– How to Communicate Crypto Secrets Secretly
Transcription
– How to Communicate Crypto Secrets Secretly
“Big Brother” is Listening… Crypto Secrets – How to Communicate Secretly by Jim Saboe Echelon is perhaps the most powerful intelligence gathering organization in the world. Reports suggest that this network is being used to spy on private citizens everywhere, including on the Internet. – American Civil Liberties Union 1999 “Is it paranoia if they really ARE listening?” - Jim Petersen © Copyright 2004, Ariza Research, All rights reserved - ABP The Problem As we enter the new millennium we have good reason to be paranoid. According to those in the know, there are snoops everywhere. Today business competitors, hackers, personal enemies, law enforcement, the federal government and just plain crazy people are all out there listening. Everytime you use any form of modern electronic communications, you should assume that someone is trying to listen in. Virtually every form of electronic communication is in jeopardy including: Telephones Internet email Cellular Phones Citizen’s Band or other portable radios Wireless Phones Corporate email Internet Surfing And it’s sad to think that the biggest single snoop is the federal government. The super-secret National Security Agency (NSA) is clearly the nosiest organization on the planet. They listen to virtually everything. Their official agency charter is classified and has never been published. But how can they listen to so much traffic? Easy – they use computers. By using modern screening software, they can scan billions of messages or phone calls searching for “key” words and phrases they consider to be of interest. If any of the targeted words are found in a message, that message gets priority attention. The recording of the message is forwarded to special computer for more intense scrutiny. If no targeted words are found, the message will be retained in case priorities change but barring future interest, it will probably end up being discarded. To be entirely safe, you simply must assume that every time you pick up your phone or send a message via any electronic means, your good old Uncle Sam is listening in. The good news is that people are onto big brother’s nefarious activities. As a result, the volume of enciphered traffic has increased dramatically over the last decade. This makes NSA’s job much more difficult. During a recent appearance in front of a senate investigating committee, the Director of the FBI whined “we can’t listen in to criminals anymore – they’re all using encipherment software!” Of course he wanted all public cryptography banned but how do you put the toothpaste back in the tube? The government shouldn’t be feared as they have to get a search warrant before they can place a tap on your phone – right? Not now. Under provisions of the so-called “Patriot Act” the feds are free to tap our phones with impunity. As a result the total number of tapped phones has recently exploded. Even if big brother illegally taps a phone, they can accomplish their goal. While it’s still true that nothing heard on an illegal tap can be used in court, the information they gather from conversations can lead to an arrest. Let’s say the criminal arranges a drug deal while the cops are listening. He says something like “I’ve got the kilo of cocaine and I’ll meet you down at Ralph’s Café at third and Elm in ten minutes”. The police can then “just happen” to have an officer stumble onto the deal at “random” and nab the perpetrators as they step out of the establishment. The criminal will wonder – but the police will just put the arrest down to “good luck”. For this reason, illegal wire taps are not all that unusual. So how are you to go about communicating securely in such an open book environment? I have some good news for you. Technology is a twoedged sword that cuts both ways. While it helps the snoops monitor and screen trillions of messages, it also places new tools into the hands of freedomloving individuals with which they can communicate in ways that will confound big brother. And since the computing power of the average personal computer has increased much more rapidly that the power of the super-computers used by the government, for the very first time we individuals now have everything we need to communicate privately. The Unbreakable Crypto System Despite some inflated advertising claims, no cryptographic software is entirely unbreakable. Any message that can be enciphered can be deciphered - given enough computer power and enough time. The “unbreakable” crypto system is, like the unicorn, a myth. That’s the bad news – now for some good news. While you can’t make your messages entirely unbreakable, you can take measures that will make your messages so secure that it will take a snoop a long, long time to “crack” and read them. Today using readily available encryption tools you can easily scramble an email message or computer file in such a way that it would take all the computers on the planet over 100 years to break it! Anyone attempting to decipher such a message will run out of patience and resources long before they see any results. Stick to the Rules By using a set of easy to