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Multiple Signature Document

Multiple Signature Document. Jim Schaad Sean Turner Russ Housley. Topics to be Covered. Multiple Signature Attribute Policy Issues in evaluating Multiple Signatures. Downgrade Attack. Downgrade attack requires: Removal of all “better” signatures

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Multiple Signature Document

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  1. Multiple Signature Document Jim Schaad Sean Turner Russ Housley

  2. Topics to be Covered • Multiple Signature Attribute • Policy Issues in evaluating Multiple Signatures

  3. Downgrade Attack • Downgrade attack requires: • Removal of all “better” signatures • 2nd pre-image attack on broken hash algorithm. • Does nothing for self issued downgrade attack.

  4. Structure Elements MultipleSignature ::= SEQUENCE { bodyHashAlg DigestAlgorithIdentifier, signAlg SignatureAlgorithmIdentifier, signAttrsHash SignAttrsHash, cert ESSCertIDV2 OPTIONAL}

  5. Processing • Generation • Algorithms are from the referenced signerInfo • Hash values set to zero for computation of this attribute • Uses multiple attribute values (one per reference and no self reference)

  6. Processing • Evaluation • Text to be written still • Reverse process by setting hash back to zero • Error text based on missing signer infos referenced from the attribute • May not care if algorithms referenced are “weak”

  7. Policy • Text still unwritten • Discuss requirements for intra- and inter-SignedData signature evaluation.

  8. Forward Looking • Should have draft by the end of the month • Look for last call after San Diego.

  9. Questions

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