Dropbox 在 2012 的時候曾經傳出被入侵盜走六百九十萬筆個人資料。結果最近媒體發現[1]，其實是被偷走 68,680,741 筆，其中31,865,280 組密碼使用 bcrypt hashing 加密，而另外的36,815,461組密碼則使用SHA1 hashing 加密。「我被黑了嗎？」(Have I been pwned[2]) 的站長 Troy Hunt[3] 拿到這批資料，驗證[4]之後確定是 Dropbox 被偷走得資料、不是假資料。

這些資料包含電子郵件與密碼，雖然這些密碼是被加密過，但是還是可能被破解猜出來。若沒有用不同密碼的習慣，別人就可能有機會用同樣帳號密碼登入不同的服務。而這些資料除了某些熟門路的人拿的到，像是 LeakedSource[5] 也提供付費版 API[6] 供人取用受害者原始資料 (亦即加密後的密碼等資料)。

比較好的習慣是使用密碼管理軟體 (Password Manager) 與雙因素授權 (Two factor authentication, 2FA)[9]。

密碼管理軟體的基本功能就是幫你產生亂數密碼，自動登入等，所以你可輕易在不同服務間使用難破解的密碼。密碼管理器的選擇很多[7][8]，我自己是使用 Lastpass[11]，它在瀏覽器與 Android 平台上整合的很方便。而且價格是 12 USD 一年，相較其他軟體更為便宜，雖然目前服務的公司有提供免費帳號，但是我已經買了好幾年了。Lastpass 雖然在 2015 也被入侵過[12]，不過由於安全設計得當，並沒有產生重大問題。

我每個月都會定期做一次 Lastpass security challenge[10]，他會檢查密碼強度、是否重複使用密碼，以及類似 Have I been pwned[2]、LeakedSource[5] 的功能，會查找已知的受害者資料庫，提醒是否為高風險需要採取任何行動。

快選一個密碼管理器吧。 https://lastpass.com/f?4133426

同場加映: Password manager security papers | Wilders Security Forums – http://www.wilderssecurity.com/threads/password-manager-security-papers.365724/

• “Password Managers: Risks, Pitfalls, and Improvements” (2014)

  We study the security of popular password managers and their policies on automatically filling in passwords in web pages. We examine browser built-in password managers, mobile password managers, and 3rd party managers. We show that there are significant differences in autofill policies among password managers. Many autofill policies can lead to disastrous consequences where a remote network attacker can extract multiple passwords from the user’s password manager without any interaction with the user. We experiment with these attacks and with techniques to enhance the security of password managers. We show that our enhancements can be adopted by existing managers.

• “Protecting Users Against XSS-based Password Manager Abuse” (2014)

  To ease the burden of repeated password authentication on multiple sites, modern Web browsers provide password managers, which offer to automatically complete password fields on Web pages, after the password has been stored once. Unfortunately, these managers operate by simply inserting the clear-text password into the document’s DOM, where it is accessible by JavaScript. Thus, a successful Cross-site Scripting attack can be leveraged by the attacker to read and leak password data which has been provided by the password manager. In this paper, we assess this potential threat through a thorough survey of the current password manager generation and observable characteristics of password fields in popular Web sites. Furthermore, we propose an alternative password manager design, which robustly prevents the identified attacks, while maintaining compatibility with the established functionality of the existing approaches.

• “Vulnerability and Risk Analysis of Two Commercial Browser and Cloud Based Password Managers” (2013)

  Web users are confronted with the daunting challenges of managing more and more passwords to protect their valuable assets on different online services. Password manager is one of the most popular solutions designed to address such challenges by saving users’ passwords and later auto-filling the login forms on behalf of users. All the major browser vendors have provided password manager as a built-in feature; third-party vendors have also provided many password managers. In this paper, we analyze the security of two very popular commercial password managers: LastPass and RoboForm. Both of them are Browser and Cloud based Password Managers (BCPMs), and both of them have millions of active users worldwide. We investigate the security design and implementation of these two BCPMs with the focus on their underlying cryptographic mechanisms. We identify several critical, high, and medium risk level vulnerabilities that could be exploited by different types of attackers to break the security of these two BCPMs. Moreover, we provide some general suggestions to help improve the security design of these and similar BCPMs. We hope our analysis and suggestions could also be valuable to other cloud-based data security products and research.

