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|
{-# LANGUAGE OverloadedStrings #-}
module TLSA
( TLSA(..)
, CertUsage(..)
, Selector(..)
, MatchingType(..)
, fromByteString
, toByteString
, match
) where
import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as L
import qualified Crypto.Hash.SHA256 as SHA256
import qualified Crypto.Hash.SHA512 as SHA512
import Data.X509 ( certPubKey, Certificate )
import Data.ASN1.Types ( toASN1 )
import Data.ASN1.Encoding ( encodeASN1 )
import Data.ASN1.BinaryEncoding
import Control.Applicative
import Data.Word
import Data.Maybe
import Data.Monoid
{- INLINE fromWord8 #-}
fromWord8 :: Enum a => Word8 -> a
fromWord8 = toEnum . fromEnum
{- INLINE toWord8 -}
toWord8 :: Enum a => a -> Word8
toWord8 = toEnum . fromEnum
-- | The Certificate Usage Field as described in RFC 6698, section 2.1.1.
data CertUsage
-- | This usage limits which CA can be used to issue certificates for a
-- given service on a host. PKIX-validated TLS connections for the domain
-- should be considered invalid if the certification path does not include
-- at least one certificate that 'match'es the 'TLSA' record.
= CAConstraint
-- | This usage limits which end entity certificate can be used by a given
-- service on a host. The TLS connection for the domain should be
-- considered invalid if the end entity certificate does not 'match' the
-- 'TLSA' record.
| ServiceCertificateConstraint
-- | This usage allows a domain name administrator to specify a new trust
-- anchor. This is useful if the domain issues its own certificates under
-- its own CA that is not expected to be in the end users' collection of
-- trust anchors. When conducting PKIX validation for the domain, any
-- certificate 'match'ing the 'TLSA' record can be treated as a trust
-- anchor that does not require further validation.
| TrustAnchorAssertion
-- | This usage allows for a domain name administrator to issue
-- certificates for a domain without involving a third-party CA. The end
-- entity certificate MUST 'match' the 'TLSA' record. Unlike for a
-- 'ServiceCertificateConstraint', PKIX validation should not be performed.
| DomainIssued
| CertUsage Word8
deriving (Eq, Ord, Show, Read)
instance Enum CertUsage where
fromEnum CAConstraint = 0
fromEnum ServiceCertificateConstraint = 1
fromEnum TrustAnchorAssertion = 2
fromEnum DomainIssued = 3
fromEnum (CertUsage n) = fromEnum n
toEnum 0 = CAConstraint
toEnum 1 = ServiceCertificateConstraint
toEnum 2 = TrustAnchorAssertion
toEnum 3 = DomainIssued
toEnum n = CertUsage (toEnum n)
-- | Indicates what sort of object should be compared with 'associationData'.
data Selector
= FullCertificate -- ^ x.509 certificate
| SubjectPublicKeyInfo -- ^ PKCS #8 formatted public key
| Selector Word8 -- ^ value 255 reserved for private use
deriving (Eq,Ord,Show)
instance Enum Selector where
fromEnum FullCertificate = 0
fromEnum SubjectPublicKeyInfo = 1
fromEnum (Selector n) = fromEnum n
toEnum 0 = FullCertificate
toEnum 1 = SubjectPublicKeyInfo
toEnum n = Selector (toEnum n)
-- | Is 'associationData' an object of the form specified by 'Selector' or is
-- it only a hash of it?
data MatchingType
= Match_Exact
| Match_SHA256
| Match_SHA512
| Match Word8 -- ^ value 255 is reserved for private use
deriving (Eq,Ord,Show)
instance Enum MatchingType where
fromEnum Match_Exact = 0
fromEnum Match_SHA256 = 1
fromEnum Match_SHA512 = 2
fromEnum (Match n) = fromEnum n
toEnum 0 = Match_Exact
toEnum 1 = Match_SHA256
toEnum 2 = Match_SHA512
toEnum n = Match (toEnum n)
-- | The parsed RDATA field of a TLSA DNS resource record (type 52) as
-- described in RFC 6698.
--
-- The 'match' function uses 'selector', 'matchingType' and 'associationData'
-- to implement a predicate on certificates obtained via the TLS protocol. The
-- 'certUsage' field indicates what that predicate means.
data TLSA = TLSA
{ certUsage :: CertUsage
, selector :: Selector
, matchingType :: MatchingType
, associationData :: BS.ByteString
}
deriving (Eq, Ord, Show)
-- | Parse RDATA for a TLSA resource record.
fromByteString :: BS.ByteString -> TLSA
fromByteString bs = TLSA (fromWord8 cu)
(fromWord8 sel)
(fromWord8 mat)
dta
where
(csm,dta) = BS.splitAt 3 bs
(cu,sel,mat) =
case BS.unpack csm of
[cu,sel,mat] -> (cu,sel,mat)
[cu,sel] -> (cu,sel,0)
[cu] -> (cu,0,0)
[] -> (0,0,0)
-- | Encode a valid RDATA field for a TLSA DNS record.
toByteString :: TLSA -> BS.ByteString
toByteString (TLSA cu sel mat dta) = csm <> dta
where
csm = BS.pack [ toWord8 cu
, toWord8 sel
, toWord8 mat ]
-- | Returns 'True' if the given certificate matches the given 'TLSA' object.
-- The algorithm for matching depends on the values of 'selector' and
-- 'matchingType' as described in RFC 6698.
match :: TLSA -> Certificate -> Bool
match tlsa cert = fromMaybe False $
(== associationData tlsa) <$> (hash <*> material)
where
encode obj = encodeASN1 DER (toASN1 obj [])
material =
case selector tlsa of
FullCertificate -> Just $ encode cert
SubjectPublicKeyInfo -> Just $ encode $ certPubKey cert
_ -> Nothing
hash =
case matchingType tlsa of
Match_Exact -> Just L.toStrict
Match_SHA256 -> Just SHA256.hashlazy
Match_SHA512 -> Just SHA512.hashlazy
_ -> Nothing
|
