A CoMETRE Profile and Tree Algorithm for the Confidential Consortium Framework

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Table of Contents

1. Introduction

The Concise Encoding of Signed Merkle Tree Proofs (CoMeTre) [I-D.steele-cose-merkle-tree-proofs] defines a common framework for defining different types of proofs, such as proof of inclusion, about verifiable data structures (also abbreviated as "logs" in this document). For instance, inclusion proofs guarantee to a verifier that a given serializable element is recorded at a given state of the log, while consistency proofs are used to establish that an inclusion proof is still consistent with the new state of the log at a later time.¶

In this document, we define a new type of log, associated with the Confidential Consortium Framework (CCF) ledger. Compared to [RFC9162], the leaves of CCF trees carry additional opaque information that is used to verify that elements are only written by the Trusted Execution Environment, which addresses the persistence of committed transactions that happen between new signatures of the Merkle Tree root.¶

2. Description of the CCF Ledger Verifiable Data Structure

This documents extends the verifiable data structure registry of [I-D.steele-cose-merkle-tree-proofs] with the following value:¶

MTH({}) = HASH().

MTH({d[0]}) = HASH(d[0]).

MTH(D_n) = HASH(MTH(D[0:k]) || MTH(D[k:n])),

CCF-leaf = [
  internal-hash: bstr ; a string of HASH_SIZE bytes;
  internal-data: bstr; a string of at most 1024 bytes; and
  data_hash: bstr ; the serialization of the element stored at this leaf.
]

3. CCF Inclusion Proofs

CCF inclusion proofs consist of a list of digests tagged with a single left-or-right bit.¶

CCF-inclusion-proof: [+ proof-element],

proof-element = [
  left: bool
  hash: bstr
]

Unlike some other tree algorithms, the index of the element in the tree is not explicit in the inclusion proof, but the list of left-or-right bits can be treated as the binary decomposition of the index, from the least significant (leaf) to the most significant (root).¶

compute_root(leaf, proof):
  h := leaf.internal-hash
       || HASH(leaf.internal-data)
       || leaf.data-hash

  for [left, hash] in proof:
      h := HASH(hash + h) if left
           HASH(h + hash) else
  return h

verify_inclusion_proof(signed_proof):
  leaf := signed_proof.unprotected_headers[LEAF_LABEL] or fail
  proof := signed_proof.unprotected_headers[INCLUSION_PROOF_LABEL] or fail
  payload := compute_root(leaf, proof)
  return verif_cose_detached(signed_proof, payload)

4. Privacy Considerations

Privacy Considerations¶

5. Security Considerations

Security Considerations¶

6. IANA Considerations

Appendix A. Attic

Not ready to throw these texts into the trash bin yet.¶

Authors' Addresses