{"id":280,"date":"2025-06-21T09:43:00","date_gmt":"2025-06-21T07:43:00","guid":{"rendered":"https:\/\/josefnemec.cz\/blog\/?p=280"},"modified":"2025-06-21T01:45:00","modified_gmt":"2025-06-20T23:45:00","slug":"sifrovani-v-minulosti-dnes-a-do-budoucna-prednaska","status":"publish","type":"post","link":"https:\/\/josefnemec.cz\/blog\/vzdelavani\/sifrovani-v-minulosti-dnes-a-do-budoucna-prednaska\/","title":{"rendered":"\u0160ifrov\u00e1n\u00ed v minulosti, dnes a do budoucna (p\u0159edn\u00e1\u0161ka)"},"content":{"rendered":"<h2>1. Prvn\u00ed \u0161ifrovac\u00ed metody<\/h2>\n<p>Historicky nejstar\u0161\u00ed \u0161ifry byly <strong>monoalfabetick\u00e9 substituce<\/strong> \u2013 ka\u017ed\u00e9 p\u00edsmeno je nahrazeno jin\u00fdm podle kl\u00ed\u010de. Nejzn\u00e1m\u011bj\u0161\u00ed je <strong>C\u00e9sarova \u0161ifra<\/strong>:<\/p>\n<pre>\u0160ifrovan\u00fd znak = ( P\u016fvodn\u00ed znak + k ) mod 26<\/pre>\n<p>Nap\u0159. A \u2192 D p\u0159i kl\u00ed\u010di <code>k = 3<\/code>.<\/p>\n<p><strong>Vigen\u00e8rova \u0161ifra<\/strong> vyu\u017e\u00edv\u00e1 kl\u00ed\u010dov\u00e9 slovo pro r\u016fzn\u00e9 posuny jednotliv\u00fdch znak\u016f:<\/p>\n<pre>Ci = (Pi + Ki) mod 26<\/pre>\n<p>\ud83d\udcd8 V\u00edce:<\/p>\n<ul>\n<li><a href=\"https:\/\/crypto.interactive-maths.com\/caesar-shift-cipher.html\" target=\"_blank\" rel=\"noopener\">Caesar cipher (interaktivn\u00ed)<\/a><\/li>\n<li><a href=\"https:\/\/en.wikipedia.org\/wiki\/Vigen%C3%A8re_cipher\" target=\"_blank\" rel=\"noopener\">Vigen\u00e8re cipher \u2013 Wikipedia<\/a><\/li>\n<\/ul>\n<h2>2. Substituce vs. transpozice<\/h2>\n<p><strong>Substituce<\/strong> m\u011bn\u00ed znaky, <strong>transpozice<\/strong> m\u011bn\u00ed jejich po\u0159ad\u00ed. Nap\u0159\u00edklad:<\/p>\n<pre>\"T\u00c1BOR\" \u2192 \"OT\u00c1BR\"<\/pre>\n<p>Transpozice vyu\u017e\u00edv\u00e1 permutace:<\/p>\n<pre>\u03c0 : {1, 2, 3} \u2192 {3, 1, 2}<\/pre>\n<p>\ud83d\udd17 <a href=\"https:\/\/en.wikipedia.org\/wiki\/Permutation_cipher\" target=\"_blank\" rel=\"noopener\">Permutation Cipher \u2013 Wikipedia<\/a><\/p>\n<h2>3. Enigma \u2013 detailn\u00ed rozbor<\/h2>\n<p><strong>Enigma<\/strong> byla \u0161ifrovac\u00ed ma\u0161ina nacistick\u00e9ho N\u011bmecka. Obsahovala rotory, reflektor a p\u0159epojovac\u00ed desku.<\/p>\n<p>\u0160ifrov\u00e1n\u00ed prob\u00edhalo slo\u017een\u00edm permutac\u00ed:<\/p>\n<pre>E = P \u2218 R\u2081 \u2218 R\u2082 \u2218 R\u2083 \u2218 U \u2218 R\u2083\u207b\u00b9 \u2218 R\u2082\u207b\u00b9 \u2218 R\u2081\u207b\u00b9 \u2218 P\u207b\u00b9<\/pre>\n<p>Ka\u017ed\u00fd znak m\u011bl jin\u00fd v\u00fdstup d\u00edky pohybuj\u00edc\u00edm se rotor\u016fm.<\/p>\n<ul>\n<li>\ud83d\udd17 <a href=\"https:\/\/enigmamachine.io\" target=\"_blank\" rel=\"noopener\">Interaktivn\u00ed Enigma simul\u00e1tor<\/a><\/li>\n<li>\ud83d\udd2c <a href=\"https:\/\/en.wikipedia.org\/wiki\/Enigma_machine\" target=\"_blank\" rel=\"noopener\">Enigma machine \u2013 Wikipedia<\/a><\/li>\n<\/ul>\n<h2>4. PGP \u2013 Pretty Good Privacy<\/h2>\n<p>PGP kombinuje symetrick\u00e9 (nap\u0159. AES) a asymetrick\u00e9 \u0161ifrov\u00e1n\u00ed (nap\u0159. RSA):<\/p>\n<ul>\n<li>Zpr\u00e1va se za\u0161ifruje symetricky<\/li>\n<li>Symetrick\u00fd kl\u00ed\u010d se za\u0161ifruje ve\u0159ejn\u00fdm kl\u00ed\u010dem p\u0159\u00edjemce<\/li>\n<\/ul>\n<p>\ud83d\udd17 <a href=\"https:\/\/gnupg.org\" target=\"_blank\" rel=\"noopener\">GnuPG<\/a> | <a href=\"https:\/\/tools.ietf.org\/html\/rfc4880\" target=\"_blank\" rel=\"noopener\">OpenPGP \u2013 RFC4880<\/a><\/p>\n<h2>5. Hashovac\u00ed funkce<\/h2>\n<p><strong>Hashovac\u00ed funkce<\/strong> tvo\u0159\u00ed otisk dat pevn\u00e9 d\u00e9lky. Nap\u0159\u00edklad <code>SHA-256<\/code> d\u00e1v\u00e1 256bitov\u00fd v\u00fdstup.