From df9c2fc6de7a99556a9688a530993ece9b8acba5 Mon Sep 17 00:00:00 2001
From: Karl-Johan Alm <karljohan-alm@garage.co.jp>
Date: Mon, 3 Dec 2018 15:07:44 +0900
Subject: bip-322: strip out proof-of-funds related stuff and fix several
 issues

---
 bip-0322.mediawiki | 63 +++++++++++++++++++++++++++---------------------------
 1 file changed, 32 insertions(+), 31 deletions(-)

(limited to 'bip-0322.mediawiki')

diff --git a/bip-0322.mediawiki b/bip-0322.mediawiki
index 5191143..606e2f7 100644
--- a/bip-0322.mediawiki
+++ b/bip-0322.mediawiki
@@ -23,9 +23,9 @@ The current message signing standard only works for P2PKH (1...) addresses. By e
 
 A new structure <code>SignatureProof</code> is added, which is a simple serializable scriptSig & witness container.
 
-Two actions "Sign" and "Verify" are defined along with two *purposes* "SignMessage" and "ProveFunds".
+=== Common Header ===
 
-=== SignatureProof container ===
+A common header used for signature proofs and challenges is defined as follows:
 
 {|class="wikitable" style="text-align: center;"
 |-
@@ -43,7 +43,9 @@ Two actions "Sign" and "Verify" are defined along with two *purposes* "SignMessa
 |Uint8||1||entries||Number of proof entries<ref><strong>Why support multiple proofs?</strong> In particular with proof of funds, it is non-trivial to check a large number of individual proofs (one per UTXO) for duplicates. Software could be written to do so, but it seems more efficient to build this check into the specification itself.</ref>
 |}
 
-The above is followed by [entries] number of signature entries:
+=== SignatureProof container ===
+
+The signature proof begins with a common header, and is followed by [entries] number of signature entries:
 
 {|class="wikitable" style="text-align: center;"
 |-
@@ -80,54 +82,53 @@ A verification call will return a result code according to the table below.
 |-
 |INVALID||One or more of the given proofs were invalid
 |-
-|SPENT||One or more of the claimed UTXO:s has been spent
-|-
 |ERROR||An error was encountered
 |}
 
-== Signing and Verifying ==
+=== SignMessage serialization ===
 
-Let there be an empty set `inputs` which is populated and tested at each call to one of the actions below.
+The SignMessage challenge begins with the common header, and is followed by [entries] entries:
 
-=== Purpose: SignMessage ===
+{|class="wikitable" style="text-align: center;"
+|-
+!Type
+!Length
+!Name
+!Comment
+|-
+|VarInt||1-8||spklen||ScriptPubKey length
+|-
+|Uint8*||[spklen]||spk||ScriptPubKey
+|}
 
-The "SignMessage" purpose generates a sighash based on a scriptPubKey and a message. It emits a VALID verification result code unless otherwise stated.
+=== Proving and Verifying ===
 
-# Return INVALID if scriptPubKey already exists in `inputs` set, otherwise insert it<ref><strong>Why track duplicates?</strong> Because a 3-entry proof is not proving 3 inputs unless they are all distinct</ref>
-# Define the message pre-image as the sequence "Bitcoin Message:" concatenated with the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD)
-# Let sighash = sha256(sha256(scriptPubKey || pre-image))
+Let there be an empty set <code>inputs</code> which is populated and tested at each call to one of the actions below.
 
-=== Purpose: ProveFunds ===
+=== Common steps ===
 
-The "ProveFunds" purpose generates a sighash and a scriptPubKey from a transaction, an output index, and a message. For multiple simultaneous proofs, it also requires access to the ordered list of proofs. It emits a VALID verification result code unless otherwise stated.
+A sighash is generated based on a scriptPubKey and a message. A VALID verification result code is emitted unless otherwise stated.
 
-# Let txid be the transaction ID of the transaction, and vout be the output index corresponding to the index of the output being spent
-# Return INVALID if the txid:vout pair already exists in `inputs` set, otherwise insert it
-# Return SPENT if the txid/vout is not a valid UTXO according to a Bitcoin node<ref><strong>Synced up or not?</strong> A normal verifier would use a synced up node. An auditor checking records from a client that were submitted in the past want to use a node that is synced up to the block corresponding to the proof, or the proof will fail, even if it may have been valid at the time of creation.</ref>
-# Extract scriptPubKey from transaction output
-# Define the message pre-image as the concatenation of the following components:<ref><strong>Why not just the UTXO data?</strong> We want the verifier to be able to challenge the prover with a custom message to sign, or anyone can reuse the POF proof for a set of UTXO:s once they have seen it, and the funds have not yet been spent</ref>
-#* the string "POF:"
-#* the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD), including the null terminating character (i.e. write strlen(message) + 1 bytes, for a C string)
-#* all transactions being proven for, as binary txid (little endian uint256) followed by index (little endian uint32), each separated by a single `0x00` byte
+# Emits INVALID if scriptPubKey already exists in <code>inputs</code>set, otherwise insert it<ref><strong>Why track duplicates?</strong> Because a 3-entry proof is not proving 3 inputs unless they are all distinct</ref>
+# Emits INVALID if the message is not a UTF-8 string encoded using Normalization Form Compatibility Decomposition (NFKD); note specifically that binary messages are not supported
+# Define the message pre-image as the sequence "Bitcoin Message:" concatenated with the message, ''excluding'' the null terminating character (if any)
 # Let sighash = sha256(sha256(scriptPubKey || pre-image))
 
-=== Action: Sign ===
+=== Proving ===
 
-The "Sign" action takes as input a purpose. It returns a signature or fails.
+Returns a signature or fails (emits INVALID).
 
-# Obtain the sighash and scriptPubKey from the purpose; FAIL if not VALID
 # Derive the private key privkey for the scriptPubKey; FAIL if not VALID
-# Generate and return a signature sig with privkey=privkey, sighash=sighash
+# Generate a signature sig with privkey=privkey, sighash=sighash
+# Return a SignatureProof container with the given signature
 
-=== Action: Verify ===
+=== Verifying ===
 
-The "Verify" action takes as input a standard flags value, a script sig, an optional witness, and a purpose.
-It emits one of INCONCLUSIVE, VALID, INVALID, or ERROR.
+Emits one of INCONCLUSIVE, VALID, or INVALID.
 
-# Obtain the sighash and scriptPubKey from the purpose; pass on result code if not VALID
 # If one or more of the standard flags are unknown, return INCONCLUSIVE
 # Verify Script with flags=standard flags, scriptSig=script sig, scriptPubKey=scriptPubKey, witness=witness, and sighash=sighash
-# Return VALID if verify succeeds, otherwise return INVALID
+# Emit VALID if verify succeeds, otherwise emit INVALID
 
 === Multiple Proofs ===
 
-- 
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