Security issues for PGP keys and Passwords

The simplest way to compromise is to have your password written somewhere, and there is no guarantee that no one else can see it except you. If someone gets your password and your private key file, the entire encryption system will be silent. Another old topic is the password not too simple, note that PGP is "password" passphase, rather than "password" password that is, you can include multiple words and spaces in the password. A wily attacker may use a famous book to find your password. So in order to get a good and difficult to guess password, you can sporogenous some sentences or find some very unusual sentences in literary texts. My personal recommendation is to use the first letter sequence in a sentence and then add a few symbols, such as ".", "-", ";" And so on, the length is better than equal to 8 characters, but also can be mixed case. Because there is the possibility of being spied on your keystroke, it is best not to use the space bar, because the sound of knocking it is very special. Also, the number keys that require a very long finger to reach are not available. For example: from "Youcan ' tgetitwithoutmypassphase" can get the "YCGI.WYP" This password, the use of exhaustive method to test this password is very unlikely, because it used uppercase and lowercase letters and symbols. An average of about 50^8 times is likely to be successful, at the speed of idea, which is not easy in general mainframe computers. So short passwords are as safe as they are random enough, and the less time you enter a password, the less likely you are to be spied on. Public key tampering and posing is the biggest threat to PGP, in the "PGP Introduction" I have been more detailed, the point is: when you use the public key, you are sure it is directly from the other side or by another credible person signed the certificate. Make sure no one can tamper with your own public key ring file. Keep your physical control of your key-ring files as much as possible in your personal computer rather than in a remote time-sharing system. Back up your own keyring file. Files that are not completely deleted the general operating system does not delete files when the file is not completely deleted data, when you encrypt clear text will be deleted, but did not physically clear the clear data. Some experienced attackers may recover plaintext from your disk data block. Of course, like Paper Shredder, there are also physical destruction of the file, they are some tool software, if not, the easiest way is to use useless information to overwrite the clear text file. This can also be achieved by adding the-w parameter to the PGP. But even if you cover all of the disk space that was used in plaintext, there will still be tiny residual magnetism left on the disk, and the dedicated device can restore the data, but the average person does not. The same problem with the key ring file you use, especially the private key ring file, is directly related to the security of your private key. Therefore, in addition to your personal computer, it is best not to copy the key ring into other machines, so that they stay on the floppy disk may be a safe way to doLaw。 Physical security This is not what PGP can give you. If the government is going to investigate you, it can be a physical violation of your privacy, as in the case of Watergate. And this attack is much cheaper than cryptanalysis. PGP cannot protect your unencrypted plaintext in an unsecured environment. Of course, physical security also includes the physical safety of PGP data such as fire, waterproof, lightning and so on, but this is not as difficult to prevent people. The leaked PGP under multi-user system was originally designed for MS-DOS, assuming itself under the direct physical control of the user. However, with the popularity of PGP, the multi-user system also appeared PGP, so that the exposure of clear text and keys or passwords may increase. For example, if you use your password in the command line of PGP on a UNIX system, other users will be able to see it directly with the PS command. The same problem is also available on MS-DOS machines connected to the LAN. I'm not saying that you can't use PGP on Unix, someone is putting a Unix system on a laptop and you can use PGP without worrying about other users. Multi-User systems are also secure, they can withstand the attacks of all intruders, or their users are trustworthy, or they are not interested in intruders at all. As discussed in the real PGP attack to be discussed below, the risk of leaks in multi-user systems is much greater. The PGP authors suggest that you try to use PGP in an isolated Single-user system, and that the system is under your direct physical control. Time stamp reliability of PGP the timestamp on a PGP signature is not trustworthy because anyone who wants to forge an "error" timestamp can achieve the goal by modifying the system time. And in business there is this use of PGP signature time to confirm the need for responsibility, so that the third party time Notarization system was established. Obviously, as long as the notary party signed the standard time in the mail, it solved the problem. In fact, the problem for handwritten signature also exists, the signature requires a notary, to prove the time of signature, digital signature is the same. The model that PGP authors envision is for a third party to provide notarial service, which the server sends back with its own signature automatically after each sent signature, leaving a record, which is open, that the person who needs the arbitration can consult. Traffic analysis Although the attacker could not read the actual contents of the ciphertext, but he can at least get some useful information by watching where the mail comes from, where it goes, how long it's going to be, and when it's sent, just as he can check