Mathematicians refer to the possibility spaces as having entropy of 29 and 75 bits, respectively. The French National Cybersecurity Agency ANSSI recommends spaces having a minimum of bits when it comes to passwords or secret keys for encryption systems that absolutely must be secure. Encryption involves representing data in a way that ensures it cannot be retrieved unless a recipient has a secret code-breaking key.
In fact, the agency recommends a possibility space of bits to guarantee security for several years. It considers 64 bits to be very small very weak ; 64 to 80 bits to be small; and 80 to bits to be medium moderately strong. For a truly strong password as defined by ANSSI, you would need, say, a sequence of 16 characters, each taken from a set of characters.
This would make a bit space, which would render the password close to impossible to memorize.
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Therefore, system designers are generally less demanding and accept low- or medium-strength passwords. They insist on long ones only when the passwords are automatically generated by the system, and users do not have to remember them. There are other ways to guard against password cracking. The simplest is well known and used by credit cards: after three unsuccessful attempts, access is blocked. Alternative ideas have also been suggested, such as doubling the waiting time after each successive failed attempt but allowing the system to reset after a long period, such as 24 hours.
These methods, however, are ineffective when an attacker is able to access the system without being detected or if the system cannot be configured to interrupt and disable failed attempts. The size, T , of the possibility space is based on the length, A , of the list of valid characters in the password and the number of characters, N , in the password. Each of the following examples specifies values of A , N , T and the number of hours, D , that hackers would have to spend to try every permutation of characters one by one. I also assume that in , a computer can explore a billion possibilities per second.
I represent this set of assumptions with the following three relationships and consider five possibilities based on values of A and N :. If the hack has not been detected, the interloper may have days or even weeks to attempt to derive the actual passwords. To understand the subtle processes exploited in such cases, take another look at the possibility space. When I spoke earlier of bit size and password space or entropy , I implicitly assumed that the user consistently chooses passwords at random. But typically the choice is not random: people tend to select a password they can remember locomotive rather than an arbitrary string of characters xdichqewax.
This practice poses a serious problem for security because it makes passwords vulnerable to so-called dictionary attacks. Lists of commonly used passwords have been collected and classified according to how frequently they are used. Attackers attempt to crack passwords by going through these lists systematically.
This method works remarkably well because, in the absence of specific constraints, people naturally choose simple words, surnames, first names and short sentences, which considerably limits the possibilities. In other words, the nonrandom selection of passwords essentially reduces possibility space, which decreases the average number of attempts needed to uncover a password. Below are the first 25 entries in one of these password dictionaries, listed in order, starting with the most common one. I took the examples from a database of five million passwords that was leaked in and analyzed by SplashData.
If you use password or iloveyou, you are not as clever as you thought! Of course, lists differ according to the country where they are collected and the Web sites involved; they also vary over time. For four-digit passwords for example, the PIN code of SIM cards on smartphones , the results are even less imaginative. In , based on a collection of 3. The least-used four-digit password was Careful, though, this ranking may no longer be true now that the result has been published.
The choice appeared only 25 times among the 3.
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The first 20 series of four digits are: ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Even without a password dictionary, using differences in frequency of letter use or double letters in a language makes it possible to plan an effective attack. Exploiting such regularities makes it possible to for hackers to speed up detection.
In the event of an attack, the use of fingerprints can make it is very difficult, if not impossible, for hackers to use what they find.
The transformation is achieved by using algorithms known as cryptographic hash functions. These are meticulously developed processes that transform a data file, F, however long it may be, into a sequence, h F , called a fingerprint of F. Changing a single character in the file completely alters its fingerprint.
For example, if the first character of Nice weather is changed to lowercase nice weather , the hash SHA will generate another fingerprint:. Good hash functions produce fingerprints that are similar to those that would be obtained if the fingerprint sequence was uniformly chosen at random. In particular, for any possible random result a sequence of 64 hexadecimal characters , it is impossible to find a data file F with this fingerprint in a reasonable amount of time. There have been several generations of hash functions. Taking all this into account, properly designed Web sites analyze the passwords proposed at the time of their creation and reject those that would be too easy to recover.
The obvious conclusion for users is that they must choose their passwords randomly. Some software does provide a random password. Be aware, however, that such password-generating software may, deliberately or not, use a poor pseudo-random generator, in which case what it provides may be imperfect. Its database includes more than million passwords obtained after various attacks.
For example, aaaaaa appeared , times; a1b2c3d4, , times; abcdcba, times; abczyx, times; acegi, times; clinton, 18, times; bush, 3, times; obama, 2, times; trump, times. It is still possible to be original. Web sites, too, follow various rules of thumb. Among the rules that a good Web server designer absolutely must adhere to is, do not store plaintext lists of usernames and passwords on the computer used to operate the Web site.
The reason is obvious: hackers could access the computer containing this list, either because the site is poorly protected or because the system or processor contains a serious flaw unknown to anyone except the attackers a so-called zero-day flaw , who can exploit it. One alternative is to encrypt the passwords on the server: use a secret code that transforms them via an encryption key into what will appear to be random character sequences to anyone who does not possess the decryption key. This method works, but it has two disadvantages. This key may therefore be detected by an attacker, which brings us back to the original problem.
The process is also called condensing or hashing. The fingerprint— h F —is a fairly short word associated with F but produced in such a way that, in practice, it is impossible to deduce F from h F. Hash functions are said to be one-way: getting from F to h F is easy; getting from h F to F is practically impossible. In addition, the hash functions used have the characteristic that even if it is possible for two data inputs, F and F', to have the same fingerprint known as a collision , in practice for a given F, it is almost impossible to find an F' with a fingerprint identical to F.
Using such hash functions allows passwords to be securely stored on a computer. Nor can they generate another password with an identical fingerprint to fool the server because it is practically impossible to create collisions. Still, no approach is foolproof, as is highlighted by frequent reports of the hacking of major sites. In , for example, data from a billion accounts were stolen from Yahoo!
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Salting is the addition of a unique random string of characters to each password. It ensures that even if two users employ the same password, the stored fingerprints will differ. The list on the server will contain three components for each user: username, fingerprint derived after salt was added to the password, and the salt itself. When the server checks the password entered by a user, it adds the salt, computes the fingerprint and compares the result with its database.
It goes without saying that hackers have their own ways of fighting back. They face a dilemma, though: their simplest options either take a lot of computing power or a lot of memory. Often neither option is viable. In the age of the Internet, supercomputers and computer networks, the science of password setting and cracking continues to evolve—as does the relentless struggle between those who strive to protect passwords and those who are determined to steal, and potentially abuse, them.
Say you are a hacker looking to exploit data that you have acquired. The password is contained in the possibility space of strings of 12 lowercase letters, which corresponds to 56 bits of information and 26 12 9. Method 1. You scroll through the entire space of passwords. You calculate the fingerprint, h P , for each password, checking to see whether it appears in the stolen data. You do not need a lot of memory, because prior results are deleted with each new attempt, although you do, of course, have to keep track of the possibilities that have been tested.
Scrolling through all the possible passwords in this way takes a long time. Are there unexplained transactions? Questionable or unauthorized changes? If so, dangerous malware installed by predators or hackers may already be lurking. Hackers and predators pose equally serious and but very different threats. An unprotected computer is like an open door for computer hackers and predators. Products like Webroot AntiVirus and Webroot Internet Security Complete thwart dangerous malware before it can enter your PC, stand guard at every possible entrance of your computer and fend off any spyware or viruses that try to enter, even the most damaging and devious strains.
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