Ace:Validating Witness and Tokens

Overview

ACE offers a two tiered method for ensuring the validity of hashes. The first tier involved calculating a summary value (CSI) for a set of hashes given to the IMS. These CSIs are composed of all hashes for a given time period (round). This CSI can be used to validate any hash submitted during its round. The second tier involves periodically publishing a witness value that is calculated from all CSI values issues during the previous day.

Validating Tokens and Hashes

Token Overview

A token contains all information needed to validate a hash. A sample token is shown below:

<?xml version="1.0" encoding="utf-8"?>
<token xmlns="http://umiacs.umd.edu/adapt/ace/token/1.0">
        <token-class>SHA-256-0</token-class>
        <digest-service>SHA-256</digest-service>
        <name>/state/myfile.txt</name>
        <round-id>319782</round-id>
        <time-stamp>2008-09-16T14:57:27.936-0400</time-stamp>
        <proof>
                <element index="0">
                        <hash>7957e058645f953f8e2d11c919414adffab7df12df3e7902eb446b02a40ac908</hash>
                </element>
                <element index="1">
                        <hash>9287c2e19f715a67dcb59da8a724084b448dd9382668f347338f1ce20f435872</hash>
                </element>
                <element index="2">
                        <hash>e9cc9417014a43e29870f60504cdbe3c49ba9472b4481bb2ff5f7a68cef147bb</hash>
                        <hash>73384002a2fd512874801fb62e1defbb1902668f04d8a96d6cb90b703d16a506</hash>
                </element>
                <element index="1">
                        <hash>d312e4551a3d3ee6d695d96b8851f3ad1574096305f18d4f052fe853bfe14482</hash>
                </element>
        </proof>
</token>

• token-class:
• digest-service:
• name: name of the file this token refers to. This was supplied by the client in a token request.
• round-id: The ID of the round this token was issued in. This is used to request a CSI from the IMS.
• time-stamp: the timestamp for this round
• proof: tree elements that can be used to locally generate a CSI given a files hash.