your long-distance phone bill, but he doesn't know what you're talking about. This is called flow analysis. PGP alone can not prevent traffic analysis, the use of some network communication protocols to prevent the exposure of this information, and even the use of other encryption communication system to assist. The real PGP attack is all about attacking methods that are impossible or too cumbersome for a typical attacker. There are actually some "viable" PGP attack, they are not attacking the PGP cipher system itself (the discussion just proved it is solid), but the implementation system of PGP. First look at passive attack: keystroke prying into a very effective passive attack method, simply by recording the user's keystrokes from which to obtain the password. The attacker spied the user's keystroke sequence through a keyboard recorder, depending on the different systems. The PGP implementation in DOS is the most vulnerable in this respect, and it has the most keyboard logger programs. And attackers can even remotely boot and stop loggers from the network, and some boot-zone viruses can do this in DOS. At least one of the loggers under Windows has emerged, which poses a threat to the windows-based PGP shell. Keyboard records in a UNIX environment are a bit complicated because root permissions are required, unless the attacker enters a password in the x-windows environment, the logger under x-windows does not use root permissions. To prevent this attack, in a word, the work environment should be carefully checked, while making good private key ring file preservation. Electromagnetic leak snooping This is very accessible, any computer equipment, especially monitors have electromagnetic leakage, through the appropriate equipment can receive the information on the target display, then your clear text display is not secret. I've got a case where the FBI is monitoring a spy's display and keyboard signals by a similar device: they are remotely receiving signals by secretly setting up a transmitter in the suspect's computer, then removing the noise from the NSA-specific FFT chip and completing the forensics work. The RF signal is approximately 22MHz, and a clear image can be obtained by adding 27KHz horizontal synchronous signal and 59.94Hz vertical sync signal at the receiving end. As for the keyboard is a serial SCM communication interface, the signal more stable. Installing a RF signal jammer can effectively prevent the display signal from leaking. Keyboard signal is not far, as long as no one in your computer, "ear" is not afraid to leak. Memory space snooping on a multiuser system such as UNIX, anyone can check the machine's physical memory with the right permissions. And the decomposition of a huge composite number, open/dev/kmem This system virtual save Exchange files, find the user's page, directly read out e,d not much worry? Disk cache snooping in a multitasking operating system such as Windows, the system has the habit of swapping content from memory to disk, and these exchange files are transparent to the user. Worse, the content will not be purged anytime soon, and may remain on disk for a long time. If in the network environment, may not even the user to feel, is stolen this information. Packet sniffing in the network environment, information is transmitted in the form of messages in the line. If you are using PGP remotely over a network, you may be able to be heard from message transmissions. If the message is stored in clear text, your password will be known to the attacker. Use some encrypted, online communication programs, like Ssh,deslogin or simply using an encrypted network protocol stack (point-to-point or end-to-end), can prevent network sniffing attacks. Because the sniffer has to deal with a lot of information, if not plaintext, they are generally not interested to study. Take a look at the active attack: Trojan Horse is an ancient strategy, about Trojan horse should everyone is not unfamiliar. I don't want to define it. Here is a virtual modern PGP Trojan: Some elite programmers have developed a new PGP Windows shell. All novice ftp to a copy. It works great, has a variety of buttons and scrollbars, even provides a bunch of WAV files, and supports SoundBlasterAWE32 's sound, so you can encrypt the file while appreciating the 16-bit CD-quality stereo. It takes up very little memory, is concise and powerful, and it intercepts the interruption of the operating system, preventing it from exchanging important information to disk for leaks. Great, huh? But the problem is, there are a few lines of malicious code in this program that record your password, and when it finds a modem on the machine, it sends a ATM0 command to the modem (turns off the modem's buzzer), and then knows where to dial and sends out your password and key. ...... Is that interesting? This is the Trojan horse. Avoiding it requires caution, prudence, and caution. Tampering with PGP code tampering with the Trojan Horse message sniffer disk cache prying into memory space spying on electromagnetic leaks snooping the PGP code is public, so there may be tampering. So it's important to verify the integrity of the PGP release package you get, and in the example above we can see that it's scary to give control of the computer to unreliable programs. Of course, someone will put the MD5 program crack, so that the tampered with the file it reports a correct hash result. It is most reliable to find a copy that is known to be intact. Conclusion I just provide a variety of materials here, the conclusions must be under your own. We can't give up an encryption method because of rumors, nor can we trust a method just because of hearsay. In short, caution is always rewarded in the area of computer security, but lack of intelligence and unnecessary paranoia is not a good result. 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