🌻Docusign(DOCU), Crowdstrike(CRWD)財報結果
上週這兩家公司發表財報了.

這兩天看了一下他們的財報結果. Again, 兩家的表現都很好, 但發現分析師給DOCU的調價(往上)幅度比較多, 就好奇研究了一下SaaS公司是怎麼被估值的. 有興趣的話可以看看(從中學習到很多. 非常推薦一讀):
https://makingsenseofusastocks.blogspot.com/2021/09/blog-post.html

(By the way, 分析師對CRWD的價格調幅沒那麼大, 主因是成長趨緩了. 而DOCU的free cash flow佔營收比, 以及顧客黏著力在這季創了新高, 是讓分析師按讚的幾個原因).

關於CRWD: "The Street is already modeling revenue growth deceleration in 2022 to 36%, down from 60% expected in 2021, which on its own might prove a hurdle for a stock already trading at a high multiple," said Bank of America analyst Tal Liani in a report.

分析師對於DOCU的評價:
• 11位buy; 給的價格分別是: $310, $320 (x2), $330 (x2), $340 (x2), $345, $350, $350, $389
• 給Buy的分析師的評語:
o Baird: The analyst continues to view them as a best in class way to play digital transformation trends with strong growth, cash flow and profitability, and a strong competitive position. Power said DocuSign remains one of his top long-term compounding growth ideas.
o Citi: While slightly shy of the double-digit billings beat in recent quarters, DocuSign still delivered a solid 8% beat to Q2 billings, which grew 47% year-over-year, Radke tells investors in a research note.
o Evercore ISI: he calls "another strong quarter." While some may have wanted to see more aggressive Q3 billings guidance, he believes estimates "continue to leave room for upside," Materne said.
o JMP Securities: While revenue growth decelerated to 50% from 58% in Q1, the company is the clear leader in electronic signature and the broader system of agreement having crossed over 1M customers with a $2B run rate this quarter, the analyst tells investors in a research note, adding that he sees lots of room for growth as DocuSign targets a $50B total addressable market.
o Needham: The analyst commented, "Docusign reported another strong quarter in 2QF22 with typical DOCU upside to revenue and profitability. Sales metrics and growth decelerated Q/Q, as we expected against a massive pandemic quarter, but at a much slower rate than we believe much of the Street was anticipating. 65k net new customers was lower than the 70k - 90 range of CY20 but was still more than 2x greater than any pre-pandemic quarter, highlighting a strong end-market driving 47% billings growth against a strong comp. Commentary on incremental Agreement Cloud demand was positive, suggesting an additional growth tailwind combined with solid international can further aid 2HF22. Although DOCU shares could be lower near-term due to weak 2H OpMg guidance, we think this guidance is conservative, as the recent OM was greater than the pre-pandemic level even with tough comps."
o RBC Capital: The quarter highlighted the sustainability of the company's tailwinds post-pandemic as most of its underlying metrics such as billings and net revenue retention were solid, the analyst tells investors in a research note, adding that the traction with CLM and Notary was also "impressive".

