api: Add preliminary SCEP support

.gitignore

@@ -64,3 +64,7 @@ node_modules/
 # Ignore autogenerated files
 certidude/static/js/nunjucks*
 certidude/static/js/templates.js
+
+# Ignore patch
+*.orig
+*.rej

certidude/api/__init__.py

@@ -210,6 +210,11 @@ def certidude_app(log_handlers=[]):
     # Bootstrap resource
     app.add_route("/api/bootstrap/", BootstrapResource())
 
+    # Add SCEP handler if we have any whitelisted subnets
+    if config.SCEP_SUBNETS:
+        from .scep import SCEPResource
+        app.add_route("/api/scep/", SCEPResource())
+
     # Add sink for serving static files
     app.add_sink(StaticResource(os.path.join(__file__, "..", "..", "static")))
 

certidude/api/scep.py

@@ -0,0 +1,273 @@
+from __future__ import unicode_literals, division, absolute_import, print_function
+import click
+import hashlib
+import os
+from asn1crypto import cms, algos, x509
+from asn1crypto.core import ObjectIdentifier, SetOf, PrintableString
+from base64 import b64decode, b64encode
+from certbuilder import pem_armor_certificate
+from certidude import authority, push, config
+from certidude.firewall import whitelist_subnets
+from oscrypto import keys, asymmetric, symmetric
+from oscrypto.errors import SignatureError
+
+# Monkey patch asn1crypto
+
+class SetOfPrintableString(SetOf):
+    _child_spec = PrintableString
+
+cms.CMSAttributeType._map['2.16.840.1.113733.1.9.2'] = "message_type"
+cms.CMSAttributeType._map['2.16.840.1.113733.1.9.3'] = "pki_status"
+cms.CMSAttributeType._map['2.16.840.1.113733.1.9.4'] = "fail_info"
+cms.CMSAttributeType._map['2.16.840.1.113733.1.9.5'] = "sender_nonce"
+cms.CMSAttributeType._map['2.16.840.1.113733.1.9.6'] = "recipient_nonce"
+cms.CMSAttributeType._map['2.16.840.1.113733.1.9.7'] = "trans_id"
+
+cms.CMSAttribute._oid_specs['message_type'] = SetOfPrintableString
+cms.CMSAttribute._oid_specs['pki_status'] = SetOfPrintableString
+cms.CMSAttribute._oid_specs['fail_info'] = SetOfPrintableString
+cms.CMSAttribute._oid_specs['sender_nonce'] = cms.SetOfOctetString
+cms.CMSAttribute._oid_specs['recipient_nonce'] = cms.SetOfOctetString
+cms.CMSAttribute._oid_specs['trans_id'] = SetOfPrintableString
+
+class SCEPError(Exception): code = 25 # system failure
+class SCEPBadAlg(SCEPError): code = 0
+class SCEPBadMessageCheck(SCEPError): code = 1
+class SCEPBadRequest(SCEPError): code = 2
+class SCEPBadTime(SCEPError): code = 3
+class SCEPBadCertId(SCEPError): code = 4
+
+class SCEPResource(object):
+    @whitelist_subnets(config.SCEP_SUBNETS)
+    def on_get(self, req, resp):
+        operation = req.get_param("operation")
+        if operation.lower() == "getcacert":
+            resp.stream = keys.parse_certificate(authority.ca_buf).dump()
+            resp.append_header("Content-Type", "application/x-x509-ca-cert")
+            return
+
+        # Parse CA certificate
+        fh = open(config.AUTHORITY_CERTIFICATE_PATH)
+        server_certificate = asymmetric.load_certificate(fh.read())
+        fh.close()
+
+        # If we bump into exceptions later
+        encrypted_container = b""
+        attr_list = [
+            cms.CMSAttribute({
+                'type': "message_type",
+                'values': ["3"]
+            }),
+            cms.CMSAttribute({
+                'type': "pki_status",
+                'values': ["2"] # rejected
+            })
+        ]
+
+        try:
+            info = cms.ContentInfo.load(b64decode(req.get_param("message", required=True)))
+
+            ###############################################
+            ### Verify signature of the outer container ###
+            ###############################################
+
+            signed_envelope = info['content']
+            encap_content_info = signed_envelope['encap_content_info']
+            encap_content = encap_content_info['content']
+
+            # TODO: try except
+            current_certificate, = signed_envelope["certificates"]
+            signer, = signed_envelope["signer_infos"]
+
+            # TODO: compare cert to current one if we are renewing
+
+            assert signer["digest_algorithm"]["algorithm"].native == "md5"
