Source: http://www.robertgraham.com/pubs/hacking-dict.html
Version 0.4.0, August 21, 2000
Copyright 1998-2000 by Robert Graham (hacking-dict@robertgraham.com. All rights reserved. This document may be reproduced only for non-commercial purposes. All reproductions must contain this exact copyright notice. Reproductions must not contain alterations except by permision.
[ 'bot | .plan | /dev/null | /dev/random | /etc | /etc/hosts | /etc/inetd.conf | /etc/passwd | /etc/services | /etc/shadow | 11 | 128-bit | 40-bit | 56-bit | 64-bit | 8 | 8-character password | 802.1q | ~user ]
Key point: The debate over strong encryption is never ending. Within the United States, law enforcement is constantly lobbying to restrict the use of strong encryption. Many resist, pointing out how often law enforcement already abuses wiretap powers (such as against Martin Luther King). At the same time, companies making products constantly lobby for the easing of export restrictions, so that they can sell strong encryption products abroad. Another funny thing is that the U.S. government's intransigence on this issue has actually led to stronger encryption abroad. U.S. export restrictions (and desire to spy on foreigners) was one of the reasons France relaxed its own law-enforcement bans on encryption use by citizens.
Key point: The random number generators within systems are often weaker than the key itself. For example, when you connect via SSL from your browser to a web-server, they choose a key for that session. That key is chosen with a random number generator. One estimate was that the average 128-bit session key contains only 47-bits of randomness. Other browsers have had even weaker systems allowing the session key to be recovered in only a few minutes.
Key point: Specialized hardware can decrypt 40-bit keys in real time. The average new desktop has enough horsepower to decrypt 40-bit messages. Thus, many people now consider 40-bit encryption to be simply obfuscated plaintext.
Key point: 40-bit often refers to the RC4 system within browsers.
Key point: In January of 1999, the EFF built a custom machine (the "Deep Crack") for $250,000 that could decrypt 56-bit DES encrypted messages in hours.
Key point: 56-bit cryptography almost always refers to DES.
Key point: Security conscious users of such systems need to make sure they use a more random mix of characters because they cannot create long passwords.
Key point: Password cracking such systems is a little easier.
Key point: Web-servers often allow access to user's directories this way. An example would be http://www.robertgraham.com/~rob.
Key point: A big hole on the Internet is that people unexpectedly open up information. For example, the file .bash_history is a hidden file in a person's directory that contains the complete text of all commands they've entered into the shell (assuming their shell is "bash", which is the most popular one on Linux).
Key point: When rooting a machine,
hackers will often redirect logging to /dev/null
For example, the command
Culture: In the vernacular, means much the same thing as "black hole". Typical usage, "if you don't like what I have to say, please direct your comments to /dev/null".
Key point: If a hacker can read files from this directory, then they can likely use the information to attack the machine.
Hack: If you can write files to a user's machine, then you can add entries to his/her hosts files to point to your own machine instead. For example, put an entry for www.microsoft.com to point to your machine, then proxy all the connections for the user. This will allow you to perform a man in the middle attack.
Key point: The passwords are encrypted, so even though everyone can read the file, it doesn't automatically guarantee access to the system. However, programs like crack are very effective at decrypting the passwords. On any system with many accounts, there is a good chance the hacker will be able to crack some of the accounts if they get hold of this file.
Key point: Modern UNIX systems allow for "shadowed" password files, stored in locations like /etc/shadow that only root has access to. The normal password file still exists, minus the password information. This provides backwards compatibility for programs that still must access the password file for account information, but which have no interest in the passwords themselves.
Key point: The chief goal of most hacks against UNIX systems is to retrieve the password file. Many attacks do not compromise the machine directly, but are able to read files from the machine, such as this file. Typical examples include:
Key point: /etc/passwd is a simple text file, with one line per account. The line is broken down into seven columns:
Key point: Its role in life is so that programs can do a getportbyname() sockets call in their code in order to get what port they should use. For example, a POP3 email daemon would do a getportbyname("pop3") in order to retrieve the number 110 that pop3 runs at. The idea is that if all POP3 daemons use getportbyname(), then no matter what POP3 daemon you run, you can always reconfigure its port number by editing /etc/services.
Misunderstanding: This file is bad in order to figure out what port numbers mean. If you want to find out what ports programs are using, you should instead use the program lsof to find out exactly which ports are bound to which processes. If running lsof is not appropriate, then you should lookup the ports in a more generic reference.
[ A | Access Control List | accountability | ACK | Acknowledgement Number | active attack | ActiveX | administrator | age | AH | algorithm | anarchy | ANI | anonymous | anti-replay | anti-virus | application/form-url-encoded | ARP | ARP redirect | ASP | asymmetric cryptograph | attack | audit | auth | authentication | Authentication Header | Authenticode | authorization ]
Key point: An Access Control List (ACL) is used to list those accounts that have access to the resource that the list applies to. When talking about firewalls, the ACL implies the list of IP addresses that have access to which ports and systems through the firewall. When talking about WinNT, the ACL implies the list of users that can access a specific file or directory on NTFS.