分析師對於CRWD的評價:
• 12位buy; 給的價格分別是: $300, $310 (x2), $313, $315 (x2) , $305, $320, $325, $330 (x2), $340
• 1位給hold: $280 (from $220 by J.P. Morgan(same))
• 給Buy的分析師的評語:
o Baird: The analyst believes the company has significant room for growth with core modules, opportunities with Humio and in cloud workload security, among others, should help drive a continuation of strong growth over a long time horizon.
o BTIG: The company's "strong" Q2 results "cleared every hurdle", even though the buy-side benchmarks may have been slightly higher, the analyst tells investors in a research note. Powell adds that Crowdstrike is clearly gaining share in its core endpoint security target market at a rapid pace and gaining traction with new products across multiple categories.
o Canaccord: The analyst said the stock is down from its recent highs, and he thinks the re-rating creates a more favorable entry point for longer-oriented investors for a foundational security name. He views Crowdstrike as a long-term secular winner in security due to its native cloud platform advantage versus closely held peers in endpoint security combined with platform expansion into tangential segments to capture greater share of security budgets.
o Goldman Sachs: CrowdStrike last night delivered "another beat and raise quarter as the company benefited from another quarter of elevated demand," Essex said. But it traded lower following net new annual recurring revenue growth guidance that was slightly less than investors had hoped for. Essex, nonetheless, said the quarter demonstrated CrowdStrike's "ability to continue to go down market efficiently."
o JMP Securities: The analyst notes the company's Q2 annualized recurring revenue of $1.34B topping his estimate of $1.30B, with "sustained" 70% ARR and revenue growth along with margin upside seen as key highlights for the quarter. Suppiger adds that the metrics reflect Crowdstrike's "strong execution and robust demand environment".
o Mizuho: "very good" fiscal Q2 results. The annual recurring revenue growth of 70% year-over-year "was strong and still nicely surpassed" the Street's 65%-66% estimate, Moskowitz tells investors in a research note. He believes "strong execution can propel" Crowdstrike's stock higher.
o Piper Sandler: The company's metrics "outperformed across the board" in Q2 with 70% annual recurring revenue and revenue growth and record net new customer adds in the quarter, Owens tells investors in a research note.
o RBC Capital: Hedberg adds that CrowdStrike's record pipeline entering Q3 should continue to fuel the company's "land-and-expand" momentum.
o Stifel: Q2 results that he said "exceeded consensus estimates across all major financial metrics." He continues to believe that Crowdstrike's growth opportunity "remains in the early days" despite the company's scale given continued share capture within its core endpoint security market and incremental module adoption on the Falcon Platform, Reback tells investors.
o UBS: the company reported "pretty good" Q2 results against high expectations.

🌻趨勢: 跨境電商 Cross-border commerce
Morgan Stanley:
From our perspective, we think many are underestimating what the cross-border eCommerce demand could ultimately be, once key friction points like FX rates, tax and duties, shipping, language, etc are smoothed—all issues that Global-E directly addresses.

Cross-border ecommerce brings new, high-yield volume: We think elevated levels of cross-border ecommerce (ex-travel) is a structural shift thathas yet to be fully contemplated in MA (and V)'s long-term forecasts. MA's cross-border CNP ex-travel volume was 69% above 2019's level in 2Q and 63% higher in 1Q. Strength reflects both broader ecommerce adoption plus globalization of commerce, as marketplaces and services that reduce cross-border friction (such as those from GLBE) make international online ordering more readily adopted. Early data at V suggests greater cross-border ecommerce spend is persisting even in areas with pre-pandemic levels of international travel. Cross-border transactions also come at a higher yield, making us more optimistic that the trend can bring incremental long-term growth to the networks.

產業的潮流是有連貫性的. 疫情讓電商更發達後, 接下來應該就是加速電商跨境了. 跨境的話, 有很多問題需要解決(稅率, 語言, etc.) 這就需要有公司來做整合的動作. 這種跨境, 也可以想像是omnichannel的一種呈現.

Harley Finkelstein (President of Shopify): "I mean I think commerce in 2021 is cross-border."

🌻SPAC熱潮退卻，初創市值蒸發750億美元
"SPAC熱潮已經退卻。分析顯示，在2月中旬以前完成合併的137家SPAC的總市值已經蒸發25%，市值回落幅度上個月一度超過1,000億美元。"

"像貝萊德(BlackRock Inc., BLK)和富達投資(Fidelity Investments Inc.)這類企業管理的基金，以及許多對沖基金、養老金管理公司和其他一些投資者，都在SPAC的回落中遭受了衝擊，他們在去年年底開始的熱潮中競相投資SPAC。其中許多基金由於在價格還很低的時候就早早入場，所以現在仍坐擁可觀收益。事實上，SPAC市值仍有約2,500億美元，高於一年前的約1,000億美元，反映出這期間股價上漲和新公司上市的影響。

但即便如此，今年年初令人炫目的回報還是讓許多後來者做了接盤俠，扎堆投資所謂穩賺不賠的領域，其永恆的風險可見一斑。在過去的幾個月裡，一些投資者眼睜睜看著帳面財富縮水。"

