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<!doctype html> < html lang = en class = no-js > < head > < meta charset = utf-8 > < meta name = viewport content = "width=device-width,initial-scale=1" > < meta name = description content = "Unofficial Monero Documentation" > < meta name = author content = "Piotr 'Qertoip' Włodarek" > < link href = https://monerodocs.org/cryptography/asymmetric/key-image/ rel = canonical > < link rel = "shortcut icon" href = ../../../assets/favicon.png > < meta name = generator content = "mkdocs-1.1.2, mkdocs-material-6.2.5" > < title > Monero Private Key Image - Monero Documentation< / title > < link rel = stylesheet href = ../../../assets/stylesheets/main.15aa0b43.min.css > < link rel = stylesheet href = ../../../assets/stylesheets/palette.75751829.min.css > < meta name = theme-color content = #ffffff > < link rel = preconnect href = https://fonts.gstatic.com crossorigin > < link rel = stylesheet href = "https://fonts.googleapis.com/css?family=Roboto:300,400,400i,700%7CRoboto+Mono&display=fallback" > < style > body , input { font-family : "Roboto" , - apple-system , BlinkMacSystemFont , Helvetica , Arial , sans-serif } code , kbd , pre { font-family : "Roboto Mono" , SFMono-Regular , Consolas , Menlo , monospace } < / style > < link rel = stylesheet href = ../../../overrides.css > < / head > < body dir = ltr data-md-color-scheme data-md-color-primary = white data-md-color-accent = indigo > < input class = md-toggle data-md-toggle = drawer type = checkbox id = __drawer autocomplete = off > < input class = md-toggle data-md-toggle = search type = checkbox id = __search autocomplete = off > < label class = md-overlay for = __drawer > < / label > < div data-md-component = skip > < a href = #monero-private-key-image class = md-skip > Skip to content < / a > < / div > < div data-md-component = announce > < / div > < header class = md-header data-md-component = header > < nav class = "md-header-nav md-grid" aria-label = Header > < a href = https://monerodocs.org title = "Monero Documentation" class = "md-header-nav__button md-logo" aria-label = "Monero Documentation" > < img src = ../../../images/monero.svg alt = logo > < / a > < label class = "md-header-nav__button md-icon" for = __drawer > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2z" / > < / svg > < / label > < div class = md-header-nav__title data-md-component = header-title > < div class = md-header-nav__ellipsis > < div class = md-header-nav__topic > < span class = md-ellipsis > Monero Documentation < / span > < / div > < div class = md-header-nav__topic > < span class = md-ellipsis > Monero Private Key Image < / span > < / div > < / div > < / div > < label class = "md-header-nav__button md-icon" for = __search > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M9.5 3A6.5 6.5 0 0116 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 019.5 16 6.5 6.5 0 013 9.5 6.5 6.5 0 019.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5z" / > < / svg > < / label > < div class = md-search data-md-component = search role = dialog > < label class = md-search__overlay for = __search > < / label > < div class = md-search__inner role = search > < form class = md-search__form name = search > < input type = text class = md-search__input name = query aria-label = Search placeholder = Search autocapitalize = off autocorrect = off autocomplete = off spellcheck = false data-md-component = search-query data-md-state = active required > < label class = "md-search__icon md-icon" for = __search > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M9.5 3A6.5 6.5 0 0116 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 019.5 16 6.5 6.5 0 013 9.5 6.5 6.5 0 019.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5z" / > < / svg > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12z" / > < / svg > < / label > < button type = reset class = "md-search__icon md-icon" aria-label = Clear data-md-component = search-reset tabindex = -1 > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M19 6.41L17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12 19 6.41z" / > < / svg > < / button > < / form > < div class = md-search__output > < div class = md-search__scrollwrap data-md-scrollfix > < div class = md-search-result data-md-component = search-res
