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维基百科，自由的百科全书
  此页面介紹的是認證用途的密碼。关于隱藏資訊的技術或學問，请见「密碼學」。关于電子遊戲中用於返回遊戲階段的資料碼，请见「密码 (电子游戏)」。
英文维基百科的登录页截图，有用户名（Username）和密码（Password）的输入框

密码（有时又称口令）是用于身份验证或授权的词语或字符串，即用于证明身份或者获得对某个资源的访问权限。密码需要对没有相应访问权限的人保密。

我们知道，使用密码的行为可以追溯到很古老的时候。哨兵在把守一个区域的时候，如果有人想要进入或者接近区域，哨兵会要求其提供密码或“暗号”，只有说对的才可以通过。现在，用户名和密码一般用于登录，实现对一些受保护资源的访问控制，例如电脑操作系统、手机、有线电视解码器、自动柜员机（ATM）等等。典型的电脑用户可将密码用于多种目的：登录账户；接收电子邮件；访问应用程序、数据库、网络、网站，甚至是阅读在线新闻等。

密码不一定是一个真正的词语或单词。实际上，用不是真正的词语作为密码会让别人更难猜出来，而“难猜”正是使用密码的人所希望的。密码一般不会特别长，以便于记忆和输入。

大多数组织会指定密码策略，对密码的组成和使用设置要求。一般有规定最小长度、需要哪些字符类型（比如大小写字母、数字、特殊字符）、禁止包含某些元素（比如自己的姓名、生日、地址、电话号码）。一些政府有国家认证网络[1]，来规定政府服务的用户认证要求，其中就包括对密码的要求。

选择既安全又好记的密码[编辑]

一个密码，如果对于使用者来说容易记住，往往也意味着容易被攻击者猜出来[2]。然而，难记的密码可能也会降低系统的安全性，原因是：第一，用户可能需要把密码写下来，或者在电子设备上存储密码；第二，用户可能会频繁地重置密码；第三，用户更可能重复使用同一个密码。同样地，对密码的强度要求越高（例如“混合使用大小写字母和数字”或者“每个月修改一次密码”），用户就越可能破坏这个系统[3]。其他人则认为，相比于包含多种字符的短密码来说，长密码能提供更高的安全性（例如“熵”）[4]。

在《密码的记忆性和安全性》[5]中，杰夫‧岩等人研究了给用户提供如何选择好密码的建议会造成什么影响。他们发现，想一个短语，然后取其中每个单词的首字母组成一个密码，这样的密码就像毫无经验地选择的密码一样好记，而且就像随机产生的密码一样难破解。把两个或更多没有关系的单词合并组成密码，这也是个不错的办法，但是仅用一个词典中的单词就不好。还有一个好办法是自创一种算法，用来生成比较晦涩的密码。

然而，让用户去记住一个“混合大小写字母”的密码，就跟让他们记住一串比特位一样。不仅难记，而且破解的难度只增大了一点点（例如，对于7个字母的密码来说，破解的难度只会增大为128倍，如果用户只把1个字母变成大写的话就增大地更少）。让用户“同时使用字母和数字”常常会导致使用容易猜出来的替代方式，像用“3”代替“E”、用“1”代替“I”，这些替代方式对攻击者来说也是很熟悉的。还有一种是把键盘上的一行按键从头到尾打出来组成一个密码，但这对于攻击者来说也只是一个一般的技巧而已[6]。

2013年，谷歌发布了一个最常用密码类型的列表，其中所有的类型都被视为不安全的，因为太容易猜出来了（特别是在社交媒体研究了一个个体之后）[7]：

  • 宠物、孩子、家庭成员或者其他重要人物的名字
  • 周年纪念日和生日
  • 出生地
  • 著名节日的名字
  • 与著名运动队相关的事物
  • "password"这个单词（在英语中是“密码”的意思）

密码系统的安全性因素[编辑]