• “Automated Password Extraction Attack on Modern Password Managers” (2013)

  To encourage users to use stronger and more secure passwords, modern web browsers offer users password management services, allowing users to save previously entered passwords locally onto their hard drives. We present Lupin, a tool that automatically extracts these saved passwords without the user’s knowledge. Lupin allows a network adversary to obtain passwords as long as the login form appears on a non-HTTPS page. Unlike existing password sniffing tools, Lupin can obtain passwords for websites users are not visiting. Furthermore, Lupin can extract passwords embedded in login forms with a destination address served in HTTPS. To determine the number of websites vulnerable to our attack, we crawled the top 45,000 most popular websites from Alexa’s top website list and discovered that at least 28% of these sites are vulnerable. To further demonstrate the feasibility of our attack, we tested Lupin under controlled conditions using one of the authors’ computers. Lupin was able to extract passwords from 1,000 websites in less than 35 seconds. We suggest techniques for web developers to protect their web applications from attack, and we propose alternative designs for a secure password manager.

• “Keys to the Cloud: Formal Analysis and Concrete Attacks on Encrypted Web Storage” (2013)

  To protect sensitive user data against server-side attacks, a number of security-conscious web applications have turned to client-side encryption, where only encrypted user data is ever stored in the cloud. We formally investigate the security of a number of such applications, including password managers, cloud storage providers, an e-voting website and a conference management system. We find that their security relies on both their use of cryptography and the way it combines with common web security mechanisms as implemented in the browser. We model these applications using the WebSpi web security library for ProVerif, we discuss novel attacks found by automated formal analysis, and we propose robust countermeasures.

• “On The Security of Password Manager Database Formats” (2012)

  Password managers are critical pieces of software relied upon by users to securely store valuable and sensitive information, from online banking passwords and login credentials to passport- and social security numbers. Surprisingly, there has been very little academic research on the security these applications provide.
  This paper presents the first rigorous analysis of storage formats used by popular password managers. We define two realistic security models, designed to represent the capabilities of real-world adversaries. We then show how specific vulnerabilities in our models allow an adversary to implement practical attacks. Our analysis shows that most password manager database formats are broken even against weak adversaries.

• From Web-based Attacks on Host-Proof Encrypted Storage (2012):

  Cloud-based storage services, such as Wuala, and password managers, such as LastPass, are examples of so-called host-proof web applications that aim to protect users from attacks on the servers that host their data. To this end, user data is encrypted on the client and the server is used only as a backup data store. Authorized users may access their data through client-side software, but for ease of use, many commercial applications also offer browser-based interfaces that enable features such as remote access, form-filling, and secure sharing.
  We describe a series of web-based attacks on popular host-proof applications that completely circumvent their cryptographic protections. Our attacks exploit standard web application vulnerabilities to expose flaws in the encryption mechanisms, authorization policies, and key management implemented by these applications. Our analysis suggests that host-proofing by itself is not enough to protect users from web attackers, who will simply shift their focus to flaws in client-side interfaces.

利益揭露: lastpass 的邀請連結是我的個人 premium referral link.

[1] Hackers Stole Account Details for Over 60 Million Dropbox Users | Motherboard – http://motherboard.vice.com/read/hackers-stole-over-60-million-dropbox-accounts
[2] Have I been pwned? Check if your email has been compromised in a data breach – https://haveibeenpwned.com/
[3] Troy Hunt, a Microsoft Regional Director and Most Valuable Professional awardee for Developer Security – https://haveibeenpwned.com/About
[4] Troy Hunt: The Dropbox hack is real – https://www.troyhunt.com/the-dropbox-hack-is-real/
[5] Find the source of your leaks – https://www.leakedsource.com/
[6] LeakedSource API Purchase – https://www.leakedsource.com/api/purchase
[7] Password Managers Compared http://www.howtogeek.com/?p=240255
[8] Best Password Manager http://www.asecurelife.com/dashlane-vs-lastpass-vs-1password-vs-roboform-vs-keepass/
[9] https://en.wikipedia.org/wiki/Multi-factor_authentication
[10] https://blog.lastpass.com/tag/lastpass-security-challenge/
[11] https://lastpass.com/f?4133426
[12] LastPass Hacked http://lifehacker.com/lastpass-hacked-time-to-change-your-master-password-1711463571