BIP143: explicitly mention the SignatureHash function

The purpose of BIP143 is to propose an updated SignatureHash function
but "sighash" only appears near the end buried in the text. By
explicitly mentioning the SignatureHash function, readers can more
readily understand the context of the proposal.

1 files changed, 1 insertions, 1 deletions

diff --git a/bip-0143.mediawiki b/bip-0143.mediawiki
index 4c6503b..1f921c0 100644
--- a/bip-0143.mediawiki
+++ b/bip-0143.mediawiki
@@ -14,7 +14,7 @@ This proposal defines a new transaction digest algorithm for signature verificat
 == Motivation ==
 There are 4 ECDSA signature verification codes in the original Bitcoin script system: CHECKSIG, CHECKSIGVERIFY, CHECKMULTISIG, CHECKMULTISIGVERIFY (“sigops”). According to the sighash type (ALL, NONE, SINGLE, ANYONECANPAY), a transaction digest is generated with a double SHA256 of a serialized subset of the transaction, and the signature is verified against this digest with a given public key. The detailed procedure is described in a Bitcoin Wiki article. <ref name=wiki>[https://en.bitcoin.it/wiki/OP_CHECKSIG]</ref>
 
-Unfortunately, there are at least 2 weaknesses in the original transaction digest algorithm:
+Unfortunately, there are at least 2 weaknesses in the original SignatureHash transaction digest algorithm:
 
 * For the verification of each signature, the amount of data hashing is proportional to the size of the transaction. Therefore, data hashing grows in O(n<sup>2</sup>) as the number of sigops in a transaction increases. While a 1 MB block would normally take 2 seconds to verify with an average computer in 2015, a 1MB transaction with 5569 sigops may take 25 seconds to verify. This could be fixed by optimizing the digest algorithm by introducing some reusable “midstate”, so the time complexity becomes O(n). <ref>[https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-2292 CVE-2013-2292]</ref><ref>[https://bitcointalk.org/?topic=140078 New Bitcoin vulnerability: A transaction that takes at least 3 minutes to verify]</ref><ref>[http://rusty.ozlabs.org/?p=522 The Megatransaction: Why Does It Take 25 Seconds?]</ref>
 * The algorithm does not involve the amount of Bitcoin being spent by the input. This is usually not a problem for online network nodes as they could request for the specified transaction to acquire the output value. For an offline transaction signing device ("cold wallet"), however, the unknowing of input amount makes it impossible to calculate the exact amount being spent and the transaction fee. To cope with this problem a cold wallet must also acquire the full transaction being spent, which could be a big obstacle in the implementation of lightweight, air-gapped wallet. By including the input value of part of the transaction digest, a cold wallet may safely sign a transaction by learning the value from an untrusted source. In the case that a wrong value is provided and signed, the signature would be invalid and no funding might be lost. <ref>[https://bitcointalk.org/index.php?topic=181734.0 SIGHASH_WITHINPUTVALUE: Super-lightweight HW wallets and offline data]</ref>