有密码保护的系统，其安全性依赖于诸多因素。当然，整个系统应该设计成有良好的安全性，防范计算机病毒、中间人攻击之类的。物理安全问题也值得关注，从阻止肩窥（英语：shoulder surfing (computer security)）到更复杂的物理威胁，如视频摄像头和键盘监听器。当然，密码的选择应当使其难以被攻击者猜出来，并且难以被攻击者发现任何（以及全部）可用的自动攻击方法进行攻击。以上涉及到密码强度和计算机安全。

现如今，计算机系统中一种常见的做法是隐藏正在输入的密码。这种措施的目的是防止旁观者看到密码。然而，一些人认为，这种做法可能会导致出错和紧张，鼓励用户选择弱密码。作为替代方案，用户应该有相应的选项来显示或隐藏正在输入的密码。[8]

有效的访问控制可能会迫使犯罪分子采取极端措施，去寻找获取密码或者生物识别标记[9]。不太极端的措施包括：勒索、软磨硬泡攻击（rubber-hose cryptanalysis）（英语：rubber hose cryptanalysis），以及旁路攻击。

以下是一些具体的密码管理问题，在思考、选择、处理密码时必须考虑这些问题。

攻击者可尝试猜密码的速率[编辑]

攻击者可能不断尝试向系统提交其猜测的密码，其可以提交的速率是决定系统安全性的一个关键因素。一些系统在输错几次密码（例如三次）之后，强加几秒钟的暂停时间。在没有其他漏洞的情况下，这样的系统使用相对简单的密码是安全的，前提是选择好密码，不会被轻易猜出来。[10]

很多系统存储密码的散列值。如果攻击者访问到了存储密码散列值的文件，猜密码就可以离线完成了，可以快速地将候选密码的散列值与正确密码的散列值比对。例如一个Web服务，攻击者猜密码的速率受限于服务响应的速度，但是离线攻击者（拿到散列值文件的人）猜密码的速率只受限于硬件的承受度。

用于生成密钥的密码（例如磁盘加密或Wi-Fi安全性）也可以进行高速率的猜测。常用密码列表使用很广泛，可以使密码攻击（英语：Password cracking）效率很高。在这些情况下，安全性取决于使用的密码是否足够复杂，使这样的攻击对攻击者而言在计算上不可行。一些系统，例如良好隐私密码法（PGP）和Wi-Fi WPA，就对密码应用了计算上不可行的散列算法，从而使此类攻击变慢。

猜密码的次数限制[编辑]

除了限制攻击者猜密码的速率，一种替代方案是限制猜密码的次数。在少量（比如5次）连续猜错密码之后，密码就会失效，需要重置；在累计大量（比如30次）猜错密码之后，就要求用户更改密码。这样，就能把猜密码的行为散布到密码的合法所有者输入正确密码的行为之间，防止攻击者任意次猜错大量密码。[11]

存储密码的形式[编辑]

有些计算机系统以明文的形式存储用户密码，当用户登录时用提供的密码与之比较。如果攻击者访问到了内部的密码存储，所有的密码和用户账户就都会受损。如果有用户在其他的系统中用了相同的密码，那些系统也会跟着一起受损。

更安全的系统会以加密保护的形式存储密码，所以即使有人访问到了系统内部，获取真实的密码也是很困难的。同时，可以实现用户访问的校验。最安全的做法是根本不存储密码，而是存储一种单向推导的结果，例如多项式、模运算，或者高级的散列函数[4]。罗杰·尼达姆（英语：Roger Needham）发明了现在常用的密码存储方式，即只存储明文密码的“散列”形式。当用户在这样一个系统中输入密码时，处理密码的程序会执行一个加密散列算法，如果根据用户输入的密码生成的散列值和密码数据库中存储的散列值相匹配，那么就允许用户访问系统。散列值是使用一个加密散列函数产生的，其输入是由用户提交的密码和（在许多实现中）所谓的“盐”构成的字符串。加“盐”可以防止攻击者很容易生成常用密码的散列表，从而根据表格反查出真实密码[12]。MD5和SHA1都是比较常用的加密散列函数，但是不推荐直接用于密码散列，除非应用在一个更大的结构之中，比如PBKDF2[13]。