"股價下跌會在SPAC領域形成惡性循環，因為投資者有權在併購交易前從空白支票公司撤資。一旦SPAC跌破發行價，投資者就更有可能這樣做，而許多SPAC的股價現在正處於這樣的水平。目前，在尚未宣布併購交易的空白支票公司中，超過95%的公司股價低於發行價。

投資者的大規模撤資會讓已經上市的空白支票公司手上的現金大幅減少，讓其更難實現業務目標，並可能加劇股價跌勢。"

https://on.wsj.com/3n6JznC

🌻BNPL (buy now pay later)
But most BNPL providers including Affirm, Klarna and Afterpay have been losing money despite breakneck revenue growth as they invest heavily in marketing to win share. Sweden-based Klarna’s credit losses more than doubled in the second quarter. Affirm has projected adjusted operating losses of $50m-$55m for the fiscal year that ended June 30.

The path to profitability for many of these companies was to achieve massive scale, analysts said.

https://www.ft.com/content/ca201a37-a16d-4223-b123-04d38350a972

Pictures: 一葉知秋; from EarningsWhispers

📜 [專欄新文章] Unirep介紹: 使用ZKP的評價系統

✍️ Ya-Wen Jeng

📥 歡迎投稿： https://medium.com/taipei-ethereum-meetup #徵技術分享文 #使用心得 #教學文 #medium

Unirep是什麼? 怎麼用?

Photo by Raphael Lovaski on Unsplash

UniRep 是一個使用零知識證明(Zero-knowledge Proof)而達到具有隱私保障的評價 (reputation) 系統。使用者有權利享有多個暫時性的身份，但又同時能提出證明，讓其他人可以驗證評價是否符合自己宣稱的數量。此外，使用者也無法拒絕接收對自己不利的評價。

想像一個情境：如果Alice是Airbnb的使用者，Alice常常透過Airbnb租房，且Alice曾經獲得獲得許多Airbnb房東的好評；有一天Alice想透過Booking.com訂房，http://xn--alicebooking-kt4so6lvyab96x7trhi5b54x.com/，所以在Booking.com上沒有任何評價，萬一Booking.com的房東不想把房子租給來路不明的客人，那Alice要如何向Booking.com的房東證明她其實都是用Airbnb租房，且獲得許多好評？

Alice雖然可以透過截圖或公開自己的資訊向Booking.com的房東證明自己擁有這些好評，但這樣Alice的隱私或許會被洩漏，例如Alice不想讓Booking.com的房東知道自己去過哪些地方、住過哪些民宿；或者Alice有可能偽造截圖，或者偽造評價，那Booking.com的房東要如何相信Alice所提供的證明文件是真的來自Airbnb的房東？除此之外有沒有更彈性的方式，Alice可以選擇性地向Booking.com的房東證明，自己至少有10個好評，但不透露自己總共有多少好評？

Photo by Andrea Davis on Unsplash

使用Unirep協定就可以解決這個問題。UniRep 取名自 Universal Reputation，希望透過區塊鏈上智能合約的可互用性 (interoperable，指智能合約容易被多方呼叫且容易透過智能合約與對方互動)，讓不管是Airbnb的房東、Booking.com的房東或是Alice都能很容易地透過Unirep的智能合約與對方互動，且透過零知識證明的方式，讓Alice的評價具有隱私的保障，Alice不用明確地向Booking.com的房東說這些評價是怎麼獲得、是什麼時候獲得，也可以彈性的證明自己至少有多少好評，或者最多有多少差評。

密碼學

Unirep主要用到的密碼學方法有

雜湊函數 hash：若有一個雜湊函數 f(x) = y 則由x可以很輕易的用f算出y，但從y推回x是幾乎不可能的，且要找到兩個不同的x對應到相同的y也是幾乎不可能的(沒有碰撞問題)。

零知識證明 zero-knowledge proof：可以將複雜的運算邏輯轉成容易驗證且具有隱私保障的驗證問題，使用者只要將變數輸入，這個零知識證明的演算法就會產生對應的證明且計算出對應的結果，使用者只要將此證明和運算結果輸入驗證的程序中，其他人就能驗證使用者是不是提出正確的證明，若驗證成功，則驗證者就能相信提出證明者高機率擁有正確的知識，也就是在計算證明時的輸入變數。

