libdpf/doc/pages/introduction.md

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<p class="hero-lead"><code>libdpf++</code> is a header-only C++17 library of distributed point functions: short keys that hide one secret index, then answer at public points as secret shares. The same tree ships a TLS party mesh, round scheduling, MPC on those leaf shares, leveled run logs, and paper-cost statistics — so readers do not have to dig the API to find them.</p>
<h2 id="features">What it does</h2>
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<a class="feature-card" href="verifiability.html"><span class="feature-kicker">Proofs</span><strong>Verifiability &amp; authenticity</strong><p>Honest correction seeds, a weight-1 sketch, and MACs on the leaves, on the same walk.</p></a>
<a class="feature-card" href="programmability.html"><span class="feature-kicker">Late binding</span><strong>Programmability</strong><p>Fill the index or the payload after the key exists. Rewrite an updatable leaf in place.</p></a>
<a class="feature-card" href="comparisons.html"><span class="feature-kicker">Predicates</span><strong>Comparisons &amp; ranges</strong><p>Less-than, equality, interval containment, and blocked checks, as keys.</p></a>
<a class="feature-card" href="multipoint_keys.html"><span class="feature-kicker">Many secrets</span><strong>Multipoint keys</strong><p>Pack many secret points into one cuckoo key. One batched proof covers the set.</p></a>
<a class="feature-card" href="multiparty.html"><span class="feature-kicker">Three parties</span><strong>Multiparty &amp; 3-server</strong><p>Any two of three open a Shamir key. Or an information-theoretic three-server DPF.</p></a>
<a class="feature-card" href="dealer_free.html"><span class="feature-kicker">No dealer</span><strong>Dealer-free keygen</strong><p>The parties already share the index. Doerner–Shelat, geneval, and IKNP finish the key.</p></a>
<a class="feature-card" href="jet_and_ring.html"><span class="feature-kicker">After the offset</span><strong>Grotto</strong><p>Jets, polynomials, carry, and exact ring changes once a public offset is open. Several LUTs share one comparison.</p></a>
<a class="feature-card" href="ppvc_manual.html"><span class="feature-kicker">Commitments</span><strong>Programmable vectors</strong><p>Bind a vector, then open one hidden coordinate or the sum.</p></a>
<a class="feature-card" href="applications.html"><span class="feature-kicker">Sketches</span><strong>Application sketches</strong><p>The DPF step of Duoram, keyword PIR, PSI, Prio, LLAMA, and the rest.</p></a>
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<h2 id="around-the-keys">Around the keys</h2>
<p class="hero-lead" style="font-size:1.05rem;margin-bottom:0.6rem">Live parties, composition, MPC on leaf shares, logging, and statistics — first-class, not buried in the reference.</p>
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<a class="feature-card" href="network_and_mpc.html"><span class="feature-kicker">Links</span><strong>Network &amp; party mesh</strong><p>TLS 1.3 party sessions, trio mesh, RoundSink rounds, lanes, and reconnect.</p></a>
<a class="feature-card" href="protocol_compose.html"><span class="feature-kicker">Schedule</span><strong>Protocol composition</strong><p>FSS walks next to Beaver opens on one RoundSink plan, with explicit reshares.</p></a>
<a class="feature-card" href="beaver_triples.html"><span class="feature-kicker">Multiplication</span><strong>Beaver triples</strong><p>Authenticated products on leaf shares, including the ABY2.0 MAC check.</p></a>
<a class="feature-card" href="arith_runtime.html"><span class="feature-kicker">Shares</span><strong>Arithmetic share runtime</strong><p>edaBits, truncate, share compare, matmul, and hidden shuffle beside FSS.</p></a>
<a class="feature-card" href="yao_leaf.html"><span class="feature-kicker">Circuits</span><strong>Yao on a leaf</strong><p>Split a leaf into bits, garble a netlist, share the answer back as a leaf.</p></a>
<a class="feature-card" href="experiment_costs.html"><span class="feature-kicker">Observability</span><strong>Logging &amp; statistics</strong><p>Leveled run logs, provenance banners, replayable seeds, and CSV wire / PRG / timing breakdowns.</p></a>
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## A complete program {#first_program}

Leaf shares are subtractive. `reconstruct` is `share0 - share1`.
The same program is `examples/mwe/point.cpp`.
More programs are on [Pick a construction](@ref which_dpf) and [Code examples](@ref listings).

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<pre class="fragment">#include "dpf.hpp"

const std::uint8_t alpha = 42;
const std::uint64_t beta = 7;
auto [k0, k1] = dpf::make_dpf(alpha, beta);

const std::uint64_t at = dpf::reconstruct(
    *dpf::eval_point(k0, alpha),
    *dpf::eval_point(k1, alpha));
// at == 7; any other public point opens to 0

// c++ -std=c++17 -march=native -I include -I thirdparty examples/mwe/point.cpp
</pre>
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