存储的数据有时叫做“密码验证值”或者“密码散列值”，经常使用模块化加密格式或者RFC 2307散列格式存储，有时存储在/etc/passwd文件或/etc/shadow文件中[14]。

主要的存储密码的方式有明文、散列、加盐散列，以及可逆加密[15]。如果攻击者访问到了密码文件，并且密码是明文存储的话，就不需要破解了。如果密码是以散列值方式存储的话，遇到彩虹表攻击（比破解效率高）就会比较脆弱。如果密码是以可逆加密的方式存储的话，假如攻击者得到了解密密钥，就不需要破解了；假如攻击者得不到解密密钥，则不可能实现破解。因此，在常用的密码存储形式中，只有当密码是以加盐散列的方式存储，攻击才是必要且可能的[15]。

如果加密散列函数设计得好，反转函数得到明文密码的行为在计算上是不可行的。不过，攻击者可以利用广泛使用的工具来尝试猜密码。这些工具的工作方法是，把猜测的密码进行散列，并用每个散列结果与真正的密码散列结果相比较。如果攻击者找到一个匹配，那么他们就猜到了相应用户的真实密码。 密码破解工具可以用蛮力的方式运行（尝试每种可能的字符组合），或者把一个列表中的每个字符串进行散列。在互联网上广泛存在很多大型列表，上面有许多种语言中可能出现的密码[4]。密码破解（英语：Password cracking）工具的存在，使得攻击者能够轻易地破解弱密码。特别是，攻击者可以快速破解那些短密码、用词典中有的词语或简单变化之后作为的密码，以及用容易猜出来的模式生成的密码[16]。早期的Unix系统曾经用的密码散列算法是基于数据加密标准（DES）算法的一个修改版本[17]。{{link-en|Crypt (Unix)|Crypt (Unix)|Crypt]]算法使用一个12位的盐值，因此其每个用户的散列值都是独一无二的，同时还将DES算法迭代25次，目的是降低散列函数的速度。两种措施都是为了破坏自动猜密码的攻击手段。用户的密码用作一个密钥，加密一个固定值。更近期的Unix或类Unix系统（如Linux或各种BSD系统）使用更安全的密码散列算法，例如PBKDF2、bcrypt，和scrypt。这些算法具有大型的盐值，以及可调节的消耗或迭代次数[18]。 设计不当的散列函数可以使攻击强密码变得可行。LM hash（英语：LM hash）就是一个不安全的例子，曾经被广泛地部署过[19]。

通过网络验证密码的方法[编辑]

密码的简单传输[编辑]

密码在传输至提供认证服务的机器或人时，是很容易被截获的（例如“嗅探”）。如果密码在不安全的物理线路上，从用户访问点到控制密码数据库的中央系统之间传输，就容易受到窃听方法的嗅探。如果密码以数据分组的形式在互联网上传输，任何人只要能看到包含登录信息的分组，都能以非常低的检测概率进行嗅探。

电子邮件有时会用于分发密码，但这一般是不安全的方法。因为大多数电子邮件是以明文的方式发送的，所以在密码传输过程中，窃听者可以毫不费力地读到包含密码的消息。而且，这个消息会在至少两台电脑上以明文方式存储：发送者的电脑和接收者的电脑。如果在传输过程中经过了一些中间系统，也会在中间系统中存储下来，至少有时候是这样。而且，消息也可能会拷贝到这些系统的备份、缓存，或者历史记录中。

