Module Netgssapi

module Netgssapi: sig .. end

GSS-API Definition

This is mainly a translation of RFC 2743/2744 to Ocaml.

Types

type oid = int array

OIDs like "1.3.6.1.5.6.2" as array of int's. The empty array means GSS_C_NO_OID.

type oid_set = oid list

A set of OID's. These lists should not contain OID's twice. The empty list means GSS_C_NO_OID_SET.

type credential = < otype : [ `Credential ] >

A credential is opaque for the caller of the GSS-API. The provider of the GSS-API can emit new credential objects, and hand them out to the caller. When the caller passes credentials back to the provider, the provider must check whether the object is known, and reject any fake objects created by the caller by raising Invalid_argument.

type context = < otype : [ `Context ]; valid : bool >

A context is also opaque, and the same rules apply as for credential.

The method valid is true as long as the context is not deleted.

type token = string

Authentication tokens. These are also opaque to the caller, but have a string representation so that they can be sent over the wire.

type interprocess_token = string

Interprocess tokens. These are also opaque to the caller, but have a string representation so that they can be sent over the wire.

type calling_error = [ `Bad_structure | `Inaccessible_read | `Inaccessible_write | `None ]

Possible errors caused by the caller

type routine_error = [ `Bad_QOP
       | `Bad_bindings
       | `Bad_mech
       | `Bad_mic
       | `Bad_name
       | `Bad_nametype
       | `Bad_status
       | `Context_expired
       | `Credentials_expired
       | `Defective_credential
       | `Defective_token
       | `Duplicate_element
       | `Failure
       | `Name_not_mn
       | `No_context
       | `No_cred
       | `None
       | `Unauthorized
       | `Unavailable ]

Possible errors caused by the provider

type suppl_status = [ `Continue_needed
       | `Duplicate_token
       | `Gap_token
       | `Old_token
       | `Unseq_token ]

Further flags

type major_status = calling_error * routine_error *
       suppl_status list

The major status consists of these three elements. The bits of the supplementary status field are represented as list

type minor_status = int32

The minor status is provider-specific. Note that GSS-API defines it as unsigned 32-bit integer whereas int32 is signed.

type name = < otype : [ `Name ] >

A name is also opaque, and the same rules apply as for credential.

type address = [ `Inet of Unix.inet_addr
       | `Local of string
       | `Nulladdr
       | `Other of int32 * string
       | `Unspecified of string ]

Addresses tagged by address types

type channel_bindings = address * address * string

Channel binding as tuple (initiator_address, acceptor_address, application_data)

type cred_usage = [ `Accept | `Both | `Initiate ]

type qop = < otype : [ `QOP ] >

Quality-of-proctection parameters are mechanism-specific

type message = Xdr_mstring.mstring list

Messages are represented as lists of mstring

type ret_flag = [ `Anon_flag
       | `Conf_flag
       | `Deleg_flag
       | `Integ_flag
       | `Mutual_flag
       | `Prot_ready_flag
       | `Replay_flag
       | `Sequence_flag
       | `Trans_flag ]

Flags for the accept_sec_context method

type req_flag = [ `Anon_flag
       | `Conf_flag
       | `Deleg_flag
       | `Integ_flag
       | `Mutual_flag
       | `Replay_flag
       | `Sequence_flag ]

Flags for the init_sec_context method

Exceptions

There are no defined exceptions.

Errors should be reported using the major_status and minor_status codes as much as possible.

Invalid_argument may be raised for clear violations of calling requirements, e.g. when an opaque object is passed to this interface that was not returned by it before.

The API

The methods have generally a type of the form

 
       m : 't . arg1 -> ... -> argN -> out:( ret1 -> ... -> retM -> 't ) -> 't

where args are input arguments (with the exception of context which is in/out), and where outputs are passed back by calling the out functions with the outputs. The return value of out is the return value of the method call.