remember rules, you can increase your security even more. Snoops will have a very hard time reading your traffic. And that includes our dear friends down at NSA - the greatest snoop of all. Uncle Sam has tons of Cray super-computers and armies of mathematicians but even with all those resources NSA won’t be able to read your mail - if you stick carefully to the rules listed below. Let me explain our situation in this way. Say you had a valuable personal possession like a rare antique vase. It’s worth a small fortune so naturally you’re concerned that someone might want to steal it. Is there anyway that you could ensure that this valuable item would be entirely safe from theft? There are a number of things you could do to protect your possession. You could have a safe installed somewhere in your home and store the vase there. That would help. You could install a technically sophisticated alarm system. You could construct a big fence around your property complete with security lighting. You could also buy a trained guard dog or you could even hire a licensed guard service to protect your home on a 24-hour basis. While no one of these security measures can guarantee you absolute safety by itself, each protective measure adds a level of difficulty which makes it that much more difficult for a thief to steal your vase. By employing all these various security measures together - the net result is that your vase is very, very secure. Not totally, but for all practical purposes your vase is safe and sound. The same sort of principle applies with cryptography. While no single program can offer you bullet-proof perfect security (despite their inflated claims), by using them properly your messages will be very highly secure even from government intrusion. Today there are a number of very “strong” cryptographic programs readily available (some are available for free on the Internet). By using several of these newer, more effective programs together, we can ensure that our private communications stay just that - private. Secure Communication Rules So here are some rules that if used carefully, can dramatically increase the security of your communications. Rule #1 Always use the best and “strongest” cryptographic software. I’ll show you which programs to use and which to avoid. And I’ll show you how to evaluate their hype. The good news is that many of the best programs are very affordable, easily obtainable and easy-to-use. Rule #2 For the very highest level protection - use double encipherment. A single program just isn’t enough. The snoops have constructed specialized computer systems specifically engineered to break messages enciphered using each of the most popular encipherment programs. By enciphering a message in one program and then enciphering the scrambled result again using a different second program, you drastically increase your communications security. Exactly how much does double encipherment increase your security? Think of it in this way. If your odds of winning the grand prize in the lottery are one in fifteen million – what are the odds of you winning the jackpot two days in a row? Would you guess the odds would be say, one in thirty million? You’d be wrong – the real odds of a double win would be 15 million TIMES 15 million! You don’t add the odds, instead you multiply them! The same principle applied to cryptography. Double enciphered messages are as close to unbreakable as you can get. While one program provides good protection, by adding a second you can make it all but impossible for a snoop to read your mail. The soviet military used double encipherment all through the cold war and according to top historians it was never broken. Double encipherment has withstood the most important test, the test of time and that’s why it’s the gold standard in the world of crypto. Rule #3 When writing your messages, never use proper language syntax, no matter what language you’re using. If you keep your spelling and syntax exactly correct, the strict format will make it a lot easier for the snoops to break your messages. This is because every language has a formal set of syntax rules which can be exploited by snoops. Always use unusual language structure and punctuation in your messages. For example, if your message is: “I met with Henry today. He didn’t have the package. He said to please have Sam contact him to arrange delivery. See you Tuesday night.” Instead, scramble the spelling and sentence structure while being sure that the original meaning of the message is still clearly evident: “met wiff henri this afterrnoooon----; He didnt hav the stufff wiff him --- he sed to havv sammy kontakkt him two arange deeliveree CU twozdayXXXXXXX” This second version clearly doesn’t adhere to any established rules of language syntax and yet is still understandable by anyone who can read English. Anyone attempting to use language structure to crack such a message would soon become very frustrated. Also notice that each phrase/sentence didn’t end with the usual period. This is yet another departure from established language structure. Get into the habit of using unusual punctuation. Dashes, slashes, or strings of letters such as X can also be used