Digital Signature Standard

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Digital Signature Standard

• FIPS PUB 186-2
• 2000 January 27
• Andrew Lehman
• May 9, 2002

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Digital Signatures

• Why do we need them?
• Electronically sign contracts, checks, emails
• Why do we need DSS/DSA?
• Want a secure standard
• Royalty-free

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Goals

• Background
• Review Digital Signatures
• Criteria for Digital Signature Standard
• Discuss DSA
• How it works
• Why it works
• Interesting features of the algorithm
• Current use
• Summary

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Criteria for DSS

• Provide solid Digital Signatures
• Authentic
• Unforgeable
• Not reusable
• Unalterable
• Non-repudiation
• NOT to provide encryption

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Controversies

• Cannot be used for encryption
• Developed by NSA trapdoor?
• Slower than RSA
• RSA is de facto standard
• Selection process was not public
• May infringe on other patents
• Key size is too small

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Speed of RSA
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How DSA Works Parameters
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How DSA Works Signing
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How DSA Works Verifying
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Example
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Why DSA Works
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Interesting DSA Features

• Subliminal channels
• Alice and Bob can secretly share information
• Secret key can be leaked
• Can be used for encryption
• ElGamal
• RSA

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Current Use

• Used by the government
• Shell Oil
• Currently
• 70 use RSA for Digital Signatures
• RSA mentioned in FIPS 186-2
• ECDSA Elliptic Curve analogue

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Summary

• DSA intended only for signatures
• Lots of controversy
• Secure but slow to verify
• NIST considering expanding key, hash sizes

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References

• Digital Signature Standard FIPS PUB 186/186-2
• Cryptography and Network Security
• Applied Cryptography by Bruce Schneier
• Subliminal Communication is Easy Using the DSA
  by Gus Simmons EUROCRYPT 93
• Secure Hash Standard FIPS PUB 180-1

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Why DSA Works (No animation)
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Future Directions
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Attacks