Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 5B3C849B for ; Tue, 14 Nov 2017 10:51:17 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-vk0-f49.google.com (mail-vk0-f49.google.com [209.85.213.49]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id CA50F136 for ; Tue, 14 Nov 2017 10:51:15 +0000 (UTC) Received: by mail-vk0-f49.google.com with SMTP id n63so2288662vkf.2 for ; Tue, 14 Nov 2017 02:51:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to:cc; bh=y21CDt2vT46TuZ6N05ZyTss9a09IFbjnOjqIQFxN93Q=; b=Gt4iNrvfZbLf5cw+lQ8+pwaBE0P//aq/n/vI5kDThQAwml7/7qtEtRFeKhSoPvnh4P NVPxLQf/A2KPsosK8RTDggwOE82AS1/D/W3CJdQ0UUwtauTu9anuAwQSKu/YFPtEUM3q Ia42+gnRqf3D9+uZtatPDCoDQINdUJVuGfJut/KQmGZdE+2aokZyJR27OT4eLBJl/KYG kagBrpBUQKIlrJHiF+BkhZbemkjYJPXhUQ35Fv/KCoiZrOD+8fVJJsScUQpA7dkZR5uP aiD/abKCEdyziH00sL6o30ytq3igU4CR2lKMTQTqD/zSkIcCX3TpRRHiMkLYX3swc3Cs pq+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:cc; bh=y21CDt2vT46TuZ6N05ZyTss9a09IFbjnOjqIQFxN93Q=; b=ZQ9oZnZPQLJ82R+U/Xuwet+jvHbc5LFjECIhypEqC5Hjr4Y76xYeW17R/u/24XMaKm cBbQ200jQy58wpzLprR1ml1d1SdImfDuY/US+2fSuAjBuf8Jsmh4ZkkHIj8VvdYBRrNa n1rWY4hMruxqgJqo61xeSJLUGoo7rprmPlEqe746xQUphoMHFhx+b5+Oa1lafcvG/bKU SDhneY9nwPpoMe90nMEOXgY66VCZKgceLnc7GF1+UmAFEnoN6ze9Ar/bsltv6npqmRSc j89lNXCGoR8IDwm0hBTZ/IHTebQ0KhaHz6yN9ZmBtXsPjlXsplAUMJpccuf5DVdato5L M4Tg== X-Gm-Message-State: AJaThX7J8G/AZ9y1uxQe5QJ9EGAzvkBfP0qePvXJtdoDFsdROpjBSFLp hVVmkd3aGziKOxLM1ku7hl/F85JwI/VZztgjTF8= X-Google-Smtp-Source: AGs4zMYJmW7MM8IPefd6AaHPzcM3Me4YsR9HNFRZ7BjlWAWi4TBAcJw1XbL9TlMrk1DDKQnmncWON0hl49vuWekIbFs= X-Received: by 10.31.72.7 with SMTP id v7mr9103285vka.124.1510656673851; Tue, 14 Nov 2017 02:51:13 -0800 (PST) MIME-Version: 1.0 Sender: gmaxwell@gmail.com Received: by 10.103.85.148 with HTTP; Tue, 14 Nov 2017 02:51:13 -0800 (PST) In-Reply-To: References: <20171114091123.GA29286@savin.petertodd.org> From: Gregory Maxwell Date: Tue, 14 Nov 2017 10:51:13 +0000 X-Google-Sender-Auth: TfJoFt692oiLeMB-jaLtKPYYU-I Message-ID: To: Peter Todd Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=0.0 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, FREEMAIL_FROM,RCVD_IN_DNSWL_NONE autolearn=disabled version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Updates on Confidential Transactions efficiency X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 14 Nov 2017 10:51:17 -0000 On Tue, Nov 14, 2017 at 10:38 AM, Gregory Maxwell wrote: > I think it's still fair to say that ring-in and tree-in approaches > (monero, and zcash) are fundamentally less scalable than > CT+valueshuffle, but more private-- though given observations of Zcash While I'm enumerating private transaction topologies there is fourth one I'm aware of (most closely related to ring-in): take N inputs, write >= N outputs, where some coins are spent and replaced with a new output, or an encrypted dummy... and other coins are simply reencrypted in a way that their owner can still decode. Provide a proof that shows you did this faithfully. So this one avoids the spent coins list by being able to malleiate the inputs. We never previously found an efficient way to construct that one in a plain DL setting, but it's probably possible w/ bulletproofs, at least for some definition of efficient.