+            assert signer["signature_algorithm"]["algorithm"].native == "rsassa_pkcs1v15"
+            message_digest = None
+            transaction_id = None
+            sender_nonce = None
+
+            for attr in signer["signed_attrs"]:
+                if attr["type"].native == "sender_nonce":
+                    sender_nonce, = attr["values"]
+                elif attr["type"].native == "trans_id":
+                    transaction_id, = attr["values"]
+                elif attr["type"].native == "message_digest":
+                    message_digest, = attr["values"]
+                    if hashlib.md5(encap_content.native).digest() != message_digest.native:
+                        raise SCEPBadMessageCheck()
+
+            assert message_digest
+            msg = signer["signed_attrs"].dump(force=True)
+            assert msg[0] == b"\xa0", repr(msg[0])
+
+            # Verify signature
+            try:
+                asymmetric.rsa_pkcs1v15_verify(
+                    asymmetric.load_certificate(current_certificate.dump()),
+                    signer["signature"].native,
+                    b"\x31" + msg[1:], # wtf?!
+                    "md5")
+            except SignatureError:
+                raise SCEPBadMessageCheck()
+
+            ###############################
+            ### Decrypt inner container ###
+            ###############################
+
+            info = cms.ContentInfo.load(encap_content.native)
+            encrypted_envelope = info['content']
+            encrypted_content_info = encrypted_envelope['encrypted_content_info']
+            iv = encrypted_content_info['content_encryption_algorithm']['parameters'].native
+
+            if encrypted_content_info['content_encryption_algorithm']["algorithm"].native != "des":
+                raise SCEPBadAlgo()
+
+            encrypted_content = encrypted_content_info['encrypted_content'].native
+            recipient, = encrypted_envelope['recipient_infos']
+
+            if recipient.native["rid"]["serial_number"] != authority.ca_cert.serial:
+                raise SCEPBadCertId()
+
+            # Since CA private key is not directly readable here, we'll redirect it to signer socket
+            key = b64decode(authority.signer_exec("decrypt-pkcs7", b64encode(recipient.native["encrypted_key"])))
+            if len(key) == 8: key = key * 3 # Convert DES to 3DES
+            buf = symmetric.tripledes_cbc_pkcs5_decrypt(key, encrypted_content, iv)
+            _, common_name = authority.store_request(buf, overwrite=True)
+            cert, buf = authority.sign(common_name, overwrite=True)
+            signed_certificate = asymmetric.load_certificate(buf)
+            content = signed_certificate.asn1.dump()
+
+        except SCEPError, e:
+            attr_list.append(cms.CMSAttribute({
+                'type': "fail_info",
+                'values': ["%d" % e.code]
+            }))
+        else:
+
+            ##################################
+            ### Degenerate inner container ###
+            ##################################
+
+            degenerate = cms.ContentInfo({
+                'content_type': 'signed_data',
+                'content': cms.SignedData({
+                    'version': 'v1',
+                    'certificates': [signed_certificate.asn1],
+                    'digest_algorithms': [cms.DigestAlgorithm({
+                        'algorithm':'md5'
+                    })],
+                    'encap_content_info': {
+                        'content_type': 'data',
+                        'content':  cms.ContentInfo({
+                            'content_type': 'signed_data',
+                            'content': None
+                        }).dump()
+                    },
+                    'signer_infos': []
+                })
+            })
+
+
+            ################################
+            ### Encrypt middle container ###
+            ################################
+
+            key = os.urandom(8)
+            iv, encrypted_content = symmetric.des_cbc_pkcs5_encrypt(key, degenerate.dump(), os.urandom(8))