使用客户端加密只能在邮件处理服务器和客户端设备的传输中进行保护。以前和以后的过程就不能得到保护了，而且邮件可能会在多台电脑上以明文存储，比如在始发和接收的电脑上就肯定是这样。

通过加密通道传输[编辑]

密码在互联网上传输时，可以使用加密保护来降低被截获的风险。最广泛使用的是传输层安全协议（TLS，曾被称为SSL），当前大多数浏览器都支持这一特性。在大多浏览器中，当使用TLS时，浏览器会显示一个锁着的锁图标或者其他标志，提示用户正在与服务器进行的信息交换是在TLS/SSL的保护之下。

更多信息：密码学

基于散列的质询响应方法[编辑]

不幸的是，在散列密码存储和基于散列的质询响应认证（英语：challenge-response authentication）之间有冲突。后者要求，客户端向服务器证明其知道共享密钥（例如密码），服务器必须能够将密码从其存储形式中获取出来。许多系统（包括Unix类型的系统）进行远程认证，共享密钥通常变成了散列形式。这样就向离线猜测攻击的人暴露了，因此很有局限性。此外，当共享密钥是一个散列值的时候，攻击者不必得到原始密码，仅需要得到散列值就可以进行远程认证。

零知识密码证明[编辑]

相比于传输密码或者传输密码的散列值，密码认证密钥协商（英语：password-authenticated key agreement）系统能够进行零知识密码证明（英语：zero-knowledge password proof），在不暴露密码知识的情况下进行证明。

更进一步说，密码认证密钥协商的扩充系统（例如AMP、{{link-en|B-SPEKE|SPEKE}、PAK-Z、SRP-6（英语：Secure Remote Password protocol））同时避免了基于散列的方法的冲突和局限。扩充系统允许客户端向服务器证明密码，而服务器仅知道（不完全是）哈希形式的密码，同时，又必须有原始密码才能得到访问权。

Procedures for changing passwords[编辑]

Usually, a system must provide a way to change a password, either because a user believes the current password has been (or might have been) compromised, or as a precautionary measure. If a new password is passed to the system in unencrypted form, security can be lost (e.g., via wiretapping) before the new password can even be installed in the password database. And, of course, if the new password is given to a compromised employee, little is gained. Some web sites include the user-selected password in an unencrypted confirmation e-mail message, with the obvious increased vulnerability.

Identity management systems are increasingly used to automate issuance of replacements for lost passwords, a feature called self service password reset. The user's identity is verified by asking questions and comparing the answers to ones previously stored (i.e., when the account was opened).

Some password reset questions ask for personal information that could be found on social media, such as mother's maiden name. As a result, some security experts recommend either making up one's own questions or giving false answers.[20]

Password longevity[编辑]

"Password ageing" is a feature of some operating systems which forces users to change passwords frequently (e.g., quarterly, monthly or even more often). Such policies usually provoke user protest and foot-dragging at best and hostility at worst. There is often an increase in the people who note down the password and leave it where it can easily be found, as well as helpdesk calls to reset a forgotten password. Users may use simpler passwords or develop variation patterns on a consistent theme to keep their passwords memorable.[21] Because of these issues, there is some debate as to whether password ageing is effective. Changing a password will not prevent abuse in most cases, since the abuse would often be immediately noticeable. However, if someone may have had access to the password through some means, such as sharing a computer or breaching a different site, changing the password limits the window for abuse.[22]

Number of users per password[编辑]

Allotting separate passwords to each user of a system is preferable to having a single password shared by legitimate users of the system, certainly from a security viewpoint. This is partly because users are more willing to tell another person (who may not be authorized) a shared password than one exclusively for their use.[來源請求] Single passwords are also much less convenient to change because many people need to be told at the same time, and they make removal of a particular user's access more difficult, as for instance on graduation or resignation.

