scittatp: statement URN used for indexing

[johnandersen777]

We need a way to say "these are my identities"

This way any instance you query returns transparent statements (and payload) which allow resolution across federated instances. This enables query in isolated or segmented networks regardless of protocol.

Use insert transparent policy and GitHub Actions schema exec SCITT policy engine to verify did:plc or other ownership on insert. We can use this to verify the post used as the users index without needing to pin it. This will become our decentralized indexing mechanism.

• SCITT URN of index statement becomes like how we post / use PGP fingerprints
  • This signed statement URN functions as the root node via the payload for OpenSSF S2C2F ING-4 discovery across trust boundaries.
  • SCITT instances federate statements which are aligned with insert policy which will verify identities of each signer, to prove that is their index root.
  • The insert policy on this instance is like your ING-4 keybase verifier

  • 8

  • We use in repo upstream.yml policy for each branch to define who we federate with
    • Instead of keys we use the URNs of each owners root index
• TODOs
  • [ ] Ensure create_statement.py code is up to date with SCITT spec
  • https://www.ietf.org/archive/id/draft-ietf-scitt-architecture-10.html#section-4.2.1
    • COSE_CertHash
  • [x] Write URN formation code
  • https://www.ietf.org/archive/id/draft-ietf-scitt-architecture-10.html#appendix-B.2

    • urn:ietf:params:scitt:{message-type}:{hash-name}:{base-encoding}:{base64url-encoded-to-be-signed-bytes-digest}

      urn:ietf:params:scitt:signed-statement:sha-256:base64url:5i6UeR...qnGmr1o

  • https://github.com/ietf-wg-scitt/draft-ietf-scitt-scrapi/blob/35274ef0fa3b2b3baa07a88a3dfe59cfa108abe9/draft-ietf-scitt-scrapi.md#register-signed-statement
    • Statement and signed statement URNs are identical
  • https://github.com/johnandersen777/scitt-api-emulator/commit/855cce7c94ec57c038fa442a7057adbff0948cad
• Future
  • [ ] SCITT instance who we trust due to being attested, that way we trust it as the identity verification and discovery service for within the trust boundary based on the software it's running and the policy it runs.

[johnandersen777]

$ python -u scitt_emulator/create_statement.py --out statement.signed --subject test --content-type 'text/plain' --payload test
urn:ietf:params:scitt:signed-statement:sha256:base64url:Q9OWRUhmW_ZOPTU3yaau9AfCGxPHO2QQ8fuP0dztdnw=

diff --git a/scitt_emulator/create_statement.py b/scitt_emulator/create_statement.py
index da1c6da..4caea85 100644
--- a/scitt_emulator/create_statement.py
+++ b/scitt_emulator/create_statement.py
@@ -2,6 +2,7 @@
 # Licensed under the MIT License.
 import base64
 import pathlib
+import hashlib
 import argparse
 from typing import Union, Optional, List

@@ -169,6 +170,26 @@ def create_claim(
     if private_key_pem_path and not private_key_pem_path.exists():
         private_key_pem_path.write_bytes(key_as_pem_bytes)

+    # https://github.com/TimothyClaeys/pycose/blob/e527e79b611f6cc6673bbb694056a7468c2eef75/pycose/messages/sign1message.py#L66C9-L79
+    msg.signature = b""
+    # https://github.com/TimothyClaeys/pycose/blob/e527e79b611f6cc6673bbb694056a7468c2eef75/pycose/messages/cosemessage.py#L143
+    claim = msg.encode(tag=True, sign=False)
+
+    # https://www.ietf.org/archive/id/draft-ietf-scitt-architecture-10.html#appendix-B.2-5
+    # signed statement and statement are identical AFAIK
+    message_type = "signed-statement"
+
+    hash_name = "sha256"
+    hash_instance = hashlib.new(hash_name)
+    hash_instance.update(claim)
+
+    base_encoding = "base64url"
+    base64url_encoded_bytes_digest = base64.urlsafe_b64encode(
+        hash_instance.digest(),
+    ).decode()
+
+    return f"urn:ietf:params:scitt:{message_type}:{hash_name}:{base_encoding}:{base64url_encoded_bytes_digest}"
+

 def cli(fn):
     p = fn("create-claim", description="Create a fake SCITT claim")
@@ -195,7 +216,8 @@ def cli(fn):
 def main(argv=None):
     parser = cli(argparse.ArgumentParser)
     args = parser.parse_args(argv)
-    args.func(args)
+    urn = args.func(args)
+    print(urn)

 if __name__ == "__main__":

• Thinking about https://pdsls.dev ATProto DID doc statement URNs using CBOR-LD