Semantics(French sémantique from ancient Greek σημαντικός - denoting) - the science of understanding certain signs, sequences of symbols and others symbols. This science is used in many fields: linguistics, proxemics, pragmatics, etymology, etc. I can’t imagine what these words mean and what all these sciences do. And it doesn’t matter, I’m interested in the issue of using semantics in website layout.

The note

I will not touch on the term Semantic Web here. At first glance, it may seem that the topics Semantic Web and semantic HTML code are almost the same thing. But in fact, the Semantic Web is a rather philosophical concept and does not have much in common with current reality.

Semantic layout - what is it?

In a language, every word has a specific meaning and purpose. When you say “sausage,” you mean a food product that is minced meat (usually meat) in an oblong casing. In short, you mean sausage, not milk or green peas.

HTML is also a language, its “words” called tags also have a certain logical meaning and purpose. For this reason, first of all semantic HTML code is a layout with the correct use HTML tags , using them for their intended purpose, as they were intended by the developers of the HTML language and web standards.

microformats.org is a community that works to bring the idealistic ideas of the Semantic Web to life by bringing page layout closer to those same semantic ideals.

Why and who needs semantic layout at all?

If information on my website is displayed the same way as on the design, why bother racking your brain and thinking about some kind of semantics?! Same extra work! Who needs this?! Who will appreciate this except another layout designer?

I often heard such questions. Let's figure it out.

Semantic HTML for web developers

Semantic code for users

Increases the availability of information on the site. First of all, this is important for alternative agents such as:

• semantic code directly affects the amount of HTML code. Less code -> lighter pages -> load faster, less required random access memory on the user side, less traffic, smaller database size. The site becomes faster and less expensive.
• voice browsers for whom tags and their attributes are important in order to pronounce the content correctly and with the right intonation, or, conversely, not to say too much.
• mobile devices which do not fully support CSS and therefore rely mainly on HTML code, displaying it on the screen according to the tags used.
• printing devices even without additional CSS, the information will be printed with better quality (closer to the design), and creating the ideal version for printing will turn into a few easy manipulations with CSS.
• In addition, there are devices and plugins that allow you to quickly navigate through a document - for example, by headings in Opera.

Semantic HTML for machines

Search engines are constantly improving their search methods to ensure that the results contain the information you want. really looking for user. Semantic HTML facilitates this because... lends itself to much better analysis - the code is cleaner, the code is logical (you can clearly see where the headings are, where the navigation is, where the content is).

Good content plus high-quality semantic layout is already a serious application for good positions in search engine results.

4.1. Encryption Basics

The essence of encryption using the replacement method is as follows. Let messages in Russian be encrypted and each letter of these messages must be replaced. Then, literally A the source alphabet is compared to a certain set of symbols (cipher replacement) M A, B – M B, …, I – M I. The cipher substitutions are chosen in such a way that any two sets ( M I And M J, i ≠ j) did not contain identical elements ( M I ∩ M J = Ø).

The table shown in Fig. 4.1 is the key of the replacement cipher. Knowing it, you can perform both encryption and decryption.

Fig.4.1. Cipher substitution table

When encrypting, each letter A open message can be replaced by any character from the set M A. If the message contains several letters A, then each of them is replaced by any character from M A. Due to this, with the help of one key it is possible to obtain different versions of the ciphergram for the same open message. Since the sets M A, M B, ..., M I do not intersect in pairs, then for each symbol of the ciphergram it is possible to unambiguously determine which set it belongs to, and, consequently, which letter of the open message it replaces. Therefore, decryption is possible and the open message is determined in a unique way.

The above description of the essence of substitution ciphers applies to all their varieties with the exception of , in which the same substitution ciphers can be used to encrypt different characters of the original alphabet (i.e. M I ∩ M J ≠ Ø, i ≠ j).

The replacement method is often implemented by many users when working on a computer. If, due to forgetfulness, you do not switch the character set on the keyboard from Latin to Cyrillic, then instead of letters of the Russian alphabet, when entering text, letters of the Latin alphabet (“cipher replacements”) will be printed.

Strictly defined alphabets are used to record original and encrypted messages. The alphabets for recording original and encrypted messages may differ. Characters of both alphabets can be represented by letters, their combinations, numbers, pictures, sounds, gestures, etc. As an example, we can cite the dancing men from the story by A. Conan Doyle () and the manuscript of the runic letter () from the novel “Journey to the Center of the Earth” by J. Verne.

Substitution ciphers can be divided into the following subclasses(varieties).

Fig.4.2. Classification of substitution ciphers

I. Regular ciphers. Cipher replacements consist of the same number of characters or are separated from each other by a separator (space, dot, dash, etc.).

Slogan code. For a given cipher, the construction of a cipher substitution table is based on a slogan (key) - an easy-to-remember word. The second line of the cipher replacement table is filled first with the slogan word (and repeated letters are discarded), and then with the remaining letters that are not included in the slogan word, in alphabetical order. For example, if the slogan word “UNCLE” is selected, then the table looks like this.

