Security Services in Information Systems

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Security Services in Information Systems
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Digital Certificates
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What is a Digital Certificate?

• Electronic counterparts to driver
  licenses,passports.
• Enable individuals and organizations to secure
  business and personal transactions across
  communication networks.

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How do they secure the data?

• Authentication
• Integrity
• Encryption
• Token verification

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What certificates are typically used for

• Secure channel TLS / SSL for web servers
• Sign emails
• Authentication
• Code signing
• Encrypt files (EFS in Windows/2000)
• IPsec (encrypt network layer)

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Certificates and PKI

• A public key certificate consists of some payload
  and a digital signature over this data.
• The certificate payload consists of a public key
  and some additional data (e.g. subject and issuer
  information, validity period, privileges,
  attributes etc.).
• The digital signature binds these additional data
  to the public key.
• It is the responsibility of a PKI (Public Key
  Infrastructure) to generate, distribute, and
  manage certificates.

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Certificates
CA
Certified Entity
FJRRH
FJRRH
FJRRH
Verifier
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Real World Analogies

• Is a certificate an electronic identity?
• Concerns
• a certificate is a binding between an identity
  and a key, not a binding between an identity and
  a real person
• one must submit its certificate to identify
  itself, but submission is not sufficient, the key
  must be used in a protocol
• anyone can submit someone elses certificate

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Real World Analogies

• Result Certificates are not picture IDs
• So, what is the real world analogy for
  certificates?
• Endorsed document/card that serves as a binding
  between the identity and signature

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Issues Related Certificates

• TRUST
• verifiers must trust CAs
• CAs need not trust the certified entities
• certified entity need not trust its CA, unless it
  is not the verifier
• What is trust in certification systems?
• Answer to the question How correct is the
  certificate information?
• related to certification policies

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Issues Related Certificates

• Certificate Revocation
• certificates have lifetimes, but they may be
  revoked before the expiration time
• Reasons
• certificate holder key compromise/lost
• CA key compromise
• end of contract (e.g. certificates for employees)
• Certificate Revocation Lists (CRLs) hold the list
  of certificates that are not expired but revoked
• each CA periodically issues such a list with
  digital signature on it

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Digital Certificate - Lifecycle
Key Pair Generated
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X.509

• ITU-T standard (recommendation)
• ISO 9495-2 is the equivalent ISO standard
• part of X.500 family for directory services
• distributed set of servers that store user
  information
• an utopia that has never been carried out
• X.509 defines the authentication services and the
  pubic-key certificate structure (certificates are
  to be stored in the directory)
• so that the directory would contain public keys
  of the users

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X.509

• Defines identity certificates
• attribute (authorization) certificates are added
  in 4th edition (2000)
• Defines certificate structure, not PKI
• Supports both hierarchical model and cross
  certificates
• End users cannot be CAs

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X.509 Certificate Format
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X.509v3 Extensions

• Not enough flexibility in X.509 v1 and v2
• mostly due to directory specific fields
• real-world security needs are different
• email/URL names should be included in a
  certificate
• key identification was missing (so should be
  included)
• policy details should indicate under which
  conditions a certificate can be used (was not the
  case in v1 and v2)
• avoidance of blind trust was not possible in v1
  and v2
• Rather than explicitly naming new fields a
  general extension method is defined
• extensions consist of extension identifier, value
  and criticality indicator

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X.509v3 Extensions

• Key and policy information
• subject issuer key identifiers
• indicators of certificate policies supported by
  the cert
• key usage (list of purposes like signature,
  encryption, etc)
• Alternative names, in alternative formats for
  certificate subject and issuer
• Certificate path constraints (for CA to CA certs)
• to restrict certificate issuance based on
• path length (restricting number of subordinate
  CAs)
• policy identifiers
• names
• Verifier could exercise its own restrictions
  during verification as well
• No blind trust to CAs

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Main parts of a digital certificate system

• Request and issue certificates (different
  categories) with verification of identity
• Storage of certificate (including the private
  key)
• Publishing of certificates (public part) to
  anyone (LDAP, HTTP)
• Pre-install root certificates in a trusted
  environment
• Support by platform, applications and services to
  use certificates
• Maintain database of issued certificates (no
  private keys!)
• Helpdesk (information, lost compromised private
  keys)
• Publishing of CRLs (and enforce apps to do
  revocation checking)

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X.509 Certificate Format
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Certification Authority
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Certification Authority(CA)

• Trusted entity which issue and manage
  certificates for a population of public-private
  key-pair holders.
• A digital certificate is issued by a CA and is
  signed with CAs private key.

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CA
Verifica CRL
Verifica certificado
?
?
X
Y
1235
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CA Policies

• CA certification policies (Certificate Practice
  Statement)
• how reliable is the CA?
• certification policies describe the methodology
  of certificate issuance
• ID-control practices
• loose control only email address
• tight control apply in person and submit picture
  IDs and/or hard documentation

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Arquitectura típica de una AC
Certificate Distribution
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VeriSign Certificates

• Several companies provide CA services Nortel,
  GTE, U.S. Postal Service and VeriSign among
  others. Of those, the most widely used is the
  latter.
• Over 35K commercial WEB sites were using VeriSign
  digital certificates as early as 1998.
• Over a million consumer digital certificates had
  been issued to users of Netscape and Microsoft
  browsers.
• VeriSign Class1 certificate cost U.S. 14.95 per
  year, or free 60-day trial edition

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VeriSign Certificates

• There are three classes of VeriSign certificates
• Class 1. VeriSign confirms the users e-mail
  address by sending a PIN and Digital ID pick-up
  to the e-mail address provided in the
  application.
• Class 2. VeriSign uses a consumer database in
  addition to performing the checkings of class 1.
  Confirmation is sent to the specific postal
  address alerting the customer that his/her
  certificate is ready for pick-up.
• Class 3. VeriSign requires a higher level of
  identity assurance. An individual must prove
  his/her identity by providing notarized
  credentials and/or applying in person.

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Public Key Infrastructure
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Organization-wide PKI

• Local PKI for organizations
• may have global connections, but the registration
  facilities remain local
• generally to solve local problems
• local secure access to resources

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PKI

• Business Practice Issue certificates and make
  money
• several CAs
• Several CAs are also necessary due to political,
  geographical and trust reasons
• 3 interconnection models
• hierarchical
• cross certificates
• hybrid

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Public Key Infrastructure (PKI)

• PKI is a complete system and well-defined
  mechanisms for certificates
• certificate issuance
• certificate revocation
• certificate storage
• certificate distribution

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Hierarchical PKI Example
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Cross Certificate Based PKI Example
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Hybrid PKI example
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Certificate Paths
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Certificate Paths

• Verifier must know public key of the first CA
• Other public keys are found out one by one
• All CAs on the path must be trusted by the
  verifier

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Certificate Paths with Reverse Certificates
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Hosted vs. Standalone PKI

• Hosted PKI
• PKI vendor acts as CA
• PKI owner is the RA
• Standalone PKI
• PKI owner is both RA and CA