diff options
Diffstat (limited to 'doc/arm/dnssec.inc.rst')
| -rw-r--r-- | doc/arm/dnssec.inc.rst | 520 |
1 files changed, 520 insertions, 0 deletions
diff --git a/doc/arm/dnssec.inc.rst b/doc/arm/dnssec.inc.rst new file mode 100644 index 0000000..c48bab1 --- /dev/null +++ b/doc/arm/dnssec.inc.rst @@ -0,0 +1,520 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec: + +DNSSEC +------ +DNS Security Extensions (DNSSEC) provide reliable protection from +`cache poisoning`_ attacks. At the same time these extensions also provide other benefits: +they limit the impact of `random subdomain attacks`_ on resolver caches and authoritative +servers, and provide the foundation for modern applications like `authenticated +and private e-mail transfer`_. + +To achieve this goal, DNSSEC adds `digital signatures`_ to DNS records in +authoritative DNS zones, and DNS resolvers verify the validity of the signatures on the +received records. If the signatures match the received data, the resolver can +be sure that the data was not modified in transit. + +.. note:: + DNSSEC and transport-level encryption are complementary! + Unlike typical transport-level encryption like DNS-over-TLS, DNS-over-HTTPS, + or VPN, DNSSEC makes DNS records verifiable at all points of the DNS + resolution chain. + +This section focuses on ways to deploy DNSSEC using BIND. For a more in-depth +discussion of DNSSEC principles (e.g. :ref:`how_does_dnssec_change_dns_lookup`) +please see :doc:`dnssec-guide`. + +.. _`cache poisoning`: https://en.wikipedia.org/wiki/DNS_cache_poisoning +.. _`random subdomain attacks`: https://www.isc.org/blogs/nsec-caching-should-limit-excessive-queries-to-dns-root/ +.. _`digital signatures`: https://en.wikipedia.org/wiki/Digital_signature +.. _`authenticated and private e-mail transfer`: https://github.com/internetstandards/toolbox-wiki/blob/main/DANE-for-SMTP-how-to.md + + +.. _dnssec_zone_signing: + +Zone Signing +~~~~~~~~~~~~ + +BIND offers several ways to generate signatures and maintain their validity +during the lifetime of a DNS zone: + + - :ref:`dnssec_kasp` - **strongly recommended** + - :ref:`dnssec_dynamic_zones` - only for special needs + - :ref:`dnssec_tools` - discouraged, use only for debugging + +.. _zone_keys: + +Zone keys +^^^^^^^^^ +Regardless of the :ref:`zone-signing <dnssec_zone_signing>` method in use, cryptographic keys are +stored in files named like :file:`Kdnssec.example.+013+12345.key` and +:file:`Kdnssec.example.+013+12345.private`. +The private key (in the ``.private`` file) is used to generate signatures, and +the public key (in the ``.key`` file) is used for signature verification. +Additionally, the :ref:`dnssec_kasp` method creates a third file, +:file:`Kdnssec.example+013+12345.state`, which is used to track DNSSEC key timings +and to perform key rollovers safely. + +These filenames contain: + + - the key name, which always matches the zone name (``dnssec.example.``), + - the `algorithm number`_ (013 is ECDSAP256SHA256, 008 is RSASHA256, etc.), + - and the key tag, i.e. a non-unique key identifier (12345 in this case). + +.. _`algorithm number`: https://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml#dns-sec-alg-numbers-1 + + +.. warning:: + Private keys are required for full disaster recovery. Back up key files in a + safe location and protect them from unauthorized access. Anyone with + access to the private key can create fake but seemingly valid DNS data. + + +.. _dnssec_kasp: + +Fully Automated (Key and Signing Policy) +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Key and Signing Policy (KASP) is a method of configuration that describes +how to maintain DNSSEC signing keys and how to sign the zone. + +This is the recommended, fully automated way to sign and maintain DNS zones. For +most use cases users can simply use the built-in default policy, which applies +up-to-date DNSSEC practices: + +.. code-block:: none + :emphasize-lines: 4 + + zone "dnssec.example" { + type primary; + file "dnssec.example.db"; + dnssec-policy default; + inline-signing yes; + }; + +The :any:`dnssec-policy` statement requires dynamic DNS to be set up, or +:any:`inline-signing` to be enabled. In the example above we use the latter. + +This