Contrast: Discretionary Access Control is the ability to have fine grained control over who has access to what resources.
Contrast: ActiveX is similar to Java applets, except that the code is not "sandboxed": it has full access to the operating system. In order to stop hostile code, ActiveX relies upon digital signatures and "zones". Microsoft browsers are configured to trust ActiveX programs from servers in the "trusted" zone, to trust signed ActiveX programs from servers in less trusted zones, and to prompt/deny unsigned ActiveX applets from untrusted zones.
Controversy: The idea of trusted zones and signed applets works pretty well in theory, but doesn't always work well in practice. The problem is that is relies upon on all users making the correct choices all the time. The Melissa virus/worm proved that this philosophy is not adequate.
Analogy: An cookbook recipe is an algorithm.
Key point: Different algorithms have different levels of complexity. For example, consider the ancient parable (Babylonian?) about a king and a wise subject who did a favor for him. The subject asked for one piece of grain to be placed on the first square of a chess board, two grains on the second, four grains on the third, and so on, doubling the amount of grain for each successive square.
This problem demonstrates an algorithm of exponential complexity. For the first 10 squares of the chess board, the series is: 1 2 4 8 16 32 64 128 256 512. Thus, for the first 10 squares, roughly a thousand grains must be paid out. However, the series continues (using K=1024): 1k 2k 4k 8k 32k 64k 128k 256k 512k. Thus, for the first 20 squares, roughly a million grains must be paid out. After 30 squares, roughly a billion grains must be paid out. For 40 squares, roughly a trillion grains must be paid out.
This is directly related to such things as key size. A 41-bit key is twice as hard to crack as a 40-bit key. A 50-bit key is a thousand times harder. A 60-bit key is a million times harder. This is why the 128-bit vs. 40-bit encryption debate is so important: 128-bit keys are a trillion trillion times harder to crack (via brute force) than 40-bit keys.
Key point: Most algorithms are public, meaning that somebody trying to decrypt your message knows all the details of the algorithm. Consequently, the message is protected solely by the key. Many people try to add additional protection by making the details of the algorithm secret as well. Experience so far has led to the belief that this actually leads to weaker security for two reasons. First, such secrets always get discovered eventually, so if security depends upon this secret, it will eventually be broken. Secondly, human intelligence is such that someone cannot create a secure algorithm on his/her own. Therefore, only by working with a community of experts over many years can humans create a secure algorithm. To date, only two such communities exist: the entire world of cryptography experts publishing the details of their work and trying to break other people's work, and the tightly knit community of cryptography experts working in secret for the NSA.
Contrast: Cyberspace anarchy and real-world anarchy are different. The main thrust is that cyber-punishment should fit cyber-crime, and physical-punishment should only be used in cases of physical-crime.
Example: Most of the cyber-anarchy focuses on cryptography, or crypto-anarchy. This is because most anarchic capabilities will be based in cryptography.
Example: Anonymous e-mail services like Hotmail put the IP address of the person sending the e-mail in the headers (which are normally hidden from view by e-mail clients). Many would-be hackers get caught this way.
Example: France is currently trying to outlaw Internet anonymity, forcing uses to disclose their identity.
Contrast: Anonymity is one aspect of privacy.
Key point: By sniffing ARP packets off the wire, you can discover a lot of stuff going on. This is especially true of cable-modem and DSL segments. Since ARP packets are broadcasts, you aren't technically breaking your user's agreement by sniffing.
Key point: You can spoof ARP requests and/or responses in order to redirect traffic through your machine.
Key point: A recurring bug in ASP has allowed hackers to read the script rather than the output of the script. These techniques rely upon changing the name of the script such that the server not longer recognizes it as a script, but as a file instead. Some techniques that have worked in the past have been:
Example: Some classifications of attacks are:
Example: When you log in with your username and give the password, you are authenticating yourself to the system. You are proving that you are you because, in theory, only you know your password.
Key point: Abstractly, anything that combats forgery is called authentication. For example, IPsec includes an Authentication Header (AH) that proves that a packet hasn't been modified in transit.
Contrast: Note that there is a small difference between authentication and authorization. In one case, once you authenticate somebody's identity, your next step is to figure out if they are authorized to do what they are asking to do (i.e. log onto the server). In other cases, authorization is independent from authentication, such as not allowing anybody to logon after midnight.
Examples:
[ back channel | back door | Back Orifice | backticking | banner | BASE64 | bash" | BGP | big-endian | binary | BIND | BinHex | biometrics | BIOS | bit | BlackNet | block cipher | Blowfish | boink | bomb | bonk | boot sector | bootp | broadcast | browser | brute force | BS7799 | BSD | buffer overflow | buffer overrun | byte-order ]
Contrast: Remote administration trojans (RATs) are NOT examples of back channels, but are instead forward channels. A RAT allows the hacker to contact the system from anywhere in the world, and allows the hacker to hide where he/she is coming from. A back channel, on the other hand, will contact the hacker, who must have a fixed IP address. This clearly fingers who the hacker is.
