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{-# LANGUAGE OverloadedStrings, ViewPatterns #-}
module TLSA
( TLSA(..)
, CertUsage(..)
, Selector(..)
, MatchingType(..)
, fromByteString
, toByteString
, match
, IssuanceTest(..)
, validate
) 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(..), SignedCertificate, getCertificate
, getSigned, getSignedData, signedObject, objectToSignedExact
, SignatureALG(SignatureALG_Unknown), SignedExact
, encodeSignedObject, decodeSignedObject ) -}
import Data.ASN1.Types ( toASN1, ASN1Object, fromASN1 )
import Data.ASN1.Encoding ( encodeASN1, decodeASN1 )
import Data.Time.Clock.POSIX ( posixSecondsToUTCTime )
import Data.ASN1.BinaryEncoding
import Control.Applicative
import Data.Word
import Data.Maybe
import Data.List
import Data.Monoid
import Data.Array.IArray
{- 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.
--
-- It is used by the 'validate' function in making a 'Validation' decision.
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 -> SignedCertificate -> Bool
match tlsa cert = fromMaybe False $
(== associationData tlsa) <$> (hash <*> material)
where
key = encodeASN1 DER $ toASN1 keyobj []
where keyobj = certPubKey $ getCertificate cert
encoded_cert = L.fromChunks [encodeSignedObject cert]
material :: Maybe L.ByteString
material =
case selector tlsa of
FullCertificate -> Just encoded_cert
SubjectPublicKeyInfo -> Just key
_ -> Nothing
hash :: Maybe (L.ByteString -> BS.ByteString)
hash =
case matchingType tlsa of
Match_Exact -> Just L.toStrict
Match_SHA256 -> Just SHA256.hashlazy
Match_SHA512 -> Just SHA512.hashlazy
_ -> Nothing
unsigned :: (Show a, ASN1Object a, Eq a) => a -> SignedExact a
unsigned obj = fst $ objectToSignedExact fakeSign obj
where fakeSign = const $ ("", SignatureALG_Unknown [], ())
{-
data Validation
= Failed [TLSA]
-- ^ All of the given constraints failed.
| TrustAnchors [SignedCertificate] [SignedCertificate]
-- ^ Perform PKI validation with the given additional trust anchors. The
-- first list are trust anchors that occured in the chain. The second list
-- are anchors that did not occur in the chain. If 'certVersion' == (-1)
-- for any certificate in the second list, then all fields except
-- 'certPubKey' should be ignored.
| Passed
-- ^ Valid end entity. Do not perform PKI.
-}
-- comb [1,2,3] = [([],[1,2,3]),([1],[2,3]),([2,1],[3])]
comb :: [x] -> [([x],[x])]
comb cs = matchLength cs $ iterate sweepLeft ([],cs)
where sweepLeft (xs,y:ys) = (y:xs,ys)
matchLength = zipWith (flip const)
-- O(n²) worst case
-- O(n) best case
-- op is an antisymmetric operation
connectedChain op x [] = [x]
connectedChain op x xs =
case filter ((x `op`) . snd) $ comb xs of
[] -> [x]
(as,y:bs):_ -> x : connectedChain op y (bs++as)
allChains :: (a -> a -> Bool) -> a -> [a] -> [[a]]
allChains op x [] = [[x]]
allChains op x xs | null ts = [[x]]
| otherwise = ts >>= f
where
ts = filter ((x `op`) . head . snd) $ comb xs
f (as,y:bs) = map (x:) $ allChains op y (as++bs)
-- | These functions are used by 'validate' to determine when a certificate is
-- validly issued by another.
data IssuanceTest = IssuanceTest
{ isIssuedBy :: SignedCertificate -> SignedCertificate -> Bool
-- ^ This is used to validate a single link in a certificate chain.
, isSignedBy :: SignedCertificate -> PubKey -> Bool
-- ^ This is used to check signatures for trust anchor keys that are
-- supplied via a 'TLSA' record but not otherwise present in the chain.
}
-- | Use the the given set of 'TLSA' records to validate or paritally validate
-- a certificate given a list of other probably relevent certificates. Results
-- are interpreted as follows:
--
-- [@ Nothing @] The certificate PASSED validation.
--
-- [@ Just \[\] @] The certificate FAILED validation.
--
-- [@ Just xss @] A set of certificate issued-by chains. If you trust any
-- certificate in any of these chains, you may consider the
-- certificate validated. Otherwise, it failed validation.