is sufficient to create the necessary signing keys, and generate +``DNSKEY``, ``RRSIG``, and ``NSEC`` records for the zone. BIND also takes +care of any DNSSEC maintenance for this zone, including replacing signatures +that are about to expire and managing :ref:`key_rollovers`. + +.. note:: + :any:`dnssec-policy` needs write access to the zone. Please see + :any:`dnssec-policy` for more details about implications for zone storage. + +The default policy creates one key that is used to sign the complete zone, +and uses ``NSEC`` to enable authenticated denial of existence (a secure way +to tell which records do not exist in a zone). This policy is recommended +and typically does not need to be changed. + +If needed, a custom policy can be defined by adding a :any:`dnssec-policy` statement +into the configuration: + +.. code-block:: none + + + dnssec-policy "custom" { + dnskey-ttl 600; + keys { + ksk lifetime P1Y algorithm ecdsap384sha384; + zsk lifetime 60d algorithm ecdsap384sha384; + }; + nsec3param iterations 0 optout no salt-length 0; + }; + +This ``custom`` policy, for example: + + - uses a very short ``DNSKEY`` TTL (600 seconds), + - uses two keys to sign the zone: a Key Signing Key (KSK) to sign the key + related RRsets (``DNSKEY``, ``CDS``, and ``CDNSKEY``), and a Zone Signing + Key (ZSK) to sign the rest of the zone. The KSK is automatically + rotated after one year and the ZSK after 60 days. + +Also: + - The configured keys have a lifetime set and use the ECDSAP384SHA384 + algorithm. + - The last line instructs BIND to generate NSEC3 records for + :ref:`Proof of Non-Existence <advanced_discussions_proof_of_nonexistence>`, + using zero extra iterations and no salt. NSEC3 opt-out is disabled, meaning + insecure delegations also get an NSEC3 record. + +For more information about KASP configuration see :any:`dnssec-policy`. + +The :ref:`dnssec_advanced_discussions` section in the DNSSEC Guide discusses the +various policy settings and may be useful for determining values for specific +needs. + +Key Rollover +============ + +When using a :any:`dnssec-policy`, a key lifetime can be set to trigger +key rollovers. ZSK rollovers are fully automatic, but for KSK and CSK rollovers +a DS record needs to be submitted to the parent. See +:ref:`secure_delegation` for possible ways to do so. + +Once the DS is in the parent (and the DS of the predecessor key is withdrawn), +BIND needs to be told that this event has happened. This can be done automatically +by configuring parental agents: + +.. code-block:: none + :emphasize-lines: 5 + + zone "dnssec.example" { + type primary; + file "dnssec.example.db"; + dnssec-policy default; + inline-signing yes; + parental-agents { 192.0.2.1; }; + }; + +Here one server, ``192.0.2.1``, is configured for BIND to send DS queries to, +to check the DS RRset for ``dnssec-example`` during key rollovers. This needs +to be a trusted server, because BIND does not validate the response. + +If setting up a parental agent is undesirable, it is also possible to tell BIND that the +DS is published in the parent with: +:option:`rndc dnssec -checkds -key 12345 published dnssec.example. <rndc dnssec>`. +and the DS for the predecessor key has been removed with: +:option:`rndc dnssec -checkds -key 54321 withdrawn dnssec.example. <rndc dnssec>`. +where 12345 and 54321 are the key tags of the successor and predecessor key, +respectively. + +To roll a key sooner than scheduled, or to roll a key that +has an unlimited lifetime, use: +:option:`rndc dnssec -rollover -key 12345 dnssec.example. <rndc dnssec>`. + +To revert a signed zone back to an insecure zone, change +the zone configuration to use the built-in "insecure" policy. Detailed +instructions are described in :ref:`revert_to_unsigned`. + +.. _dnssec_dynamic_zones: + +Manual Key Management +^^^^^^^^^^^^^^^^^^^^^ + +.. warning:: + The method described here allows full control over the keys used to sign + the zone. This is required only for very special cases and is generally + discouraged. Under normal circumstances, please use :ref:`dnssec_kasp`. + + +.. _dnssec_dynamic_zones_multisigner_model: + +Multi-Signer Model +================== + +Dynamic zones provide the ability to sign