Key point: Typical back channel protocols are X Windows (xterm) and shells like Telnet. These programs are often built into the victim's system, so many attacks that can't otherwise compromise the system can still trigger a back channel that allows a remote shell.
See also: covert channel
Example:
Key point: Key features of backdoors are:
Key point: Back doors are frequently programmed into systems either benignly or maliciously. Most computers shipped today allow BIOS passwords to be set that will prevent the booting of the computer without the administrator first typing the password. However, since many people lose their password, such BIOSes often have a back door passwords that allows the real password to be set. Similarly, a lot of remotely manageable network equipment (routers, switches, dialup banks, etc.) have backdoors for remote Telnet or SNMP. The frequency of such back doors is due to the fact that people are stupid, set passwords, forget them, then whine to customer support.
Key point: A backdoor can be added to any system. For example, when generating random session keys, a programmer may actually subvert the random number generator. Such subversion would then allow decrypting of the message by those who knew the specifics. This has already been done accidentally; some paranoids believe that some encryption products do this intentionally in order to get export approval of 128-bit products.
See also: trap-door
Key point: Many banners reveal the exact version of the product. Over time, exploits are found for specific versions of products. Therefore, the intruder can simply lookup the version numbers in a list to find which exploit will work on the system. In the examples below, the version numbers that reveal the service has known exploitable weaknesses are highlighted.
Example: The example below is a Red Hat Linux box with most the default service enabled. The examples below show only the text-based services that show banners upon connection (in some cases, a little bit of input was provided in order to trigger the banners). Note that this is an older version of Linux; exploits exist for most these services that would allow a hacker to break into this box (most are buffer-overflow exploits).
| Protocol | Port | Banner |
|---|---|---|
| FTP | 21 | 220 rh5.robertgraham.com FTP server (Version wu-2.4.2-academ[BETA-15](1) Sat Nov 1 03:08:32 EST 1997) ready. |
| ssh | 22 | SSH-2.0-2.1.0 SSH Secure Shell (non-commercial) |
| Telnet | 23 |
Red Hat Linux release 5.0 (Hurricane) Kernel 2.0.31 on an i486 login: |
| SMTP | 25 | 220 rh5.robertgraham.com ESMTP Sendmail 8.8.7/8.8.7; Mon, 29 Nov 1999 23:28:31 -0800 |
| finger | 79 |
Login Name Tty Idle Login Time Office Office Phone rob Robert David Graham p0 Nov 29 22:51 (gandalf) root root p1 Nov 29 23:34 (10.17.128.201:0.0) |
| HTTP | 80 |
HTTP/1.0 200 OK Date: Tue, 30 Nov 1999 07:34:59 GMT Server: Apache/1.2.4 Last-Modified: Thu, 06 Nov 1997 18:20:06 GMT Accept-Ranges: bytes Content-Length: 1928 Content-Type: text/html |
| POP3 | 110 | +OK POP3 rh5.robertgraham.com v4.39 server ready |
| identd | 113 | 0 , 0 : ERROR : UNKNOWN-ERROR |
| IMAP4 | 143 | * OK rh5.robertgraham.com IMAP4rev1 v10.190 server ready |
| lp | 515 | lpd: lp: Malformed from address |
| uucp | 540 | login: |
Defenses: Many systems allow banners to be suppressed. You should read the software documentation for more information on this.
Key point: BGP can be subverted in numerous ways. BGP is generally unauthenticated, and rogue ISPs can play havoc.
Contrast: The word binary usually means not text. In computers, every 8 binary digits are used to represent a byte. However, only 7 binary digits are needed to convey text (26 upper case, 26 layer case 10 decimal digits, a number of punctuation characters, etc). Therefore, data using just 7 binary digits per bytes is always text data. It is pointless to say binary computer data, since all computer data is binary. When someone says binary, rather than being redundant, what they are really trying to convey is that the data in question isn't text data. For example, FTP is a text protocol, whereas SMB is a binary protocol.
Misconception: The word is also a noun (as well as the usual adjectival sense). A binary is a file containing binary (as opposed to text) data. In particular, you might hear the phrase "hackers replace the binaries on a the victim's machine". What this really means is that the hackers have replaced many of the software programs (with trojans). This phrase comes about because executable programs contains binary, not text data. Therefore, a machine's binaries are its programs.
See also: A common issue is how to send binary data within a text protocol/message. For example, how can we send a binary within a text e-mail message? The answer is to "encode" the data. See the word encoding for more details.
