An Introduction to Identity-based Cryptography

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An Introduction to Identity-based Cryptography

• Carl Youngblood
• CSEP 590
• 3/8/06

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Problems with PKI

• Sender must have recipients certificate
• Complexity of certificate management and CRLs
• Security paradox Certificate database exposes
  organization

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Enter Identity-Based Cryptography

• Cryptography for unprepared users
• Public keys are some attribute of a users
  identity, such as an email address, phone number,
  or biometric data
• Sender only needs to know recipients identity
  attribute to send an encrypted message
• Recipient need not interact with the system until
  after receiving an encrypted message.

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History of IDC

• Proposed by Shamir in 1984
• Shamir came up with a working system for
  identity-based signature (IDS), but no system for
  identity-based encryption (IDE)
• First IDE system discovered in 2001 by Boneh and
  Franklin, based on Weil pairing.
• Currently hot topic in cryptography

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Identity-based encryption (IDE)
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Identity-based signature (IDS)
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Security of IDC

• Most IDC schemes are based on bilinear
  non-degenerate maps. These have the property
• Pair(a X, b Y) Pair(b X, a Y)
• Operator refers to multiplication of a point on
  an elliptic curve by integers
• Though unproven, the assumption is that these
  maps are one-way.
• Bilinear Diffie-Hellman Assumption, because BDH
  problem reduces to it.

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Advantages of IDC

• No user preparation required most compelling
  advantage
• No PKI management or certificate database
• Inherent key escrow, though a drawback, allows
  for some additional benefits
• No client-side installation required PKG can
  encrypt and sign messages for the user, in a
  web-based messaging application, for example.
• Policy-based automatic outbound message
  encryption
• Users keys may be kept on the PKG, which is more
  secure than users workstations.
• Chameleon signatures only recipient can
  verify

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Disadvantages of IDC

• Inherent key escrow
• Weakens non-repudiation
• Variants being developed to overcome this
  weakness
• No key revocation
• If private key gets compromised, do I have to get
  a new identity?
• Can be fixed by appending validity timestamp to
  public key
• PKG requires extremely high level of assurance,
  since it holds all private keys and must remain
  online.

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Implementations

• Stanford IBE system http//crypto.stanford.edu/ibe
  /
• MIRACL http//indigo.ie/mscott/
• Voltage Security, Inc. http//www.voltage.com/
• Proofpoint, Inc. http//www.proofpoint.com/

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Summary

• IBC has some weaknesses but is much easier to use
  than PKI
• For its advocates, IBC provides a more reasonable
  balance between security and usability
• High level of research is a good demonstration of
  its potential