a zone by multiple providers, meaning +each provider signs and serves the same zone independently. Such a setup requires +some coordination between providers when it comes to key rollovers, and may be +better suited to be configured with ``auto-dnssec allow;``. This permits keys to +be updated and the zone to be re-signed only if the user issues the command +:option:`rndc sign zonename <rndc sign>`. + +A zone can also be configured with ``auto-dnssec maintain``, which automatically +adjusts the zone's DNSSEC keys on a schedule according to the key timing +metadata. However, keys still need to be generated separately, for +example with :iscman:`dnssec-keygen`. + +Of course, dynamic zones can also use :any:`dnssec-policy` to fully automate DNSSEC +maintenance. The next sections assume that more key +management control is needed, and describe how to use dynamic DNS update to perform +various DNSSEC operations. + +.. _dnssec_dynamic_zones_enabling_dnssec: + +Enabling DNSSEC Manually +======================== +As an alternative to fully automated zone signing using :ref:`dnssec-policy +<dnssec_kasp>`, a zone can be changed from insecure to secure using a dynamic +DNS update. :iscman:`named` must be configured so that it can see the ``K*`` +files which contain the public and private parts of the `zone keys`_ that are +used to sign the zone. Key files should be placed in the :any:`key-directory`, as +specified in :iscman:`named.conf`: + +:: + + zone update.example { + type primary; + update-policy local; + auto-dnssec allow; + file "dynamic/update.example.db"; + key-directory "keys/update.example/"; + }; + +If there are both a KSK and a ZSK available (or a CSK), this configuration causes the +zone to be signed. An ``NSEC`` chain is generated as part of the initial signing +process. + +In any secure zone which supports dynamic updates, :iscman:`named` periodically +re-signs RRsets which have not been re-signed as a result of some update action. +The signature lifetimes are adjusted to spread the re-sign load over time rather +than all at once. + +.. _dnssec_dynamic_zones_publishing_dnskey_records: + +Publishing DNSKEY Records +========================= + +To insert the keys via dynamic update: + +:: + + % nsupdate + > ttl 3600 + > update add update.example DNSKEY 256 3 7 AwEAAZn17pUF0KpbPA2c7Gz76Vb18v0teKT3EyAGfBfL8eQ8al35zz3Y I1m/SAQBxIqMfLtIwqWPdgthsu36azGQAX8= + > update add update.example DNSKEY 257 3 7 AwEAAd/7odU/64o2LGsifbLtQmtO8dFDtTAZXSX2+X3e/UNlq9IHq3Y0 XtC0Iuawl/qkaKVxXe2lo8Ct+dM6UehyCqk= + > send + +In order to sign with these keys, the corresponding key files should also be +placed in the :any:`key-directory`. + +.. _dnssec_dynamic_zones_nsec3: + +NSEC3 +===== + +To sign using :ref:`NSEC3 <advanced_discussions_nsec3>` instead of :ref:`NSEC +<advanced_discussions_nsec>`, add an NSEC3PARAM record to the initial update +request. The :term:`OPTOUT <Opt-out>` bit in the NSEC3 +chain can be set in the flags field of the +NSEC3PARAM record. + +:: + + % nsupdate + > ttl 3600 + > update add update.example DNSKEY 256 3 7 AwEAAZn17pUF0KpbPA2c7Gz76Vb18v0teKT3EyAGfBfL8eQ8al35zz3Y I1m/SAQBxIqMfLtIwqWPdgthsu36azGQAX8= + > update add update.example DNSKEY 257 3 7 AwEAAd/7odU/64o2LGsifbLtQmtO8dFDtTAZXSX2+X3e/UNlq9IHq3Y0 XtC0Iuawl/qkaKVxXe2lo8Ct+dM6UehyCqk= + > update add update.example NSEC3PARAM 1 0 0 - + > send + +Note that the ``NSEC3PARAM`` record does not show up until :iscman:`named` has +had a chance to build/remove the relevant chain. A private type record is +created to record the state of the operation (see below for more details), and +is removed once the operation completes. + +The ``NSEC3`` chain is generated and the ``NSEC3PARAM`` record is added before +the ``NSEC`` chain is destroyed. + +While the initial signing and ``NSEC``/``NSEC3`` chain generation are occurring, +other updates are possible as well. + +A new ``NSEC3PARAM`` record can be added via dynamic update. When the new +``NSEC3`` chain has been generated, the ``NSEC3PARAM`` flag field is set to +zero. At that point, the old ``NSEC3PARAM`` record can be removed. The old +chain is removed after the update request completes. + +:iscman:`named` only supports creating new ``NSEC3`` chains