Example: retina, iris, palm print, fingerprint, thumbprint, hand geometry, handwriting, signature, speech/voice, gait, typing characteristics, scent, facial features, DNA
Contrast: There are roughly three "factors" used in authentication
Contrast: Biometrics is based upon your real identity (who you are). Most other authentication methods are based upon a virtual identity. Your username/password doesn't identify you, but your account on the computer. Similarly, root on a UNIX machine isn't a real person, but a role account.
Key Point: Biometrics has a number of problems. The first is that biometrics degrade over time. People's signatures change over time. An injury can change fingerprints. Voice recognition systems fail when people have cold. Thus, biometric systems fail quite often.
Key point: The BIOS stores configuration settings in NVRAM (Non-Volatile RAM). Remember that the contents of your normal RAM/memory are lost when you power-off your computer. The contents of NVRAM, in contrast, are retained when power goes off. Most NVRAM consists of CMOS (low-power) chips with a small battery that constantly feeds power to the chips (such batteries last about 5-years). A common trick of hackers and viruses is to corrupt the CMOS settings causing the computer to fail to boot. Removing the battery connection (usually a jumper on the motherboard) will cause the CMOS settings to be lost and be reset back to default (good) state.
Key point: All of today's BIOSes are stored in programmable ROMs, which allows them to be reprogrammed (usually with bug fixes from the manufacturer). This allows the hacker to reprogram them as well. While in theory the hacker could reprogram his/her own code into the BIOS, in practice this has not been done yet. Instead, hackers can sometimes use this programming feature to corrupt the BIOS code (in much the same way they corrupt the BIOS settings mentioned above). This will usually prevent the system from booting even to a point where a fresh BIOS can be re-programmed into the system. This requires that the system be brought back to the vendor in order to have the BIOS reprogrammed. Note that you can often set a jumper on the motherboard that denies the ability to reprogram the BIOS.
Key point: BIND provides about 80% of all DNS services. It is also enabled by default on a lot of Linux distributions. As a result, any exploit discovered for BIND has immediate and large impact on the Internet. As of November, 1999, all versions of BIND previous to 8.2.2-P5/4.9.7 have known holes that can be exploited. It is likely that these newer versions also have undiscovered exploitable holes as well.
Key point: BIND comes in two versions, 4.x and 8.x. This is largely due to backwards compatibility: people are running a lot of older servers and would rather patch them than upgrade to a newer version. Also, the newer 8.x code-base has not be extensively peer-reviewed and is thought to be a lot less secure than the 4.x source base.
Key point: In many contexts, each additional bit means "twice as much". 8 extra bits means 256 times as much. 16 extra bits means 65536 times as much. Therefore, it takes 65536 times longer to brute force crack a 56-bit key than a 40-bit key.
In the class of hostile software, a logic bomb is some code left behind by a program that "goes off" at a particular time (such as deleting all the files on the computer on New Years Eve). One theory was that Y2K consultants left logic bombs inside the code they were fixing in order to earn even more money after Y2K.
A mail bomb is the effect of sending somebody tons of e-mail, overloading their mailbox and/or network connection. Sometimes this can be done with a program, other times it can be done simply by signing up the victim to huge numbers of e-mailing lists. Finally, it can be accidental, as happened once to Apple Computer when its mailing list software got out of control.
History: In the old days of UNIX terminals, an e-mail message containing VT100 control codes in a logic bomb could completely hose a user's terminal, forcing them to log out. DOS machines supporting the ANSI.SYS driver also had that problem.
Key point: DHCP is simply an extension on top of bootp. This is important because without an IP address, clients cannot reach bootp servers that reside across routers. Virtually all routers have an extension for bootp forwarding that fixes this issue. Since DHCP had the same requires, the designers just stuck it inside bootp packets rather than requiring yet another change to the routing infrastructure.
Key point: Until macro viruses came along, boot sector viruses where the most common variant. They spread through companies via floppy disks. Users would leave floppy disks in the drive and when the computer restarted, it would attempt to boot from the floppy. This would run the virus, which then infected the boot sector on the hard drive. Any further floppies plugged into the system would then be infected by the virus.
Countermeasures: I worked at a company with anal anti-virus procedures (anti-virus on all desktops, regular wiping of floppy disks). It was never able to completely free itself from the boot sector virus problem; one of the viruses was never successfully eradicated from the company. My own personal policy is to disconnect the floppies on 90% of the machines, and disable floppy bootup on the remaining machines.
Example: A cancel-bot is a program that attempts to cancel lots of messages within USENET newsgroups. These are sometimes used by the USENET Death Penalty or rogue cancellers. *
Example: Search engine spiders that index the web follow web-page links, going from site to site, downloading web-pages.
Example: In the IRC wars, hackers run automated bots to control channels. These are programs (usually in C) that help in administering channels, protection against hackers, flooding, and so forth.
Key point: Netsape and Microsoft have not yet produced a browser that is hardened against predation from hostile websites.
