proof
       | `Invalid_username_encoding
       | `No_resources
       | `Other_error
       | `Server_does_support_channel_binding
       | `Unknown_user
       | `Unsupported_channel_binding_type ]

Error codes of this protocol

type client_session

Session context for clients

type server_session

Session context for servers

exception Invalid_encoding of string * string

Raised by clients when something cannot be decoded. First string is an error message, the second string the raw message that cannot be decoded

exception Invalid_username_encoding of string * string

Raised by clients when the username does not match the requirements. Arguments as for Invalid_encoding.

exception Extensions_not_supported of string * string

Raised by clients when the server enables an unsupported extension. Arguments as for Invalid_encoding.

exception Protocol_error of string

Raised by clients when the server violates the protocol. The argument is a message.

exception Invalid_server_signature

Raised by clients when the signature sent by the server is invalid (i.e. the server does not know the client password)

exception Server_error of server_error

Raised by clients when the server sent an error code

val profile : ?return_unknown_user:bool ->
       ?iteration_count_limit:int -> ptype -> profile

Creates a profile

val string_of_server_error : server_error -> string

val server_error_of_string : string -> server_error

Conversion

Clients

The idea is to create a client session s first. The functions client_emit_flag and client_recv_flag indicate now whether the client needs to emit a new message, or whether it needs to receive a message, respectively. Emission is done by client_emit_message, reception by client_recv_message. If everything goes well, the protocol state advances, and finally client_finish_flag is true. This indicates that the client is authenticated and that the server knows the client's password. If an error occurs, an exception is raised (see above for possibilities), and client_error_flag signals true.

val create_client_session : profile -> string -> string -> client_session

create_client_session p username password: Creates a new client session for profile p so that the client authenticates as user username, and proves its identify with the given password.

val client_configure_channel_binding : client_session -> string -> unit

Instruct the client to require a channel binding. The passed string is the c parameter (before encoding it via Base64. The function needs to be called before sending the second message to the server. It fails if called too late.

val client_emit_flag : client_session -> bool

Whether client_emit_message can now be called

val client_recv_flag : client_session -> bool

Whether client_recv_message can now be called

val client_finish_flag : client_session -> bool

Whether the client is authenticated and the server verified

val client_error_flag : client_session -> bool

Whether an error occurred, and the protocol cannot advance anymore

val client_channel_binding : client_session -> string

Returns the channel binding ("" of none)

val client_emit_message : client_session -> string

Emits the next message to be sent to the server

val client_recv_message : client_session -> string -> unit

Receives the next message from the server

val client_protocol_key : client_session -> string option

The 128-bit protocol key for encrypting messages. This is available as soon as the second client message is emitted.

val client_user_name : client_session -> string

The user name

val client_export : client_session -> string

val client_import : string -> client_session

Exports a client session as string, and imports the string again. Only established sessions are allowed to be exported (for which client_finish_flag is true).

The export format is just a marshalled Ocaml value.

Servers

The idea is to create a server session s first. The functions server_emit_flag and server_recv_flag indicate now whether the server needs to emit a new message, or whether it needs to receive a message, respectively. Emission is done by server_emit_message, reception by server_recv_message. If everything goes well, the protocol state advances, and finally server_finish_flag is true. This indicates that the client could be authenticated.

If an error occurs, no exception is raised, and the protocol advances nevertheless, and finally the server sends an error token to the client. After this, server_error_flag returns true.

val create_server_session : profile ->
       (string -> string * string * int) -> server_session

create_server_session p auth: Creates a new server session with profile p and authenticator function auth.

The function is auth is called when the credentials of the client have been received to check whether the client can be authenticated. It is called as

      let (salted_password, salt, iteration_count) = auth username

where username is the user name. The function can now raise Not_found if the user is unknown, or it can return the shown triple. Note that the cleartext password needs not to be known. salt is a random string, and iteration_count a security parameter that should be at least 4096. Whereas salt should be different for each user, the iteration_count can be chosen as a constant (e.g. 4096). Now salted_password can be computed from the cleartext password and these two extra parameters. See salt_password below.

val create_salt : unit -> string

Creates a random string suited as salt

val salt_password : string -> string -> int -> string

let salted_password = salt_password password salt iteration_count

As we do not implement SASLprep only passwords consisting of US-ASCII characters are accepted (Invalid_encoding otherwise).

val server_emit_flag : server_session -> bool

Whether server_emit_message can now be called

val server_recv_flag : server_session -> bool

Whether server_recv_message can now be called

val server_finish_flag : server_session -> bool

Whether the client is authenticated

val server_error_flag : server_session -> bool

Whether an error occurred, and the protocol cannot advance anymore

val server_emit_message : server_session -> string

Emits the next message to be sent to the client

val server_recv_message : server_session -> string -> unit

Receives the next message from the client

val server_protocol_key : server_session -> string option

The 128-bit protocol key for encrypting messages. This is available as soon as the second client message has been received.

val server_channel_binding : server_session -> string option

Returns the channel binding requirement (the "c" parameter). It is up to the application to enforce the binding. This information is available as soon as the second client message has been received

val server_user_name : server_session -> string option

The user name as transmitted from the client. This is returned here even before the authentication is completed!

val server_export : server_session -> string

val server_import : string -> server_session

Exports a server session as string, and imports the string again. Only established sessions are allowed to be exported (for which server_finish_flag is true).

The export format is just a marshalled Ocaml value.

Confidentiality

type specific_keys = {

	`kc : string;`
	`ke : string;`
	`ki : string;`

}

The specific keys to use

module AES_CTS: sig .. end

This module implements AES in Ciphertext Stealing mode (see RFC 3962)

module Cryptosystem: sig .. end

This is the cryptosystem as defined in RFC 3961, so far needed here.

module Debug: sig .. end

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