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fill="none" stroke-width="2" height="18" class="_shrink-0 _rounded-sm _p-0.5 hover:_bg-gray-800/5 dark:hover:_bg-gray-100/5 motion-reduce:*:_transition-none *:_origin-center *:_transition-transform *:rtl:_-rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button><div class="_transform-gpu _transition-all _ease-in-out motion-reduce:_transition-none _opacity-0 _overflow-hidden" style="height:0;transition-duration:300ms"><div><ul class="_flex _flex-col _gap-1 _relative before:_absolute before:_inset-y-1 before:_w-px before:_bg-gray-200 before:_content-[""] dark:before:_bg-neutral-800 ltr:_pl-3 ltr:before:_left-0 rtl:_pr-3 rtl:before:_right-0 _pt-1 ltr:_ml-3 rtl:_mr-3"><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/how-to/c-boilerplate">C Boilerplate</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/how-to/rust-boilerplate">Rust Boilerplate</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/how-to/plugin">Ethereum Plugin</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/how-to/clone">Clone Coin Application</a></li></ul></div></div></li><li class=""><button class="_transition _items-center _justify-between _gap-2 _text-left _w-full _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" data-href="/docs/device-app/integration/design-guidelines" type="button" data-headlessui-state="">Graphic Library Usage Guidelines<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="18" class="_shrink-0 _rounded-sm _p-0.5 hover:_bg-gray-800/5 dark:hover:_bg-gray-100/5 motion-reduce:*:_transition-none *:_origin-center *:_transition-transform *:rtl:_-rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button><div class="_transform-gpu _transition-all _ease-in-out motion-reduce:_transition-none _opacity-0 _overflow-hidden" style="height:0;transition-duration:300ms"><div><ul class="_flex _flex-col _gap-1 _relative before:_absolute before:_inset-y-1 before:_w-px before:_bg-gray-200 before:_content-[""] dark:before:_bg-neutral-800 ltr:_pl-3 ltr:before:_left-0 rtl:_pr-3 rtl:before:_right-0 _pt-1 ltr:_ml-3 rtl:_mr-3"><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/design-guidelines/intro">Introduction</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/design-guidelines/home">App's homepage</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/design-guidelines/info-settings">App info and settings</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/design-guidelines/transactions">Signing transactions and messages</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/design-guidelines/address">Address verification</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/integration/design-guidelines/advanced">Advanced interactions</a></li></ul></div></div></li></ul></div></div></li><li class=""><button class="_transition _items-center _justify-between _gap-2 _text-left _w-full _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" data-href="/docs/device-app/references" type="button" data-headlessui-state="">References<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="18" class="_shrink-0 _rounded-sm _p-0.5 hover:_bg-gray-800/5 dark:hover:_bg-gray-100/5 motion-reduce:*:_transition-none *:_origin-center *:_transition-transform *:rtl:_-rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button><div class="_transform-gpu _transition-all _ease-in-out motion-reduce:_transition-none _opacity-0 _overflow-hidden" style="height:0;transition-duration:300ms"><div><ul class="_flex _flex-col _gap-1 _relative before:_absolute before:_inset-y-1 before:_w-px before:_bg-gray-200 before:_content-[""] dark:before:_bg-neutral-800 ltr:_pl-3 ltr:before:_left-0 rtl:_pr-3 rtl:before:_right-0 _pt-1 ltr:_ml-3 rtl:_mr-3"><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/references/framework">Development framework</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/references/tools">Developing tools overview</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/references/app-permissions">App permissions</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/references/cryptography-api">Cryptography API</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/references/cryptography-api-examples">Cryptography API examples</a></li></ul></div></div></li><li class="open"><button class="_transition _items-center _justify-between _gap-2 _text-left _w-full _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" data-href="/docs/device-app/explanation" type="button" data-headlessui-state="">Explanation<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="18" class="_shrink-0 _rounded-sm _p-0.5 hover:_bg-gray-800/5 dark:hover:_bg-gray-100/5 motion-reduce:*:_transition-none *:_origin-center *:_transition-transform *:rtl:_-rotate-180 *:ltr:_rotate-90 *:rtl:_rotate-[-270deg]"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button><div class="_transform-gpu _transition-all _ease-in-out motion-reduce:_transition-none _opacity-100" style="transition-duration:500ms"><div><ul class="_flex _flex-col _gap-1 _relative before:_absolute before:_inset-y-1 before:_w-px before:_bg-gray-200 before:_content-[""] dark:before:_bg-neutral-800 ltr:_pl-3 ltr:before:_left-0 rtl:_pr-3 rtl:before:_right-0 _pt-1 ltr:_ml-3 rtl:_mr-3"><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/device-app-role">What is the role of the device app?