1 files changed, 263 insertions, 0 deletions

diff --git a/src/btfaddr.cpp b/src/btfaddr.cpp
new file mode 100644
index 0000000..6edcc91
--- /dev/null
+++ b/src/btfaddr.cpp
@@ -0,0 +1,263 @@
+// Copyright (c) 2026 Bitflash developers
+// Distributed under the MIT/X11 software license.
+//
+// Bitflash `.btf` self-certifying addresses + service descriptors.
+// Ported from the Itzal hidden.rs design. See btfaddr.h.
+
+#include "btfaddr.h"
+
+#include <openssl/sha.h>
+// See the note in nostr.cpp: the makefiles pass -DSECP256K1_STATIC too.
+#ifndef SECP256K1_STATIC
+#define SECP256K1_STATIC
+#endif
+#include <secp256k1.h>
+#include <secp256k1_schnorrsig.h>
+#include <secp256k1_extrakeys.h>
+#include <nlohmann/json.hpp>
+
+#include <cstring>
+#include <algorithm>
+#include <cctype>
+
+using json = nlohmann::json;
+
+namespace btf
+{
+
+const char* TLD = ".btf";
+
+static const char* B32 = "abcdefghijklmnopqrstuvwxyz234567";
+
+std::string Base32Encode(const unsigned char* data, size_t n)
+{
+    std::string out;
+    out.reserve(n * 8 / 5 + 1);
+    uint64_t buf = 0;
+    uint32_t bits = 0;
+    for (size_t i = 0; i < n; i++)
+    {
+        buf = (buf << 8) | data[i];
+        bits += 8;
+        while (bits >= 5)
+        {
+            bits -= 5;
+            out.push_back(B32[(buf >> bits) & 0x1f]);
+        }
+        buf &= (bits == 0) ? 0 : ((1ULL << bits) - 1);
+    }
+    if (bits > 0)
+        out.push_back(B32[(buf << (5 - bits)) & 0x1f]);
+    return out;
+}
+
+bool Base32Decode(const std::string& s, std::vector<unsigned char>& out)
+{
+    out.clear();
+    out.reserve(s.size() * 5 / 8);
+    uint64_t buf = 0;
+    uint32_t bits = 0;
+    for (unsigned char c : s)
+    {
+        uint64_t val;
+        if (c >= 'a' && c <= 'z')      val = c - 'a';
+        else if (c >= 'A' && c <= 'Z') val = c - 'A';
+        else if (c >= '2' && c <= '7') val = c - '2' + 26;
+        else return false;
+        buf = (buf << 5) | val;
+        bits += 5;
+        if (bits >= 8)
+        {
+            bits -= 8;
+            out.push_back((unsigned char)((buf >> bits) & 0xff));
+        }
+        buf &= (bits == 0) ? 0 : ((1ULL << bits) - 1);
+    }
+    return true;
+}
+
+static std::string ToLowerTrim(const std::string& in)
+{
+    std::string s = in;
+    // trim whitespace
+    size_t a = s.find_first_not_of(" \t\r\n");
+    size_t b = s.find_last_not_of(" \t\r\n");
+    if (a == std::string::npos) return std::string();
+    s = s.substr(a, b - a + 1);
+    // strip trailing dots (fully-qualified hostname form)
+    while (!s.empty() && s.back() == '.') s.pop_back();
+    for (char& c : s) c = (char)std::tolower((unsigned char)c);
+    return s;
+}
+
+// Two-byte checksum, domain-separated so it can't collide with any other hash use.
+static void Checksum(const unsigned char pubkey[32], unsigned char out[2])
+{
+    static const char* DS = ".btf-checksum-v1";
+    SHA256_CTX ctx;
+    SHA256_Init(&ctx);
+    SHA256_Update(&ctx, (const unsigned char*)DS, strlen(DS));
+    SHA256_Update(&ctx, pubkey, 32);
+    unsigned char d[32];
+    SHA256_Final(d, &ctx);
+    out[0] = d[0];
+    out[1] = d[1];
+}
+
+std::string Address(const unsigned char pubkey[32])
+{
+    unsigned char raw[34];
+    memcpy(raw, pubkey, 32);
+    Checksum(pubkey, raw + 32);
+    return Base32Encode(raw, 34) + TLD;
+}
+
+bool IsBtf(const std::string& host)
+{
+    std::string s = ToLowerTrim(host);
+    std::string tld = TLD;
+    if (s.size() < tld.size()) return false;
+    return s.compare(s.size() - tld.size(), tld.size(), tld) == 0;
+}
+
+bool ParseAddress(const std::string& addr, unsigned char pubkeyOut[32])
+{
+    std::string s = ToLowerTrim(addr);
+    std::string tld = TLD;
+    if (s.size() < tld.size()) return false;
+    if (s.compare(s.size() - tld.size(), tld.size(), tld) != 0) return false;
+    std::string label = s.substr(0, s.size() - tld.size());
+
+    std::vector<unsigned char> raw;
+    if (!Base32Decode(label, raw)) return false;
+    if (raw.size() < 34) return false;
+
+    unsigned char pk[32];
+    memcpy(pk, &raw[0], 32);
+    unsigned char sum[2];
+    Checksum(pk, sum);
+    if (raw[32] != sum[0] || raw[33] != sum[1]) return false;
+
+    memcpy(pubkeyOut, pk, 32);
+    return true;
+}
+
+
+// ---- descriptor ------------------------------------------------------------
+
+static std::string HexEncode(const unsigned char* p, size_t n)
+{
+    static const char* h = "0123456789abcdef";
+    std::string s;
+    s.reserve(n * 2);
+    for (size_t i = 0; i < n; i++) { s += h[p[i] >> 4]; s += h[p[i] & 0xf]; }
+    return s;
+}
+
+static bool HexDecode(const std::string& s, unsigned char* out, size_t n)
+{
+    if (s.size() != n * 2) return false;
+    for (size_t i = 0; i < n; i++)
+    {
+        unsigned int b;
+        if (sscanf(s.c_str() + i * 2, "%2x", &b) != 1) return false;
+        out[i] = (unsigned char)b;
+    }
+    return true;
+}
+
+// Digest signed over the descriptor fields (domain-separated).