where all the +``NSEC3`` records in the zone have the same ``OPTOUT`` state. :iscman:`named` +supports updates to zones where the ``NSEC3`` records in the chain have mixed +``OPTOUT`` state. :iscman:`named` does not support changing the ``OPTOUT`` +state of an individual ``NSEC3`` record; if the ``OPTOUT`` state of an +individual ``NSEC3`` needs to be changed, the entire chain must be changed. + +To switch back to ``NSEC``, use :iscman:`nsupdate` to remove any ``NSEC3PARAM`` +records. The ``NSEC`` chain is generated before the ``NSEC3`` chain is removed. + +.. _dnssec_dynamic_zones_dnskey_rollovers: + +DNSKEY Rollovers +================ + +To perform key rollovers via a dynamic update, the ``K*`` files for the new keys +must be added so that :iscman:`named` can find them. The new ``DNSKEY`` RRs can +then be added via dynamic update. When the zones are being signed, they are +signed with the new key set; when the signing is complete, the private type +records are updated so that the last octet is non-zero. + +If this is for a KSK, the parent and any trust anchor repositories of the new +KSK must be informed. + +The maximum TTL in the zone must expire before removing the old ``DNSKEY``. If +it is a KSK that is being updated, the DS RRset in the parent must also be +updated and its TTL allowed to expire. This ensures that all clients are able to +verify at least one signature when the old ``DNSKEY`` is removed. + +The old ``DNSKEY`` can be removed via ``UPDATE``, taking care to specify the +correct key. :iscman:`named` cleans out any signatures generated by the old +key after the update completes. + +.. _dnssec_dynamic_zones_going_insecure: + +Going Insecure +============== + +To convert a signed zone to unsigned using dynamic DNS, delete all the +``DNSKEY`` records from the zone apex using :iscman:`nsupdate`. All signatures, +``NSEC`` or ``NSEC3`` chains, and associated ``NSEC3PARAM`` records are removed +automatically when the zone is supposed to be re-signed. + +This requires the :any:`dnssec-secure-to-insecure` option to be set to ``yes`` in +:iscman:`named.conf`. + +In addition, if the ``auto-dnssec maintain`` or a :any:`dnssec-policy` is used, it +should be removed or changed to ``allow`` instead; otherwise it will re-sign. + +.. _dnssec_tools: + +Manual Signing +^^^^^^^^^^^^^^ + +There are several tools available to manually sign a zone. + +.. warning:: + + Please note manual procedures are available mainly for backwards + compatibility and should be used only by expert users with specific needs. + +To set up a DNSSEC secure zone manually, a series of steps +must be followed. Please see chapter +:ref:`advanced_discussions_manual_key_management_and_signing` in the +:doc:`dnssec-guide` for more information. + +Monitoring with Private Type Records +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The state of the signing process is signaled by private type records (with a +default type value of 65534). When signing is complete, those records with a +non-zero initial octet have a non-zero value for the final octet. + +If the first octet of a private type record is non-zero, the record indicates +either that the zone needs to be signed with the key matching the record, or +that all signatures that match the record should be removed. Here are the +meanings of the different values of the first octet: + + - algorithm (octet 1) + + - key ID in network order (octet 2 and 3) + + - removal flag (octet 4) + + - complete flag (octet 5) + +Only records flagged as "complete" can be removed via dynamic update; attempts +to remove other private type records are silently ignored. + +If the first octet is zero (this is a reserved algorithm number that should +never appear in a ``DNSKEY`` record), the record indicates that changes to the +``NSEC3`` chains are in progress. The rest of the record contains an +``NSEC3PARAM`` record, while the flag field tells what operation to perform +based on the flag bits: + + 0x01 OPTOUT + + 0x80 CREATE + + 0x40 REMOVE + + 0x20 NONSEC + +.. _secure_delegation: + +Secure Delegation +~~~~~~~~~~~~~~~~~ + +Once a zone is signed on the authoritative servers, the last remaining step +is to establish chain of trust [#validation]_ between the parent zone +(``example.