Certificate Limitation Policy
draft-belyavskiy-certificate-limitation-policy-01

Network Working Group
Internet-Draft                                              July 1, 2017
Intended status: Experimental
Expires: January 2, 2018

                     Certificate Limitation Policy
           draft-belyavskiy-certificate-limitation-policy-01

Abstract

   The document provides a specification of the application-level trust
   model.  Being provided at the application level, the limitations of
   trust can be distributed separately using cryptographically protected
   format instead of hardcoding the checks into the application itself.

Status of This Memo

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   This Internet-Draft will expire on January 2, 2018.

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1.  Introduction

   Binary trust model standardized as a set of trusted anchors and CRLs/
   OCSP services does not cover all corner cases in the modern crypto
   world.  There is a need in more differentiated limitations.  Some of
   them are suggested [1] by Google when it limits the usage of
   Symantec's certificates.  The CRL profile does not fit the purpose of
   such limitations.  The CRLs are issued by the same CAs that are
   subject to be limited.

   Currently the set of CAs trusted by OS can be used for the validation
   purposes.  In case when a large enough CA becomes untrusted, it
   cannot be deleted from the storage of trusted CAs because it may
   cause error of validation of many certificates.  The measures usually
   taken in such cases usually include application-level limitation of
   certificates lifetimes, refusing to accept EV-certificates in other
   way than DV, requirements to use Certificate Transparency, etc.

   This document suggests a cryptographically signed format dubbed
   Certificate Limitation Profile (CLP) designed for description of such
   limitations.  This format can be used by applications that use
   system-wide set of trust anchors for validating purposes or by
   applications with own wide enough set of trusted anchors in case when
   the trust anchor for the entity found misbehaving cannot be revoked.

   Currently the only way to provide such limitations is hard coding
   them in application itself.  Using of CLPs does not allow to
   completely avoid hard coding but allows to hard code only the minimal
   set of rarely changing data:

      the fact that application uses CLP

      the certificate to verify the signature under the CLP file

      minimal date of the CLP to be used for the current version of
      application.

   It will be possible to move the checks for the limitations to the
   external cryptographical libraries, such as OpenSSL, instead of
   checking them at the application level.

2.  Certificate Limitations Profile

   A proposed syntax and overall structure of CLP is very similar to the
   one defined for CRLs [2].  CertificateList ::= SEQUENCE { tbsCertList
   TBSCertList, signatureAlgorithm AlgorithmIdentifier, signatureValue
   BIT STRING } TBSCertList ::= SEQUENCE { version Version OPTIONAL, --
   if present, MUST be v1 signature AlgorithmIdentifier, issuer Name,

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   thisUpdate Time, limitedCertificates SEQUENCE OF SEQUENCE {
   userCertificate CertificateSerialNumber, sertificateIssuer Name,
   limitationDate Time, limitationPropagation Enum, fingerprint SEQUENCE
   { fingerprintAlgorithm AlgorithmIdentifier, fingerprintValue OCTET
   STRING } OPTIONAL, limitations SEQUENCE, } OPTIONAL, };

2.1.  CLP fields

   TBD

2.2.  CLP signature

   The key used for signing the CLP files should have a special Key
   Usage value and/or an Extended Key Usage value.

2.3.  CLP entry fields

   Each entry in list contains the following fields:

      The issuer of the certificate with limited trust.

      The serial of the certificate with limited trust.

      The fingerprint of the certificate with limited trust (optional).

      limitationPropagation.  This field indicates whether limitations
      are applied to the certificate itself, to all of its descendants
      in the chain of trust, or both.

   and a subset of the following limitations:

      maxIssued - do not trust the certs issued after the specified date

      maxValidity - do not trust the certs after the specified date

      validityPeriod, days - take minimal value from "native" validity
      period and specified in the limitation file

      ignoredX509Extensions - list of X.509 extensions of limited
      certificate that MUST be ignored for the specified certificate
      (e.g.  EV-indicating extensions)

      requiredX509extensions - list of X.509 extensions that MUST be
      present in the certificate to be trusted.

   The limitations are identified by OIDs

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2.3.1.  Limitations

2.3.1.1.  maxIssued

   When this limitation is present, any certificate matching the entry
   and issued after the specified date MUST NOT be trusted

2.3.1.2.  maxValidity

   When this limitation is present, any certificate matching the entry
   MUST NOT be trusted after the specified date.

2.3.1.3.  validityPeriod

   When this limitation is present, no certificate matching the entry
   should be treated as valid after specified period from its validFrom.

2.3.1.4.  ignoredX509Extensions

   When this limitation is present, the extensions listed in this
   element should be ignored for the matching certificate.

2.3.1.5.  requiredX509extensions

   When this limitation is present, the extensions listed in this
   element should be present for the matching certificate.

3.  Verification of CLP

   The verification of CLP SHOULD be performed by the application.  The
   application should check whether the provided CLP matches the
   internal requirements and is correclty signed by the specified key.

4.  Verification with CLP

   In case of using CLP the checks enforced by CLP should be applied
   after the other checks.

   The limitation provided by CLP MUST NOT extend the trustworthy of the
   checked certificate.

   The limitations are applied after cryptographic validation of the
   certificate and building its chain of trust.  If the certificate or
   any of its ascendants in the chain of trust matches any record in the
   CLP, the limitations are applied from the ascendant to descendants.
   The maxIssued and maxValidity limitations are applied to find out the
   actual validity periods for the any certificate in the chain of
   trust.  If the CLP prescribes to have a particular extension(s) and

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   the certificate does not have it, the certificate MUST NOT be
   trusted.

5.  ASN.1 notation

   TBD

6.  Security considerations

   In case when an application uses CLP, it is recommended to specify
   the minimal date of issuing of the CLP document somewhere in code.
   It allows to avoid an attack of CLP rollback when the stale version
   of CLP is used.

   It is recommended to distribute CLPs using the channels that are used
   for distribution of the applications themselves to avoid possible DoS
   consequences.

7.  IANA considerations

8.  Acknoledgements

   Special thaks to Rich Salz, Igor Ustinov, Vasily Dolmatov, Stanislav
   Smyishlyaev, Patrik Faeltstroem.

9.  References

   The current version of the document is available on GitHub
   https://github.com/beldmit/clp

10.  References

10.1.  URIs

   [1] https://groups.google.com/a/chromium.org/forum/#!msg/blink-
       dev/eUAKwjihhBs/rpxMXjZHCQAJ

   [2] https://tools.ietf.org/html/rfc5280#section-5

Author's Address

   Dmitry Belyavskiy

   Email: beldmit@gmail.com

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