--
validate :: IssuanceTest -> [TLSA] -> SignedCertificate -> [SignedCertificate]
-> Maybe [[SignedCertificate]]
validate (IssuanceTest isIssuedBy isSignedBy) rs cert chain
| domainIssued = Nothing
| any hasAnchor chains = Nothing
| null rs = Just $ (certv !) .: chains
| otherwise = Just $ (certv !) .: filter satisfiesConstraints chains
where
domainIssued = any (`match` cert) daneEEs
threshold = length chain
len = threshold + length anchor_certs
certv :: Array Int SignedCertificate
certv = listArray (0,len) $ cert:chain ++ anchor_certs
(.:) = fmap . fmap
a .<+ b = (certv ! a) `isIssuedBy` (certv ! b)
a .<- b = (certv ! a) `isSignedBy` b
isAnchor n = or [ n > threshold
, n `elem` anchors
, any (n .<-) anchor_keys ]
chains = allChains (.<+) 0 [1..len]
hasAnchor = any isAnchor
( anchor_certs, anchor_keys, anchors )
= ( mapMaybe rightToMaybe absent
, mapMaybe leftToMaybe absent
, fmap fst $ ns >>= snd )
where
(bs,ns) = partition (null . snd)
$ pairings (\r (_,c) -> match r c) daneTAs
$ zip [0..] (cert:chain)
absent = mapMaybe (certOrKey . fst) bs
rightToMaybe (Right x) = Just x
rightToMaybe _ = Nothing
leftToMaybe (Left x) = Just x
leftToMaybe _ = Nothing
satisfiesConstraints (c:cs) = any eeSatisfied pkixEEs
|| any caSatisfied pkixTAs
where
eeSatisfied = (`match` (certv ! c))
caSatisfied r = any ((r `match`) . (certv !)) cs
r .~ u = certUsage r == u
(daneEEs,rs2) = partition (.~ DomainIssued) rs
(daneTAs,rs3) = partition (.~ TrustAnchorAssertion) rs2
(pkixEEs,rs4) = partition (.~ ServiceCertificateConstraint) rs3
(pkixTAs,_) = partition (.~ CAConstraint) rs4
pairings :: (a -> b -> Bool) -> [a] -> [b] -> [(a,[b])]
pairings op = loop
where
loop [] cs = []
loop (m:ms) cs =
case filter (op m . head . snd) $ comb cs of
[] -> (m,[]):loop ms cs
(as,b:bs):_ -> (m,[b]):loop ms (as++bs)
{-
validate :: [TLSA] -> SignedCertificate -> [SignedCertificate] -> Validation
validate rs cert chain
| some domainIssued = Passed
| null constraints || some passed = TrustAnchors anchors absent
| otherwise = Failed constraints
where
domainIssued = filter (`match` cert) daneEEs
(bs,ns) = partition (null . snd) $ pairings match daneTAs (cert:chain)
anchors = concatMap snd ns
absent = mapMaybe (extractCert . fst) bs
constraints = pkixEEs ++ pkixTAs
passed = passedEEs ++ passedTAs
where
passedEEs = filter (`match` cert) pkixEEs
-- TODO
-- These passedTAs are only truly passed if the
-- certs that match them are reachable.
-- Where a cert is "reachable" if it is the end entity
-- cert or if it is the issuer of a reachable cert.
passedTAs = filter (`matchAny` (cert:chain)) pkixTAs
matchAny t = any (t `match`)
some = not . null
r .~ u = certUsage r == u
(daneEEs,rs2) = partition (.~ DomainIssued) rs
(daneTAs,rs3) = partition (.~ TrustAnchorAssertion) rs2
(pkixEEs,rs4) = partition (.~ ServiceCertificateConstraint) rs3
(pkixTAs,_) = partition (.~ CAConstraint) rs4
-}
certOrKey :: TLSA -> Maybe (Either PubKey SignedCertificate)
certOrKey tlsa@(matchingType->Match_Exact) =
case selector tlsa of
FullCertificate -> either (const Nothing)
(Just . Right)
(decodeSignedObject $ associationData tlsa)
SubjectPublicKeyInfo -> do
a <- hush $ decodeASN1 DER $ L.fromChunks [associationData tlsa]
(key,_) <- hush $ fromASN1 a
return $ Left key
where
hush (Left _) = Nothing
hush (Right a) = Just a
extractCert :: TLSA -> Maybe SignedCertificate
extractCert tlsa@(matchingType->Match_Exact) =
case selector tlsa of
FullCertificate -> either (const Nothing)
Just
(decodeSignedObject $ associationData tlsa)
SubjectPublicKeyInfo -> do
a <- hush $ decodeASN1 DER $ L.fromChunks [associationData tlsa]
(key,_) <- hush $ fromASN1 a
return $ certificateFromKey key
where
hush (Left _) = Nothing
hush (Right a) = Just a
extractCert _ = Nothing
certificateFromKey :: PubKey -> SignedCertificate
certificateFromKey key = unsigned cert
where
cert = Certificate { certPubKey = key
, certVersion = (-1)
, certSerial = 0
, certSignatureAlg = SignatureALG_Unknown []
, certIssuerDN = DistinguishedName []
, certValidity = ( posixSecondsToUTCTime (-1/0)
, posixSecondsToUTCTime (1/0))
, certSubjectDN = DistinguishedName []
, certExtensions = Extensions Nothing
}
|