+            assert degenerate.dump() == symmetric.tripledes_cbc_pkcs5_decrypt(key*3, encrypted_content, iv)
+
+            ri = cms.RecipientInfo({
+                'ktri': cms.KeyTransRecipientInfo({
+                    'version': 'v0',
+                    'rid': cms.RecipientIdentifier({
+                        'issuer_and_serial_number': cms.IssuerAndSerialNumber({
+                            'issuer': current_certificate.chosen["tbs_certificate"]["issuer"],
+                            'serial_number': current_certificate.chosen["tbs_certificate"]["serial_number"],
+                        }),
+                    }),
+                    'key_encryption_algorithm': {
+                        'algorithm': 'rsa'
+                    },
+                    'encrypted_key': asymmetric.rsa_pkcs1v15_encrypt(
+                        asymmetric.load_certificate(current_certificate.chosen.dump()), key)
+                })
+            })
+
+            encrypted_container = cms.ContentInfo({
+                'content_type': 'enveloped_data',
+                'content': cms.EnvelopedData({
+                    'version': 'v1',
+                    'recipient_infos': [ri],
+                    'encrypted_content_info': {
+                        'content_type': 'data',
+                        'content_encryption_algorithm': {
+                            'algorithm': 'des',
+                            'parameters': iv
+                        },
+                        'encrypted_content': encrypted_content
+                    }
+                })
+            }).dump()
+
+            attr_list = [
+                cms.CMSAttribute({
+                    'type': 'message_digest',
+                    'values': [hashlib.sha1(encrypted_container).digest()]
+                }),
+                cms.CMSAttribute({
+                    'type': "message_type",
+                    'values': ["3"]
+                }),
+                cms.CMSAttribute({
+                    'type': "pki_status",
+                    'values': ["0"] # ok
+                })
+            ]
+        finally:
+
+            ##############################
+            ### Signed outer container ###
+            ##############################
+
+            attrs = cms.CMSAttributes(attr_list + [
+                cms.CMSAttribute({
+                    'type': "recipient_nonce",
+                    'values': [sender_nonce]
+                }),
+                cms.CMSAttribute({
+                    'type': 'trans_id',
+                    'values': [transaction_id]
+                })
+            ])
+
+            signer = cms.SignerInfo({
+                "signed_attrs": attrs,
+                'version':'v1',
+                'sid': cms.SignerIdentifier({
+                    'issuer_and_serial_number': cms.IssuerAndSerialNumber({
+                        'issuer': server_certificate.asn1["tbs_certificate"]["issuer"],
+                        'serial_number': server_certificate.asn1["tbs_certificate"]["serial_number"],
+                    }),
+                }),
+                'digest_algorithm': algos.DigestAlgorithm({'algorithm': 'sha1'}),
+                'signature_algorithm': algos.SignedDigestAlgorithm({'algorithm': 'rsassa_pkcs1v15'}),
+                'signature': b64decode(authority.signer_exec("sign-pkcs7", b64encode(b"\x31" + attrs.dump()[1:])))
+            })
+
+            resp.append_header("Content-Type", "application/x-pki-message")
+            resp.body = cms.ContentInfo({
+                'content_type': 'signed_data',
+                'content': cms.SignedData({
+                    'version': 'v1',
+                    'certificates': [x509.Certificate.load(server_certificate.asn1.dump())], # wat
+                    'digest_algorithms': [cms.DigestAlgorithm({
+                        'algorithm':'sha1'
+                    })],
+                    'encap_content_info': {
+                        'content_type': 'data',
+                        'content': encrypted_container
+                    },
+                    'signer_infos': [signer]
+                })
+            }).dump()