Password security architecture[编辑]

Common techniques used to improve the security of computer systems protected by a password include:

  • Not displaying the password on the display screen as it is being entered or obscuring it as it is typed by using asterisks (*) or bullets (•).
  • Allowing passwords of adequate length. (Some legacy operating systems, including early versions[哪個／哪些？] of Unix and Windows, limited passwords to an 8 character maximum,[23][24][25] reducing security.)
  • Requiring users to re-enter their password after a period of inactivity (a semi log-off policy).
  • Enforcing a password policy to increase password strength and security.
    • Requiring periodic password changes.
    • Assigning randomly chosen passwords.
    • Requiring minimum password lengths.[13]
    • Some systems require characters from various character classes in a password—for example, "must have at least one uppercase and at least one lowercase letter". However, all-lowercase passwords are more secure per keystroke than mixed capitalization passwords.[26]
    • Providing an alternative to keyboard entry (e.g., spoken passwords, or biometric passwords).
    • Requiring more than one authentication system, such as 2-factor authentication (something a user has and something the user knows).
  • Using encrypted tunnels or password-authenticated key agreement to prevent access to transmitted passwords via network attacks
  • Limiting the number of allowed failures within a given time period (to prevent repeated password guessing). After the limit is reached, further attempts will fail (including correct password attempts) until the beginning of the next time period. However, this is vulnerable to a form of denial of service attack.
  • Introducing a delay between password submission attempts to slow down automated password guessing programs.

Some of the more stringent policy enforcement measures can pose a risk of alienating users, possibly decreasing security as a result.

Password reuse[编辑]

It is common practice amongst computer users to reuse the same password on multiple sites. This presents a substantial security risk, since an attacker need only compromise a single site in order to gain access to other sites the victim uses. This problem is exacerbated by also reusing usernames, and by websites requiring email logins, as it makes it easier for an attacker to track a single user across multiple sites. Password reuse can be avoided or minimused by using mnemonic techniques, writing passwords down on paper, or using a password manager.[27]

It has been argued by Redmond researchers Dinei Florencio and Cormac Herley, together with Paul C. van Oorschot of Carleton University, Canada, that password reuse is inevitable, and that users should reuse passwords for low-security websites (which contain little personal data and no financial information, for example) and instead focus their efforts on remember long, complex passwords for a few important accounts, such as banks accounts.[28] Similar arguments were made by Forbes cybersecurity columnist, Joseph Steinberg, who also argued that people should not change passwords as often as many "experts" advise, due to the same limitations in human memory.[21]

Writing down passwords on paper[编辑]

Historically, many security experts asked people to memorize their passwords: "Never write down a password". More recently, many security experts such as Bruce Schneier recommend that people use passwords that are too complicated to memorize, write them down on paper, and keep them in a wallet.[29][30][31][32][33][34][35]

Password manager software can also store passwords relatively safely, in an encrypted file sealed with a single master password.

After death[编辑]

According to a survey by the University of London, one in ten people are now leaving their passwords in their wills to pass on this important information when they die. One third of people, according to the poll, agree that their password protected data is important enough to pass on in their will.[36]

Password cracking[编辑]

主条目：Password cracking

Attempting to crack passwords by trying as many possibilities as time and money permit is a brute force attack. A related method, rather more efficient in most cases, is a dictionary attack. In a dictionary attack, all words in one or more dictionaries are tested. Lists of common passwords are also typically tested.

Password strength is the likelihood that a password cannot be guessed or discovered, and varies with the attack algorithm used. Cryptologists and computer scientists often refer to the strength or 'hardness' in terms of entropy.[4]

Passwords easily discovered are termed weak or vulnerable; passwords very difficult or impossible to discover are considered strong. There are several programs available for password attack (or even auditing and recovery by systems personnel) such as L0phtCrack, John the Ripper, and Cain; some of which use password design vulnerabilities (as found in the Microsoft LANManager system) to increase efficiency. These programs are sometimes used by system administrators to detect weak passwords proposed by users.