Fig.4.4. Table of cipher replacements for the slogan cipher

When encrypting the original message “ABRAMOV” using the above key, the ciphergram will look like “DYAPDKMI”.

Polybian square. The cipher was invented by the Greek statesman, commander and historian Polybius (203-120 BC). In relation to the Russian alphabet and Indian (Arabic) numerals, the essence of encryption was as follows. Letters are written in a 6x6 square (not necessarily in alphabetical order).

Fig.4.5. Table of cipher substitutions for the Polybian square

The encrypted letter is replaced by the coordinates of the square (row-column) in which it is written. For example, if the original message is “ABRAMOV”, then the ciphergram is “11 12 36 11 32 34 13”. In Ancient Greece, messages were transmitted using optical telegraphy (using torches). For each letter of the message, first the number of torches corresponding to the letter's row number and then the column number were raised.

Table 4.1. Frequency of appearance of Russian letters in texts

There are similar tables for pairs of letters (bigrams). For example, frequently encountered bigrams are “to”, “but”, “st”, “po”, “en”, etc. Another technique for breaking ciphergrams is based on eliminating possible combinations of letters. For example, in texts (if they are written without spelling errors) you cannot find the combinations “chya”, “shchi”, “b”, etc.

To complicate the task of breaking one-to-one ciphers, even in ancient times, spaces and/or vowels were removed from the original messages before encryption. Another method that makes it difficult to open is encryption bigrams(in pairs of letters).

4.3. Polygram ciphers

Polygram substitution ciphers- these are ciphers in which one cipher substitution corresponds to several characters of the source text at once.

Bigram Cipher Ports. Porta's cipher, presented in table form, is the first known bigram cipher. The size of his table was 20 x 20 cells; the standard alphabet was written at the top horizontally and vertically at the left (it did not contain the letters J, K, U, W, X and Z). Any numbers, letters or symbols could be written in the table cells - Giovanni Porta himself used symbols - provided that the contents of none of the cells were repeated. In relation to the Russian language, the table of cipher substitutions may look like this.

Fig.4.10. Cipher replacement table for the Ports cipher

Encryption is performed using letter pairs of the original message. The first letter of the pair indicates the cipher replacement row, the second - the column. If there is an odd number of letters in the original message, an auxiliary character (“blank character”) is added to it. For example, the original message “AB RA MO V”, encrypted - “002 466 355 093”. The letter “I” is used as an auxiliary symbol.

Playfair cipher (English: “Fair game”). In the early 1850s. Charles Wheatstone invented the so-called "rectangular cipher". Leon Playfair, a close friend of Wheatstone, spoke about this cipher during an official dinner in 1854 to the Home Secretary, Lord Palmerston, and Prince Albert. And since Playfair was well known in military and diplomatic circles, the name “Playfair cipher” was forever assigned to Wheatstone’s creation.

This cipher was the first alphabetic bigram cipher (Porta's bigram table used symbols, not letters). It was designed to ensure the secrecy of telegraph communications and was used by British troops in the Boer and First World Wars. It was also used by the Australian Islands Coast Guard during World War II.

The cipher provides encryption of pairs of symbols (digrams). Thus, this cipher is more resistant to cracking compared to a simple substitution cipher, since frequency analysis is more difficult. It can be carried out, but not for 26 possible characters (Latin alphabet), but for 26 x 26 = 676 possible bigrams. Bigram frequency analysis is possible, but is significantly more difficult and requires a much larger amount of ciphertext.

To encrypt a message, it is necessary to split it into bigrams (groups of two symbols), and if two identical symbols are found in the bigram, then a pre-agreed auxiliary symbol is added between them (in the original - X, for the Russian alphabet - I). For example, "encrypted message" becomes "encrypted message" I communication I" To form a key table, a slogan is selected and then it is filled in according to the rules of the Trisemus encryption system. For example, for the slogan “UNCLE” the key table looks like this.

Fig.4.11. Key table for the Playfair cipher

Then, guided by the following rules, the pairs of characters in the source text are encrypted:

1. If source text bigram symbols occur in one line, then these symbols are replaced by symbols located in the nearest columns to the right of the corresponding symbols. If the character is the last in a line, then it is replaced with the first character of the same line.

2. If the bigram characters of the source text occur in one column, then they are converted to the characters of the same column located directly below them. If a character is the bottom character in a column, then it is replaced by the first character of the same column.

3. If the bigram characters of the source text are in different columns and different lines, then they are replaced with characters located in the same lines, but corresponding to other corners of the rectangle.

Encryption example.