<\/p>\n<p>Vlastnosti:<\/p>\n<ul>\n<li>Nezvratnost<\/li>\n<li>Odolnost v\u016f\u010di koliz\u00edm<\/li>\n<li>Citlivost na zm\u011bnu vstupu<\/li>\n<\/ul>\n<table style=\"border-collapse: collapse; width: 100%;\">\n<tbody>\n<tr>\n<th style=\"border: 1px solid #ccc; padding: 4px;\">N\u00e1zev<\/th>\n<th style=\"border: 1px solid #ccc; padding: 4px;\">Bit\u016f<\/th>\n<th style=\"border: 1px solid #ccc; padding: 4px;\">Pozn\u00e1mka<\/th>\n<\/tr>\n<tr>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">SHA-256<\/td>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">256<\/td>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">bezpe\u010dn\u00e1<\/td>\n<\/tr>\n<tr>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">Whirlpool<\/td>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">512<\/td>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">zalo\u017een\u00e1 na AES<\/td>\n<\/tr>\n<tr>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">Streebog<\/td>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">256\/512<\/td>\n<td style=\"border: 1px solid #ccc; padding: 4px;\">rusk\u00fd standard<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>\ud83d\udd17 <a href=\"https:\/\/emn178.github.io\/online-tools\/\" target=\"_blank\" rel=\"noopener\">Online n\u00e1stroje pro hashov\u00e1n\u00ed<\/a><\/p>\n<h2>6. AES vs. RSA<\/h2>\n<p><strong>AES<\/strong>: blokov\u00e1 \u0161ifra (128\u2013256 bit\u016f), rychl\u00e1, symetrick\u00e1.<br \/>\n<strong>RSA<\/strong>: asymetrick\u00e1, pou\u017e\u00edv\u00e1 prvo\u010d\u00edseln\u00e9 sou\u010diny:<\/p>\n<pre>c = m^e mod n | m = c^d mod n<\/pre>\n<p>\ud83d\udd17 <a href=\"https:\/\/nvlpubs.nist.gov\/nistpubs\/FIPS\/NIST.FIPS.197.pdf\" target=\"_blank\" rel=\"noopener\">AES standard<\/a> | <a href=\"https:\/\/datatracker.ietf.org\/doc\/html\/rfc8017\" target=\"_blank\" rel=\"noopener\">RSA \u2013 RFC8017<\/a><\/p>\n<h2>7. Dal\u0161\u00ed \u0161ifry<\/h2>\n<ul>\n<li><strong>Camellia<\/strong> \u2013 japonsk\u00fd ekvivalent AES<\/li>\n<li><strong>Serpent<\/strong> \u2013 velmi bezpe\u010dn\u00e1, 32 kol<\/li>\n<li><strong>Twofish<\/strong> \u2013 Feistelova s\u00ed\u0165, finalista AES sout\u011b\u017ee<\/li>\n<\/ul>\n<p>\ud83d\udd17 <a href=\"https:\/\/www.schneier.com\/academic\/archives\/1998\/12\/twofish-a_128-bit.html\" target=\"_blank\" rel=\"noopener\">Twofish (Bruce Schneier)<\/a><\/p>\n<h2>8. Ve\u0159ejn\u00fd a soukrom\u00fd kl\u00ed\u010d<\/h2>\n<p><strong>Ve\u0159ejn\u00fd kl\u00ed\u010d (E)<\/strong> se pou\u017e\u00edv\u00e1 pro \u0161ifrov\u00e1n\u00ed, <strong>soukrom\u00fd kl\u00ed\u010d (D)<\/strong> pro de\u0161ifrov\u00e1n\u00ed nebo podpisy.<\/p>\n<h2>9. Postkvantov\u00e9 \u0161ifrov\u00e1n\u00ed<\/h2>\n<p>Kvantov\u00e9 po\u010d\u00edta\u010de ohro\u017euj\u00ed RSA a ECC (Shor\u016fv algoritmus).