ZKP Proof System

ZKP Verification System

Semaphore：semaphore 是設計為可以用零知識證明驗證的身份認證系統。Unirep 中用來產生私鑰 (identity) 和公鑰的 hash 值(identity commitment)，讓使用者不必公開 identity 仍能透過零知識證明驗證其公私鑰的對應性。

雜湊樹 Merkle trees：Unirep 中大量運用雜湊樹的方式確保評價紀錄，而其中用到的雜湊樹又分兩種：Incremental merkle tree 和 Sparse merkle tree

Incremental merkle tree: 從 index 0 開始依序插入雜湊樹中的樹葉。為了使 ZKP 的 circuit 大小固定， Unirep 中使用固定高度的 Incremental merkle tree。

Sparse merkle tree: 在特定的 index i 插入樹葉

Incremental merkle tree and sparse merkle tree

UniRep中用到的名詞定義

Epoch

指一段特定的時間，例如7天

UniRep 的 Epoch 從 1 開始計算，7天過後Epoch數加一，即 Epoch 變為 2

Epoch Key

每個使用者在每個 Epoch 都能產生 n 把 Epoch key，用來收取評價 epoch_key = hash (id, epoch, nonce)

id: 這裡指用 semaphore 產生的 identity

epoch: 表示這是在第幾個 epoch 產生的 epoch key

nonce: 若 Unirep 規定使用者能在一個 epoch 產生 5 把 epoch key，則使用者可以選從 0 到 4 為此 nonce

因為雜湊函數的性質，算出來的 epoch key 很難推回原本的 id, epoch, nonce， 所以看到 epoch key 並不能推回使用者是誰。

以Alice為例，當Alice住完Airbnb，房東會透過 epoch key 給予 Alice 評價，但房東無法知道 Alice 在同個 epoch 的其他 epoch key 是哪一把，也無法知道 Alice 在別的 epoch 獲得的評價，除非 Alice 在這個 epoch 重複使用同一把 epoch key 收取評價。

User 使用者

用 semaphore 產生 identity 並使用此 identity 註冊的使用者

使用者是接收評價、證明評價、或是花費評價的人，用 epoch key 跟其他人互動，因為 epoch key 會隨著 epoch 增加而改變，所以對使用者來說每個 epoch 能產生的 epoch key 都不同，具有保護隱私的效果。

在上面的例子中使用者指的是 Alice, Bob, Airbnb 的房東, Booking.com的房東

Attester 證人

用 Ethereum address 或 smart contract address 註冊的用戶

是會被使用者記錄下來的評價給予者

Unirep 會給這些 address 一個 attester ID，而這個 attester ID 不會隨著 epoch 增加而改變，使用者可以知道這個評價是來自哪一個 attester。

在上面的例子中指的是 Airbnb 跟 Booking.com，因為 attester ID 不變，所以使用者可以證明這些評價是來自於 Airbnb 或是 Booking.com

User State Tree (UST)

是一 Sparse merkle tree

每個使用者都有自己的 User State Tree，其中樹葉表示所收到的評價的hash值，而葉子的 index 表示 attester ID，UST 樹葉的定義為

USTLeaf = hash(posRep, negRep, graffiti)

例如 Airbnb 的 ID 是1，Booking.com 的 ID 是 3，那 Alice 的 User State Tree 中 index 為 1 的地方會有自己在 Airbnb 獲得的總評價的 hash 值，而 index 為三的地方則為空的評價。另一個使用者 Bob 的 User State Tree 亦同，在 index 為 1 的地方會有自己在 Airbnb 獲得的評價，在 index 為 3 的地方會有自己在 Booking.com的評價。

Global State Tree (GST)

是一固定樹高的 Incremental merkle tree

Global State Tree 的葉子到樹根都是公開的資訊，當有使用者註冊或者更新 User State Tree 時會在 Global State Tree 裡新增一個新的樹葉，GST 樹葉的定義為：