``) and the local zone (``dnssec.example.``). + +Generally the procedure is: + + - **Wait** for stale data to expire from caches. The amount of time required + is equal to the maximum TTL value used in the zone before signing. This + step ensures that unsigned data expire from caches and resolvers do not get + confused by missing signatures. + - Insert/update DS records in the parent zone (``dnssec.example. DS`` record). + +There are multiple ways to update DS records in the parent zone. Refer to the +documentation for the parent zone to find out which options are applicable to +a given case zone. Generally the options are, from most- to least-recommended: + + - Automatically update the DS record in the parent zone using + ``CDS``/``CDNSKEY`` records automatically generated by BIND. This requires + support for :rfc:`7344` in either parent zone, registry, or registrar. In + that case, configure BIND to :ref:`monitor DS records in the parent + zone <cds_cdnskey>` and everything will happen automatically at the right + time. + - Query the zone for automatically generated ``CDS`` or ``CDNSKEY`` records using + :iscman:`dig`, and then insert these records into the parent zone using + the method specified by the parent zone (web form, e-mail, API, ...). + - Generate DS records manually using the :iscman:`dnssec-dsfromkey` utility on + `zone keys`_, and then insert them into the parent zone. + +.. [#validation] For further details on how the chain of trust is used in practice, see + :ref:`dnssec_12_steps` in the :doc:`dnssec-guide`. + + + +DNSSEC Validation +~~~~~~~~~~~~~~~~~ + +The BIND resolver validates answers from authoritative servers by default. This +behavior is controlled by the configuration statement :namedconf:ref:`dnssec-validation`. + +By default a trust anchor for the DNS root zone is used. +This trust anchor is provided as part of BIND and is kept up-to-date using +:ref:`rfc5011.support`. + +.. note:: + DNSSEC validation works "out of the box" and does not require + additional configuration. Additional configuration options are intended only + for special cases. + +To validate answers, the resolver needs at least one trusted starting point, +a "trust anchor." Essentially, trust anchors are copies of ``DNSKEY`` RRs for +zones that are used to form the first link in the cryptographic chain of trust. +Alternative trust anchors can be specified using :any:`trust-anchors`, but +this setup is very unusual and is recommended only for expert use. +For more information, see :ref:`trust_anchors_description` in the +:doc:`dnssec-guide`. + +The BIND authoritative server does not verify signatures on load, so zone keys +for authoritative zones do not need to be specified in the configuration +file. + +Validation Failures +^^^^^^^^^^^^^^^^^^^ + +When DNSSEC validation is configured, the resolver rejects any answers from +signed, secure zones which fail to validate, and returns SERVFAIL to the +client. + +Responses may fail to validate for any of several reasons, including +missing, expired, or invalid signatures; a key which does not match the +DS RRset in the parent zone; or an insecure response from a zone which, +according to its parent, should have been secure. + +For more information see :ref:`dnssec_troubleshooting`. + +Coexistence With Unsigned (Insecure) Zones +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Zones not protected by DNSSEC are called "insecure," and these zones seamlessly +coexist with signed zones. + +When the validator receives a response from an unsigned zone that has +a signed parent, it must confirm with the parent that the zone was +intentionally left unsigned. It does this by verifying, via signed +and validated :ref:`NSEC/NSEC3 records +<advanced_discussions_proof_of_nonexistence>`, that the parent zone contains no +DS records for the child. + +If the validator *can* prove that the zone is insecure, then the +response is accepted. However, if it cannot, the validator must assume an +insecure response to be a forgery; it rejects the response and logs +an error. + +The logged error reads "insecurity proof failed" and "got insecure +response; parent indicates it should be secure." |