<\/p>\n<p><strong>Bezpe\u010dn\u00e9 alternativy:<\/strong><\/p>\n<ul>\n<li><strong>Lattice-based:<\/strong> Kyber, FrodoKEM<\/li>\n<li><strong>Code-based:<\/strong> McEliece<\/li>\n<li><strong>Isogenie:<\/strong> SIDH\/SIKE (prolomeno)<\/li>\n<\/ul>\n<p>\ud83d\udd17 <a href=\"https:\/\/csrc.nist.gov\/projects\/post-quantum-cryptography\" target=\"_blank\" rel=\"noopener\">NIST Post-Quantum Project<\/a><\/p>\n<h2>10. Pro\u010d \u0161ifrovat?<\/h2>\n<ul>\n<li>Soukrom\u00ed a ochrana dat<\/li>\n<li>Digit\u00e1ln\u00ed podpisy a autenticita<\/li>\n<li>Z\u00e1konn\u00e9 po\u017eadavky (GDPR, HIPAA)<\/li>\n<\/ul>\n<p>Debaty o <strong>zadn\u00edch vr\u00e1tk\u00e1ch<\/strong> a vl\u00e1dn\u00edm dohledu (nap\u0159. PRISM, Snowden) st\u00e1le pokra\u010duj\u00ed.<\/p>\n<p>\ud83d\udd17 <a href=\"https:\/\/www.eff.org\/deeplinks\/2015\/01\/government-backdoors-encryption-are-dangerous\" target=\"_blank\" rel=\"noopener\">EFF o backdoorech<\/a><\/p>\n<h2>Z\u00e1v\u011br<\/h2>\n<p>\u0160ifrov\u00e1n\u00ed je kl\u00ed\u010dem k digit\u00e1ln\u00ed bezpe\u010dnosti a svobod\u011b. Od rotuj\u00edc\u00edch rotor\u016f po m\u0159\u00ed\u017ekov\u00e9 \u0161ifry \u2013 kdo ovl\u00e1d\u00e1 kryptografii, ovl\u00e1d\u00e1 budoucnost.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>1. Prvn\u00ed \u0161ifrovac\u00ed metody Historicky nejstar\u0161\u00ed \u0161ifry byly monoalfabetick\u00e9 substituce \u2013 ka\u017ed\u00e9 p\u00edsmeno je nahrazeno jin\u00fdm podle kl\u00ed\u010de. Nejzn\u00e1m\u011bj\u0161\u00ed je C\u00e9sarova \u0161ifra: \u0160ifrovan\u00fd znak = ( P\u016fvodn\u00ed znak + k ) mod 26 Nap\u0159. A \u2192 D p\u0159i kl\u00ed\u010di k<\/p>\n","protected":false},"author":1,"featured_media":208,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[77,60],"tags":[149,151,159,157,147,155,148,152,150,146,154,156,153,158],"class_list":["post-280","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-technologie","category-vzdelavani","tag-aes","tag-camellia","tag-enigma","tag-hash","tag-pgp","tag-prism","tag-rsa","tag-serpent","tag-sha","tag-sifry","tag-snowden","tag-streebog","tag-twofish","tag-whirlpool"],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/josefnemec.cz\/blog\/wp-content\/uploads\/2025\/01\/DALL%C2%B7E-2025-01-16-22.20.45-A-futuristic-quantum-computer-with-glowing-qubits-interconnected-by-energy-waves-representing-quantum-entanglement.-The-computer-is-placed-in-a-high-.webp?fit=1024%2C1024&ssl=1","jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/posts\/280","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/comments?post=280"}],"version-history":[{"count":3,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/posts\/280\/revisions"}],"predecessor-version":[{"id":284,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/posts\/280\/revisions\/284"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/media\/208"}],"wp:attachment":[{"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/media?parent=280"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/categories?post=280"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/josefnemec.cz\/blog\/wp-json\/wp\/v2\/tags?post=280"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}