1. ERS to XML Introduction to ERS syntax in XML format
68th IETF meeting, Prague, March 2007

2. Introduction ERS syntax ASN.1 vs XML format XML processing rules
Next steps
Other
March 2007
68th IETF Meeting,Prague

3. ERS ASN.1 Syntax Overview
Syntax information – container for
Long term demonstration of
Data integrity
Data time existence
Based on
Time stamp / Time stamp chains
Hash trees
ERS ASN.1 general overview
Version
Digest Algorithms
Algorithm Identifier,
Cryptographic Information
Encryption Information
Archive Time Stamp Sequence → Archive Time Chain → Archive Time Stamp
March 2007
68th IETF Meeting,Prague

4. ERS ASN.1 Syntax Overview
Archive Time Stamp
Digest Algorithm
Attributes
Reduced Hash Tree
Partial Hash Tree
Sequence of (ordered) octet strings
Archive Time Stamp Sequence
Sequence of Archive Time Stamp Chain
Sequence of Archive Time Stamp
March 2007
68th IETF Meeting,Prague

5. ERS ASN.1 Syntax overview
Encryption Information
Sequence of Encryption Information Type and
Encryption Information Value
March 2007
68th IETF Meeting,Prague

6. ERS in XML format Structure Version Archive Time Stamp (+Order)
Digest Method used for hash / hash trees
Hash Tree (optional)
Content
Time Stamp
Complementary Data (optional)
March 2007
68th IETF Meeting,Prague

7. ERS in XML format
Digest Method → reference to digest method algorithm URI
Time Stamp structure → any (RFC3161 or Entrust XML Time Stamp Schema)
Complementary Data → replaces cryptographic information (in ASN.1)
Hash Trees → collection of significant values of protected objects (input objects and generated evidence within archival period)
March 2007
68th IETF Meeting,Prague

8. ERS in XML Differences Hash values (of e.g. hash trees) Pros Cons
Calculated only for the objects (not of ERS XML structures which hold those objects)
When needed to bind many objects with single significant value → hash values of objects are sorted, concatenated and hashed
Pros
Hashes of protected items do not depend on specific ERS-XML structures, used to hold them
Cons
Not in the line with ERS-ASN.1 draft, where for the purpose of renewal hashes are calculated from the specifically formatted objects (order etc.)
March 2007
68th IETF Meeting,Prague

9. ERS in XML Differences Simplified structure Pros Cons
No structure for Sequences and Chains → only ordered sequence of Archive Time-stamps (ATS)
Pros
Simplified processing rules for generation and verification
Cons
Not in the line with ERS-ASN1 draft, where a first ATS in a chain holds ATS, created by the complex renewal process and others created by simple renewal process;
March 2007
68th IETF Meeting,Prague

10. ERS in XML format Next steps Confirm general structure and procedures
New version ready as of May 2007
Implementations and cross evaluation
March 2007
68th IETF Meeting,Prague

11. General information Prepared by Aleksej Jerman Blazic Svetlana Saljic
Tobias Gordon
March 2007
68th IETF Meeting,Prague