ITU Workshop on “Caller ID Spoofing”
(Geneva, Switzerland, 2 June 2014)
Introduction to
public-key infrastructure (PKI)
Erik Andersen,
Q.11 Rapporteur,
ITU-T Study Group 17
era@x500.eu
Geneva, Switzerland, 2 June 2014
PKI and PMI
Public-key certificates: The basis for
public-key infrastructure (PKI)
Attribute certificates: The basis for
privilege management infrastructure
(PMI)
Rec. ITU-T X.509 | ISO/IEC 9594-8
base specification for both types of
infrastructure
Geneva, Switzerland, 2 June 2014
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Facts about X.509
Part of the X.500 Series of
Recommendations
Also issued as ISO/IEC 9594-8
Issued in seven editions
First edition in 1988
Eight edition on its way
Number one in downloads
Defines:
Public key/private key principles
Public-key certificates
Public-key infrastructure (PKI)
Attribute certificates
Privilege management
infrastructure (PMI)
Geneva, Switzerland, 2 June 2014
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Asymmetric cryptography
Asymmetric cryptography is basic
technology behind PKI and PMI
A
B
Private key
Public key
Action using
private key
Resolving using
public key
Resolving using
private key
Action using
public key
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PKI entities
End
entity
Certificate
&
CRL
repository
(e.g., an
LDAP or
X.500
directory)
Registration
Authority
CA
CRL
Issuer
CA
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Certifying the identity using
public-key certificates
Certification Authority
Geneva, Switzerland, 2 June 2014
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Public-key certificate
Version
Serial number
Algorithm
Issuer
Validity
Subject
Public key info
Issuer unique id
Subject unique id
Extensions
Version 2 (do not use!)
Version 3 - Important
Digital signature of issuer
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Extensions
The extension concept allows adding
additional information to a publickey certificate.
Organizations may define own
extensions.
If the information changes, the
public-key certificate has to be
renewed.
Certification authority (CA)
NOT: Certificate authority
Verify the identity of the subject
Verify the position of the key-pair
Verify the other information as
required
Issues and sign the public-key
certificate
Maintain revocation status
Publishes revocation status
Geneva, Switzerland, 2 June 2014
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Checking the credentials
Subject
Relying party
A passport is a type of
certificate binding a picture
to a subject ID
Has to be issued by a
trustworthy authority
A passport may be false
It is checked by the
validator, also called the
relying party
Geneva, Switzerland, 2 June 2014
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Trust
Would you buy
a certificate of
this man?
Certificates
Geneva, Switzerland, 2 June 2014
Would you trust
a certificate
issued by this
man?
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Hierarchical Structure
Trust anchor
CA
CA
CA
EE
CA
EE
EE
CA
EE
CA = Certification authority
EE = End entity
EE
CA
EE
EE
EE
Trust anchor
Trusted by a relying party
Trust anchor information:
Configured into relying
party
Public-key certificate
or similar information
Geneva, Switzerland, 2 June 2014
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Certificate Revocation
List (CRLs)
Version
Algorithm
Issuer
Time for this update
Time for next update
Certificate Serial
Number
Revocation Date
Extensions
Certificate Serial
Number
Revocation Date
Extensions
CRL Extensions
Digital signature of issuer
Revoked
Certificate
Revoked
Certificate
Online Certificate Status Protocol
(OCSP)
OCSP
responder
OCSP client
OCSP
request
OCSP
response
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Validation procedure
Storing of
Trust Anchor
Information
User system B
(Relying Party)
Check of
revocation
Signed
data
Trust
Ancho
r
CA
CA
User system
A
(end entity)
Where to go
The central source for information on the
X.500 Directory Standard including X.509.
www.x500standard.com
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