%%% Copyright (c) 2014-2015, NORDUnet A/S. %%% See LICENSE for licensing information. -module(x509). -export([normalise_chain/2, cert_string/1, read_pemfiles_from_dir/1, self_signed/1, detox/2]). -include_lib("public_key/include/public_key.hrl"). -include_lib("eunit/include/eunit.hrl"). -import(lists, [nth/2, filter/2]). -type reason() :: {chain_too_long | root_unknown | signature_mismatch | encoding_invalid}. -define(MAX_CHAIN_LENGTH, 10). -define(LEAF_POISON_OID, {1,3,6,1,4,1,11129,2,4,3}). -define(LEAF_POISON_VAL, [5,0]). -define(CA_POISON_OID, {1,3,6,1,4,1,11129,2,4,4}). -spec normalise_chain([binary()], [binary()]) -> {ok, [binary()]} | {error, reason()}. normalise_chain(AcceptableRootCerts, CertChain) -> case normalise_chain(AcceptableRootCerts, CertChain, ?MAX_CHAIN_LENGTH) of {false, Reason} -> {error, Reason}; {true, Root} -> {ok, CertChain ++ Root} end. -spec cert_string(binary()) -> string(). cert_string(Der) -> mochihex:to_hex(crypto:hash(sha, Der)). -spec read_pemfiles_from_dir(file:filename()) -> [binary()]. %% @doc Reading certificates from files. Flattening the result -- all %% certs in all files are returned in a single list. read_pemfiles_from_dir(Dir) -> case file:list_dir(Dir) of {error, enoent} -> lager:error("directory does not exist: ~p", [Dir]), []; {error, Reason} -> lager:error("unable to read directory ~p: ~p", [Dir, Reason]), []; {ok, Filenames} -> Files = lists:filter( fun(F) -> string:equal(".pem", filename:extension(F)) end, Filenames), ders_from_pemfiles(Dir, Files) end. -spec self_signed([binary()]) -> [binary()]. %% @doc Return a list of certs in L that are self signed. self_signed(L) -> lists:filter(fun(Cert) -> signed_by_p(Cert, Cert) end, L). -spec detox(binary(), [binary()]) -> {binary(), binary()}. %% @doc Return a detoxed LeafDer and its issuer. detox(LeafDer, ChainDer) -> detox_precert(LeafDer, nth(1, ChainDer), nth(2, ChainDer)). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Private functions. -spec normalise_chain([binary()], [binary()], integer()) -> {false, reason()} | {true, [binary()]}. %% @doc Verify that the leaf cert or precert has a valid chain back to %% an acceptable root cert. The order of certificates in the second %% argument is: leaf cert in head, chain in tail. Order of first %% argument is irrelevant. %% %% Return {false, Reason} or {true, ListWithRoot}. Note that %% ListWithRoot allways contain exactly one element -- a CA cert from %% first argument (AcceptableRootCerts) signing the root of the %% chain. FIXME: Any point in returning this as a list? normalise_chain(_, _, MaxChainLength) when MaxChainLength =< 0 -> %% Chain too long. {false, chain_too_long}; normalise_chain(AcceptableRootCerts, [TopCert], MaxChainLength) -> %% Check root of chain. case lists:member(TopCert, AcceptableRootCerts) of true -> %% Top cert is part of chain. {true, [TopCert]}; false when MaxChainLength =< 1 -> %% Chain too long. {false, chain_too_long}; false -> %% Top cert _might_ be signed by a cert in truststore. case signer(TopCert, AcceptableRootCerts) of notfound -> {false, root_unknown}; Root -> {true, [Root]} end end; normalise_chain(AcceptableRootCerts, [BottomCert|Rest], MaxChainLength) -> case signed_by_p(BottomCert, hd(Rest)) of true -> normalise_chain(AcceptableRootCerts, Rest, MaxChainLength - 1); false -> {false, signature_mismatch} end. -spec signer(binary(), [binary()]) -> notfound | binary(). %% @doc Return first cert in list signing Cert, or notfound. NOTE: %% This is potentially expensive. It'd be more efficient to search for %% Cert.issuer in a list of Issuer.subject's. If so, maybe make the %% matching somewhat fuzzy unless that too is expensive. signer(_Cert, []) -> notfound; signer(Cert, [H|T]) -> case signed_by_p(Cert, H) of true -> H; false -> signer(Cert, T) end. -spec encoded_tbs_cert(binary()) -> binary(). %% Code from pubkey_cert:encoded_tbs_cert/1. encoded_tbs_cert(DerCert) -> {ok, PKIXCert} = 'OTP-PUB-KEY':decode_TBSCert_exclusive(DerCert), {'Certificate', {'Certificate_tbsCertificate', EncodedTBSCert}, _, _} = PKIXCert, EncodedTBSCert. -spec decode_cert(binary()) -> #'Certificate'{} | error. decode_cert(Der) -> case (catch public_key:pkix_decode_cert(Der, plain)) of #'Certificate'{} = Cert -> Cert; {'EXIT', Reason} -> lager:info("invalid certificate: ~p: ~p", [cert_string(Der), Reason]), dump_unparsable_cert(Der), error; Unknown -> lager:info("unknown error decoding cert: ~p: ~p", [cert_string(Der), Unknown]), error end. parsable_cert_p(Der) -> case decode_cert(Der) of error -> false; _ -> true end. %% @doc Is Cert signed by Issuer? Only verify that the signature %% matches and don't check things like Cert.issuer == Issuer.subject. -spec signed_by_p(binary(), binary()) -> boolean(). signed_by_p(SubjectDer, IssuerDer) -> SubjectCert = decode_cert(SubjectDer), IssuerCert = decode_cert(IssuerDer), case {SubjectCert, IssuerCert} of {#'Certificate'{}, #'Certificate'{tbsCertificate = #'TBSCertificate'{subjectPublicKeyInfo = IssuerSPKI}}} -> %% Dig out digest, digest type and signature from subject cert and %% verify signature. case extract_verify_data(decode_cert(SubjectDer), SubjectDer) of error -> false; {ok, SubjectData} -> verify_sig(IssuerSPKI, SubjectData) end; _ -> false end. verify_sig(IssuerSPKI, {DigestOrPlainText, DigestType, Signature}) -> %% Dig out alg, params and key from issuer. #'SubjectPublicKeyInfo'{ algorithm = #'AlgorithmIdentifier'{algorithm = Alg, parameters = Params}, subjectPublicKey = {0, Key0}} = IssuerSPKI, KeyType = pubkey_cert_records:supportedPublicKeyAlgorithms(Alg), IssuerKey = case KeyType of 'RSAPublicKey' -> public_key:der_decode(KeyType, Key0); 'ECPoint' -> Point = #'ECPoint'{point = Key0}, ECParams = public_key:der_decode('EcpkParameters', Params), {Point, ECParams}; _ -> % FIXME: 'DSAPublicKey' lager:error("NIY: Issuer key type ~p", [KeyType]), false end, %% Verify the signature. public_key:verify(DigestOrPlainText, DigestType, Signature, IssuerKey). -spec extract_verify_data(#'Certificate'{}, binary()) -> {ok, tuple()} | error. %% @doc Return DER encoded TBScertificate, digest type and signature. %% Code from pubkey_cert:extract_verify_data/2. extract_verify_data(Cert, DerCert) -> PlainText = encoded_tbs_cert(DerCert), {_, Sig} = Cert#'Certificate'.signature, SigAlgRecord = Cert#'Certificate'.signatureAlgorithm, SigAlg = SigAlgRecord#'AlgorithmIdentifier'.algorithm, try {DigestType, _} = public_key:pkix_sign_types(SigAlg), {ok, {PlainText, DigestType, Sig}} catch error:function_clause -> lager:debug("~p: signature algorithm not supported: ~p", [cert_string(DerCert), SigAlg]), error end. %% Precerts according to RFC6962. %% %% Submitted precerts have a special critical poison extension -- OID %% 1.3.6.1.4.1.11129.2.4.3, whose extnValue OCTET STRING contains %% ASN.1 