Re: ERS RFC 4998 question

[Tilo Kienitz <tk-tlslist@xxxxxxxxxxxxxx>]

Peter Sylvester wrote:
> In a recent discussion I was asked to explain how the timestamp
> in an ERS ArchiveTimeStamp is created.
> The text does not seem to be clear, point 5 on page 11:
>
> 5 Obtain a timestamp for this root hash value.
> Does it mean that the hash value will be presented directly
> or a hash of that value.
>
> If it is presented directly, what has to be done for the root
> when the algorithm supported by a TSA and the digestAlgorithm
> indicated in the ArchiveTimeStamp are not the same?

We had the same problem and implemented the following:

The hash tree uses SHA-256.

a) If the TSA supports SHA-256, then the root hash value is
   presented directly to the TSA.
b) If the TSA only supports SHA-1, then an SHA-1 hash over the
   root hash is computed and sent to the TSA.

As Thomas Kunz writes, b is not exactly what the RFC wants. However,
we had no other choice, because we need qualified time stamps
according to the german signature law. Such timestamps were not
available with SHA-256 until about a year ago. So we had to use
SHA-1 timestamps for a while.

Kind regards
Tilo