XMLDSIG
Open Syntax Questions 2
Donald E. Eastlake 3rd
<dee3@us.ibm.com>
9 November 1999, 46th IETF Meeting
Open Syntax Questions 2
- Algorithm Parameters
- Unsigned Location/Transforms
- Composite / Orthogonal (Signature) Algorithms
Algorithm Parameters
- Possibilities
<Parameter type="http:
hmac-trunctation-length">100</Parameter>
<Integer xmlns="http:
hmac-trunctation-length">100</Paramter>
<hmac-truncation-length xmlns="
">100
</hman-truncation-length>
Generic Element
<SignatureMethod Algorithm="dsig:hmacX">
<Parameter xmlns="dsig:hmac-truncation-length>
100
</Parameter>
<Parameter xmlns="dsig:other" Encoding="dsig:base64">
2f/0cb==
</Parameter>
</SignatureMethod>
Type Element
<SignatureMethod Algorithm="dsig:hmacX">
<Integer xmlns="dsig:hmac-truncation-length>
100
</Integer>
<Binary xmlns="dsig:other" Encoding="dsig:base64">
2f/0cb==
</Binary>
</SignatureMethod>
Algorithm Specific Element 1
<SignatureMethod Algorithm="dsig:hmacX">
<hmac-truncation-length xmlns="dsig:hmacX">
100
</hmac-truncation-length>
<Other xmlns="dsig:hmacX" Encoding="dsig:base64">
2f/0cb==
</Other>
</SignatureMethod>
Algorithm Specific Element 2
<SignatureMethod Algorithm="dsig:hmacX" xmlns:a="dsig:hmacX">
<a:hmac-truncation-length>
100
</ hmac-truncation-length>
<a:Other Encoding="dsig:base64">
2f/0CbW8zp= =
</Other>
</SignatureMethod>
Unsigned Location/Transforms
- Desire to have data that can move around
- Nested Manifests
- clever URIs for Location
- iotp:transaction-id#idref
- http://example.com/cgi/finder?doc-1234
- Move Location outside of SignedInfo
- Allow Transforms of SignedInfo to remove Location
- In general, different locations need different transforms
Nested Manifests
- SignedInfo ObjectReference points to a Manifest which points to a Manifest.
- Con: Depends on application verification behavior. Bulky.
- Pro: Fits current syntax. 2nd level Manifest can be separately signed.
Location Outside SignedInfo
- Need to also move Transforms out
- Con: Need to drop multiple ObjectReferences or add a link to DigestMethod/Value inside
SignedInfo. Need some way to securing Location if you want to.
Clever URIs for Locations
- Con: Are permanent URN's possible?
- Implies clever Transforms which is even hairier.
- Pro: fits in current syntax
Allow Transform of SignedInfo
- Can simply drop out Locations and/or Transforms.
- Con: Increases complexity in signature core. Can be dangerous (but not much worse than
other uses of Transforms).
- Pro: very powerful, can satisfy many desires.
Composite / Orthogonal Algorithms
- Acceptance of multiple combinations reduces security to that of the weakest
- Composite: RSA-SHA1-Xpad
- less verbose
- combinatorial explosion
- Orhogonal: <RSA><SHA1/><Xpad/></RSA>