Password Enabled Public-Key Infrastructure (PKI): Virtual Smartcards vs. Virtual Soft Tokens - PowerPoint PPT Presentation

Password Enabled Public-Key Infrastructure (PKI):Virtual Smartcards vs. Virtual Soft Tokens

Ravi Sandhu

Chief Scientist

SingleSignOn.Net

&

Professor, George Mason University

Mihir Bellare

Chief Cryptographer

SingleSignOn.Net

&

Professor, Univ. of California--San Diego

Ravi Ganesan

Chief Executive

Officer

SingleSignOn.Net

11417 Sunset Hills Rd., Reston, VA 20190

• Smartcards have not happened
• It’s the smartcard readers stupid!
• Roaming capability is critical
• Even DoD is stretched in large-scale deployment
• Trends are not in favor of smartcards
• Deployment scale of 10’s or even 100’s of millions of users
• Computing devices are proliferating
• Large installed base of reader-less computers

Smartcards are likely to remain a high-assurance niche application

• Result
• Phased migration path
• No “quantum jump”
• PKI integral, not silo’d

Strong PKI Systems

PKI with Password Convenience

Password Usability

PKI Capability

PKI Hardened Passwords

No change for users

No change for issuer

Eliminate weaknesses

Weak Password Systems

• Fact: Password based systems are often vulnerable to attacks
• Myth: Passwords are inherently insecure.
• Fact: It is completely possible to design a sufficiently secure password system.

Designing sufficiently secure password-based systems is non-trivial but it is possible.

• Fact: Users hate current password systems that require
• too many passwords and
• force too many changes
• Myth: Users inherently hate passwords.
• Fact: It is completely possible to design a user friendly password system with PKI-enabled Single Sign On.

Designing user-friendly and sufficiently secure password-enabled PKI systems is non-trivial but it is possible.

• Bad password selection
• enforce complexity rules
• On-line guessing attack
• throttling mechanism
• Off-line guessing (dictionary attacks)
• don’t reveal required information (we know how to design such protocols)
• Undetected theft and sharing
• online intrusion detection to discover
• deter sharing, e.g., sharing reveals sensitive user information
• Use of same password at strong and weak servers
• user awareness and education
• Password reuse
• don’t force unnecessary password changes
• Server spoofing
• use secure protocols to prove knowledge of password w/o sending it
• limit password exposure to trusted servers
• Server compromise
• use hardened servers or multiple servers

• Instant roaming capability
• Proven user acceptance
• 100’s of millions of passwords usages per day in cyberspace
• Cheap
• Self-maintained
• Password resets
• Password change

• How to distribute public-keys
• Digital Certificates
• Certificate Revocation Lists
• How to distribute private-keys (long-term)
• Smartcards
• The private key never leaves the smartcard
• Often called a hard token
• How to distribute private-keys (short-term)
• Password protected on the hard disk
• Not very mobile
• Password protected on a floppy disk
• Often called a soft token

• How to distribute public-keys
• Digital Certificates
• Certificate Revocation Lists
• On-line servers for certificate validation
• How to distribute private-keys (long-term)
• Smartcards
• The private key never leaves the smartcard
• Often called a hard token
• How to distribute private-keys (short-term)
• Password protected on the hard disk
• Not very mobile
• Password protected on a floppy disk
• Often called a soft token
• On-line servers for password-enabled mobility

How to marry PKI and Passwords?

• Approach 1: Virtual Soft Token

Use password to encrypt private key and store it on remote server(s).

Need password to RETREIVE private key.

• Approach 2: Virtual Smartcard

The password is part of the composite private key.

Need password to USE private key.

• Private key encrypted with user’s password is stored on an on-line server

Epwd(private-key)

• Anyone is allowed to retrieve the encrypted private key
• Only the user can decrypt it using the password
• Unacceptable risk due to dictionary attack

• Epwd(private-key)
• Dictionary attack
• Knowledge of public key allows attacker to obtain known plaintext
• So prohibit knowledge of public key resulting in closed public-key system

• Store Epwd(private-key) on server
• Transmit EK(Epwd(private-key)) where K is a strong symmetric key
• K is established using password-based authenticated key exchange protocol (such as EKE or SPEKE)
• Immune to off-line dictionary attack

• User’s “hardened password” is retrieved at any computer from two on-line servers
• Compromise of both servers is required to compromise “hardened password”
• Successful retrieval of “hardened password” requires knowledge of user’s password
• User’s private key is retrieved by means of “hardened password”
• Once retrieved the user’s private key can be freely used on this computer

Credential Servers 1 & 2

Alice knows Password,Pa

Step 5: Ask for Credentials

Step 1: Alice sends Pa

Long term private key is locked

with ‘hardened password’ H.

Need duplicate credentials server

for redundancy.

Client

Computer

Step 2: Client Computer starts process

Step 6: Check if Cert

is revoked

Step 7: Return Cert and H (D)

Step 3: Get H1

Security Servers 1 & 2

Step 4: GetH2

Step 9: Finally get around to logon

or sign operation!

Revocation Servers 1 & 2

Security server with partial knowledge

of ‘H’ (H1). Need duplicate server

for redundancy.

