Original text:
Trees, sparse/indexed Merkle Trees, full blockchains, and many other variants.  The Registry is only required to support concise Receipts (i.e., whose size grows at most logarithmically in the number of <del> entries in the Registry).  This does not necessarily rule out blockchains as a Registry, but may necessitate advanced Receipt schemes that use arguments of knowledge and other verifiable computing techniques. Since the details of how to verify a Receipt are specific to the data structure, no particular Registry format is specified in this document.  Instead, two initial formats for Registry in I-D.birkholz- scitt-receipts using historical and sparse Merkle Trees are proposed. Beyond the format of Receipts, generic properties that should be satisfied by the components in the Transparency Services that have the ability to write to the Registry are required. </del>  5.2.3.1.

Reviewer comments:
As proposed in at the WG meeting in Tokyo, we would like to move receipts as a generic primitive in COSE. (see issue ) This PR removes all explicit references to the SCITT receipt ID and instead defines Receipts based on . Note that I also incorporated 2 proposed changes to make SCITT statement and receipt signature more symmetrical: Receipts now include the DID of the transparency service. This can be optionally used to discover the receipt signing key. This change was originally proposed at the IETF WG meeting in London. It simplifies statement authorization, as verifiers can only trust the stable DID of the TS instead of worry about keys or certificate that may be rotated Transparency services can now indicate the registration policies that were actually applied. This is very helpful for verifier, for instance to check the freshness of claims. This was proposed in Tokyo
LGTM, see this implementation: URL and demo: URL
NAME can you help resolve the errors?
Hi, Does this change mean that implementations based on native merkle tries (eg will have to translate proofs to this format ? And if that is so, what is the basis for trusting the service that does that ? Or is there scope for registering trie algorithms based on native proofs like ERC 1186 ?
As we're working to complete for 116, I'm assigning to 116
See for a proposed implementation
Closing as has been merged
I'd like to more generally discuss additional information provided by the TS as it issues receipts: Some information "at the root" refers to its signing (timestamp, keying, ID, etc) but implicitly applies to every statement recorded so far. As discussed at the last hackathon, some information "at the leaf" is the outcome of applying the TS registration policy to each signed statement, including e.g. the configuration of the TS at that point (timestamp, authorized keys, DID resolution results, etc) LGTM

Revised text:
Trees, sparse/indexed Merkle Trees, full blockchains, and many other variants.  The Registry is only required to support concise Receipts (i.e., whose size grows at most logarithmically in the number of  <ins> entries in the Registry) that can be encoded as a COSE Signed Merkle Tree Proof. It is possible to offer multiple signature algorithms for the COSE signature of receipts' Signed Merkle Tree, or to change the signing algorithm at a later points.  However, the Merkle Tree algorithm (including its internal hash function) cannot easily be changed without beaking the consistency of the Registry.  It is possible to maintain separate Registries for each algorithm in parallel but the Transparency Service is then responsible for proving their mutual consistency. </ins> 5.2.3.1.