effectively. If both parties in a link speak a second language, it would be wise to mix the two languages freely. Obviously each language has its own structural rules. Spanish has quite a different structure than English. Mixing the two would further enhance communication security. Rule #4 Always “salt” your messages. In this context salt refers to strings of extra characters that have no meaning but further enhance communication security by breaking syntax rules even further. The usual practice here is to add strings of unusual characters at random intervals. For example, If the message is” “Talked with Peter today. He’s mad that he’s not involved in the Smith deal. Can you talk to him?” A modified and salted version would look something like: “talked two Petey twoday. XXXXXX hez madd cause hes not in on the smitty deall. YYYYY Kan U talkk to himm - questionmark ZZZZZZZZZZOOOZZZZ44343” Rule #5 Send “dummy” messages. From time to time send a dummy message that contains only random scrambled letters. Just tap away at the keyboard as randomly as possible. Or use your favorite poem. Snoops use a technique known as “Communication Flow Analysis”. In this way they can learn more than you might suspect about your operations without actually having to break your cipher and read your messages. By sending dummy messages, you make it all but impossible to learn anything from your traffic flow. When things are slow you might want to consider sending some dummy messages. This might give a snoop the idea that you’re busy when you’re really not. And at the same time mask periods of increased activity. Rule #6 Change things from time to time. Always change your encryption password regularly. Be sure to change it before sending a particularly sensitive message. Make sure your password is as secure as possible. You’ll find directions for creating truly powerful passwords elsewhere in this report. You may want to also change the encryption software you use every two months or so just to keep the snoops off balance. Rule #7 Use private untraceable web-based mailboxes. There are a number of firms on the Internet that will allow you to set up relatively anonymous email accounts with them. Hotmail, ZipLip and Yahoo are several of the larger outfits that offer this valuable service. With them you can set up numerous mail accounts, send and receive email through them and later replace them with new ones. You can create as many different email addresses as you like and use them in manner you choose. You can open a mailbox, use it to send and/or receive a few messages and then abandon it all with no financial cost. Some others services are located overseas which further enhances your security. (Do a Google search on “foreign email systems”) When you sign up, provide the service with little or no personal information. In particular, do not give them your main email address when asked. If you must provide an email address, use an anonymous one from another free web-based system. Hushmail Check out Hushmail at www.hushmail.com. This is a popular system and appears to be a very secure system that employs sophisticated link encryption that is transparent and extremely easy to use. The security concern here is – exactly who runs this system and what are they up to? These boxes are very useful but I should warn you that they will not shield you if you’re involved in illegal activities. These outfits cooperate fully with law enforcement officials. You should also know that some of these services have problems when it comes to handling larger messages. So it’s always best to break your message into numerous smaller messages. If you use one of these services and are tempted to add additional services such as increased storage capacity, you should know that once you provide them with your credit card number – your privacy is gone. Rule #8 Use secret codes whenever possible. This is an old “mob” favorite. If you want to know if an associate has completed a given task, have him use a code that sounds routine and uninteresting to a snoop but effectively communicates an important message. For example, if the task was completed on schedule have your associate mention his “Aunt Susan”. And if the task did not go off as planned, have him mention his “Uncle Ralph”. The snoop will never realize that meaningful data is being exchanged right under his nose. While it’s difficult to convey a lot of information in this manner, it is very secure. Rule #9 Use anonymous re-mailers whenever you want to forward a message anonymously. These firms, many of which are overseas, accept your email message, strip it of all it’s identifying data and then forward it on to it’s destination without any identifying information attached. (Finland seems to be a favorite location as the government there has not yielded to US government pressure to close down their anonymous re-mailers) Uncle Sam has been applying heat to these guys lately so you may have to look around a bit. Also there is the issue of trust. Do you trust them? Should you trust them? Sorry, can’t help you here. Rule #10 Never, ever, under any circumstances re-use passwords or keys. When you re-use a password or key, you make the snoop’s