The bigram “for” forms a rectangle - it is replaced by “zhb”;

The bigram "shi" is in one column - replaced by "yu";

The bigram “fr” is in one line - replaced by “xc”;

The bigram “ov” forms a rectangle - it is replaced by “yzh”;

The bigram “an” is in one line - it is replaced by “ba”;

The bigram “but” forms a rectangle - it is replaced by “am”;

The bigram “es” forms a rectangle - it is replaced by “gt”;

The bigram “oya” forms a rectangle - it is replaced by “ka”;

The bigram “about” forms a rectangle - it is replaced by “pa”;

The bigram “shche” forms a rectangle - it is replaced by “shyo”;

The bigram “ni” forms a rectangle - is replaced by “an”;

The bigram “ee” forms a rectangle and is replaced by “gi”.

The code is “zhb yue xs yzh ba am gt ka pa she an gi.”

To decrypt, you must use the inversion of these rules, discarding the characters I(or X) if they do not make sense in the original message.

It consisted of two disks - an external fixed disk and an internal movable disk, on which the letters of the alphabet were printed. The encryption process involved finding the letter of the plaintext on external drive and replacing it with the letter from the internal disk underneath it. After this, the internal disk was shifted one position and the second letter was encrypted using the new cipher alphabet. The key to this cipher was the order of letters on the disks and the initial position of the internal disk relative to the external one.

Trisemus table. One of the ciphers invented by the German abbot Trisemus was a multi-alphabetic cipher based on the so-called “Trisemus table” - a table with sides equal to n, Where n– the number of characters in the alphabet. In the first row of the matrix the letters are written in the order of their order in the alphabet, in the second - the same sequence of letters, but with a cyclic shift by one position to the left, in the third - with a cyclic shift by two positions to the left, etc.

Fig.4.17. Trisemus Table

The first line is also an alphabet for plaintext letters. The first letter of the text is encrypted on the first line, the second letter on the second, and so on. After use last line return to the first one again. So the message “ABRAMOV” will take the form “AVTGRUZ”.

Vigenère encryption system. In 1586, the French diplomat Blaise Vigenère presented before the commission of Henry III a description of a simple but fairly strong cipher, which was based on the Trisemus table.

Before encryption, a key is selected from the alphabet characters. The encryption procedure itself is as follows. The i-th character of the open message in the first line determines the column, and the i-th character of the key in the leftmost column determines the row. At the intersection of the row and column there will be the i-th character placed in the ciphergram. If the key length is less than the message, then it is reused. For example, the original message is “ABRAMOV”, the key is “UNCLE”, the encryption code is “DAFIYOYE”.

In fairness, it should be noted that the authorship of this cipher belongs to the Italian Giovanni Battista Bellaso, who described it in 1553. History “ignored an important fact and named the cipher after Vigenère, despite the fact that he did nothing to create it.” Bellazo suggested calling a secret word or phrase password(Italian password; French parole - word).

In 1863, Friedrich Kasiski published an algorithm for attacking this cipher, although there are known cases of his cipher breaking by some experienced cryptanalysts before. In particular, in 1854 the cipher was cracked by the inventor of the first analytical computer Charles Babbage, although this fact became known only in the 20th century, when a group of scientists analyzed Babbage's calculations and personal notes. Despite this, the Vigenère cipher had a reputation for being extremely resistant to manual cracking for a long time. Thus, the famous writer and mathematician Charles Lutwidge Dodgson (Lewis Carroll), in his article “The Alphabetic Cipher,” published in a children's magazine in 1868, called the Vigenère cipher unbreakable. In 1917, the popular science magazine Scientific American also described the Vigenère cipher as unbreakable.

Rotary machines. The ideas of Alberti and Bellaso were used to create electromechanical rotary machines in the first half of the twentieth century. Some of them were used in different countries until the 1980s. Most of them used rotors (mechanical wheels), the relative position of which determined the current cipher alphabet used to perform the substitution. The most famous of the rotary machines is the German World War II Enigma machine.

The output pins of one rotor are connected to the input pins of the next rotor and when the original message symbol is pressed on the keyboard, an electrical circuit is completed, as a result of which the light bulb with the cipher replacement symbol lights up.

Fig.4.19. Enigma rotary system [www.cryptomuseum.com]

The encryption effect of the Enigma is shown for two keys pressed in succession - the current flows through the rotors, is “reflected” from the reflector, then again through the rotors.

Fig.4.20. Encryption scheme

Note. The gray lines show other possible electrical circuits within each rotor. Letter A is encrypted differently when successive key presses are made, first in G, then in C. The signal takes a different route due to the rotation of one of the rotors after pressing the previous letter of the original message.

3. Describe the types of substitution ciphers.

The semantics of HTML code is always a hot topic. Some developers try to always write semantic code. Others criticize dogmatic adherents. And some even have no idea what it is and why it is needed. Semantics are defined in HTML in tags, classes, IDs, and attributes that describe the purpose but do not specify the exact content they contain. That is, we are talking about separating content and its format.

Let's start with an obvious example.

Bad code semantics

Good code semantics

Whether you think HTML5 is ready for use or not, the use of the