Bishop: Chapter 14 Representing Identity

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Bishop Chapter 14Representing Identity
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Outline

• Introduction
• Naming Certificates
• Identity on the web
• Anonymity

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What is identity?

• An identity specifies a principal.
• A principal is a unique entity.
• What can be an entity?
• Subjects users, groups, roles
• e.g., a user identification number (UID)
  identifies a user in a UNIX system
• Objects files, web pages, etc. subjects
• e.g., an URL identifies an object by specifying
  its location and the protocol used (such as
  http//sce.cl.uh.edu/).

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Authentication vs identity

• Authentication binds a principal to a
  representation of identity internal to the
  computer.
• Two main purposes of using identities
• Accountability (logging, auditing)
• Access control

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Identity Naming and Certificates

• In X.509 certificates, distinguished names (that
  is, X.500 Distinguished Name) are used to
  identify entities.
• e.g., /OUHCL/OUSCE/CNAndrew Yang/LHouston/SPT
  exas/CUS
• e.g., /OUHCL/OUSCE/CNUnixLabAdministrator/LHou
  ston/SPTexas/CUS
• A certification authority (CA) vouches, at some
  level, for the identity of the principals to
  which the certificate is issued.

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Structure of CAs

• RFC 1422, S. Kent, 1993 Privacy Enhancement for
  internet Electronic Mail Part II,
  Certificate-Based Key Management
• The certificate-based key management
  infrastructure organizes CAs into a hierarchical,
  tree-based structure.
• Each node in the tree corresponds to a CA.
• A Higher-level CA set policies that all
  subordinate CAs must follow it certifies the
  subordinate CAs.

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Certificates Trust

• A certificate is the binding of an external
  identity to a cryptographic key and a
  Distinguished Name.
• If the certificate issuer can be fooled, all who
  rely on that certificate may also be fooled.
• The authentication policy defines the way in
  which principals prove their identities, relying
  on nonelectronic proofs of identity such as
  biometrics, documents, or personal knowledge.

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Certificates Trust

• The goal of certificates is to bind a correct
  pair of identity and public key.
• PGP certificates include a series of signature
  fields, each of which contains a level of trust.
• The OpenPGP specification defines 4 levels of
  trusts
• Generic no assertions
• Persona (i.e., anonymous) no verification of the
  binding between the user name and the principal
• Casual some verification
• Positive substantial verification

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Certificates Trust

• Issues with the OpenPGPs levels of trusts
• The trust is not quantifiable.
• The same terms (such as substantial
  verification) can imply different levels of
  assurance to different signers.
• The interpretations are left to the verifiers.
• The point
• Knowing the policy or the trust level with which
  the certificate is signed is not enough to
  evaluate how likely it is that the identity
  identifies the correct principal.
• Other knowledge is needed e.g., how the CA or
  signer interprets the policy and enforces its
  requirements

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Identity on the Internet

• Host identity How is a computer identified on
  the Internet?
• ISO/OSI 7-layer model
• The possibility of spoofing a computers IP or
  MAC address
• Static vs Dynamic Identifiers
• The NAT (Network Address Translation) protocol

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Domain Name Services

• DNS provides an association between a host name
  and an IP address.
• If the association is corrupted, the identifier
  in question will be associated with the wrong
  host (sometimes the malicious one).
• Attacks on the DNS Bellovin, Schuba

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State and Cookies

• The HTTP protocol is a stateless protocol
  basically request/response
• Other mechanisms (such as cookies or sessions)
  are needed to maintain states between a client
  and a server.
• Def. 14-4 A cookie is a token that contains
  information about the state of a transaction on a
  network.
• pp.369-370 Values in the cookies
• Cookies may contain sensitive information.
  Protecting the confidentiality of the cookies may
  be critical.

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Anonymity on the Web

• Anonymity The ability to hide the identity of a
  host
• When would anonymity be needed?
• Examples anonymous remailers, mixers
• More details in the network security course