Key point: Disabling Java, JavaScript, and ActiveX will lock out virtually all hacks against the browser. However, this will also lock out many websites.
Analogy: If you somehow steal somebody's ATM card, you could try to use it in a bank machine. PIN numbers are only 4 digits, meaning 10,000 possible combinations. If you were patient, you could stand at the cash machine trying all possible 10,000 combinations. (Of course, ATM machines will always eat the cards after a few unsuccessful tries in order to stop this).
Key point: The term brute force often means "the most difficult way". In the above example of the PIN number, you can always find the PIN number after guessing 10,000 combinations. But sometimes there are easier ways. For example, a bank may choose to assign PIN numbers based upon a combination of the issuing date and the user's name. Therefore, the problem is reduced to guessing when a card was issued, which may consist of only a few hundred guesses.
Therefore, any technique that is more difficult than brute force is pointless. Likewise, brute force is very difficult, so hackers continually search for techniques that are less difficult.
Key point: The possibility of doing brute-force key-space searches is often compared to the age of the universe, number of atoms in the planet earth, and the yearly output of the sun. For example, Bruce Schneier has calculated that according to what we know of quantum mechanics today, that the entire energy output of the sun is insufficient to break a 197-bit key.
Misconception: Certification doesn't been the business cannot get hacked. Rather, it certifies that the business is aware of its security risks, has identified how it is going to manage those risks, and has communicated this information broadly within the organization. For example, a business could put out a website with the statement "we don't care if it gets hacked" and be within compliance. They just need to identify this fact and publish it within the organization.
See also: Common Criteria, CDSA
Analogy: Consider two popular bathroom sink designs. One design is a simple sink with a single drain. The other design includes a backup drain near the top of the sink. The first design is easy and often looks better, but suffers from the problem that if the drain is plugged and the water is left running, the sink will overflow all over the bathroom. The second design prevents the sink from overflowing, as the water level can never get past the top drain.
Example: In much the same way, programmers often forget to validate input. They (rightly) believe that a legal username is less than 32 characters long, and (wrongly) reserve more than enough memory for it, typically 200 characters. The assume that nobody will enter in a name longer than 200 characters, and don't verify this. Malicious hackers exploit this condition by purposely entering in user names a 1000 characters long.
Key point: This is a classic programming bug that afflicts almost all systems. The average system on the Internet is vulnerable to a well known buffer overflow attack. Many Windows NT servers have IIS services vulnerable to a buffer overflow in ".htr" handler, many Solaris servers have vulnerable RPC services like cmsd, ToolTalk, and statd; many Linux boxes have vulnerable IMAP4, POP3, or FTP services.
Key point: Programs written in C are most vulnerable, C++ is somewhat less vulnerable. Programs written in scripting level languages like VisualBasic and Java are generally not vulnerable. The reason is that C requires the programmer to check buffer lengths, but scripting languages generally make these checks whether the programmer wants them or not.
Key point: Buffer overflows are usually a Denial-of-Service in that they will crash/hang a service/system. The most interesting ones, however, can cause the system to execute code provided by the hacker as part of the exploit.
Defenses: There are a number of ways to avoid buffer-overflows in code:
Key point: The NOOP (no operation) machine language instruction for x86 CPUs is 0x90. Buffer overflows often have long strings of these characters when attacking x86 computers (Windows, Linux).
Key point: In a successful buffer overflow exploit, the hacker forces the system to run his own code. Since most network services run as "root" or "administrator", the exploit would give complete control over the machine. For this reason, more and more services are being configured to run with lower privileges.
[ C | CA | cable-modem | cache | CALEA | camping | cancel-bot | Carnivore | carrier-scanning | CDSA | central office | certificate | Certificate Authority | CGI | cgi-bin | chaining | challenge | chat | checksum | chosen plaintext | cipher | ciphertext | circuit switched network | clear-text | cmos | CO | Code | codebook | colo | command-line | Common Criteria | community strings | compiler | complexity | compression | con | confidentiality | cookie | covert channel | crack | cracker | crackz | CRC | credentials | cron | cryptanalysis | crypto | cryptographic | cryptography | CSN | culture | cyberpunk ]
Point: The language is quirky, difficult for beginners to learn, and really just an accident of history. Despite this, one must grok the language in order to become an elite hacker.
Key point: The large number of buffer overflow exploits is directly related to poor way that C protects programmers from doing the wrong thing. On the other hand, these lack of protections leads directly to its high speed.
Key point: If you built your own hardware, you could likely build a sniffer to spy on your neighbor's Internet traffic. Some cable-modem segments can even be sniffed without special hardware by anybody who reconfigures their machine. Some cable-modem segments allow you to redirect a neighbor's traffic through your machine, which you can then sniff.
