1. TAG Presentation 18th May 2004 Paul Butler
ABC’s of PKI
TAG Presentation
18th May 2004
Paul Butler

2. Agenda Role of trust PKI concepts PKI components Management framework
Passport signing requirement
Deployment issues
Operational Issues
Guidance

3. Security Model Must answer the questions:
What data are we protecting?
integrity of biometric information on chip in passport
Why are we protecting it?
Maintain integrity of passport
Who or what are we protecting it against?
Those who would seek to alter data to falsify passport
When are we protecting it?
Throughout the life of the passport
For passport issuers, the model revolves around TRUST

4. The Role of Trust Trust is usually based on some form of identity
Direct Trust
Based on personal relationship, where trust is handled directly
Breaks down when too many members in trusted relationship to handle directly
Third Party trust
Trust in individual changes to trust in a system
Passports represent the national identity of an individual

5. PKI Concept
Public Key Infrastructure based on asymmetric cryptography. Relies on a key pair, one private and one public
Private key is secret
Public key is freely available, linked to identity of certificate owner
Private key cannot be computed from public key
Concept is then applied into applications
Mathematical construct known as trapdoor algorithm developed in the 1970’s supports concept of public and private keys implemented in software. Public key is readily available, private key is not. “Computationally unfeasible” to derive private key from public key. Used for electronic signature (signing key) or for encrypting data (encryption key). Need to ensure supporting technology 9encryption algorithm and key length stay current so this continues to be true

6. Public Key Infrastructure
Business uses include:
Authentication of identity for individual, organization or device (authentication)
Confirmation that data has not been tampered with (integrity)
Confirmation that transaction took place (non-repudiation)
Maintain data confidentiality (encryption)
Guarantee that transaction took place at specific time (secure time stamp)

7. PKI Components Mechanism to issue certificates
Certificate authority (CA)
Mechanism to validate certificates
Directory services
Certificate Revocation List
Key history
Potentially, source of trusted time for stamping
Controlled Process to enroll and manage certificate holders - Registration Authority (RA)
Process to revoke certificates which are no longer valid (distinct from rollover of expired certificate keys)
Processes defined by certificate policy (CP) and certification practice statements (CPS)

8. Passport PKI Requirement
New passports to include biometric identifier on chip. Concerns about tampering (integrity) led to need for PKI signature to confirm data on chip unchanged since production of TD (integrity)
PKI does NOT guarantee identity of passport holder – it guarantees that TD biometric is unchanged since production by a specific producer (non-repudiation)
Based on DIGITAL SIGNATURE
Use of encryption not a current requirement

9. Use of digital signature
During passport print process, data chip will be loaded
CA will be requested for a signature
Signature and certificate will be added to chip
Chip is then locked to prevent further write operations

10. PKI Signing Process To sign a document:
A hash is prepared derived from the document content
It is encoded with the signing algorithm from the signer’s PRIVATE KEY
The signature and a copy of the public key certificate is attached to the document
It is then available for validation

11. PKI Signing Process (2) To validate the signature:
The PUBLIC KEY is used to prepare a hash of the document using the same signing key algorithm as the private key
The new hash is compared with the original
If they are the same, it proves that the document is unchanged since it was signed
For a TD, it means that TRUST can be placed on the validity of the document

12. PKI Signing Process (3)
If relying party wishes to further validate the certificate, a path must exist to the CA which issued the certificate
Check validity of issuer
Check certificate not revoked
Implies border crossing points must have internet facing capability linked to card readers which can go to a source and validate that the certificate presented is in fact valid
No such infrastructure is yet in place

14. Deployment Issues
Need for international standards among TD producers for mutual acceptance of biometric, PKI-authenticated TD’s
Need for accreditation process to accept each new national CA into infrastructure
Complex management challenge
Need to incorporate passport CA with national policy for PKI administration
Align with national trust model

15. Operational Issues Process for adoption of new technology standards
Essential to maintain underlying cryptographic technology current
All nations move ahead together
Avoid complexity of cross certification by publishing certificates in common location
Location must be specified from outset in certificate

16. Key management
To reduce risk of compromise, key should “roll over” frequently
Need to maintain key history for lifetime of passport issued under that key
In event of compromise, publish compromised certificate data to Certificate revocation list (directory)
Secure time stamping could be used to determine when a compromise occurred, or for calculations regarding validity period of passport
If key is compromised, all signatures issued by that key become invalid
Therefore need to keep the “window” as small as operationally feasible

17. Guidance Common tendency to focus on underlying technology – wrong!
PKI is 20% technology, 80% process
Key element lies in “trust model”
To be trusted, technology must be supported by business processes which demonstrate the integrity of the PKI
Entitlement processes must match integrity levels of entitlement process – no more, no less
Setting up a CA is technically fairly simple
Processes to manage

18. Questions?