From 2b987b57112af9767f888ed65b17c894ee4b34a6 Mon Sep 17 00:00:00 2001
From: Tim Ruffing <crypto@timruffing.de>
Date: Sun, 8 Sep 2019 16:38:15 +0200
Subject: Rework Applications section

---
 bip-schnorr.mediawiki | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

(limited to 'bip-schnorr.mediawiki')

diff --git a/bip-schnorr.mediawiki b/bip-schnorr.mediawiki
index de55ded..f88660e 100644
--- a/bip-schnorr.mediawiki
+++ b/bip-schnorr.mediawiki
@@ -8,17 +8,17 @@
   Post-History: 2018-07-06: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-July/016203.html [bitcoin-dev] Schnorr signatures BIP
 </pre>
 
-==Introduction==
+== Introduction ==
 
-===Abstract===
+=== Abstract ===
 
 This document proposes a standard for 64-byte Schnorr signatures over the elliptic curve ''secp256k1''.
 
-===Copyright===
+=== Copyright ===
 
 This document is licensed under the 2-clause BSD license.
 
-===Motivation===
+=== Motivation ===
 
 Bitcoin has traditionally used
 [https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm ECDSA] signatures over the [http://www.secg.org/sec2-v2.pdf secp256k1 curve] for authenticating
@@ -205,13 +205,13 @@ Many techniques are known for optimizing elliptic curve implementations. Several
 There are several interesting applications beyond simple signatures.
 While recent academic papers claim that they are also possible with ECDSA, consensus support for Schnorr signature verification would significantly simplify the constructions.
 
-===Multisignatures and Threshold Signatures===
+=== Multisignatures and Threshold Signatures ===
 
-By means of an interactive scheme such as [https://eprint.iacr.org/2018/068 MuSig], participants can produce a combined public key which they can jointly sign for. This allows n-of-n multisignatures which, from a verifier's perspective, are no different from ordinary signatures, giving improved privacy and efficiency versus ''CHECKMULTISIG'' or other means.
+By means of an interactive scheme such as [https://eprint.iacr.org/2018/068 MuSig], participants can aggregate their public keys into a single public key which they can jointly sign for. This allows n-of-n multisignatures which, from a verifier's perspective, are no different from ordinary signatures, giving improved privacy and efficiency versus ''CHECKMULTISIG'' or other means.
 
-Further, by combining Schnorr signatures with [https://link.springer.com/content/pdf/10.1007/3-540-46766-1_9.pdf Pedersen Secret Sharing], it is possible to obtain [http://cacr.uwaterloo.ca/techreports/2001/corr2001-13.ps an interactive threshold signature scheme] that ensures that signatures can only be produced by arbitrary but predetermined sets of signers. For example, k-of-n threshold signatures can be realized this way. Furthermore, it is possible to replace the combination of participant keys in this scheme with MuSig, though the security of that combination still needs analysis.
+Moreover, Schnorr signatures are compatible with [https://web.archive.org/web/20031003232851/http://www.research.ibm.com/security/dkg.ps distributed key generation], which enables interactive threshold signatures schemes, e.g., the schemes described by [http://cacr.uwaterloo.ca/techreports/2001/corr2001-13.ps Stinson and Strobl (2001)] or [https://web.archive.org/web/20060911151529/http://theory.lcs.mit.edu/~stasio/Papers/gjkr03.pdf Genaro, Jarecki and Krawczyk (2003)]. These protocols make it possible to realize k-of-n threshold signatures, which ensure that any subset of size k of the set of n signers can sign but no subset of size less than k can produce a valid Schnorr signature. However, the practicality of the existing schemes is limited: most schemes in the literature have been proven secure only for the case k < n/2, are not secure when used concurrently in multiple sessions, or require a reliable broadcast mechanism to be secure. Further research is necessary to improve this situation.
 
-===Adaptor Signatures===
+=== Adaptor Signatures ===
 
 [https://download.wpsoftware.net/bitcoin/wizardry/mw-slides/2018-05-18-l2/slides.pdf Adaptor signatures] can be produced by a signer by offsetting his public nonce with a known point ''T = tG'', but not offsetting his secret nonce.
 A correct signature (or partial signature, as individual signers' contributions to a multisignature are called) on the same message with same nonce will then be equal to the adaptor signature offset by ''t'', meaning that learning ''t'' is equivalent to learning a correct signature.
@@ -219,12 +219,11 @@ This can be used to enable atomic swaps or even [https://eprint.iacr.org/2018/47
 
 Adaptor signatures, beyond the efficiency and privacy benefits of encoding script semantics into constant-sized signatures, have additional benefits over traditional hash-based payment channels. Specifically, the secret values ''t'' may be reblinded between hops, allowing long chains of transactions to be made atomic while even the participants cannot identify which transactions are part of the chain. Also, because the secret values are chosen at signing time, rather than key generation time, existing outputs may be repurposed for different applications without recourse to the blockchain, even multiple times.
 
-===Blind Signatures===
+=== Blind Signatures ===
 
-Schnorr signatures admit a very [https://www.math.uni-frankfurt.de/~dmst/research/papers/schnorr.blind_sigs_attack.2001.pdf simple '''blind signature''' construction] which is a signature that a signer produces at the behest of another party without learning what he has signed.
-These can for example be used in [https://github.com/jonasnick/scriptless-scripts/blob/blind-swaps/md/partially-blind-swap.md Partially Blind Atomic Swaps], a construction to enable transferring of coins, mediated by an untrusted escrow agent, without connecting the transactors in the public blockchain transaction graph.
+A blind signature protocol is an interactive protocol that enables a signer to sign a message at the behest of another party without learning the signer learning any information about the signed message or the signature. Schnorr signatures admit a very [https://www.math.uni-frankfurt.de/~dmst/research/papers/schnorr.blind_sigs_attack.2001.pdf simple blind signature scheme] which is however insecure because it's vulnerable to [https://www.iacr.org/archive/crypto2002/24420288/24420288.pdf Wagner's attack]. A known mitigation is to let the signer abort a signing session with a certain probability, and the resulting scheme can be [https://eprint.iacr.org/2019/877 proven secure under non-standard cryptographic assumptions].
 
-While the traditional Schnorr blind signatures are vulnerable to [https://www.iacr.org/archive/crypto2002/24420288/24420288.pdf Wagner's attack], there are [https://www.math.uni-frankfurt.de/~dmst/teaching/SS2012/Vorlesung/EBS5.pdf a number of mitigations] which allow them to be usable in practice without any known attacks. Nevertheless, more analysis is required to be confident about the security of the blind signature scheme.
+Blind Schnorr signatures could for example be used in [https://github.com/jonasnick/scriptless-scripts/blob/blind-swaps/md/partially-blind-swap.md Partially Blind Atomic Swaps], a construction to enable transferring of coins, mediated by an untrusted escrow agent, without connecting the transactors in the public blockchain transaction graph.
 
 == Test Vectors and Reference Code ==
 
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