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An Introduction to Identity-based Cryptography

An Introduction to Identity-based Cryptography. Carl Youngblood CSEP 590 3/8/06. Problems with PKI. Sender must have recipient’s certificate Complexity of certificate management and CRLs Security paradox – Certificate database exposes organization. e3eab1253b682fda7af153f6550ccb6e.

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An Introduction to Identity-based Cryptography

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  1. An Introduction to Identity-based Cryptography Carl Youngblood CSEP 590 3/8/06

  2. Problems with PKI • Sender must have recipient’s certificate • Complexity of certificate management and CRLs • Security paradox – Certificate database exposes organization e3eab1253b682fda7af153f6550ccb6e

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

  4. 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

  5. Identity-based encryption (IDE)

  6. Identity-based signature (IDS)

  7. 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.

  8. 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

  9. 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.

  10. 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/

  11. 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

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