certidude/authority.py

@@ -12,6 +12,7 @@ from cryptography import x509
 from cryptography.x509.oid import NameOID, ExtensionOID, ExtendedKeyUsageOID
 from cryptography.hazmat.primitives.asymmetric import rsa
 from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives.serialization import Encoding
 from certidude import config, push, mailer, const
 from certidude import errors
 from jinja2 import Template
@@ -81,7 +82,13 @@ def store_request(buf, overwrite=False):
     if not buf:
         raise ValueError("No signing request supplied")
 
+    if isinstance(buf, unicode):
         csr = x509.load_pem_x509_csr(buf, backend=default_backend())
+    elif isinstance(buf, str):
+        csr = x509.load_der_x509_csr(buf, backend=default_backend())
+        buf = csr.public_bytes(Encoding.PEM)
+    else:
+        raise ValueError("Invalid type, expected str for PEM and bytes for DER")
     common_name, = csr.subject.get_attributes_for_oid(NameOID.COMMON_NAME)
     # TODO: validate common name again
 
@@ -92,7 +99,7 @@ def store_request(buf, overwrite=False):
 
 
     # If there is cert, check if it's the same
-    if os.path.exists(request_path):
+    if os.path.exists(request_path) and not overwrite:
         if open(request_path).read() == buf:
             raise errors.RequestExists("Request already exists")
         else:
@@ -106,7 +113,7 @@ def store_request(buf, overwrite=False):
     mailer.send("request-stored.md",
         attachments=(attach_csr,),
         common_name=common_name.value)
-    return csr
+    return csr, common_name.value
 
 
 def signer_exec(cmd, *bits):

certidude/config.py

@@ -32,6 +32,8 @@ AUTOSIGN_SUBNETS = set([ipaddress.ip_network(j) for j in
     cp.get("authorization", "autosign subnets").split(" ") if j])
 REQUEST_SUBNETS = set([ipaddress.ip_network(j) for j in
     cp.get("authorization", "request subnets").split(" ") if j]).union(AUTOSIGN_SUBNETS)
+SCEP_SUBNETS = set([ipaddress.ip_network(j) for j in
+    cp.get("authorization", "scep subnets").split(" ") if j])
 
 AUTHORITY_DIR = "/var/lib/certidude"
 AUTHORITY_PRIVATE_KEY_PATH = cp.get("authority", "private key path")

certidude/signer.py

@@ -5,11 +5,13 @@ import socket
 import os
 import asyncore
 import asynchat
+from base64 import b64decode, b64encode
 from certidude import const, config
 from cryptography import x509
 from cryptography.hazmat.backends import default_backend
-from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives import hashes, padding, serialization
 from cryptography.hazmat.primitives.serialization import Encoding
+from cryptography.hazmat.primitives.asymmetric import padding
 from datetime import datetime, timedelta
 from cryptography.x509.oid import NameOID, ExtendedKeyUsageOID, AuthorityInformationAccessOID
 import random
@@ -64,6 +66,18 @@ class SignHandler(asynchat.async_chat):
             self.close()
             raise asyncore.ExitNow()
 
+        elif cmd == "sign-pkcs7":
+            signer = self.server.private_key.signer(
+                padding.PKCS1v15(),
+                hashes.SHA1()
+            )
+            signer.update(b64decode(body))
+            self.send(b64encode(signer.finalize()))
+
+        elif cmd == "decrypt-pkcs7":
+            self.send(b64encode(self.server.private_key.decrypt(b64decode(body), padding.PKCS1v15())))
+            self.close()
+
         elif cmd == "sign-request":
             # Only common name and public key are used from request
             request = x509.load_pem_x509_csr(body, default_backend())

certidude/templates/server/server.conf

@@ -56,6 +56,9 @@ request subnets = 0.0.0.0/0
 # Certificates are automatically signed for these subnets
 autosign subnets = 127.0.0.0/8 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
 
+# Simple Certificate Enrollment Protocol enabled subnets
+scep subnets =
+
 [logging]
 # Disable logging
 ;backend =