Tested mbedtls to see how other code bases handle thus. mbedtls rejects the EvilCA certificate when connecting to openssl s_server (as opposed to openssl c_client -verify that accepts the connection). Verify requested for (Depth 1): cert. version : 3 serial number : 10:00 issuer name : C=SE, ST=Root, L=Root, O=Root, OU=Root, CN=Root subject name : C=SE, ST=EvilCA, L=EvilCA, O=EvilCA, OU=EvilCA, CN=EvilCA issued on : 2018-10-08 08:20:21 expires on : 2028-10-05 08:20:21 signed using : RSA with SHA-256 RSA key size : 4096 bits basic constraints : CA=true, max_pathlen=0 key usage : Key Cert Sign, CRL Sign ! The certificate is not correctly signed by the trusted CA The handshake fails after this error, mbedtls_ssl_handshake returned -9984. On Mon, Oct 8, 2018 at 2:51 PM Peter Magnusson <blaufish.public.email@xxxxxxxxx> wrote: > > sorry, typo on the verify line, this was what I should have written: > VERIFY(max_path_length>0) error upon preparing transition from i=2 > (EvilCA) to i=2 (EvilServer). > On Mon, Oct 8, 2018 at 2:47 PM Peter Magnusson > <blaufish.public.email@xxxxxxxxx> wrote: > > > > That is not correct behaviour as far as I can understand. > > > > RFC5280 Certification Path Validation algorithm process from root to > > leaf, i.e. (Root, EvilCA, EvilServer). 6.1.2 Initialization and 6.1.4 > > Preparation for Certificate i+1 is expected to occur upon Root > > certificate, i.e. the following should be expected behaviour: > > * max_path_length=n (initialisation) > > * max_path_length=n-1 (first decrement) > > * max_path_length=0 (copied from root certificate constraint) > > * VERIFY(max_path_length>0) error upon preparing transition from i=1 > > (Root) to i=2 (EvilCA). > > > > OpenSSL does everything in a slightly different reverse algorithm, but > > should perform the same controls and behaivor as the RFC imho. > > > > And aside from the RFC algorithm checking for this condition, it is > > also analog with the description of the expected behaviour: > > > > The pathLenConstraint field is meaningful only if the cA boolean is > > asserted and the key usage extension, if present, asserts the > > keyCertSign bit (Section 4.2.1.3). In this case, it gives the > > maximum number of non-self-issued intermediate certificates that may > > follow this certificate in a valid certification path. (Note: The > > last certificate in the certification path is not an intermediate > > certificate, and is not included in this limit. Usually, the last > > certificate is an end entity certificate, but it can be a CA > > certificate.) A pathLenConstraint of zero indicates that no non- > > self-issued intermediate CA certificates may follow in a valid > > certification path. Where it appears, the pathLenConstraint field > > MUST be greater than or equal to zero. Where pathLenConstraint does > > not appear, no limit is imposed. > > > > So my understanding is that the OpenSSL algorithm is confused and > > fails to perform a check that is applicable to self-issued > > certificates. The decrement of max_path_length (aka plen++ in OpenSSL > > implementation) should not occur for self issued certificates, but the > > validation of max_path_length>0 (aka plen>(constraint+1)) should > > occur. > > On Mon, Oct 8, 2018 at 1:27 PM J Decker <d3ck0r@xxxxxxxxx> wrote: > > > > > > It was my interpretation that 0 pathlen on the root self signed meant infinite. > > > The pathlen only applies on the certs between root and the leaf (which obviously can be 0, and CA true or not, but bad form to say true I'd imagine.) > > > > > > On Mon, Oct 8, 2018 at 1:57 AM Peter Magnusson <blaufish.public.email@xxxxxxxxx> wrote: > > >> > > >> One more logic confusion in the OpenSSL Path Length Constraint check. > > >> Any Path Length Constraint set by Root (or any other Self-Issued > > >> Certificate) is ignored. > > >> Root cause appears to be !