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CA/Browser Forum 上的會議記錄:關於密碼與 2FA 的強制要求

CA/Browser Forum 會定時將會議記錄與最後的結論公開放在網站上,有時候有些資訊還蠻有趣的。像是前幾天在「Ballot 221 - Two-Factor Authentication and Password Improvements - CAB Forum」這邊看到 CA/Browser Forum 的成員對密碼與 2FA 提出了修正提案,其中瀏覽器端只有 Microsoft 參與投票,但是被否決了...

不知道否決的原因,但是大概可以猜到幾個點。

第一個是提案提到了 NSANIST 800-63B Appendix A,這個單位不太受歡迎啊...

第二個則是「For accounts that are accessible only within Secure Zones or High Security Zones, require that passwords have at least twelve (12) characters;」這段強迫使用密碼,而現在有比密碼更安全的方案存在 (以 public key cryptography 為認證基礎的方案),像是早期的 U2F 以及今年定案的 WebAuthn

應該是這些原因吧...

U2F Security Key 產品測試?

Adam Langley 的「Testing Security Keys」這篇測試了不少有支援 U2F Security Key 的產品,這邊作者是以 Linux 環境測試。

tl;dr:在 Linux 環境下,除了 Yubico 的產品沒問題外,其他的都有問題... (只是差在問題多與少而已)

Yubico 的沒找到問題:

Easy one first: I can find no flaws in Yubico's U2F Security Key.

VASCO SecureClick 的則是 vendor ID 與 product ID 會跑掉:

If you're using Linux and you configure udev to grant access to the vendor ID & product ID of the token as it appears normally, nothing will work because the vendor ID and product ID are different when it's active. The Chrome extension will get very confused about this.

Feitian ePass 的 ASN.1 DER 編碼是錯的:

ASN.1 DER is designed to be a “distinguished” encoding, i.e. there should be a unique serialisation for a given value and all other representations are invalid. As such, numbers are supposed to be encoded minimally, with no leading zeros (unless necessary to make a number positive). Feitian doesn't get that right with this security key: numbers that start with 9 leading zero bits have an invalid zero byte at the beginning. Presumably, numbers starting with 17 zero bits have two invalid zero bytes at the beginning and so on, but I wasn't able to press the button enough times to get such an example. Thus something like one in 256 signatures produced by this security key are invalid.

Thetis 根本沒照 spec 走,然後也有相同的 ASN.1 DER 編碼問題:

With this device, I can't test things like key handle mutability and whether the appID is being checked because of some odd behaviour. The response to the first Check is invalid, according to the spec: it returns status 0x9000 (“NO_ERROR”), when it should be 0x6985 or 0x6a80. After that, it starts rejecting all key handles (even valid ones) with 0x6a80 until it's unplugged and reinserted.

This device has the same non-minimal signature encoding issue as the Feitian ePass. Also, if you click too fast, this security key gets upset and rejects a few requests with status 0x6ffe.

U2F Zero 直接 crash 沒辦法測 XDDD:

A 1KiB ping message crashes this device (i.e. it stops responding to USB messages and needs to be unplugged and reinserted). Testing a corrupted key handle also crashes it and thus I wasn't able to run many tests.

KEY-ID (網站連 HTTPS 都沒上...) / HyperFIDO 也有編碼問題但更嚴重:

The Key-ID (and HyperFIDO devices, which have the same firmware, I think) have the same non-minimal encoding issue as the Feitian ePass, but also have a second ASN.1 flaw. In ASN.1 DER, if the most-significant bit of a number is set, that number is negative. If it's not supposed to be negative, then a zero pad byte is needed. I think what happened here is that, when testing the most-significant bit, the security key checks whether the first byte is > 0x80, but it should be checking whether it's >= 0x80. The upshot is the sometimes it produces signatures that contain negative numbers and are thus invalid.

所以還是乖乖用 GitHub 帳號買 Yubico 吧...

GitHub 推出軟體版的 U2F Authenticator (目前只有 macOS)

用軟體實做 U2F,目前是開發在 macOS 上:「Introducing Soft U2F, a software U2F authenticator for macOS」。

實在是不愛這種方式,由於是軟體式的,安全性低了不少... (機器被入侵後就都沒有防護了)

不過 U2F 是目前少數可以在 protocol 層抵抗 phishing 的方式,相較於一般 OTP 的方式還是得很注意網址,所以站在推廣的立場的確是希望能多一點人用...

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