NULL data (0x05 0x00). %% %% They are signed with either the CA cert that will sign the final %% cert or a Precertificate Signing Certificate directly signed by the %% CA cert that will sign the final cert. A Precertificate Signing %% Certificate has CA:true and Extended Key Usage: Certificate %% Transparency, OID 1.3.6.1.4.1.11129.2.4.4. %% %% PreCert in SignedCertificateTimestamp does _not_ contain the poison %% extension, nor does it have an issuer which is a Precertificate %% Signing Certificate. This means that we have to 1) remove the %% poison extension and 2) potentially change issuer and Authority Key %% Identifier. See RFC6962 Section 3.2. %% %% Changes in draft-ietf-trans-rfc6962-bis-??: TODO. -spec detox_precert(binary(), binary(), binary()) -> {binary(), binary()}. %% @doc Return {DetoxedLeaf, IssuerPubKeyHash} where i) DetoxedLeaf is %% the tbsCertificate w/o poison and adjusted issuer and authkeyid; %% and ii) IssuerPubKeyHash is the hash over issuing cert's public %% key. detox_precert(LeafDer, ParentDer, GrandParentDer) -> Leaf = public_key:pkix_decode_cert(LeafDer, plain), Parent = public_key:pkix_decode_cert(ParentDer, plain), GrandParent = public_key:pkix_decode_cert(GrandParentDer, plain), DetoxedLeafTBS = remove_poison_ext(Leaf), %% If parent is a precert signing cert, change issuer and %% potential authority key id to refer to grandparent. {C, IssuerKeyHash} = case is_precert_signer(Parent) of true -> {set_issuer_and_authkeyid(DetoxedLeafTBS, Parent), extract_pub_key(GrandParent)}; false -> {DetoxedLeafTBS, extract_pub_key(Parent)} end, {public_key:pkix_encode('TBSCertificate', C, plain), crypto:hash(sha256, public_key:pkix_encode( 'SubjectPublicKeyInfo', IssuerKeyHash, plain))}. -spec extract_pub_key(#'Certificate'{}) -> #'SubjectPublicKeyInfo'{}. extract_pub_key(#'Certificate'{ tbsCertificate = #'TBSCertificate'{ subjectPublicKeyInfo = SPKI}}) -> SPKI. -spec set_issuer_and_authkeyid(#'TBSCertificate'{}, #'Certificate'{}) -> #'TBSCertificate'{}. %% @doc Return Cert with issuer and AuthorityKeyIdentifier from Parent. set_issuer_and_authkeyid(TBSCert, #'Certificate'{ tbsCertificate = #'TBSCertificate'{ issuer = ParentIssuer, extensions = ParentExtensions}}) -> case pubkey_cert:select_extension(?'id-ce-authorityKeyIdentifier', ParentExtensions) of undefined -> lager:debug("setting issuer only", []), TBSCert#'TBSCertificate'{issuer = ParentIssuer}; ParentAuthKeyExt -> NewExtensions = lists:map( fun(E) -> case E of #'Extension'{extnID = ?'id-ce-authorityKeyIdentifier'} -> lager:debug("swapping auth key id to ~p", [ParentAuthKeyExt]), ParentAuthKeyExt; _ -> E end end, TBSCert#'TBSCertificate'.extensions), lager:debug("setting issuer and auth key id", []), TBSCert#'TBSCertificate'{issuer = ParentIssuer, extensions = NewExtensions} end. -spec is_precert_signer(#'Certificate'{}) -> boolean(). is_precert_signer(#'Certificate'{tbsCertificate = TBSCert}) -> Extensions = pubkey_cert:extensions_list(TBSCert#'TBSCertificate'.extensions), %% NOTE: It's OK to look at only the first extension found since %% "A certificate MUST NOT include more than one instance of a %% particular extension." --RFC5280 Sect 4.2 case pubkey_cert:select_extension(?'id-ce-extKeyUsage', Extensions) of #'Extension'{extnValue = Val} -> case 'OTP-PUB-KEY':decode('ExtKeyUsageSyntax', Val) of %% NOTE: We require that the poisoned OID is the %% _only_ extkeyusage