Studies of production computer systems have consistently shown that a large fraction of all user-chosen passwords are readily guessed automatically. For example, Columbia University found 22% of user passwords could be recovered with little effort.[37] According to Bruce Schneier, examining data from a 2006 phishing attack, 55% of MySpace passwords would be crackable in 8 hours using a commercially available Password Recovery Toolkit capable of testing 200,000 passwords per second in 2006.[38] He also reported that the single most common password was password1, confirming yet again the general lack of informed care in choosing passwords among users. (He nevertheless maintained, based on these data, that the general quality of passwords has improved over the years—for example, average length was up to eight characters from under seven in previous surveys, and less than 4% were dictionary words.[39])

Incidents[编辑]

  • On July 16, 1998, CERT reported an incident where an attacker had found 186,126 encrypted passwords. At the time the attacker was discovered, 47,642 passwords had already been cracked.[40]
  • In September, 2001, after the deaths of 960 New York employees in the September 11 attacks, financial services firm Cantor Fitzgerald through Microsoft broke the passwords of deceased employees to gain access to files needed for servicing client accounts.[41] Technicians used brute-force attacks, and interviewers contacted families to gather personalized information that might reduce the search time for weaker passwords.[41]
  • In December 2009, a major password breach of the Rockyou.com website occurred that led to the release of 32 million passwords. The hacker then leaked the full list of the 32 million passwords (with no other identifiable information) to the Internet. Passwords were stored in cleartext in the database and were extracted through a SQL injection vulnerability. The Imperva Application Defense Center (ADC) did an analysis on the strength of the passwords.[42]
  • In June, 2011, NATO (North Atlantic Treaty Organization) experienced a security breach that led to the public release of first and last names, usernames, and passwords for more than 11,000 registered users of their e-bookshop. The data was leaked as part of Operation AntiSec, a movement that includes Anonymous, LulzSec, as well as other hacking groups and individuals. The aim of AntiSec is to expose personal, sensitive, and restricted information to the world, using any means necessary.[43]
  • On July 11, 2011, Booz Allen Hamilton, a consulting firm that does work for the Pentagon, had their servers hacked by Anonymous and leaked the same day. "The leak, dubbed 'Military Meltdown Monday,' includes 90,000 logins of military personnel—including personnel from USCENTCOM, SOCOM, the Marine corps, various Air Force facilities, Homeland Security, State Department staff, and what looks like private sector contractors."[44] These leaked passwords wound up being hashed in SHA1, and were later decrypted and analyzed by the ADC team at Imperva, revealing that even military personnel look for shortcuts and ways around the password requirements.[45]

Alternatives to passwords for authentication[编辑]

The numerous ways in which permanent or semi-permanent passwords can be compromised has prompted the development of other techniques. Unfortunately, some are inadequate in practice, and in any case few have become universally available for users seeking a more secure alternative.[來源請求] A 2012 paper[46] examines why passwords have proved so hard to supplant (despite numerous predictions that they would soon be a thing of the past[47]); in examining thirty representative proposed replacements with respect to security, usability and deployability they conclude "none even retains the full set of benefits that legacy passwords already provide."