</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/plugin">Ethereum Plugins and Ethereum Clone Apps: What's the Difference?</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/architecture-diagram">Architecture diagram</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/architecture-good-practices">Architecture good practices</a></li><li class="_flex _flex-col _gap-1 active"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _bg-primary-100 _font-semibold _text-primary-800 dark:_bg-primary-400/10 dark:_text-primary-600 contrast-more:_border-primary-500 contrast-more:dark:_border-primary-500" href="/docs/device-app/explanation/io">Application Structure and I/O</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/cryptography">Cryptography general concepts</a></li><li class=""><button class="_transition _items-center _justify-between _gap-2 _text-left _w-full _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" data-href="/docs/device-app/explanation/psd" type="button" data-headlessui-state="">Personal Security Devices<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="18" class="_shrink-0 _rounded-sm _p-0.5 hover:_bg-gray-800/5 dark:hover:_bg-gray-100/5 motion-reduce:*:_transition-none *:_origin-center *:_transition-transform *:rtl:_-rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button><div class="_transform-gpu _transition-all _ease-in-out motion-reduce:_transition-none _opacity-0 _overflow-hidden" style="height:0;transition-duration:300ms"><div><ul class="_flex _flex-col _gap-1 _relative before:_absolute before:_inset-y-1 before:_w-px before:_bg-gray-200 before:_content-[""] dark:before:_bg-neutral-800 ltr:_pl-3 ltr:before:_left-0 rtl:_pr-3 rtl:before:_right-0 _pt-1 ltr:_ml-3 rtl:_mr-3"><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/psd/introduction">Introduction</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/psd/masterseed">The master seed</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/psd/keys">HD key generation</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/psd/applications">Application for HD trees</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/psd/application-isolation">Application isolation</a></li></ul></div></div></li><li class=""><button class="_transition _items-center _justify-between _gap-2 _text-left _w-full _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" data-href="/docs/device-app/explanation/ledger-os" type="button" data-headlessui-state="">LedgerOS<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="18" class="_shrink-0 _rounded-sm _p-0.5 hover:_bg-gray-800/5 dark:hover:_bg-gray-100/5 motion-reduce:*:_transition-none *:_origin-center *:_transition-transform *:rtl:_-rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button><div class="_transform-gpu _transition-all _ease-in-out motion-reduce:_transition-none _opacity-0 _overflow-hidden" style="height:0;transition-duration:300ms"><div><ul class="_flex _flex-col _gap-1 _relative before:_absolute before:_inset-y-1 before:_w-px before:_bg-gray-200 before:_content-[""] dark:before:_bg-neutral-800 ltr:_pl-3 ltr:before:_left-0 rtl:_pr-3 rtl:before:_right-0 _pt-1 ltr:_ml-3 rtl:_mr-3"><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/ledger-os/introduction">Introduction to Ledger OS</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/ledger-os/features">Ledger OS features</a></li><li class="_flex _flex-col 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contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/memory/persistent-storage">Persistent storage</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/memory/position-independent-code">Position-independant code</a></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/memory/memory-alignment">Memory alignment</a></li></ul></div></div></li><li class="_flex _flex-col _gap-1"><a class="nextra-focus _flex _rounded _px-2 _py-1.5 _text-sm _transition-colors [word-break:break-word] _cursor-pointer contrast-more:_border _text-gray-500 hover:_bg-gray-100 hover:_text-gray-900 dark:_text-neutral-400 dark:hover:_bg-primary-100/5 dark:hover:_text-gray-50 contrast-more:_text-gray-900 contrast-more:dark:_text-gray-50 contrast-more:_border-transparent contrast-more:hover:_border-gray-900 contrast-more:dark:hover:_border-gray-50" href="/docs/device-app/explanation/security-specificities">Security specificities</a></li></ul></div></div></li><li class=""><button class="_transition 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Give us feedback →</a><a class="nextra-focus _text-xs _font-medium _text-gray-600 dark:_text-gray-400 hover:_text-gray-800 dark:hover:_text-gray-200 contrast-more:_text-gray-700 contrast-more:dark:_text-gray-100" href="https://github.com/LedgerHQ/developer-portal/blob/main/pages/docs/device-app/explanation/io.mdx">Edit this page</a><button>Copy page URL</button><button class="_transition _flex _items-center _gap-1.5 _whitespace-nowrap _opacity-0 _text-xs _font-medium _text-gray-600 