Key point: Your neighbors are open to lots of hacking techniques that are not generally possible from across the Internet. First, your machine will receive broadcasts from your neighbors. These broadcasts basically advertise your neighbor's presence telling you how to hack into them. For example, neighbors who share their hard-drives will advertise themselves in the Window's Network Neighborhood. UNIX machines will also advertise a lot of information, such as through the 'rwho' mechanism. There are also lots of non-Internet protocols that appear on the local wire that can be used to break into your neighbors.
Key point: Sometimes systems can be exploited through the cache. Examples are:
See also: key recovery, Carnivore, ECPA
Key point: When dialing up to an ISP, the first 10 minutes are the most dangerous.
Misconception: The FBI does not install this on networks. They have to provide a search warrant to an ISP for the e-mail. Carnivore is one of the ways the ISP can fulfill the demands of the search warrant.
See also: CALEA
Key point: Certificates can be revoked. This means that a company who believes that their site has been compromised can put up a server on the Internet that tells everyone else that the certificate is no longer valid.
Key point: The Verisign embedded certificates in older browsers (IE 3.0, Netscape 4.0) have expiration dates of January 1, 2000. This means that anybody using older browsers will get nasty warnings when they visit e-commerce sites or attempt to verify files with authenticode.
Key point: The way it is supposed to work is that you have a certificate that claims to be Microsoft signed by Verisign (a popular CA), then you trust that Verisign has done a reasonable job both ensuring that Microsoft is who they say they are, and that Microsoft has done a reasonably good job protecting their private keys from theft.
Contrast: Microsoft could create a "self-signed" certificate, but then anybody else could create a self-signed certificate claiming to be Microsoft. Therefore, you trust a CA-signed certificate more than a self-signed certificate, as long as you trust the CA.
Key point: How do you trust a CA? The answer is marketing. First, a company like Verisign has spent millions of dollars creating a reputable company that would be destroyed if a flaw was found in their process (i.e. thieves were able to steal their private keys). Second, Verisign (and a few other CAs) have managed to embed their public keys within Internet Explorer and Netscape Navigator. This means that any website using SSL must obtain a certificate signed by one of these built-in CAs, or else users get confusing warning messages.
Humor: Microsoft uses certificates signed by Verisign, because it is trusted by many people. The reason so many people trust Verisign these days is because its root keys are included with Microsoft's browsers.
Key point: One of the chief RISKS is the theft of the private key used to sign things. If a hacker/thief is able to steal it, then they can masquerade as someone
Key point: Several important CA certificates (i.e. Verisign) expired on Dec. 31, 1999. Since it is feasible to eventually compromise a certificates, they usually expire at some date. The certificates for trusting root CAs that are built-in many browsers (Internet Explorer 4.0 and earlier, Netscape Navigator 4.06 and earlier) were created in 1995, and were made for a 5-year lifespan. One of the creators of these certificates now says he wished he'd put the expiration date a little off, such as on Dec. 15, in order to avoid the Y2K madness.
Key point: In most cases the user is prompted for the password, which the client then stores in memory. In the use of smart cards, however, the system may give the user the challenge string, which the user then types into the smart card. The smart card then produces a response, which the user must type back into the system. In this way, the user validates that they have the smart card.
Key point: Challenge-response systems are thought to be more secure because the challenge/response is different every time. This guards against replay attacks as well as making cracking more difficult.
Key point: Favorite because it provides real-time anonymous communication.
Key point: Checksums are not secure against intentional changes by hackers. For that, you need a cryptographic hash.
Key point: A block cipher is one that encrypts a block of data at a time. For example, DES uses a block size of 64-bits. Each input block must correspond to exactly one output block (like a codebook). A block-cipher suffers from the fact the same data repeated in a message would be encoded in the same way. Consider a block size of 8-bit encrypting English text; you could therefore figure out all the letter 'e's in the cipher text because they are the most common letter used. Therefore, block-ciphers are often used in a chaining mode such that the same pattern will indeed be decrypted differently.
Key point: A stream cipher is essentially a chained block cipher with a block size of 1 (either 1-bit or 1-byte). It generates a keystream against which it XORs the plaintext, operating much like a one-time pad, though less secure in theory but more secure in practice.
Contrast: clear-text, plaintext.
Misunderstanding: The word text comes from traditional cryptography that meant the text of messages, though these days text can refer to binary computer data as well.
Key point: In block-ciphers, the key represents a codebook. In other words, you could use the key to generate a huge book of matching pairs whereby each plaintext block would match to exactly one ciphertext block. Then, you could encrypt messages by looking them up in this table.
Key point: The term ECB or Electronic Code-Book refers to the use this mode of using a block-cipher. However, since it leaks information, many people prefer to chain blocks of ciphertext and plaintext together in order to make sure that the same pattern will be encrypted differently when it appears multiple times in a message.
Key point: The average hacker does all his/her work from the command-line. Virtually all hacker tools are command-line oriented.