present. RFC6962 Sect 3.1 is not %% really clear. {ok, [?CA_POISON_OID]} -> is_ca(TBSCert); _ -> false end; _ -> false end. -spec is_ca(#'TBSCertificate'{}) -> boolean(). is_ca(#'TBSCertificate'{extensions = Extensions}) -> case pubkey_cert:select_extension(?'id-ce-basicConstraints', Extensions) of #'Extension'{critical = true, extnValue = Val} -> case 'OTP-PUB-KEY':decode('BasicConstraints', Val) of {ok, {'BasicConstraints', true, _}} -> true; _ -> false end; _ -> false end. -spec remove_poison_ext(#'Certificate'{}) -> #'TBSCertificate'{}. remove_poison_ext(#'Certificate'{tbsCertificate = TBSCert}) -> Extensions = filter(fun(E) -> not poisoned_leaf_p(E) end, pubkey_cert:extensions_list(TBSCert#'TBSCertificate'.extensions)), TBSCert#'TBSCertificate'{extensions = Extensions}. -spec poisoned_leaf_p(binary()) -> boolean(). poisoned_leaf_p(#'Extension'{extnID = ?LEAF_POISON_OID, critical = true, extnValue = ?LEAF_POISON_VAL}) -> true; poisoned_leaf_p(_) -> false. %%%% PEM files. -spec ders_from_pemfiles(string(), [string()]) -> [binary()]. ders_from_pemfiles(Dir, Filenames) -> lists:flatten( [ders_from_pemfile(filename:join(Dir, X)) || X <- Filenames]). -spec ders_from_pemfile(string()) -> [binary()]. ders_from_pemfile(Filename) -> lager:debug("reading PEM from ~s", [Filename]), PemBins = pems_from_file(Filename), Pems = case (catch public_key:pem_decode(PemBins)) of {'EXIT', Reason} -> lager:info("~p: invalid PEM-encoding: ~p", [Filename, Reason]), []; P -> P end, [der_from_pem(X) || X <- Pems]. -spec der_from_pem(binary()) -> binary(). der_from_pem(Pem) -> case Pem of {_Type, Der, not_encrypted} -> case parsable_cert_p(Der) of true -> Der; false -> dump_unparsable_cert(Der), [] end; Fail -> lager:info("ignoring PEM-encoded data: ~p~n", [Fail]), [] end. -spec pems_from_file(file:filename()) -> binary(). pems_from_file(Filename) -> {ok, Pems} = file:read_file(Filename), Pems. -spec dump_unparsable_cert(binary()) -> ok | {error, atom()} | not_logged. dump_unparsable_cert(Der) -> case application:get_env(catlfish, rejected_certs_path) of {ok, Directory} -> {NowMegaSec, NowSec, NowMicroSec} = now(), Filename = filename:join(Directory, io_lib:format("~p:~p.~p", [cert_string(Der), NowMegaSec * 1000 * 1000 + NowSec, NowMicroSec])), lager:info("dumping cert to ~p~n", [Filename]), file:write_file(Filename, Der); _ -> not_logged end. %%%%%%%%%%%%%%%%%%%% %% Testing private functions. -include("x509_test.hrl"). sign_test_() -> {setup, fun() -> ok end, fun(_) -> ok end, fun(_) -> [?_assertMatch(true, signed_by_p(?C0, ?C1))] end}. valid_cert_test_() -> {setup, fun() -> {read_pemfiles_from_dir("test/testdata/known_roots"), read_certs("test/testdata/chains")} end, fun(_) -> ok end, fun({KnownRoots, Chains}) -> [ %% Self-signed but verified against itself so pass. %% Note that this certificate is rejected by the %% stricter OTP-PKIX.asn1 specification generating %% #'OTPCertificate'{}. The error is %% {invalid_choice_tag,{22,<<"US">>}}}} in %% 'OTP-PUB-KEY':Func('OTP-X520countryname', Value0). ?_assertMatch({true, _}, normalise_chain(nth(1, Chains), nth(1, Chains), 10)), %% Self-signed so fail. ?_assertMatch({false, root_unknown}, normalise_chain(KnownRoots, nth(2, Chains), 10)), %% Leaf signed by known CA, pass. ?