+static void DescriptorDigest(const unsigned char pubkey[32], const std::string& enc,
+                             const std::string& meeting_node, uint64_t created,
+                             unsigned char out[32])
+{
+    static const char* DS = ".btf-descriptor-v2";
+    SHA256_CTX ctx;
+    SHA256_Init(&ctx);
+    SHA256_Update(&ctx, (const unsigned char*)DS, strlen(DS));
+    SHA256_Update(&ctx, pubkey, 32);
+    SHA256_Update(&ctx, (const unsigned char*)enc.data(), enc.size());
+    SHA256_Update(&ctx, (const unsigned char*)meeting_node.data(), meeting_node.size());
+    unsigned char be[8];
+    for (int i = 0; i < 8; i++) be[i] = (unsigned char)((created >> (8 * (7 - i))) & 0xff);
+    SHA256_Update(&ctx, be, 8);
+    SHA256_Final(out, &ctx);
+}
+
+std::string SignDescriptor(void* ctxv, const unsigned char seckey[32],
+                           const std::string& enc, const std::string& meeting_node,
+                           uint64_t created)
+{
+    secp256k1_context* ctx = (secp256k1_context*)ctxv;
+    secp256k1_keypair kp;
+    if (!secp256k1_keypair_create(ctx, &kp, seckey)) return std::string();
+    secp256k1_xonly_pubkey xpub;
+    if (!secp256k1_keypair_xonly_pub(ctx, &xpub, NULL, &kp)) return std::string();
+    unsigned char pubkey[32];
+    secp256k1_xonly_pubkey_serialize(ctx, pubkey, &xpub);
+
+    unsigned char digest[32];
+    DescriptorDigest(pubkey, enc, meeting_node, created, digest);
+
+    unsigned char sig[64];
+    // Deterministic signature (NULL aux_rand), matching Itzal's no-aux-rand signing.
+    if (!secp256k1_schnorrsig_sign32(ctx, sig, digest, &kp, NULL)) return std::string();
+
+    json v = json::object();
+    v["v"]            = 2;
+    v["pubkey"]       = HexEncode(pubkey, 32);
+    v["enc"]          = enc;
+    v["meeting_node"] = meeting_node;
+    v["created"]      = created;
+    v["sig"]          = HexEncode(sig, 64);
+    return v.dump();
+}
+
+bool VerifyDescriptor(void* ctxv, const std::string& jsonStr,
+                      const unsigned char expect_pubkey[32], Descriptor& out)
+{
+    secp256k1_context* ctx = (secp256k1_context*)ctxv;
+    // Descriptors arrive from untrusted peers (via Nostr relays). Guard the whole
+    // parse: a malformed or wrong-typed field must be rejected, never throw.
+    try
+    {
+        json v = json::parse(jsonStr);
+        if (!v.is_object()) return false;
+        if (!v.contains("pubkey") || !v.contains("enc") || !v.contains("meeting_node")
+            || !v.contains("created") || !v.contains("sig")) return false;
+        // Reject wrong field types before extracting (json::get would otherwise throw).
+        if (!v["pubkey"].is_string() || !v["enc"].is_string() ||
+            !v["meeting_node"].is_string() || !v["sig"].is_string() ||
+            !v["created"].is_number_unsigned()) return false;
+
+        unsigned char pubkey[32];
+        if (!HexDecode(v["pubkey"].get<std::string>(), pubkey, 32)) return false;
+        if (memcmp(pubkey, expect_pubkey, 32) != 0) return false; // descriptor is for a different key
+
+        std::string enc          = v["enc"].get<std::string>();
+        std::string meeting_node = v["meeting_node"].get<std::string>();
+        uint64_t    created      = v["created"].get<uint64_t>();
+
+        unsigned char sig[64];
+        if (!HexDecode(v["sig"].get<std::string>(), sig, 64)) return false;
+
+        unsigned char digest[32];
+        DescriptorDigest(expect_pubkey, enc, meeting_node, created, digest);
+
+        secp256k1_xonly_pubkey xpub;
+        if (!secp256k1_xonly_pubkey_parse(ctx, &xpub, expect_pubkey)) return false;
+        if (!secp256k1_schnorrsig_verify(ctx, sig, digest, 32, &xpub)) return false;
+
+        memcpy(out.pubkey, expect_pubkey, 32);
+        out.enc = enc;
+        out.meeting_node = meeting_node;
+        out.created = created;
+        return true;
+    }
+    catch (...)
+    {
+        return false; // malformed / wrong-typed descriptor -> reject, don't crash
+    }
+}
+
+} // namespace btf