job a whole lot easier. In both the first and second world wars, critical battles were won and many brave soldiers died needlessly because a crypto clerk got careless (or simply ran out of new key) and re-used some old material. One Nazi clerk reused a German Enigma key one morning and it allowed the allies to read several tons of Hitler’s personal orders which shortened the European war by months. Also, you’re going to have to come up with a way to share your password list with whomever you intend to communicate with. Do not send a list of passwords to your associate electronically. It’s just not secure. Some send a CD full of random key through the mail. The best system is to meet in person and agree on a list of passwords without ever mentioning them on a phone or in an email message. If you’re unable to do that, you should consider the “book code” discussed below. The Book Code Here is a rather secure method of communicating over any distance. You arrange to buy two copies of the exact same edition of the same book. Send one to your friend by the most secure system possible (I prefer high-priority overnight shipment that doesn’t leave much time for government scrutiny). Or have him buy his own copy locally just be sure that it’s exactly the same book. You can use this system to communicate the text of a message or to effectively and secretly communicate passwords for use with encipherment software. To communicate the proper password to your associate, simply send him a fraction. The fraction 7/34 refers to the 34th word on the seventh page. Anyone seeing your fraction will have no idea what it means. They would have to know that you’re using a book code and then know which of the millions of books out there was used. Your associate simply turns to page seven and counts down to the 34th word - which is “courtyard”. To increase the security of this system, don’t use any of the top current best sellers or that old favorite of spies – “Alice in Wonderland”. For best results, always use a rather obscure book. Some have found tables of old novels that didn’t sell in the bargain department of a bookstore useful. The books are both obscure and also very cheap. Physical Security When the government of one country cannot penetrate the cryptographic system of another, they attempt to gain access to one of their embassies in an attempt to get a peek at the place. They hope to catch a glimpse of a crypto clerk at work, his equipment or even steal some of his materials in order to increase their understanding of the system they’re using. And if they can’t see anything helpful, they may be forced into casing the place for a later break-in. If you can, do as little work as possible on any system that is connected to the internet. Everything on that system’s hard drive can be read through the Internet under the right conditions. The best approach here is to have two systems. One system is connected to the Internet while the second system is entirely disconnected from any form of data transmission. You keep all your most sensitive files on the standalone system. You encipher your messages on that system and then when the file is ready for transmission, place it on a diskette and hand carry it to your Internet system for transmission. When you receive a message over the Internet, do the reverse. Pretend that any files on your Internet connected system are open to inspection by anyone who cares to look. You can also store sensitive files on an external IOMega backup cartridge drive. The cartridges can be stored under lock and key and/or enciphered using a strong crypto program like PGP. Always keep as much of your communication materials as possible under lock and key. Put as little as possible on your hard drive and instead store as much as you can on diskettes. If diskettes don’t provide enough storage space you might consider purchasing an external drive which provides much more storage space on removable cartridges that can be locked up under lock and key. Get a good safe installed, or hide your materials in some out of the way place. I know one guy that stores his stuff in his grandmother’s basement. Other friends have chosen to keep their materials at their side at all times. In the end, your overall communication security is only as good as your physical security. One Time Pad This is an old system that’s been around since the days of world war I. It’s proven itself over and over and is still of use today if you observe a few rules. Unfortunately it’s rather cumbersome and time consuming but believe me, it’s secure. First you prepare your message text (clear text). Then you reorganize it into five letter groups. Then place your random key characters one under each message character. Like this: Message Text: Random Key HELLO THERE QSJKK PEAXA ------------- ------------- Now you generate the encrypted characters that you’ll send to your recipient. You do this by using “triads”. For each two character combination there is a single resultant character. (See the triad tables at the end of this report) For example, if the two letters are an H and a Q the only resultant character (from the triad table) is the letter C. Message Text: Random Key