A Transaction Ledger Verifiable Structure for COSE Merkle Tree Proofs

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Table of Contents

1. Introduction

The Concise Encoding of Signed Merkle Tree Proofs (CoMeTre) [I-D.ietf-cose-merkle-tree-proofs] defines a common framework for defining different types of proofs 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. This log carries indexed transaction information in a binary Merkle Tree, where new transactions are appended to the right, so that the binary decomposition of the index of a transaction can be interpreted as the position in the tree if 0 represents the left branch and 1 the right branch. 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. Format of CCF Ledger

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

This document defines inclusion proofs and consistency proof formats for CCF ledgers. Verifiers MUST reject all other proof types.¶

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: [
  leaf: CCF-leaf ;
  path: [+ ccf-proof-element] ;
]

ccf-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(proof):
  let h = proof.leaf.internal-hash
       || HASH(proof.leaf.internal-data)
       || proof.leaf.data-hash
  for [left, hash] in proof.path:
      h := HASH(hash + h) if left
           HASH(h + hash) else
  return h

verify_inclusion_receipt(inclusion_receipt):
  let proofs = inclusion_receipt.unprotected_headers[-222] or fail
  let payload = nil
  assert(inclusion_receipt.payload == nil)

  for proof in proofs
    let root = compute_root(proof)
    if payload = nil then payload := root
    else assert(root == payload)

  # Use the Merkle Root as the detached payload
  return verif_cose(inclusion_receipt, 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