CC is a set of government-oriented standards designed to create a commonly agreed upon criteria in which to describe and judge infosec. For example, if you want to purchase a "secure" computer from a vendor, the CC gives you a common set of criteria with which to evaluate that system. If you want to talk about infosec issues, the CC gives you a language in which to describe them. These common criteria were put together by government departments from Canada, France, Germany, the Netherlands, Great Britain, and the United States (both NIST and the NSA).
Controversy: The CC defines terminology uses terminology that is far from the infosec mainstream. Furthermore, many believe that products that match the criteria would be secure, they would also be worthless (in much the same way that a computer turned off, unplugged, and locked in the basement is secure from remote attacks).
Key point: The CC breaks down security functionality into the following areas:
Resources: http://csrc.ncsl.nist.gov/cc/
Key point: A compiler is a form of lossy compression and one-way encryption. All the information meaningful to humans is removed from the code leaving only the information necessary for the computer. This means that humans can no longer easily read the resulting program directly. Because of the "one-way" nature of the operation, programs cannot be used to recover the existing source code. This effect is different in various languages. C++ is the worst language in terms of decompilation; Java is the best. Most Java applets can be decompiled back to some semblance of their previous form. This has led to a market for programs that further obfuscate Java binaries in an effort to hide the original source code. Some compilers do leave human-readable symbols behind for debugging purposes. They won't reveal the original source, but can still be useful for reverse engineering They can be "stripped" from the binary.
The best way to understand complexity is to consider the ancient parable (Babylonian?) about a king and a wise subject who did a favor for him. The subject asked for one piece of grain to be placed on the first square of a chess board, two grains on the second, four grains on the third, and so on, doubling the amount of grain for each successive square.
| 1 | 2 | 4 | 8 | 16 | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
| --- | --- | --- | --- | --- | --- | --- | --- |
The question is: how much grain does this come out to? Your possible choices are:
The problem is known as having exponential complexity. The average computer scientist, when confronted with this problem, would intuitively guess the correct answer, which is that the amount of grain is a billion times a billion, or more than all the grain ever harvested by mankind.
| 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 |
| 256 | 512 | 1024 | 2048 | 4096 | 8192 | 16384 | 32768 |
| 65536 | 131072 | 262144 | 524288 | 1048576 | 2097152 | 4194304 | 8388608 |
| 16777216 | 33554432 | 67108864 | 134217728 | 268435456 | 536870912 | 1073741824 | 2147483648 |
| 4294967296 | 8589934592 | 17179869184 | 34359738368 | 68719476736 | 137438953472 | 274877906944 | 549755813888 |
| 1099511627776 | 2199023255552 | 4398046511104 | 8796093022208 | 17592186044416 | 35184372088832 | 70368744177664 | 140737488355328 |
| 281474976710656 | 562949953421312 | 1125899906842624 | 2251799813685248 | 4503599627370496 | 9007199254740992 | 18014398509481984 | 36028797018963968 |
| 72057594037927936 | 144115188075855872 | 288230376151711744 | 576460752303423488 | 1152921504606846976 | 2305843009213693952 | 4611686018427387904 | 9223372036854775808 |
Example: Let's say that a dictionary was not sorted. This means that you would have to start at the begining and look at every word until you found the definition you were looking for. This is an algorithm with linear complexity. The time it takes you to lookup a word in such a dictionary is related to the number of words in the dictionary: if you double the size of such a dictionary, you will double the amount of time it takes to lookup a word. In other words, the time to lookup a word in this dictionary is on the order of the size of the dictionary. This is expressed as O(n), where n is the size of the dictionary.
Example: Dictionaries are sorted before printing. This means that you can quickly find the word you are looking for. In terms of complexity we are more interested in how much longer it will take you to lookup a word if we double the size of the dictionary. In other words, the Oxford English Dictionary (OED) is about 8 times larger than a more abridged English dictionary. However, it only takes about 3 times longer to lookup a word in the OED. As the problem size grows, the amount of effort it takes to figure out the problem grows less slowly. If the OED were 16-times larger, then it would take only 4-times longer to search. If the OED were 32-times larger, it would take only 5-times longer to search. This mathematical relationship is known as a logarithm. The increase in computing power needed to solve such a problem grows on the order of the logarithm of size of the problem. This is expressed as O(logn). Logarithm problems are much easier to solve than linear ones, which is why we sort dictionaries.
Example: The chessboard problem mentioned above is similar to encryption keys. Every additional square on the chessboard doubles the size of the problem; every additional bit added to a key doubles the amount of time it would take to crack it. This means that a 32-bit key would take roughly a billion trials in order to crack, a 64-bit key would be roughly a billion times harder than that to crack, and a 128-bit key is a billion billion times harder to crack than a 64-bit key. This complexity is expressed as O(2n).