Enciphered Text: HELLO QSJKK ------------CDFEB THERE PEAXA -------------ROVLV You send the enciphered text to your recipient. He then reverses the process and the result is your plain English message text. Enciphered Text: Random Key Message Text: CDFEB QSJKK ------------HELLO ROVLV PEAXA -------------THERE The key to this system is simple yet elusive. The letters on the pad (key text) must be as random as possible. If you choose letters from the pages of a newspaper, they will have the same distribution as any letters in the English language. They’re not anywhere near random and useless for our purposes. So how can you come up with some highly random text against which you can encipher your messages? There is a simple, inexpensive but unfortunately it’s both cumbersome and time consuming. Buy a “spinner” from some board game. You know the metal arrow spinner mounted on a piece of cardboard. You spin the thing and it ends up pointing in one direction. Draw a line down the center of the board. Divide each half into 13 separate equal sized slots. Then write a single letter in each division. Now you can spin away and get a long list of very random letters. Warning: An email message that’s made up of a number of five letter groups will attract big brother’s attention. For the ultimate in protection, create your enciphered message in a word processing file and encipher the entire file using a strong crypto program such as PGP. The file can be loaded on a diskette and sent anywhere in the world. The level of security is the highest possible (assuming your random key is truly random) How to Evaluate Cryptographic Software The Longer the Key the Better The length of the key used by a particular software package is of the utmost importance. Assuming the key is highly random, the longer the key the better. Even the addition of a single bit to the key could make a substantial difference in how long it will take a snoop to read your mail. Many of the most popular email encryption programs use keys shorter than 100 bits. While a 128 bit long key is considered to be “strong crypto”. Programs that use a 56 key are much, much more vulnerable. 256 bit key length would be ideal. The other factor to take into consideration is the basic formula or algorithm the program uses. Actually the modern computer is not a very good random number generator. Computers are very precise and logical devices. They do math well but when it comes to generating random numbers, they leave a lot to be desired. Though they’re supposed to be able to create random numbers, the random numbers they produce are actually very long sequences that eventually repeat themselves. And since these sequences are well known, their value as crypto keys are very near worthless. So just how would you go about coming up with several thousand highly random numbers? Remember these numbers must be both very highly random and completely unpredictable. (If they can be predicted with any degree of accuracy, a snoop can create them just as you did and quickly read your mail. Let’s say that I have a one square yard piece of plywood which I place outside just as it’s about to start raining. The first drop hits the board slightly to the left of the center of the board. Now, can you tell me where on the board the next drop will land? I didn’t think so. What if I gave you a million dollars to spend – would that help you make the prediction? No, it wouldn’t because there isn’t any possible way you could go about calculating where a drop that falls thousands of feet out of the sky will hit. There are just too many variables involved which makes any kind of calculation utterly possible. This little experiment illustrates an important point. To come up with a really random number you’ll have to use a natural process (like rain). Any attempt to use a logical device like a computer would, from the outset be doomed to failure. The second and third drops fall in entirely random places. Another technique that takes advantage of a natural process is the noise system. You take a high-quality portable tape recorder with a built-in microphone for a walk down a busy (and presumably noisy) city street. What you end up with is a long recording of random street noises. No one on earth can exactly duplicate your tape unless they were carrying the same brand of tape recorder and walking within a few feet of you. And since you could see that no one was walking along with you, your tape is unique. The tape is then played through a converter that converts the random sounds into a stream of digital bits which will provide a highly random key. So how do the most successful PC crypto programs come up with random numbers? They use some very tricky tactics. PGP asks the user to enter some info through the keyboard. Each keystroke is used to generate a highly random number. Imagine a counter that counts from zero up to 65,535 and then starts over again automatically. It’s constantly counting. When you hit a keyboard key the counter is suddenly stopped at a particular number. Is there anyway to anticipate the number that results? Each number is entirely random. Add together a dozen such numbers and you get a highly random number