package tls

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Transport layer security

TLS is an implementation of transport layer security in OCaml. TLS is a widely used security protocol which establishes an end-to-end secure channel (with optional (mutual) authentication) between two endpoints. It uses TCP/IP as transport. This library supports all three versions of TLS: 1.2, RFC5246, 1.1, RFC4346, and 1.0, RFC2246. SSL, the previous protocol definition, is not supported.

TLS is algorithmically agile: protocol version, key exchange algorithm, symmetric cipher, and message authentication code are negotiated upon connection.

This library implements several extensions of TLS, AES ciphers, TLS extensions (such as server name indication, SNI), Renegotiation extension, Session Hash and Extended Master Secret Extension.

This library does not contain insecure cipher suites (such as single DES, export ciphers, ...). It does not expose the server time in the server random, requires secure renegotiation.

This library consists of a core, implemented in a purely functional matter (Engine, this module), and effectful parts: Tls_lwt and Tls_mirage.

v0.16.0

Abstract state type

type state

The abstract type of a TLS state.

Constructors

val client : Config.client -> state * Cstruct.t

client client is tls * out where tls is the initial state, and out the initial client hello

val server : Config.server -> state

server server is tls where tls is the initial server state

Protocol failures

type error = [
  1. | `AuthenticationFailure of X509.Validation.validation_error
  2. | `NoConfiguredCiphersuite of Ciphersuite.ciphersuite list
  3. | `NoConfiguredVersions of Core.tls_version list
  4. | `NoConfiguredSignatureAlgorithm of Core.signature_algorithm list
  5. | `NoMatchingCertificateFound of string
  6. | `NoCertificateConfigured
  7. | `CouldntSelectCertificate
]

failures which can be mitigated by reconfiguration

type client_hello_errors = [
  1. | `EmptyCiphersuites
  2. | `NotSetCiphersuites of Packet.any_ciphersuite list
  3. | `NoSupportedCiphersuite of Packet.any_ciphersuite list
  4. | `NotSetExtension of Core.client_extension list
  5. | `NoSignatureAlgorithmsExtension
  6. | `NoGoodSignatureAlgorithms of Core.signature_algorithm list
  7. | `NoKeyShareExtension
  8. | `NoSupportedGroupExtension
  9. | `NotSetSupportedGroup of Packet.named_group list
  10. | `NotSetKeyShare of (Packet.named_group * Cstruct.t) list
  11. | `NotSubsetKeyShareSupportedGroup of Packet.named_group list * (Packet.named_group * Cstruct.t) list
  12. | `Has0rttAfterHRR
  13. | `NoCookie
]
type fatal = [
  1. | `NoSecureRenegotiation
  2. | `NoSupportedGroup
  3. | `NoVersions of Core.tls_any_version list
  4. | `ReaderError of Reader.error
  5. | `NoCertificateReceived
  6. | `NoCertificateVerifyReceived
  7. | `NotRSACertificate
  8. | `KeyTooSmall
  9. | `SignatureVerificationFailed of string
  10. | `SigningFailed of string
  11. | `BadCertificateChain
  12. | `MACMismatch
  13. | `MACUnderflow
  14. | `RecordOverflow of int
  15. | `UnknownRecordVersion of int * int
  16. | `UnknownContentType of int
  17. | `CannotHandleApplicationDataYet
  18. | `NoHeartbeat
  19. | `BadRecordVersion of Core.tls_any_version
  20. | `BadFinished
  21. | `HandshakeFragmentsNotEmpty
  22. | `InsufficientDH
  23. | `InvalidDH
  24. | `BadECDH of Mirage_crypto_ec.error
  25. | `InvalidRenegotiation
  26. | `InvalidClientHello of client_hello_errors
  27. | `InvalidServerHello
  28. | `InvalidRenegotiationVersion of Core.tls_version
  29. | `InappropriateFallback
  30. | `UnexpectedCCS
  31. | `UnexpectedHandshake of Core.tls_handshake
  32. | `InvalidCertificateUsage
  33. | `InvalidCertificateExtendedUsage
  34. | `InvalidSession
  35. | `NoApplicationProtocol
  36. | `HelloRetryRequest
  37. | `InvalidMessage
  38. | `Toomany0rttbytes
  39. | `MissingContentType
  40. | `Downgrade12
  41. | `Downgrade11
]

failures from received garbage or lack of features

type failure = [
  1. | `Error of error
  2. | `Fatal of fatal
]

type of failures

val sexp_of_failure : failure -> Sexplib0.Sexp.t
val alert_of_failure : failure -> Packet.alert_type

alert_of_failure failure is alert, the TLS alert type for this failure.

val string_of_failure : failure -> string

string_of_failure failure is string, the string representation of the failure.

Protocol handling

type ret = ([ `Ok of state | `Eof | `Alert of Packet.alert_type ] * [ `Response of Cstruct.t option ] * [ `Data of Cstruct.t option ], failure * [ `Response of Cstruct.t ]) Stdlib.result

result type of handle_tls: either failed to handle the incoming buffer (`Fail) with failure and potentially a message to send to the other endpoint, or sucessful operation (`Ok) with a new state, an end of file (`Eof), or an incoming (`Alert). Possibly some `Response to the other endpoint is needed, and potentially some `Data for the application was received.

val handle_tls : state -> Cstruct.t -> ret

handle_tls state buffer is ret, depending on incoming state and buffer, the result is the appropriate ret

val can_handle_appdata : state -> bool

can_handle_appdata state is a predicate which indicates when the connection has already completed a handshake.

val handshake_in_progress : state -> bool

handshake_in_progrss state is a predicate which indicates whether there is a handshake in progress or scheduled.

val send_application_data : state -> Cstruct.t list -> (state * Cstruct.t) option

send_application_data tls outs is (tls' * out) option where tls' is the new tls state, and out the cstruct to send over the wire (encrypted outs).

val send_close_notify : state -> state * Cstruct.t

send_close_notify tls is tls' * out where tls' is the new tls state, and out the (possible encrypted) close notify alert.

val reneg : ?authenticator:X509.Authenticator.t -> ?acceptable_cas:X509.Distinguished_name.t list -> ?cert:Config.own_cert -> state -> (state * Cstruct.t) option

reneg ~authenticator ~acceptable_cas ~cert tls initiates a renegotation on tls, using the provided authenticator. It is tls' * out where tls' is the new tls state, and out either a client hello or hello request (depending on which communication endpoint tls is).

val key_update : ?request:bool -> state -> (state * Cstruct.t, failure) Stdlib.result

key_update ~request state initiates a KeyUpdate (TLS 1.3 only). If request is provided and true (the default), the KeyUpdate message contains a request that the peer should update their traffic key as well.

Session information

type epoch = [
  1. | `InitialEpoch
  2. | `Epoch of Core.epoch_data
]

polymorphic variant of session information. The first variant `InitialEpoch will only be used for TLS states without completed handshake. The second variant, `Epoch, contains actual session data.

val sexp_of_epoch : epoch -> Sexplib0.Sexp.t
val epoch : state -> epoch

epoch state is epoch, which contains the session information.