GSTLeaf = hash(id, USTRoot)

先送出的樹葉先插入到較前面的 index，之後的樹葉依序插入 GST 中。

以 Alice的例子來說，當 Alice跟 Bob註冊 Unirep時，都會產生一個 GST的樹葉，更新 GST的樹根，若 Alice先註冊，則 Alice的 index會較 Bob前面。注意，這邊的 Airbnb 和 Booking.com 等 attester 並不是用這棵 Global State Tree註冊。

Epoch Tree

是一個 Sparse merkle tree

Epoch Tree 跟 Global State Tree 一樣從葉子到樹根都是公開的資訊，Epoch Tree 中樹葉的 index 為 epoch key，而樹葉的值為該 epoch key 的 sealed hash chain

每個 epoch key 都有一個 hash chain，hash chain 的定義為

hashedReputation = hash(attestIdx, attesterID, posRep, negRep, graffiti)hashChain[epochKey] = hash(hashedReputation, hashChain[epochKey])

此 hash chain 是為了防止使用者漏收了哪一筆評價，如果使用者少收了其中一筆評價，則 hash chain 的結果會完全不同。最後驗證時如果其中一個 epoch key 的 hash chain 改變，會造成 epoch tree 樹根跟原本的 epoch tree 的樹根不同。

而 Sealed hash chain 是在每個 epoch 結束後，Unirep 智能合約會再將這條 hash chain 再 hash 一次

sealedHashChain[epochKey] = hash(1, hashChain[epochKey]) isEpochKeyHashChainSealed[epochKey] = true

需要再把這條 hash chain 封起來的用意是，避免這把 epoch key 過了這個 epoch 之後再繼續接收評價，所以 epoch tree 會用這個 epoch key 最後的 sealed hash chain 去計算樹根。

Nullifier

中文翻譯為註銷符，當我們要防止一件事情重複發生時，就可以使用這個 Nullifier

Unirep 中使用到 Epoch key nullifier：此 nullifier 是用來限制使用者不能在不同的 epoch 使用重複的 epoch key 去收取評價，也不能被其他使用者使用；此外也可以用來檢視使用者是否重複執行 UST 的更新

Nullifier 也用 hash 計算，但多使用一個 domain 變數，避免與 epoch key 產生相同的 nullifier 而洩露自己擁有的 epoch key，也可以用不同的 domain 產生不同用途的 nullifier

epochKeyNullifier = hash(EPOCH_KEY_DOMAIN, id, epoch, nonce)

Epoch Transition

一個 epoch 結束過後，要透過 epoch transition 的步驟，更新 Unirep 及使用者的狀態

其中要做的事包含將智能合約上的 epoch 數加一，還有將所有 epoch key 的 hash chain 封起來

接著使用者就可以執行 User State Transition 更新自己的 UST

User State Transition

到下一個 epoch 後，使用者可以透過自己的 identity，找出自己在前一個 epoch 所有的 epoch key，並根據每把 epoch key 收到的評價更新到自己的 UST，最後計算出最新的評價狀態，產生一個 GST的樹葉，插入 GST 中 (如同註冊時一樣)。

使用者之後如果要花費評價或者產生下一個 epoch 的 epoch key 時，因為必須確認自己的 UST 在當前的 epoch，所以需要經過 User State Transition 確保自己有一個 GST 的樹葉在 GST 中。

Unirep 協定

有了 Unirep 的名詞定義後，接著介紹 Unirep 是如何運作的。

註冊

Unirep 的 user 和 attester 的註冊方式不同：

User signup and attester signup in Unirep

User

User 透過 semaphore 產生 identity 和 identity commitment，identity 就如同私鑰，identity commitment 就如同公鑰

將 identity commitment 和預設的 UST 樹根經由 hash 計算得 GST 的一個樹葉

若使用者要證明自己在某個 epoch 有註冊或者有更新自己的 UST，則證明自己是 GST 的某一個樹葉，利用零知識證明的方法，輸入 identity、UST 樹根，還有 merkle tree 中要計算 hash 值的相鄰節點，則最後可得到一個 GST 的 root，其他人可以驗證這個 GST 的 root 是否符合這顆公開的 GST。

