{"id":31079,"date":"2019-10-31T21:39:19","date_gmt":"2019-10-31T18:39:19","guid":{"rendered":"https:\/\/prohoster.info\/blog\/tcp-steganografiya-ili-kak-skryt-peredachu-dannyh-v-internete\/"},"modified":"2019-10-31T21:39:19","modified_gmt":"2019-10-31T18:39:19","slug":"tcp-steganografiya-ili-kak-skryt-peredachu-dannyh-v-internete","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sk\/blog\/administrirovanie\/tcp-steganografiya-ili-kak-skryt-peredachu-dannyh-v-internete","title":{"rendered":"TCP steganografia alebo ako skry\u0165 prenos d\u00e1t na internete","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

\"TCP
\n
\nPo\u013esk\u00ed v\u00fdskumn\u00edci navrhli nov\u00fd sp\u00f4sob sie\u0165ovej steganografie zalo\u017een\u00fd na \u0161pecifik\u00e1ch fungovania \u0161iroko roz\u0161\u00edren\u00e9ho protokolu na transportnej \u00farovni TCP. Autori tejto pr\u00e1ce sa domnievaj\u00fa, \u017ee ich sch\u00e9ma m\u00f4\u017ee sl\u00fa\u017ei\u0165 napr\u00edklad na prenos skryt\u00fdch spr\u00e1v v totalitn\u00fdch krajin\u00e1ch, ktor\u00e9 zav\u00e1dzaj\u00fa pr\u00edsnu internetov\u00fa cenz\u00faru. Po\u010fme sa pok\u00fasi\u0165 pochopi\u0165, v \u010dom vlastne spo\u010d\u00edva toto nov\u00e1, a ak\u00e1 je jej skuto\u010dn\u00e1 u\u017eito\u010dnos\u0165.<\/p>\n

<\/a><\/noindex><\/p>\n

Na prvom mieste je potrebn\u00e9 ur\u010di\u0165, \u010do je to steganografia. Tak\u017ee steganografia je veda o skrytej transmission of messages. To znamen\u00e1, \u017ee pomocou jej met\u00f3d sa strany sna\u017eia skry\u0165 s\u00e1m fakt prenosu<\/b>. V tom spo\u010d\u00edva rozdiel medzi touto vedou a kryptografiou, ktor\u00e1 sa sna\u017e\u00ed spr\u00edstupni\u0165 obsah spr\u00e1vy na \u010d\u00edtanie<\/b>. Je potrebn\u00e9 poznamena\u0165, \u017ee profesion\u00e1lna komunita kryptografov je vo\u010di steganografii pomerne poh\u0155daj\u00faca, kv\u00f4li bl\u00edzkosti jej ideol\u00f3gie k princ\u00edpu \u201eSecurity through obscurity\u201c (neviem, ako to znie po slovensky, nie\u010do ako \u201eBezpe\u010dnos\u0165 cez nevedomos\u0165\u201c). Tento princ\u00edp, napr\u00edklad, vyu\u017e\u00edva spolo\u010dnos\u0165 Skype Inc. \u2014 zdrojov\u00fd k\u00f3d popul\u00e1rneho telefonick\u00e9ho softv\u00e9ru je uzavret\u00fd a nikto presne nevie, ako sa zabezpe\u010duje \u0161ifrovanie d\u00e1t. Ned\u00e1vno, mimochodom, si na to s\u0165a\u017eovali v NSA, o \u010dom zn\u00e1my odborn\u00edk Bruce Schneier nap\u00edsal<\/a><\/noindex> p\u00edsal vo svojom blogu. <\/p>\n