that is almost impossible to predict. And since each person has an almost unique typing style, it’s almost impossible to accurately predict how many milliseconds will elapse between each keystroke. This is the main reason why PGP is such a widely respected crypto program. Crypto Programs and Their Reputations Winzip password protection useful – quick and easy to use but crypto protection is low-level, fine for keeping amateurs out of your files. Blowfish No known effective attacks – appears to be very strong Widely tested Cast Strong – very effective DES Avoid – widely suspected that government has a secret “back door” that allows fast and easy penetration GOST Russian made algorithm. Not as widely tested as some but appears to be quite secure. IDEA Good but expensive due to licensing being required MARS Appears strong MISTY Created by Mitsubishi Corp. – appears strong but experts suspect it might have some weaknesses RC6 Appears strong RIJNDAEL Public domain algorithm that appears to be very strong RSA Developed at MIT – Very strong SKIPJACK Medium level protection due to limited key length (80-bits) TEA Very fast algorithm – 128-bit key – public domain – appears strong TWOFISH Has been extensively examined and has stood the test of time. Very strong One Time Pad “Triad” Tables A A B C D E F G H I J K L M N O P Q R S T U V WX Y Z A A A A A A A A A A A A A A A A A A A A A A A A A A Z Y X WV U T S R Q P O N M L K J I H G F E D C B A B A B C D E F G H I J K L M N O P Q R S T U V WX Y Z B B B B B B B B B B B B B B B B B B B B B B B B B B Y X WV U T S R Q P O N M L K J I H G F E D C B A Z C A B C D E F G H I J K L M N O P Q R S T U V WX Y Z C C C C C C C C C C C C C C C C C C C C C C C C C C X WV U T S R Q P O N M L K J I H G F E D C B A Z Y D A B C D E F G H I J K L M N O P Q R S T U V WX Y Z D D D D D D D D D D D D D D D D D D D D D D D D D D WV U T S R Q P O N M L K J I H G F E D C B A Z Y X E A B C D E F G H I J K L M N O P Q R S T U V WX Y Z E E E E E E E E E E E E E E E E E E E E E E E E E E V U T S R QP ON ML K J I H GF E D C B A Z Y X W F A B C D E F G H I J K L M N O P Q R S T U V WX Y Z F F F F F F F F F F F F F F F F F F F F F F F F F F U T S R Q P O N M L K J I H G F E D C B A Z Y X WV G A B C D E F G H I J K L M N O P Q R S T U V WX Y Z GGGGGGGGGGGGGGGGGGGGGGGGGG T S R Q P O N M L K J I H G F E D C B A Z Y X WV U H A B C D E F G H I J K L M N O P Q R S T U V WX Y Z H H H H H H H H H H H H H H H H H H H H H H H H H H S R Q P O N M L K J I H G F E D C B A Z Y X WV U T I A B C D E F G H I J K L M N O P Q R S T U V WX Y Z I I I I I I I I I I I I I I I I I I I I I I I I I I R Q P O N M L K J I H G F E D C B A Z Y X WV U T S J A B C D E F G H I J K L M N O P Q R S T U V WX Y Z J J J J J J J J J J J J J J J J J J J J J J J J J J Q P O N M L K J I H G F E D C B A Z Y X WV U T S R K A B C D E F G H I J K L M N O P Q R S T U V WX Y Z K K K K K K K K K K K K K K K K K K K K K K K K K K P O N M L K J I H G F E D C B A Z Y X WV U T S R Q L A B C D E F G H I J K L M N O P Q R S T U V WX Y Z L L L L L L L L L L L L L L L L L L L L L L L L L L O N M L K J I H G F E D C B A Z Y X WV U T S R Q P M A B C D E F G H I J K L M N O P Q R S T U V WX Y Z MD MMMMMMMMMMMMMMMMMMMMMMMM N M L K J I H G F E D C B A Z Y X WV U T S R Q P O N A B C D E F G H I J K L M N O P Q R S T U V WX Y Z N N N N N N N N N N N N N N N N N N N N N N N N N N M L K J I H G F E D C B A Z Y X WV U T S R Q P O N O A B C D E F G H I J K L M N O P Q R S T U V WX Y Z OOOOOOOOOOOOOOOOOOOOOOOOOO L K J I H G F E D C B A Z Y X WV U T S R Q P O N M P A B C D E F G H I J K L M N O P Q R S T U V WX Y Z P P P P P P P P P P P P P P P P P P P P P P P P P P K J I H G F E D C B A Z Y X WV U T S R Q P O N M L Q A B C D E F G H I J K L M N O P Q R S T U V WX Y Z QQQQQQQQQQQQQQQQQQQQQQQQQQ J I H G F E D C B A Z Y X WV U T S R Q P O N M L K R A B C D E F G H I J K L M N O P Q R S T U V WX Y Z R R R R R R R R R R R R R R R R R R R R R R R R R R I H G F E D C B A Z Y X WV U T S R Q P O N M L K J S A B C D E F G H I J K L M N O P Q R S T U V WX Y Z S S S S S S S S S S S S S S S S S S S S S S S S S S H G F E D C B A Z Y X WV U T S R Q P O N M L K J I T A B C D E F G H I J K L M N O P Q R S T U V WX Y Z T T T T T T T T T T T T T T T T T T T T T T T T T T G F E D C B A Z Y X WV U T S R Q P O N M L K J I H U A B C D E F G H I J K L M N O P Q R S T U V WX Y Z U U U U U U U U U U U U U U U U U U U U U U U U U U F E D C B A Z Y X WV U T S R Q P O N M L K J I H G V A B C D E F G H I J K L M N O P Q R S T U V WX Y Z V V V V V V V V V V V V V V V V V V V V V V V V V V E D C B A Z Y X WV U T S R Q P O N M L K J I H G F W A B C D E F G H I J K L M N O P Q R S T U V WX Y Z WWWWWWWWWWWWWWWWWWWWWWWWWW D C B A Z Y X WV U T S R Q P O N M L K J I H G F E X A B C D E F G H I J K L M N O P Q R S T U V WX Y Z X X X X X X X X X X X X X X X X X X X X X X X X X X C B A Z Y X WV U T S R Q P O N M L K J I H G F E D Y A B C D E F G H I J K L M N O P Q R S T U V WX Y Z Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y B A Z Y X WV U T S R Q P O N M L K J I H G F E D C Z A B C D E F G H I J K L M N O P Q R S T U V WX Y Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z A Z Y X WV U T S R Q P O N M L K J I H G F E D C B