Attester

Attester 則是用自己的錢包，或者用智能合約的地址註冊，呼叫 attester sign up 的 function 後，Unirep 會指定一個 attester ID 給這個地址，往後 attester 用相同錢包或合約地址給予評價時，Unirep 會檢查此地址是否被註冊，若有註冊則可以給予 epoch key 評價。

以 Alice 和 Bob 為例，Alice、Bob、Airbnb的房東、Booking.com的房東會產生 identity 並且透過 Unirep 合約用 user 的註冊方式獲得一個 GST 的樹葉代表自己；
而 Airbnb 和 Booking.com 會透過 attester 的註冊方式，使用特定的錢包地址或是撰寫智能合約呼叫 Unirep 的 attester sign up function。
當然 Alice 或 Bob 如果想用自己的錢包註冊為 attester 也是可以，這時合約就會紀錄 Alice 和 Bob 的錢包地址，並給予一個新的 attester ID。

給予評價

在 Unirep 中評價的接收者是 epoch key，接著介紹 user 和 attester 是如何互動。

How an attester gives reputation to an epoch key

Alice 在 Unirep 註冊過後，就可以產生 epoch key 接收評價

epochKey = hash(identity, epoch, nonce)

但 Airbnb 的房東看到這把 epoch key，要如何知道 Alice 確實是 Unirep 的合法使用者，且 epoch key 的 是合法的，例如 nonce 小於 5，或者 epoch 是當前的 epoch？

如果 Alice 直接提供 epoch 和 nonce，別人沒有 identity 也無法計算此 epoch key，更不用說如果 Alice 提供 identity 會造成 Alice 完全沒有隱私可言，所有人都可以計算出 Alice 收過哪些評價。

因此我們用一個零知識證明，證明此 epoch key 是合法的。細節請參考 epoch key proof，主要是證明使用者有一個合法的 GST 樹葉在 GST 中，並且 epoch 和 nonce 也都符合。

房東得到 Alice 提供的 epoch key 和 epoch key 的證明，並且透過 Unirep 的合約驗證通過之後，就可以給予評價。

獲得空投評價、使用者可以給予評價的限制可以由各個應用自行定義，例如 Airbnb 可以決定空投 30 個正評給使用者， Booking.com 可以決定空投 20 個正評給使用者。

另外，為了確認房東也是合法的使用者，也為了防止房東重複花費 (double spending) 自己的評價點數，Unirep 上的應用也可以用 reputation nullifier 及其 proof 去證明使用者合法使用自己的評價。

例如，此 reputation nullifier 可以用下列計算方式取得：

reputationNullifier = hash(REPUTATION_DOMAIN, id, epoch, nonce)

當 reputation nullifier 及 proof 產生後，就會與房東要給的評價一起發送到 Airbnb 的智能合約上，智能合約會驗證 proof 是否合法，nullifier 是否有被發送過，若檢查都通過的話則 Unirep 會紀錄此評價給 epoch key，並將 hash chain 更新。

接收評價

使用者即使可以證明自己擁有哪一把 epoch key 並且大家都知道這把 epoch key 有多少評價，但這有可能造成使用者故意忽略其他把 epoch key 中對自己不好的評價，因此 Unirep 限制使用者只能在每個 epoch 結束，每把 epoch key 都封起來之後，才能用 User State Transition 更新自己的評價。

User State Transition in Unirep

這裏也是用 User State Transition Proof 去保證使用者是根據正確的方式計算出最新的 UST，且用 epoch tree 限制使用者必須處理每一把 epoch key 的結果。

亦即，需要等到 epoch 結束後，Alice 才能透過 User State Transition 獲得 Airbnb 房東的評價，更新自己的使用者狀態。

證明評價

當使用者通過 User State Transition 之後會有最新的 UST 狀態，此時 Alice 就可以透過 reputation proof 向 Booking.com 她有來自 Airbnb 的評價，在reputation proof 中檢查使用者是否有其宣稱的 UST (例如總共有多少好評、多少差評來自哪一個 attester ID)，並且此 UST 的狀態儲存在當前 epoch 的 GST 中。