For example, if only output_token of the accept_sec_context method is needed, one could call this method as in

      let output_token =
	gss_api # accept_sec_context 
	   ... 
	   ~out:(fun ~src_name ~mech_type ~output_token ~ret_flags
		     ~time_rec ~delegated_cred_handle ~minor_status
		     ~major_status ->
		  output_token
		)

Output values may not be defined when major_status indicates an error. (But see the RFC for details; especially init_sec_contect and accept_sec_context may emit tokens even when major_status indicates an error.)

The names of the parameters are taken from RFC 2744, only suffixes like _handle have been removed. When the prefixes input_ and output_ are meaningless, they are also removed. All prefixes like "GSS" are removed anyway.

class type gss_api = object .. end

Utility functions

These functions convert values to strings. Useful for generating log messages.

val string_of_calling_error : calling_error -> string

val string_of_routine_error : routine_error -> string

val string_of_suppl_status : suppl_status -> string

val string_of_major_status : major_status -> string

Common OID's for name types

See RFC 2078, section 4

val nt_hostbased_service : oid

names like "service

val nt_user_name : oid

names like "username"

val nt_machine_uid_name : oid

user ID in host byte order

val nt_string_uid_name : oid

user ID as string of digits

val nt_anonymous : oid

anonymous name

val nt_export_name : oid

an export name

val parse_hostbased_service : string -> string * string

Returns (service,host) for "service

Encodings

There is some chance that some of these routines will finally be moved to netstring

val oid_to_string : oid -> string

val string_to_oid : string -> oid

Convert OID's to/from curly brace notation

val oid_to_der : oid -> string

val der_to_oid : string -> int Pervasives.ref -> oid

Convert OID's to/from DER. der_to_oid takes a cursor as second arg.

val wire_encode_token : oid -> token -> string

val wire_decode_token : string -> int Pervasives.ref -> oid * token

Encode tokens as described in section 3.1 of RFC 2078. This is usually only done for the initiating token.

val encode_exported_name : oid -> string -> string

val decode_exported_name : string -> int Pervasives.ref -> oid * string

Encode names as described in section 3.2 of RFC 2078

Create tokens

Format of the tokens: see RFC 4121

val create_mic_token : sent_by_acceptor:bool ->
       acceptor_subkey:bool ->
       sequence_number:int64 ->
       get_mic:(message -> string) -> message:message -> string

Create a MIC token:

sent_by_acceptor: whether this token comes from the acceptor
acceptor_subkey: see RFC
sequence_number: a sequence number
get_mic: the checksum function (e.g. Netmech_scram.Cryptosystem.get_mic)
message: the message to be signed

The function returns the MIC token

val parse_mic_token_header : string -> bool * bool * int64

Returns the triple (sent_by_acceptor, acceptor_subkey, sequence_number) from the header of a MIC token that is passed to this function as string. Fails if not parsable

val verify_mic_token : get_mic:(message -> string) ->
       message:message -> token:string -> bool

Verifies the MIC token with get_mic, and returns true if the verification is successful

val create_wrap_token_conf : sent_by_acceptor:bool ->
       acceptor_subkey:bool ->
       sequence_number:int64 ->
       get_ec:(int -> int) ->
       encrypt_and_sign:(message -> message) ->
       message:message -> message

Wraps a message so that it is encrypted and signed (confidential).

sent_by_acceptor: whether this token comes from the acceptor
acceptor_subkey: see RFC
sequence_number: a sequence number
get_ec: This function returns the "extra count" number for the size of the plaintext w/o filler (e.g. use Netmech_scram.Cryptosystem.get_ec).
encrypt_and_sign: the encryption function from the cryptosystem. The plaintext is passed to this function, and the ciphertext with the appended signature must be returned in the string.
message: the payload message

The function returns the token wrapping the message.

val parse_wrap_token_header : message -> bool * bool * bool * int64

let (sent_by_acceptor, sealed, acceptor_subkey, sequence_number) =
      parse_wrap_token_header token

Fails if the token cannot be parsed.

val unwrap_wrap_token_conf : decrypt_and_verify:(message -> message) ->
       token:message -> message

Unwraps the token using the decryption function decrypt_and_verify from the cryptosystem.

The functions fails if there is a format error, or the integrity check fails.

Non-confidential messages cannot be unwrapped with this function.

Token functions for non-confidential messages are still missing

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