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Introduction to Public Key Infrastructure
January 2004 CSG Meeting
Jim Jokl
Cryptography
• Symmetric key cryptography
– A pre-shared secret is used to encrypt the data
– Some examples: DES, 3-DES, RC4, etc
• Public key cryptography
– A pair of mathematically related keys are generated
• One of the keys, the Public Key, is freely distributed
• The other key, the Private Key, is kept confidential
– Given one keys, it is computationally very hard to
compute the other
Public Key Cryptography
one key
Plain
Text
the other key
Encrypted
Text
– Data encrypted using the public key can only be
decrypted by the person with the private key
– Likewise, data encrypted with the private key can
be decrypted by anyone having a copy of the
public key
• Assuming that the private key is protected and held by
an individual, this is the basis for a digital signature
Digital Signatures and Document
Encryption
• Public Key operations are too computationally
expensive for large volumes of data
• Typical digital signature process
– Compute the hash of the document
– Encrypt the hash using the signer’s private key
• Typical document encryption process
– Generate a random symmetric cipher key
– Encrypt the document using this key
– Encrypt the symmetric cipher key using the recipient’s
public key
Digital Certificates
• A Digital Certificate is:
– An object used to bind the identity of a person
to their public key
– Contains attributes about the person
– Contains some information about the identity
binding and infrastructure
– Digitally signed by a Certification Authority
(CA)
Certificate Profiles
• A description of the fields in a certificate
–
–
–
–
Recommended fields to use
Field values
Critical flags
Recommendations for implementers
– Example Profile
Certification Authorities (CA)
• Certification Authorities
– Accept certificate requests from users
– Validate the user’s identity
– Generate and sign the user’s certificate attesting
to the mapping of the identity to the public key
– Revoke certificates if needed
– Operate under a set of policies and practices
• Levels of Assurance
Certification Authorities and Trust
• You determine if you trust
a certificate by validating
all of the certificates
starting from the user’s
Intermediate
Intermediate
cert up to a root that you
Certificate
Certificate
trust
User A
User B
• 100+ root certificates in
Cert
Cert
my Microsoft store
User D User E • The “I” in PKI
User C
Root
Certificate
Cert
Cert
Cert
PKI Bridge Path Validation
PKI, Privacy, and the Pseudoanonymous CA
• As stated earlier: “A certificate binds a
person’s identity to their public key”
• Typically the “identity” is their name, email
address, computing identifier, etc
– Poses some interesting privacy concerns in
some applications
• A pseudo-anonymous CA uses an opaque
identifier instead of name/id information
Operating System Support for PKI
• Windows 2000/XP
–
–
–
–
–
–
–
Well integrated out of the box support for PKI
OS-based certificate/key store
APIs for access to crypto providers
Microsoft applications generally support PKI
Many 3rd party applications use OS PKI services
Bridge path validation in XP
Windows 2000 server includes a CA
Operating System Support for PKI
• MacOS
– Apple has excellent plans to improve their level of
OS PKI support to match that of Windows
– OS-based certificate/key store exists now and is
used by some Apple applications
– 3rd party applications should start to use the native
support in the future
• Linux and general Unix
– PKI support generally implemented in applications
Trust, Private Key Protection and
Non-repudiation
• Digital signatures - based on the idea that only
the user has access their private key
• A user’s private key is generally protected by
the workstation’s operating system
– Typical protection is no better than for any password
that the user lets the operating system store
• Hardware tokens can be used for strong private
key protection, mobility, and as a component in
a non-repudiation strategy
Two classes of campus PKI
applications?
• Existing normal processes
– A PKI using a light policy/practices
framework
– Better technology and ease of use for existing
services
– New applications where passwords would
have been sufficient in the past
Two classes of campus PKI
applications?
• Newer High Assurance services
– Access control for critical systems
– Authentication for high-value services
• HiPAA/FERPA/GLBA
– Digital signatures for business processes
Some Campus CA Options
• In-source
– Commercial CA software
– Develop your own or use freely available CA
software (typically based on OpenSSL)
– KX509
• Outsource to commercial CA
– Campus still performs the RA function
Agenda for remainder of session
• Motivations for campus PKI deployments
– Focus on applications using end-user certificates
• Introduction to likely campus PKI applications
• National activities
– HEBCA, USHER, PKILab, HEPKI, etc
• Examples of campus PKI deployments
• Wrap-up and discussion