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Introduction |
Introduction |
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============ |
============ |
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- Documents on the Web transient |
.. Documents on the Web transient |
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- A long-term storage system where past versions |
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remain accessible as long as someone wants to |
Documents on the Web are transient: They exist only as long |
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access them |
as their publisher cares to maintain them. Often enough, |
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- Digital signatures for updateable documents |
a link from a 1999 mailing list archive will not be |
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retrievable today, only a few years later. |
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.. A long-term storage system where past versions |
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remain accessible as long as someone wants to |
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access them |
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We envision a long-term storage system, in which documents |
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can be found as long as a copy exists *anywhere* in the |
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system, i.e., as long as *someone* still cares to |
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maintain a copy. After a document is updated, it should |
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still be possible to access its previous versions-- |
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provided that somebody has kept a copy. |
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It should not be possible for a publisher-- or for the |
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publisher's government-- to remove a document version |
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from the system, as long as someone-- possibly in a |
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different legislative domain-- holds a copy. |
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In such a system, document identifiers must be |
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self-verifying; that is, having downloaded an |
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alleged copy of a document from some server in the network, |
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it must be possible to verify that this is a 'real' |
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copy of the document, not a forged version. |
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For individual versions of documents, a cryptographic hash |
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of the version can be used as a self-verifying identifier. |
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In this document, we consider the more difficult problem |
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of providing self-verifying identifiers for documents |
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that can change over time. |
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.. Digital signatures for updateable documents |
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A simple approach would be to use |
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- Keys expire and are revoked |
- Keys expire and are revoked |
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- The usual approach: Certificate Authorities (CAs) |
- The usual approach: Certificate Authorities (CAs) |
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plus Time Stamping Services (TSSs) |
plus Time Stamping Services (TSSs) |