(x->ex_flags & EXFLAG_SI)=0 incorrectly > > >> applied to the checker (i.e. the checker and the calculation logic > > >> have been mixed up). > > >> > > >> https://github.com/blaufish/openssl-pathlen/tree/master/testcase_2 > > >> > > >> openssl x509 -text -in root.pem | grep -a1 "X509v3 Basic" > > >> Certificate Sign, CRL Sign > > >> X509v3 Basic Constraints: critical > > >> CA:TRUE, pathlen:0 > > >> openssl x509 -text -in evilca.pem | grep -a1 "X509v3 Basic" > > >> Certificate Sign, CRL Sign > > >> X509v3 Basic Constraints: critical > > >> CA:TRUE, pathlen:0 > > >> openssl x509 -text -in evilserver.pem | grep -a1 "X509v3 Basic" > > >> X509v3 extensions: > > >> X509v3 Basic Constraints: critical > > >> CA:FALSE > > >> ---- > > >> openssl x509 -text -in root.pem | egrep -a1 "X509v3 .* Key Identifier" > > >> X509v3 extensions: > > >> X509v3 Subject Key Identifier: > > >> 49:39:72:82:78:39:E8:60:AD:17:79:83:DB:65:B8:5C:E6:A7:84:B5 > > >> -- > > >> -- > > >> 49:39:72:82:78:39:E8:60:AD:17:79:83:DB:65:B8:5C:E6:A7:84:B5 > > >> X509v3 Authority Key Identifier: > > >> > > >> keyid:49:39:72:82:78:39:E8:60:AD:17:79:83:DB:65:B8:5C:E6:A7:84:B5 > > >> openssl x509 -text -in evilca.pem | grep -a1 "X509v3 .* Key Identifier" > > >> X509v3 extensions: > > >> X509v3 Subject Key Identifier: > > >> B6:B4:75:66:18:B5:D2:4F:57:10:53:93:4F:CD:51:71:A4:27:84:7C > > >> -- > > >> -- > > >> B6:B4:75:66:18:B5:D2:4F:57:10:53:93:4F:CD:51:71:A4:27:84:7C > > >> X509v3 Authority Key Identifier: > > >> > > >> keyid:49:39:72:82:78:39:E8:60:AD:17:79:83:DB:65:B8:5C:E6:A7:84:B5 > > >> openssl x509 -text -in evilserver.pem | egrep -a1 "X509v3 .* Key Identifier" > > >> TLS Web Server Authentication > > >> X509v3 Subject Key Identifier: > > >> 03:C6:48:91:09:73:F5:DF:EF:B5:9D:A4:66:00:16:C3:E9:DB:99:EE > > >> -- > > >> -- > > >> 03:C6:48:91:09:73:F5:DF:EF:B5:9D:A4:66:00:16:C3:E9:DB:99:EE > > >> X509v3 Authority Key Identifier: > > >> > > >> keyid:B6:B4:75:66:18:B5:D2:4F:57:10:53:93:4F:CD:51:71:A4:27:84:7C > > >> ---- > > >> ../openssl-1.1.1/apps/openssl verify -show_chain -verbose -CAfile > > >> root.pem -untrusted evilca.pem evilserver.pem > > >> ******* important variables ******* > > >> *** check_chain_extensions:524 i=0 > > >> *** check_chain_extensions:525 plen=0 > > >> *** check_chain_extensions:526 x->ex_pathlen=-1 > > >> ******* if statement components ******* > > >> *** check_chain_extensions:528 i > 1=0 > > >> *** check_chain_extensions:529 !(x->ex_flags & EXFLAG_SI)=1 > > >> *** check_chain_extensions:530 (x->ex_pathlen != -1)=0 > > >> *** check_chain_extensions:531 (plen > (x->ex_pathlen + > > >> proxy_path_length + 1))=0 > > >> ******* important variables ******* > > >> *** check_chain_extensions:524 i=1 > > >> *** check_chain_extensions:525 plen=1 > > >> *** check_chain_extensions:526 x->ex_pathlen=0 > > >> ******* if statement components ******* > > >> *** check_chain_extensions:528 i > 1=0 > > >> *** check_chain_extensions:529 !(x->ex_flags & EXFLAG_SI)=1 > > >> *** check_chain_extensions:530 (x->ex_pathlen != -1)=1 > > >> *** check_chain_extensions:531 (plen > (x->ex_pathlen + > > >> proxy_path_length + 1))=0 > > >> ******* important variables ******* > > >> *** check_chain_extensions:524 i=2 > > >> *** check_chain_extensions:525 plen=2 > > >> *** check_chain_extensions:526 x->ex_pathlen=0 > > >> ******* if statement components ******* > > >> *** check_chain_extensions:528 i > 1=1 > > >> *** check_chain_extensions:529 !(x->ex_flags & EXFLAG_SI)=0 > > >> *** check_chain_extensions:530 (x->ex_pathlen != -1)=1 > > >> *** check_chain_extensions:531 (plen > (x->ex_pathlen + > > >> proxy_path_length + 1))=1 > > >> evilserver.pem: OK > > >> Chain: > > >> depth=0: C = SE, ST = EvilServer, L = EvilServer, O = EvilServer, OU = > > >> EvilServer, CN = EvilServer (untrusted) > > >> depth=1: C = SE, ST = EvilCA, L = EvilCA, O = EvilCA, OU = EvilCA, CN > > >> = EvilCA (untrusted) > > >> depth=2: C = SE, ST = Root, L = Root, O = Root, OU = Root, CN = Root > > >> -- > > >> openssl-users mailing list > > >> To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-users > > > > > > -- > > > openssl-users 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