  • Single-use passwords. Having passwords which are only valid once makes many potential attacks ineffective. Most users find single use passwords extremely inconvenient. They have, however, been widely implemented in personal online banking, where they are known as Transaction Authentication Numbers (TANs). As most home users only perform a small number of transactions each week, the single use issue has not led to intolerable customer dissatisfaction in this case.
  • Time-synchronized one-time passwords are similar in some ways to single-use passwords, but the value to be entered is displayed on a small (generally pocketable) item and changes every minute or so.
  • PassWindow one-time passwords are used as single-use passwords, but the dynamic characters to be entered are visible only when a user superimposes a unique printed visual key over a server generated challenge image shown on the user's screen.
  • Access controls based on public key cryptography e.g. ssh. The necessary keys are usually too large to memorize (but see proposal Passmaze)[48] and must be stored on a local computer, security token or portable memory device, such as a USB flash drive or even floppy disk.
  • Biometric methods promise authentication based on unalterable personal characteristics, but currently (2008) have high error rates and require additional hardware to scan, for example, fingerprints, irises, etc. They have proven easy to spoof in some famous incidents testing commercially available systems, for example, the gummie fingerprint spoof demonstration,[49] and, because these characteristics are unalterable, they cannot be changed if compromised; this is a highly important consideration in access control as a compromised access token is necessarily insecure.
  • Single sign-on technology is claimed to eliminate the need for having multiple passwords. Such schemes do not relieve user and administrators from choosing reasonable single passwords, nor system designers or administrators from ensuring that private access control information passed among systems enabling single sign-on is secure against attack. As yet, no satisfactory standard has been developed.
  • Envaulting technology is a password-free way to secure data on e.g. removable storage devices such as USB flash drives. Instead of user passwords, access control is based on the user's access to a network resource.
  • Non-text-based passwords, such as graphical passwords or mouse-movement based passwords.[50] Graphical passwords are an alternative means of authentication for log-in intended to be used in place of conventional password; they use images, graphics or colours instead of letters, digits or special characters. One system requires users to select a series of faces as a password, utilizing the human brain's ability to recall faces easily.[51] In some implementations the user is required to pick from a series of images in the correct sequence in order to gain access.[52] Another graphical password solution creates a one-time password using a randomly generated grid of images. Each time the user is required to authenticate, they look for the images that fit their pre-chosen categories and enter the randomly generated alphanumeric character that appears in the image to form the one-time password.[53][54] So far, graphical passwords are promising, but are not widely used. Studies on this subject have been made to determine its usability in the real world. While some believe that graphical passwords would be harder to crack, others suggest that people will be just as likely to pick common images or sequences as they are to pick common passwords.[來源請求]
  • 2D Key (2-Dimensional Key)[55] is a 2D matrix-like key input method having the key styles of multiline passphrase, crossword, ASCII/Unicode art, with optional textual semantic noises, to create big password/key beyond 128 bits to realize the MePKC (Memorizable Public-Key Cryptography)[56] using fully memorizable private key upon the current private key management technologies like encrypted private key, split private key, and roaming private key.
  • Cognitive passwords use question and answer cue/response pairs to verify identity.

"The Password is dead"[编辑]

That "the password is dead" is a recurring idea in Computer Security. It often accompanies arguments that the replacement of passwords by a more secure means of authentication is both necessary and imminent. This claim has been made by numerous people at least since 2004. Notably, Bill Gates, speaking at the 2004 RSA Conference predicted the demise of passwords saying "they just don't meet the challenge for anything you really want to secure."[47] In 2011 IBM predicted that, within five years, "You will never need a password again."[57] Matt Honan, a journalist at Wired, who was the victim of a hacking incident, in 2012 wrote "The age of the password has come to an end."[58] Heather Adkins, manager of Information Security at Google, in 2013 said that "passwords are done at Google."[59] Eric Grosse, VP of security engineering at Google, states that "passwords and simple bearer tokens, such as cookies, are no longer sufficient to keep users safe."[60] Christopher Mims, writing in the Wall Street Journal said the password "is finally dying" and predicted their replacement by device-based authentication.[61] Avivah Litan of Gartner said in 2014 "Passwords were dead a few years ago. Now they are more than dead."[62] The reasons given often include reference to the Usability as well as security problems of passwords.