dark:_text-gray-400 hover:_text-gray-800 dark:hover:_text-gray-200 contrast-more:_text-gray-700 contrast-more:dark:_text-gray-100" aria-hidden="true" type="button" disabled="" data-headlessui-state="disabled" data-disabled="">Scroll to top<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="16" class="_-rotate-90 _border _rounded-full _border-current"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></button></div></div></nav><div id="reach-skip-nav"></div><article class="_w-full _break-words nextra-content _flex _min-h-[calc(100vh-var(--nextra-navbar-height))] _min-w-0 _justify-center _pb-8 _pr-[calc(env(safe-area-inset-right)-1.5rem)]"><main class="_w-full _min-w-0 _max-w-6xl _px-6 _pt-4 md:_px-12"><div class="nextra-breadcrumb _mt-1.5 _flex _items-center _gap-1 _overflow-hidden _text-sm _text-gray-500 dark:_text-gray-400 contrast-more:_text-current"><a class="_whitespace-nowrap _transition-colors _min-w-6 _overflow-hidden _text-ellipsis nextra-focus _ring-inset hover:_text-gray-900 dark:hover:_text-gray-100" title="Documentation" href="/docs/news">Documentation</a><svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="14" class="_shrink-0 rtl:_rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg><span class="_whitespace-nowrap _transition-colors _min-w-6 _overflow-hidden _text-ellipsis" title="Device App">Device App</span><svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="14" class="_shrink-0 rtl:_rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg><a class="_whitespace-nowrap _transition-colors _min-w-6 _overflow-hidden _text-ellipsis nextra-focus _ring-inset hover:_text-gray-900 dark:hover:_text-gray-100" title="Explanation" href="/docs/device-app/explanation/device-app-role">Explanation</a><svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" height="14" class="_shrink-0 rtl:_rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg><span class="_whitespace-nowrap _transition-colors _font-medium _text-gray-700 contrast-more:_font-bold contrast-more:_text-current dark:_text-gray-100 contrast-more:dark:_text-current" title="Application Structure and I/O">Application Structure and I/O</span></div><h1 class="_mt-2 _text-4xl _font-bold _tracking-tight _text-slate-900 dark:_text-slate-100">Application Structure and I/O</h1> <h2 id="introduction" class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Introduction<a href="#introduction" class="nextra-focus subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Many of the existing Ledger OS applications are based on a smartcard architecture. This is because Ledger OS applications are not meant to run standalone, but rather assist a host process (on a computer / smartphone) to perform a secure task (signing a message, encryption / decryption, etc.). Therefore the device is commonly addressed using a command / response scheme. Numerous design decisions have been made when developing the SDKs in order to support this model.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">However, the Event / Commands / Status model is designed to avoid limitations on the application, as it does not follow the command / response synchronous model. Developers are free to work around the model and redesign a custom event processing loop to suit their needs.</p> <h2 id="apdu-interpretation-loop" class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">APDU Interpretation Loop<a href="#apdu-interpretation-loop" class="nextra-focus subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The command / response scheme used to address the device is similar to the <a class="nextra-focus _text-primary-600 _underline hover:_no-underline _decoration-from-font [text-underline-position:from-font]" href="https://en.wikipedia.org/wiki/Smart_card_application_protocol_data_unit" target="_blank" rel="noreferrer">ISO/IEC 7816-4</a> smartcard protocol. Each command / response packet is called an APDU (application protocol data unit). The application is driven by a never-ending APDU interpretation loop called straight from the application main function.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Each cycle of the APDU interpretation loop calls <code class="nextra-code" dir="ltr">io_exchange(...)</code> from the SDK, which first sends a response APDU (unless it’s the first call, in which case it sends nothing), and then receives the next APDU command.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">However, sometimes, a user confirmation to perform a security action must be performed before replying to an APDU (for example, when signing a message). Such behaviour is handled by replying no data to the command in the APDU interpreter by using the <code class="nextra-code" dir="ltr">IO_ASYNCH_REPLY</code> flag, then following the user action calling <code class="nextra-code" dir="ltr">io_exchange</code> with the <code class="nextra-code" dir="ltr">IO_RETURN_AFTER_TX</code> flag and with the amount of data to reply to the stalled command.