Encryption and the Law: The need for a legal regulatory framework for PKI Yee Fen Lim Department of Law Macquarie University.

Encryption and the Law: The need for a legal

regulatory framework for PKI

Yee Fen LimDepartment of Law

Macquarie University

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Outline

• Introduction• Handwritten signatures• Requirements of electronic signatures• Digital Signatures• Public Key Cryptography• Public Key Infrastructure• Digital Certificates• Allocation of Liability

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Introduction

• Signature issues in the digital environment

• Importance– Commercial: e-commerce (all sectors)– Non-commercial

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Handwritten Signatures

• Signature v. autograph– Intention of the signer

• Signature is any mark that has been affixed by the signer with the intent to be bound by the contents of the document

• Once affixed, the signature and the document becomes one composite thing

Integrity

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Proof of Handwritten Signatures

• If a handwritten signature is disputed, then call on the following:– witness to the signature– a person with intimate knowledge of the

person’s signature– handwriting expert

Authentication and Non-repudiation

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Requirements of Electronic Signatures –

“legal status”• Integrity

– “I love you” does not become “I love you not”

• Non-repudiation– “Not me!”

• Authentication– Did Superman really write the message?

• Confidentiality– Superman wants to keep his messages private

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Types of Electronic Signatures

• Biometric signatures– eg iris scans, finger-prints, voice

(none totally perfect yet).

• Non-biometric signatures– eg digital signatures

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Digital Signatures

• Insecure – eg initials at the end of emails

• Secure– Uses encryption to code and decode– Ensures confidentiality – but what about integrity,

authentication, non-repudiation?

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Public Key Cryptography

• 2 key pairs: 1 private key and an associated public key

• Private key kept secret by owner• Public key published widely• Golden rule: anything encrypted

with a public key can only be decoded with the private key, and vice versa

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Public Key Cryptography: Superman example

• Superman writes: “I love you”• Superman encrypts message with

his private key• Anyone with Superman’s public

key can decode the message

Authenticity

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Public Key Cryptography: Superman example

• How does Superman ensure only Lois Lane can read his message?

• Superman encrypts his already encrypted message with Lois Lane’s public key

• Only Lois Lane can decode the message as she is the one with the private key

Confidentiality

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Public Key Cryptography: Superman example

• What about integrity?• Include a pre-agreed one-way hash

function with the original message• eg “I love you”

– Use a=1 b=2 c=3 ….z=26– i=9 l=12 o=15 v=22 e=5 y=25 o=15 u=21– Use sum:

9+12+15+22+5+25+15+21=124– Hash is 124

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Public Key Cryptography: Superman example

• Include the hash of 124 in the message that is double encrypted.

• When Lois Lane receives the message, she can run the message through the pre-agreed hash function

• If she gets 124 as the result, then integrity is ensured. If not, then the message may have been tampered with.

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Public Key Cryptography: Superman example

• To save on processing, rather than encrypt the full message with the private key, most systems just encrypt the hash with the private key, and this becomes the digital signature ie different every time

• The private-key-encrypted hash plus the message is then encrypted with the recipient’s public key to ensure only the recipient can read the message.

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Public Key Cryptography: Superman example

• What about non-repudiation?• Who is the signer?• Was it really Superman?• Related to authentication

Public key infrastructure (PKI)

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Public Key Infrastructure (PKI)

• System for distribution of public keys– Reliability

• eg a web page simply listing the public keys of persons is not reliable as to source

• “Web of trust”• Trusted third party to verify that the

public key really does belong to whom it is said to belong

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Public Key Infrastructure (PKI)

• Trusted third party is Certification Authority (CA)

• CA issues digital certificate verifying the owner of the public key

• A CA may use a third-party, a Registration Authority (RA), to perform the necessary checks on the person or entity requesting the certificate

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Public Key Infrastructure (PKI)

• Can we trust the CA? • Higher CA, Root CA (self-

authenticates)• Cross-verification creating

certificate chain - web of trust

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Public Key Infrastructure (PKI): Digital Certificates

• Serial number - unique number from CA• Key length• Signature algorithm – identity of algorithm• Hashing algorithm• Issuer name• Validity period• Subscriber – details of owner of public key• Subject public key - actual key certified• Signature of CA

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Public Key Infrastructure (PKI): Digital Certificates

Digital Certificates should:• provide strong and substantial evidence

of the identity of the owner of public key (signer)

• Be used during operational period of valid digital certificate

• Have the rebuttable presumption that the digital signature on the digital certificate is that of the subscriber listed

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PKI: Rebutting the presumption

• Was the CA in the wrong?• Was it an imposter’s public key that

the CA has registered?• Did someone else use Superman’s

public/private key without permission?

• Did Superman safeguard his private key properly?

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PKI: Revocation of Digital Certificates

Credit card analogy:• If Superman’s private key has been

compromised, he should notify the CA• CA can revoke Superman’s digital certificate• CA then posts the certificate on the

certificate revocation list (CRL)• Limitations upon the right of a recipient of a

digital certificate to rely upon them• Unreliable Digital Signatures; Reasonable of

Reliance

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PKI: Allocation of Liability

• Hardest Legal Issues involve the allocation of liability among Subscriber (key owner), CA and Relying Party – eg1 Liability of CA to a Relying Party for

binding the wrong public key to the identity of the subscriber named in the certificate.

– eg2 Liability of the Subscriber to the Relying Party upon unauthorised use of Subscriber’s private key following compromise of the private key

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PKI: Allocation of Liability

• For a Relying Party, the allocation of liability is paramount

• If a Relying Party does not know whether the CA can be trusted, or if the Subscriber is genuinely who they claim to be, then the Relying Party would not rely on the Digital Certificate

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PKI: Allocation of Liability

Examples of where problems arise:• Inaccuracies in the Certificate• Misrepresentation in the Certificate• CA fails to revoke an invalid

Certificate

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PKI: Allocation of Liability

• Closed systems

• Open systems (Internet)

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PKI: Allocation of Liability – closed system example

• GatekeeperHealth eSignature Authority (RA)– Betrusted (formerly Securenet) is CA– Individual certificates, location

certificates– Referrals, reports

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PKI: Allocation of Liability – closed system example

• 5.4 Keys and Certificates should only be used for Health related messages

• in transactions with HIC, or • in transactions created by subscribers

within the Health Sector but not where the transaction value is greater than $10,000

• Lists obligations and duties for each party

• Limit on liability - $1,000/$5,000

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PKI – Australia

• Contract law (if there is a contract)– including protection against unfair

contractual liability allocation eg undue influence, unconscionable dealing, Contracts Review Act, ss51AA, 51AB & 51AC TPA

• Law of negligence• s52 Trade Practices Act• Consumer protection legislation

$500 transaction?

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PKI Regulation – Preferred approach

• Strict liability– avoidance of concepts of negligence

• Reliance limits• Actions key can be used for

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