Ke\u010f sa vraciame k steganografii, odpovedzme na ot\u00e1zku, pre\u010do je v\u00f4bec potrebn\u00e1, ak m\u00e1me kryptografiu. Skuto\u010dne, m\u00f4\u017eeme spr\u00e1vy za\u0161ifrova\u0165 pomocou modern\u00e9ho algoritmu a pri pou\u017eit\u00ed dostato\u010dne dlh\u00e9ho k\u013e\u00fa\u010da ich nikto nebude m\u00f4c\u0165 pre\u010d\u00edta\u0165, pokia\u013e to sami nechceme. Napriek tomu m\u00f4\u017ee by\u0165 niekedy u\u017eito\u010dnej\u0161ie skry\u0165 samotn\u00fd fakt tajn\u00e9ho prenosu. Napr\u00edklad, ak pr\u00edslu\u0161n\u00e9 org\u00e1ny zachytili va\u0161u za\u0161ifrovan\u00fa spr\u00e1vu, nem\u00f4\u017eu ju de\u0161ifrova\u0165, ale i tak by ve\u013emi chceli, a nakoniec existuj\u00fa aj met\u00f3dy zasahovania a z\u00edskavania inform\u00e1ci\u00ed, ktor\u00e9 nie s\u00fa po\u010d\u00edta\u010dov\u00e9. Znie to dystopicky, ale s\u00fahlas\u00edte, \u017ee je to v z\u00e1sade mo\u017en\u00e9. Preto by bolo lep\u0161ie zabezpe\u010di\u0165, aby t\u00ed, ktor\u00fdm to nie je povolen\u00e9, v\u00f4bec nevedeli, \u017ee k prenosu do\u0161lo. Po\u013esk\u00ed v\u00fdskumn\u00edci presne navrhli tak\u00fato met\u00f3du. A to v\u0161etko navrhuj\u00fa realizova\u0165 pomocou protokolu, ktor\u00fd ka\u017ed\u00fd pou\u017e\u00edvate\u013e internetu vyu\u017e\u00edva tis\u00edckr\u00e1t denne.<\/p>\n

Tento text n\u00e1s prevedie na Transmission Control Protocol (TCP). Vysvet\u013eova\u0165 v\u0161etky detaily by bola zbyto\u010dn\u00e1 pr\u00e1ca \u2014 je to dlh\u00e9 a nudn\u00e9, t\u00ed, ktor\u00ed to potrebuj\u00fa, to u\u017e vedia. Stru\u010dne povedan\u00e9, TCP je protokol transportnej vrstvy (t.j. funguje \u201enad\u201c IP a \u201epod\u201c aplika\u010dn\u00fdmi protokolmi, ako napr\u00edklad HTTP, FTP alebo SMTP), ktor\u00fd zabezpe\u010duje spo\u013eahliv\u00fa dod\u00e1vku \u00fadajov od odosielate\u013ea k pr\u00edjemcovi. Spo\u013eahliv\u00e1 dod\u00e1vka znamen\u00e1, \u017ee ak sa nejak\u00fd paket strat\u00ed alebo doraz\u00ed zmenen\u00fd, TCP sa postar\u00e1 o jeho op\u00e4tovn\u00e9 odoslanie. Je d\u00f4le\u017eit\u00e9 poznamena\u0165, \u017ee zmeny v pakete tu znamenaj\u00fa nie \u00famyseln\u00e9 skreslenie \u00fadajov, ale chyby v prenosoch, ktor\u00e9 vznikaj\u00fa na fyzickej \u00farovni. Napr\u00edklad, k\u00fdm paket putuje po meden\u00fdch dr\u00f4toch, m\u00f4\u017ee p\u00e1r bitov zmeni\u0165 svoje hodnoty na opa\u010dn\u00e9, alebo sa m\u00f4\u017eu \u00faplne strati\u0165 v \u0161ume (pre Ethernet sa zvy\u010dajne hodnota Bit Error Rate pova\u017euje za pribli\u017ene 10\u207b\u2078). Strata paketov na ceste je tie\u017e relat\u00edvne \u010dast\u00fdm javom na internete. M\u00f4\u017ee sa vyskytn\u00fa\u0165 napr\u00edklad v d\u00f4sledku pre\u0165a\u017eenia smerova\u010dov, \u010do vedie k naplneniu buffers a n\u00e1sledn\u00e9mu odmietnutiu v\u0161etk\u00fdch nov\u00fdch prich\u00e1dzaj\u00facich paketov. Zvy\u010dajne podiel stratenej paketov predstavuje okolo 0,1 %, a pri hodnot\u00e1ch nieko\u013ek\u00fdch percent TCP prest\u00e1va spr\u00e1vne fungova\u0165 \u2014 pou\u017e\u00edvate\u013e bude za\u017e\u00edva\u0165 v\u00fdrazn\u00e9 spomalenie.<\/p>\n