< / code > < / pre > < / div > < p > Where:< / p > < ul > < li > < code > I< / code > - private key image (or "key image" for short)< / li > < li > < code > x< / code > - one-time private key used to unlock an unspent output< / li > < li > < code > P< / code > - one-time public key of an unspent output< / li > < li > < code > Hp()< / code > - hash function accepting an EC point as an argument < / li > < / ul > < p > The < code > P< / code > comes from this:< / p > < div class = highlight > < pre > < span > < / span > < code > P = xG
< / code > < / pre > < / div > < p > Where < code > G< / code > is the < a href = /cryptography/asymmetric/edwards25519 > edwards25519< / a > base point. < / p > < p > Substitute < code > P< / code > with < code > xG< / code > and we get:< / p > < div class = highlight > < pre > < span > < / span > < code > I = x*Hp(xG)
< / code > < / pre > < / div > < p > The key image < code > I< / code > is a one-way function of the private key < code > x< / code > .< / p > < h2 id = reference > Reference< a class = headerlink href = #reference title = "Permanent link" > ¶ < / a > < / h2 > < ul > < li > < a href = https://monero.stackexchange.com/questions/2883/what-is-a-key-image > StackExchange answer< / a > < / li > < li > < a href = https://monero.stackexchange.com/questions/2158/what-is-moneros-mechanism-for-defending-against-a-double-spend-attack > Another SE answer< / a > < / li > < li > < a href = https://getmonero.org/2017/05/17/disclosure-of-a-major-bug-in-cryptonote-based-currencies.html > Critical bug< / a > regarding key image verification that was once present in Monero < / li > < / ul > < / article > < / div > < / div > < / main > < footer class = md-footer > < div class = md-footer-nav > < nav class = "md-footer-nav__inner md-grid" aria-label = Footer > < a href = ../edwards25519/ class = "md-footer-nav__link md-footer-nav__link--prev" rel = prev > < div class = "md-footer-nav__button md-icon" > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12z" / > < / svg > < / div > < div class = md-footer-nav__title > < div class = md-ellipsis > < span class = md-footer-nav__direction > Previous < / span > Edwards25519 curve < / div > < / div > < / a > < a href = ../../base58/ class = "md-footer-nav__link md-footer-nav__link--next" rel = next > < div class = md-footer-nav__title > < div class = md-ellipsis > < span class = md-footer-nav__direction > Next < / span > Base58 < / div > < / div > < div class = "md-footer-nav__button md-icon" > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 24 24" > < path d = "M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11H4z" / > < / svg > < / div > < / a > < / nav > < / div > < div class = "md-footer-meta md-typeset" > < div class = "md-footer-meta__inner md-grid" > < div class = md-footer-copyright style = "margin: auto;" > < a href = http://bumz4sduzxzlobbgzy5fiufdflg3mo2jyecdwdx5rphrqldms7wlmiid.onion/ > Tor onion version< / a > | < a href = https://qertoip.com/ > contact< / a > | © 2021 MoneroDocs under < a href = https://opensource.org/licenses/MIT > MIT< / a > | built w/ < a href = https://www.mkdocs.org/ > mkdocs< / a > and < a href = https://squidfunk.github.io/mkdocs-material/ > squidfunk/material< / a > < / div > < / div > < / div > < / footer > < / div > < script src = ../../../assets/javascripts/vendor.93c04032.min.js > < / script > < script src = ../../../assets/javascripts/bundle.83e5331e.min.js > < / script > < script id = __lang type = application/json > { "clipboard.copy" : "Copy to clipboard" , "clipboard.copied" : "Copied to clipboard" , "search.config.lang" : "en" , "search.config.pipeline" : "trimmer, stopWordFilter" , "search.config.separator" : "[\\s\\-]+" , "search.placeholder" : "Search" , "search.result.placeholder" : "Type to start searching" , "search.result.none" : "No matching documents" , "search.result.one" : "1 matching document" , "search.result.other" : "# matching documents" , "search.result.more.one" : "1 more on this page" , "search.result.more.other" : "# more on this page" , "search.result.term.missing" : "Missing" } < / script > < script >
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