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">For an example of this feature, refer to <a class="nextra-focus _text-primary-600 _underline hover:_no-underline _decoration-from-font [text-underline-position:from-font]" href="https://github.com/LedgerHQ/blue-sample-apps/blob/2fb0f8f68ef68bbecd601cf476e532177288a0fa/blue-app-samplesign/src/main.c" target="_blank" rel="noreferrer">blue-app-samplesign</a>. In this app, when the command APDU to sign a message is received (line 510), the flag <code class="nextra-code" dir="ltr">IO_ASYNCH_REPLY</code> is set and no response APDU is sent. If the user approves the action, then the button push handler calls <code class="nextra-code" dir="ltr">io_seproxyhal_touch_approve(...)</code> which sends the response APDU using another call to <code class="nextra-code" dir="ltr">io_exchange(...)</code> with the <code class="nextra-code" dir="ltr">IO_RETURN_AFTER_TX</code> flag set (line 434). The same occurs if the user denies the action, in which case <code class="nextra-code" dir="ltr">io_seproxyhal_touch_deny(...)</code> is triggered.</p> <h2 id="protocols" class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Protocols<a href="#protocols" class="nextra-focus subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">It’s important to understand that the APDU protocol used by most Ledger OS applications is not implemented by Ledger OS itself. Instead, the APDU interpretation is performed entirely by the SDK. This means that applications can choose to implement another protocol on top of the transport layer (USB HID, USB CCID, BLE, …) instead of APDU. In fact, the same is true for the transport layer protocols. Applications can customize the way the application is enumerated as a USB device by the host.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7"><img alt="Common protocols across Ledger OS applications" loading="lazy" width="1300" height="720" decoding="async" data-nimg="1" style="color:transparent;background-size:cover;background-position:50% 50%;background-repeat:no-repeat;background-image:url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 320 160'%3E%3Cfilter id='b' color-interpolation-filters='sRGB'%3E%3CfeGaussianBlur stdDeviation='20'/%3E%3CfeColorMatrix values='1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 100 -1' result='s'/%3E%3CfeFlood x='0' y='0' width='100%25' height='100%25'/%3E%3CfeComposite operator='out' in='s'/%3E%3CfeComposite in2='SourceGraphic'/%3E%3CfeGaussianBlur stdDeviation='20'/%3E%3C/filter%3E%3Cimage width='100%25' height='100%25' x='0' y='0' preserveAspectRatio='none' style='filter: url(%23b);' href='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAgAAAAECAMAAACEE47CAAAAElBMVEXd3uDk5eXr6+v39/b////X2NrmutVKAAAACXBIWXMAAAsSAAALEgHS3X78AAAAIElEQVR4nAXBAQEAAAzCoE19/8oHYrttgCQtctwRoqB5BRsAP+g3M38AAAAASUVORK5CYII='/%3E%3C/svg%3E")" srcSet="/_next/image?url=%2F_next%2Fstatic%2Fmedia%2Fcommon_protocols.693285c9.png&w=1920&q=75 1x, /_next/image?url=%2F_next%2Fstatic%2Fmedia%2Fcommon_protocols.693285c9.png&w=3840&q=75 2x" src="/_next/image?url=%2F_next%2Fstatic%2Fmedia%2Fcommon_protocols.693285c9.png&w=3840&q=75"/> <em>Common protocols across Ledger OS applications</em></p><div class="_mt-16"></div><div class="_mb-8 _flex _items-center _border-t _pt-8 dark:_border-neutral-800 contrast-more:_border-neutral-400 dark:contrast-more:_border-neutral-400 print:_hidden"><a title="Architecture good practices" class="nextra-focus _text-gray-600 dark:_text-gray-400 hover:_text-gray-800 dark:hover:_text-gray-200 contrast-more:_text-gray-700 contrast-more:dark:_text-gray-100 _flex _max-w-[50%] _items-center _gap-1 _py-4 _text-base _font-medium _transition-colors [word-break:break-word] md:_text-lg ltr:_pr-4 rtl:_pl-4" href="/docs/device-app/explanation/architecture-good-practices"><svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" class="_inline _h-5 _shrink-0 ltr:_rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg>Architecture good practices</a><a title="Cryptography general concepts" class="nextra-focus _text-gray-600 dark:_text-gray-400 hover:_text-gray-800 dark:hover:_text-gray-200 contrast-more:_text-gray-700 contrast-more:dark:_text-gray-100 _flex _max-w-[50%] _items-center _gap-1 _py-4 _text-base _font-medium _transition-colors [word-break:break-word] md:_text-lg ltr:_ml-auto ltr:_pl-4 ltr:_text-right rtl:_mr-auto rtl:_pr-4 rtl:_text-left" href="/docs/device-app/explanation/cryptography">Cryptography general concepts<svg viewBox="0 0 24 24" stroke="currentColor" fill="none" stroke-width="2" class="_inline _h-5 _shrink-0 rtl:_rotate-180"><path d="M9 5l7 7-7 7" stroke-linecap="round" stroke-linejoin="round"></path></svg></a></div></main></article></div><div class="bg-black"><div class="h-[1px] w-full bg-white"></div><div class="max-w-[1440px] mx-auto"><div class="py-20 px-4 md:px-28 z-10"><div class="flex flex-col md:flex-row gap-6 md:gap-16"><div class="flex flex-col gap-9 md:w-60"><a class="relative h-10 w-28" href="https://www.ledger.com"><img alt="Ledger" loading="lazy" decoding="async" data-nimg="fill" style="position:absolute;height:100%;width:100%;left:0;top:0;right:0;bottom:0;color:transparent" src="/homepage/ledger-logo-long-white.svg"/></a><div class="text-p-caption text-grey-600">Copyright © Ledger SAS. 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