Tak vid\u00edme, \u017ee preposielanie (retransmisia) paketov je pre TCP \u010dast\u00fd a v podstate u\u017eito\u010dn\u00fd jav. Pre\u010do teda nevyu\u017ei\u0165 tento protokol na \u00fa\u010dely steganografie, ke\u010f, ako u\u017e bolo spomenut\u00e9 vy\u0161\u0161ie, je TCP pou\u017e\u00edvan\u00e9 v\u0161ade (pod\u013ea r\u00f4znych odhadov dnes dosahuje podiel TCP na internete 80-95 %). Podstata navrhnut\u00e9ho sp\u00f4sobu spo\u010d\u00edva v tom, \u017ee v posielanej spr\u00e1ve sa neposiela to, \u010do bolo v p\u00f4vodnom pakete, ale \u00fadaje, ktor\u00e9 sa sna\u017e\u00edme skry\u0165. A odhali\u0165 tak\u00fato zmenu nie je v\u00f4bec jednoduch\u00e9. Treba vedie\u0165, kam sa pozrie\u0165 \u2014 po\u010det s\u00fa\u010dasn\u00fdch TCP spojen\u00ed, ktor\u00e9 prech\u00e1dzaj\u00fa cez providera, je obrovsk\u00fd. Ak pozn\u00e1me pribli\u017en\u00fa \u00farove\u0148 retransmisie v sieti, m\u00f4\u017eeme nastavi\u0165 mechanizmus steganografickej retransmisie tak, aby sa va\u0161e spojenie nijako neodli\u0161ovalo od ostatn\u00fdch. <\/p>\n

Samozrejme, t\u00e1to met\u00f3da nie je bez nedostatkov. Napr\u00edklad, z praktick\u00e9ho h\u013eadiska bude jej implement\u00e1cia dos\u0165 n\u00e1ro\u010dn\u00e1 \u2014 vy\u017eaduje to zmenu sie\u0165ov\u00e9ho z\u00e1sobn\u00edka v opera\u010dn\u00fdch syst\u00e9moch, hoci to nie je nijako extr\u00e9mne zlo\u017eit\u00e9. Okrem toho, pri dostato\u010dnom mno\u017estve zdrojov je mo\u017en\u00e9 odhali\u0165 \u201eskryt\u00e9\u201c pakety, na to je potrebn\u00e9 prehliada\u0165 a analyzova\u0165 ka\u017ed\u00fd paket v sieti. Av\u0161ak, zvy\u010dajne je to prakticky nemo\u017en\u00e9, a preto sa oby\u010dajne h\u013eadaj\u00fa iba nie\u010d\u00edm v\u00fdnimo\u010dn\u00e9 pakety a spojenia, pri\u010dom navrhnut\u00e1 met\u00f3da rob\u00ed va\u0161u sie\u0165ov\u00fa komunik\u00e1ciu nev\u0161ednou. A nikto v\u00e1m nebr\u00e1ni za\u0161ifrova\u0165 skryt\u00e9 d\u00e1ta pre ka\u017ed\u00fa n\u00e1hodu. Pri tom m\u00f4\u017ee by\u0165 samotn\u00e9 spojenie nezabezpe\u010den\u00e9, aby vyvol\u00e1valo menej podozren\u00ed.<\/p>\n

Autori diela (mimochodom, koho to zauj\u00edma, tu<\/a><\/noindex> to) na \u00farovni simul\u00e1ci\u00ed uk\u00e1zali, \u017ee navrhnut\u00e1 met\u00f3da funguje tak, ako mala. Mo\u017eno v bud\u00facnosti niekto uvedie ich my\u0161lienku do praxe. A vtedy, d\u00fafajme, na internete bude o nie\u010do menej cenz\u00fary.
\n
Zdroj: habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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