在生成 reputation proof 時，即使 Alice 總共有 100 個好評，但 Alice 仍可以產生「至少有10個好評」的證明，Booking.com 的房東若驗證成功，則只能知道 Alice 宣稱的「至少有 10 個好評」而不能知道 Alice 總共有 100 個好評。

常見問題

Alice 能不能給 Airbnb 的房東評價？ Alice 能不能給 Bob 評價？

可以。

Airbnb 的房東和 Bob 也都能產生 epoch key，因此如果 Alice 有兩者的 epoch key 及合法的 proof 則可以給予評價。此時 Alice 可以選擇透過 Airbnb、Booking.com、或甚至自己的 Ethereum account 當作證人給予評價 (也必須選擇一個證人)。

Alice 可以透過 Unirep 給 Airbnb 評價嗎？

如果 Airbnb 也透過 Unirep 註冊為使用者，並且產生 epoch key 的話就可以。但如果 Airbnb 只註冊為證人的話不行。

Alice 可以證明評價來自哪一個 Airbnb 房東嗎？

如果 Airbnb 的房東沒有註冊為證人，則 Alice 不能證明評價來自哪個房東。

若 Airbnb 的房東用自己的 Ethereum account 註冊為證人，則 Alice 只能證明評價來自這個 Ethereum account，但無法知道這個 account 是一個 Airbnb 的房東。

從 Airbnb 獲得的評價可以在 Booking.com 花費嗎？

需看 Booking.com 的智能合約如何定義，但一般來說不行，因為 attester ID不同，但未來可能會開發各個應用程式之間的兌換評價功能。

如果遲遲不執行 User State Transition 會發生什麼事？會不會收不到之前的評價？

若 Alice 在第一個 epoch 註冊，並在第一個 epoch 產生 epoch key 接收評價，但 Alice 到第五個 epoch 才執行 User State Transition，那 Alice 會根據第一個 epoch 的 GST、epoch tree 執行 User State Transition，因此仍然可以在第五個 epoch 收到來自第一個 epoch 的評價；而在第二到第四個 epoch 因為 Alice 無法產生出合法的 epoch key proof，因此無法接收評價。

User State Transition 可以自動執行嗎？

不行。

只有使用者主動給出私鑰，即 semaphore 的 identity，才可以產生合法的 User State Transition proof，若將私鑰交給第三方幫忙執行可能會侵害使用者的隱私。

結論

Unirep 是一個具有隱私保障的評價系統，透過 ZKP 的保護使用者可以在匿名的情況下收取評價、給予評價、並且向他人證明自己的評價。Unirep 可以用於跨應用程式間的評價證明，可以在 A 應用程式中獲得評價，並向 B 應用程式證明在 A 應用程式中獲得多少評價。若想了解更多有關 Unirep ，可以參考 Github、文件或加入 telegram 群組討論。

本文感謝 CC, Nic, Kevin, Doris 協助審稿。

Unirep介紹: 使用ZKP的評價系統 was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.

👏 歡迎轉載分享鼓掌

90 min Long Run with a 10-15 min incremental pace at the end of it ✅

Yesterday evening did a 5 X 1000m repeats with 60 seconds rest per rep + a 5 X 200m at 3 min cycle (target to hit 30-35s for the 200m).

It was tough to slot this two sessions with a night break. Didn't rest well last night due to the power outage from 10+pm to 12am.

Started my run at 8.47am, and so glad that the weather was still good to me.

Felt good all the way but the tiredness kicked in after halfway point. Began to struggle and at the same time trying to be relax.

I got myself focusing on my running mechanic and stride by stride, flow on it.

Eventually, I got into the zone and be in the flow. Got out of the flow at 80 minutes mark as I need to pick up the pace for the final 10 min.

Therefore, I dig deep and step up the pace but I realized there was nothing much left in the tank. The only thing I can do is to focus on my armswing and putting in the effort to swing it hard and fast to enable my leg to open up the stride.