The claim that "the password is dead" is often used by advocates of alternatives to passwords, such as Biometrics, Two-factor authentication or Single sign-on. Many initiatives have been launched with the explicit goal of eliminating passwords. These include Microsoft's Cardspace, the Higgins project, the Liberty Alliance, NSTIC, the FIDO Alliance and various Identity 2.0 proposals. Jeremy Grant, head of NSTIC initiative (the US Dept. of Commerce National Strategy for Trusted Identities in Cyberspace), declared "Passwords are a disaster from a security perspective, we want to shoot them dead."[63] The FIDO Alliance promises a "passwordless experience" in its 2015 specification document.[64]

In spite of these predictions and efforts to replace them passwords still appear the dominant form of authentication on the web. In "The Persistence of Passwords," Cormac Herley and Paul van Oorschot suggest that every effort should be made to end the "spectacularly incorrect assumption" that passwords are dead.[65] They argue that "no other single technology matches their combination of cost, immediacy and convenience" and that "passwords are themselves the bestfit for many of the scenarios in which they are currently used."

Website password systems[编辑]

Passwords are used on websites to authenticate users and are usually maintained on the Web server, meaning the browser on a remote system sends a password to the server (by HTTP POST), the server checks the password and sends back the relevant content (or an access denied message). This process eliminates the possibility of local reverse engineering as the code used to authenticate the password does not reside on the local machine.

Transmission of the password, via the browser, in plaintext means it can be intercepted along its journey to the server. Many web authentication systems use SSL to establish an encrypted session between the browser and the server, and is usually the underlying meaning of claims to have a "secure Web site". This is done automatically by the browser and increases integrity of the session, assuming neither end has been compromised and that the SSL/TLS implementations used are high quality ones.

History of passwords[编辑]

Passwords or watchwords have been used since ancient times. Polybius describes the system for the distribution of watchwords in the Roman military as follows:

The way in which they secure the passing round of the watchword for the night is as follows: from the tenth maniple of each class of infantry and cavalry, the maniple which is encamped at the lower end of the street, a man is chosen who is relieved from guard duty, and he attends every day at sunset at the tent of the tribune, and receiving from him the watchword — that is a wooden tablet with the word inscribed on it – takes his leave, and on returning to his quarters passes on the watchword and tablet before witnesses to the commander of the next maniple, who in turn passes it to the one next him. All do the same until it reaches the first maniples, those encamped near the tents of the tribunes. These latter are obliged to deliver the tablet to the tribunes before dark. So that if all those issued are returned, the tribune knows that the watchword has been given to all the maniples, and has passed through all on its way back to him. If any one of them is missing, he makes inquiry at once, as he knows by the marks from what quarter the tablet has not returned, and whoever is responsible for the stoppage meets with the punishment he merits.[66]

Passwords in military use evolved to include not just a password, but a password and a counterpassword; for example in the opening days of the Battle of Normandy, paratroopers of the U.S. 101st Airborne Division used a password — flash — which was presented as a challenge, and answered with the correct response — thunder. The challenge and response were changed every three days. American paratroopers also famously used a device known as a "cricket" on D-Day in place of a password system as a temporarily unique method of identification; one metallic click given by the device in lieu of a password was to be met by two clicks in reply.[67]

Passwords have been used with computers since the earliest days of computing. MIT's CTSS, one of the first time sharing systems, was introduced in 1961. It had a LOGIN command that requested a user password. "After typing PASSWORD, the system turns off the printing mechanism, if possible, so that the user may type in his password with privacy."[68] In the early 1970s, Robert Morris developed a system of storing login passwords in a hashed form as part of the Unix operating system. The system was based on a simulated Hagelin rotor crypto machine, and first appeared in 6th Edition Unix in 1974. A later version of his algorithm, known as crypt(3), used a 12-bit salt and invoked a modified form of the DES algorithm 25 times to reduce the risk of pre-computed dictionary attacks.[69]

See also[编辑]

References[编辑]

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  2. ^ Vance, Ashlee. If Your Password Is 123456, Just Make It HackMe. The New York Times. 2010-01-10. 
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  6. ^ Lewis, Dave. Ctrl-Alt-Delete. 2011: 17 [10 July 2015]. ISBN 147101911X. 
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External links[编辑]

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