_assertMatch({true, _}, normalise_chain(KnownRoots, nth(3, Chains), 10)), %% Proper 3-depth chain with root in KnownRoots, pass. %% Bug CATLFISH-19 --> [info] rejecting "3ee62cb678014c14d22ebf96f44cc899adea72f1": chain_broken %% leaf sha1: 3ee62cb678014c14d22ebf96f44cc899adea72f1 %% leaf Subject: C=KR, O=Government of Korea, OU=Group of Server, OU=\xEA\xB5\x90\xEC\x9C\xA1\xEA\xB3\xBC\xED\x95\x99\xEA\xB8\xB0\xEC\x88\xA0\xEB\xB6\x80, CN=www.berea.ac.kr, CN=haksa.bits.ac.kr ?_assertMatch({true, _}, normalise_chain(KnownRoots, nth(4, Chains), 3)), %% Verify against self, pass. %% Bug CATLFISH-??, can't handle issuer keytype ECPoint. %% Issuer sha1: 6969562e4080f424a1e7199f14baf3ee58ab6abb ?_assertMatch(true, signed_by_p(hd(nth(5, Chains)), hd(nth(5, Chains)))), %% Unsupported signature algorithm MD2-RSA, fail. %% Signature Algorithm: md2WithRSAEncryption %% CA cert with sha1 96974cd6b663a7184526b1d648ad815cf51e801a ?_assertMatch(false, signed_by_p(hd(nth(6, Chains)), hd(nth(6, Chains)))), %% Supposedly problematic chains from Google Aviator, fatal. %% 00459972: asn1: syntax error: sequence truncated ?_assertMatch({true, _}, normalise_chain(nth(7, Chains), nth(7, Chains), 10)), %% 1402673: x509: RSA modulus is not a positive number ?_assertMatch({true, _}, normalise_chain(nth(8, Chains), nth(8, Chains), 10)), %% 1345105: asn1: syntax error: IA5String contains invalid character ?_assertMatch({true, _}, normalise_chain(nth(9, Chains), nth(9, Chains), 10)), %% 1557693: asn1: structure error: integer too large ?_assertMatch({true, _}, normalise_chain(nth(10, Chains), nth(10, Chains), 10)), %% Supposedly problematic chains from Google Aviator, non-fatal. %% 16800: x509: negative serial number %% a.pem ?_assertMatch({true, _}, normalise_chain(nth(11, Chains), nth(11, Chains), 10)), %% 22487: x509: unhandled critical extension ([2 5 29 32]) %% b.pem ?_assertMatch({true, _}, normalise_chain(nth(12, Chains), nth(12, Chains), 10)), %% 5198: x509: certificate contained IP address of length 8 %% c.pem ?_assertMatch({true, _}, normalise_chain(nth(13, Chains), nth(13, Chains), 10)) ] end}. chain_test_() -> {setup, fun() -> {?C0, ?C1} end, fun(_) -> ok end, fun({C0, C1}) -> chain_test(C0, C1) end}. chain_test(C0, C1) -> [ %% Root not in chain but in trust store. ?_assertEqual({true, [C1]}, normalise_chain([C1], [C0], 10)), ?_assertEqual({true, [C1]}, normalise_chain([C1], [C0], 2)), %% Chain too long. ?_assertMatch({false, chain_too_long}, normalise_chain([C1], [C0], 1)), %% Root in chain and in trust store. ?_assertEqual({true, [C1]}, normalise_chain([C1], [C0, C1], 2)), %% Chain too long. ?_assertMatch({false, chain_too_long}, normalise_chain([C1], [C0, C1], 1)), %% Root not in trust store. ?_assertMatch({false, root_unknown}, normalise_chain([], [C0, C1], 10)), %% Selfsigned. Actually OK. ?_assertMatch({true, [C0]}, normalise_chain([C0], [C0], 10)), ?_assertMatch({true, [C0]}, normalise_chain([C0], [C0], 1)), %% Max chain length 0 is not OK. ?_assertMatch({false, chain_too_long}, normalise_chain([C0], [C0], 0)) ]. %%-spec read_certs(file:filename()) -> [string:string()]. -spec read_certs(file:filename()) -> [[binary()]]. read_certs(Dir) -> {ok, Fnames} = file:list_dir(Dir), PemBins = [Pems || {ok, Pems} <- [file:read_file(filename:join(Dir, F)) || F <- lists:sort( lists:filter( fun(FN) -> string:equal( ".pem", filename:extension(FN)) end, Fnames))]], PemEntries = [public_key:pem_decode(P) || P <- PemBins], lists:map(fun(L) -> [Der || {'Certificate', Der, not_encrypted} <- L] end, PemEntries).