Security Servers 3 & 4

OCSP server to check for revocation

Security server with remaining knowledge

of ‘H’ (H2). Need duplicate server

for redundancy.

Step 8: UseH to decrypt

private key D

How to marry PKI and Passwords?

• Approach 1: Virtual Soft Token

Use password to encrypt private key and store it on remote server(s).

Need password to RETREIVE private key.

• Approach 2: Virtual Smartcard

The password is part of the composite private key.

Need password to USE private key.

• Keep the private key on an on-line server
• Use the password as authentication to enable use of the private key on the server
• Lose non-repudiation

M

A

A

M

M

And creates

A

A

A

ID: Castle Corp

FN: Castle

LN: Corp

.

.

• Alice takes

M

M

And creates

CC

• But (presto!)

!!!

M

CA

M

=

A

A

A

• Appliance takes

Password

M

• Alice has password P which ONLY she knows. Password P expands to key d1 on computer.

CA

A

A

ID: Castle Corp

FN: Castle

LN: Corp

.

.

• A Secure Identity Appliance has key d2 for Alice which ONLY it knows.

• As before, Alice has public cert, with public key e, signed by a CA.

CC

CA

A

A

Secure Identity Appliance

• Process
• Alice authenticates to appliance, sets up secure channel and sends M.
• Appliance performs partial signature on M with its key for Alice d2.
• Alice completes signature with her key d1.

• Practical PKITM
• Keys:
• Alice Public = e
• Alice PKCS5(password, salt, iteration count) = d1
• Alice Cert = C
• Alice appliance key = d2
• Signing:
• Alice logs on to appliance using d1 and creates secure channel
• Spartial = Sign(M,d2)
• S = Sign(Spartial,d1)
• Send [S, C] to Bob
• Bob:
• Gets e from C
• Does Verify(S,e) = M?

Traditional PKI

Keys:

• Alice Public = e
• Alice Private = d
• Alice Cert = C

Signing:

a) S = Sign (M,d)

Send [S, C] to Bob

Bob:

Gets e from C

Does Verify(S,e) = M?

Difference #1: Alice has short convenient password

Difference #2: Alice has to interact with appliance to sign.

• Practical PKITM
• Keys:
• Alice Public = e
• Alice PKCS5(password, salt, iteration count) = d1
• Alice Cert = C
• Alice appliance key = d2
• Signing:
• Alice logs on to appliance using d1 and creates secure channel
• Spartial = Sign(M,d2)
• S = Sign(Spartial,d1)
• Send [S, C] to Bob
• Bob:
• Gets e from C
• Does Verify(S,e) = M?

Traditional PKI

Keys:

• Alice Public = e
• Alice Private = d
• Alice Cert = C

Signing:

a) S = Sign (M,d)

Send [S, C] to Bob

Bob:

Gets e from C

Does Verify(S,e) = M?

NOTHING ELSE CHANGES!!!!

• Practical PKITM
• Keys:
• Alice Public = e
• Alice PKCS5(password, salt, iteration count) = d1
• Alice Cert = C
• Alice appliance key = d2
• Signing:
• Alice logs on to appliance using d1 and creates secure channel
• Spartial = Sign(M,d2)
• S = Sign(Spartial,d1)
• Send [S, C] to Bob
• Bob:
• Gets e from C
• Does Verify(S,e) = M?

Traditional PKI

Keys:

• Alice Public = e
• Alice Private = d
• Alice Cert = C

Signing:

a) S = Sign (M,d)

Send [S, C] to Bob

Bob:

Gets e from C

Does Verify(S,e) = M?

A

Velocity

Checking

Easy

to report

ID: Alice

FN: Alice

LN: Smith

Email:alice@cc.com

.

.

CA

CA

ID

stolen

Theft

detected

Theft

reported

CA revokes

ID

Recipient (we hope)

stops accepting ID

Strong Fraud Management

ID CANNOT BE USED ANY FURTHER!

INSTANT, COMPLETE, REVOCATION

Every signature requires appliance interaction. So appliance logs can be used for velocity checking.

Every signature requires appliance interaction. Once revoked key cannot be used further! Instant, complete revocation!

Consumer or CSR can use password to revoke instantly!

A

Velocity

Checking

Easy

to report

ID: Alice

FN: Alice

LN: Smith

Email:alice@cc.com

.

.

CA

CA

ID

stolen

Theft

detected

Theft

reported

CA revokes

ID

Recipient (we hope)

stops accepting ID

Strong Fraud Management

ID CANNOT BE USED ANY FURTHER!

INSTANT, COMPLETE, REVOCATION

• Practical PKITM solution
• Ease of use: password based
• Quick to deploy
• Simple to manage with least privilege
• Velocity checking and instant revocation
• Reusable for multiple applications
• Web, Wireless, VPN, email, etc.
• Use existing standards and widely deployed technologies

• Password enabled solutions are poised to jump start the stalled PKI car.
• Major vendors jumping into password enabled solutions using on-line servers is a good sign.
• “Many servers” are not all good, and have quality/security downside.
• Making password a part of the composite private key (virtual smartcards) provides substantial advantages over using password to retrieve private key (virtual soft tokens).