Key point: The following table shows the complexity of some algorithms.
| big-O | complexity | problem = 8 elements | problem = 32 elements |
| O(logn) | logarithmic | 3 seconds | 5 seconds |
| O(n) | linear | 8 seconds | 32 seconds |
| O(n2) | quadratic | 1 minute | 15 minutes |
| O(n3) | cubic | 9 minutes | 9 hours |
| O(2n) | exponential | 4 minutes | 136 years |
Contrast: For the most part, the words confidentiality and privacy are interchangeable. We typically apply the word privacy to individuals, and include ideas like anonymity and unobservability. We use works like confidentiality to refer governments and corporations who wish to defend against eavesdropping.
Key point: We use encryption to protect secrets from being eavesdropped.
Misconception: Cookies are not a security/privacy risk. However, when combined with HTTP Referer field and cross-site imbedded images, they can be used to track user's activities. Users have sued sites like DoubleClick that have massive cross-site imbedded images over the privacy information they collect. Cookies receive most of the blame for this.
Example: The biggest privacy hole is when cookies are combined with the HTTP Referer field. If many sites imbed images (like advertisements) from a single site, that single site can use cookies in order to track a user going among those sites. The cookie does not identify who the user is, but can track what the user does. Other information, like web-site logons, can then be combined with this information in order to track how the person is.
Example: JavaScript has a long history of problems with cookies such that one website can retrieve the cookie information for another website. Since cookie information often contains username/password information, this can compromise the site.
Key point: Turning off cookies is not practical. The best you can hope for is "cookie management" -- choose which sites you want to allow cookies for but deny them to all the rest.
Key point: One rootkit uses ICMP as a covert channel. It creates a virtual TCP-like circuit inside of ping packets.
Key point: Covert channels can become extremely covert. In theory, one can create a covert channel where only the IP identification field (16-bits) carries the data.
Key point: URLs and DNS queries pass through virtually everything (including proxies). Therefore, it is easy to export information from inside a company to the outside using this technique.
History: When the UNIX operating system was first developed, passwords were stored in the file /etc/passwd. This file was made readable by everyone, but the passwords were encrypted so that a user could not figure out who a person's password was. The passwords were encrypted in such a manner that you could test a password to see if it was valid, but you really couldn't decrypt the entry. (Note: not even administrators are able to figure out user's passwords; they can change them, but not decrypt them). However, a program called "crack" was developed that would simply test all the words in the dictionary against the passwords in /etc/passwd. This would find all user accounts whose passwords where chosen from the dictionary. Typical dictionaries also included people's names since a common practice is to choose a spouse's or child's name.
Contrast: A "crack" program is one that takes existing encrypted passwords and attempts to find some that are "weak" and easily discovered. However, it is not a "password guessing" program that tries to login with many passwords, that is known as a grind
Key point: The sources of encrypted passwords typically include the following:
Key point: The "crack" program is a useful tool for system administrators. By running the program on their own systems, they can quickly find users who have chosen weak passwords. In other words, it is a policy enforcement tool.
Tools: on UNIX, the most commonly used program is called simply "crack". On Windows, a popular program is called "l0phtCrack" from http://www.l0pht.com.
Controversy: See the word hacker for a disagreement about the way that "cracker" is used in the computer enthusiast community vs. the security community.
Key point: Like a checksum, a CRC is not able to detect intentional changes.
Culture: Cracking programs is its own little underground 'scene' independent of other hacking activities. Groups and individuals often compete to be the first to break a new copy protection scheme in popular programs. There are many sites that catalogue cracked programs.
Key point: When the machine is compromised, intruders will often put backdoor jobs into the crontab. When the victim tries to clean up his/her machine, the jobs in the crontab will run giving the intruder control again. This sort of thing happened in the famous attack against the New York Times; they kept cleaning up the machine, but cron kept giving control back to the intruder. Typically, these jobs would run during the wee hours of the morning when nobody is looking.
Key point: The different kinds of cryptanalysis are:
Misconception: Movies often show people easily breaking crypto. In real life, crypto is generally unbreakable when done properly. Law enforcement and hackers rarely have to resort to breaking crypto, but instead attack the human actions around it.
History: So far, there are four major eras in cryptography.
Point:
The best example is the "checksum" vs. "hash". A checksum verifies that data hasn't been corrupted unintentionally. For example, all IP packets are checksumed in case they corrupted accidentally between sender and receiver. A cryptographic hash verifies that data hasn't been corrupted intentionally. Hackers can (and do) alter IP packets between the sender and receiver in order to carry out an attack. Since IP's checksum is not cryptographically secure against hackers.
There are two features that are required in order to be cryptographic. The first is that the algorithm be secure against attack. A checksum uses simple addition, while hashes use a complex set of mathematical operations. The second is that the key must be of a sufficient size in order to prevent brute force attacks. The IP checksum is only two-bytes long, so that even if the algorithm were secure, it would require only 65536 tries for the hacker to get it right, which can be done in real-time.
Key points: The two defining books of cyberpunk are Neuromancer by William Gibson and Snow Crash by Neal Stephenson. Neuromancer is considered "hard core" cyberpunk that launched the genre.
See also: anarchy
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