So grateful to end the run by giving everything I got towards the end of it. Time for a good rest after being in the flow state.

Another long easy stairs session to end the week.

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▼放送するアカウント
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#ねが

? คลิปรถใหม่ 2019-2020 มาแล้วครับ คลิกที่นี่ https://www.youtube.com/channel/UCSebcviE-UeYMxVRNozwqtw/videos

2018 Honda Forza 125
Honda’s segment-leading sports/GT Forza 125 scooter maintains its rapid upward trajectory, receiving a thorough-going restyle, plus electrically adjustable screen, LED indicators, new instrumentation, two all-new colour options. increased underseat storage space and an optional 45-litre Smart Key-linked top box that improve still further its all-round premium appeal.

Honda’s Forza 125 was designed specifically for discerning European scooter customers who demand the maximum out of their ride in every respect – style, presence, performance and specification. And right from its introduction in 2015 it has met and exceeded all expectations, evolving year on year with owner feedback and selling over 30,000 units to date.

Straight out of the crate the Forza 125 hit the ground rolling, deftly mixing traffic-busting agility – thanks to its compact dimensions – with ample ability for longer-range highway commute thanks to its engine performance, wind protection and comfort. It combines the comfort of a ‘GT’ (Grand Touring) scooter with a sports-oriented attitude and handling ability, while offering plenty of storage, a host of premium details plus Honda’s engineering innovation and high build quality.

Classy and agile, and expanding on its obvious success, the Forza 125 is not standing still: for 2018, maintaining a steep development curve, it has been redrawn with fresh new lines and several significant rider-focused upgrades.

- Adjustable electric screen controlled from the left handlebar
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- The Smart Key also now operates an optional 45-litre top box
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The Forza 125’s fully-refreshed look flows back from the new electric screen, which adjusts smoothly through 140mm and is designed to provide wind protection (with airflow directed around and over the rider’s head) and reduce wind noise. Stability and comfort at higher speeds – and for long distances – can be instantly exchanged for a greater sense of freedom with the screen in its lower position by simply pushing a switch on the left handlebar to move it to any point in the 140mm range.

Handlebar width remains 754mm as does mirror height of 1125mm, the perfect dimensions for slipping through streets clogged with cars – one of the Forza 125’s incremental development steps already in place from 2017 was to raise its own mirror height to avoid issues with car mirrors. Seat height is unchanged at 780mm; there’s plenty of room for two and the sit-in riding position cups the rider securely. The front and rear indicators are now LED, matching the headlight and taillight.

Two full-face helmets can be stored under the seat, which now offers increased storage space of 53.5 litres, up from 48 litres. It’s also possible to partition the storage area to house a helmet and/or rain gear and A4 sized bags. The front left inner fairing pocket is lockable, and its internal space can be arranged for the rider’s convenience, to hold a phone and water bottle, for instance. It also houses a 12V-1A charging socket.

The Forza 125’s Smart Key – as well as controlling the main ignition switch knob and compartment locking – also now manages the optional 45L removable top box, a first on a Honda scooter. With the Smart Key in the rider’s pocket the box automatically locks when the rider walks away. It can also be locked from the key. The top box switch is on its bottom surface, and to maintain the internal volume of the box the actuator mechanism is located in the rear body of the machine.

Revised instruments present analogue speedometer and rev-counter dials flanking a digital display that can switch between 3 modes (controlled by a switch on the left handlebar); odometer, range remaining and current fuel consumption; trip meter, average fuel consumption and timer; or ambient temperature thermometer and battery sensor.

The Forza’s sharp design lines and distinctive contemporary presence have played a big part in its success since launch in 2015. Now for the 2018 model, the design has been substantially re-worked. While the bold design lines remain instantly recognizable as a Forza 125, every panel has been revised to give the machine a slightly smoother, more mature appearance, with a more rounded, ‘stubby’ feel to the front end and slightly softer design lines throughout. Further heightening the new look, black signature points around the nose, front and side cowls give an added sense of sportiness.

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In the near future, the secrets of the universe will be unlocked in the chicken egg. You have decided to get in on the gold rush and sell as many eggs as you can.

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