diff options
Diffstat (limited to 'src/crypto')
| -rw-r--r-- | src/crypto/crypto.cpp | 24 | ||||
| -rw-r--r-- | src/crypto/crypto.h | 20 |
2 files changed, 43 insertions, 1 deletions
diff --git a/src/crypto/crypto.cpp b/src/crypto/crypto.cpp index 1f46164d7..77a36069a 100644 --- a/src/crypto/crypto.cpp +++ b/src/crypto/crypto.cpp @@ -749,4 +749,28 @@ POP_WARNINGS sc_sub(&h, &h, &sum); return sc_isnonzero(&h) == 0; } + + void crypto_ops::derive_view_tag(const key_derivation &derivation, size_t output_index, view_tag &view_tag) { + #pragma pack(push, 1) + struct { + char salt[8]; // view tag domain-separator + key_derivation derivation; + char output_index[(sizeof(size_t) * 8 + 6) / 7]; + } buf; + #pragma pack(pop) + + char *end = buf.output_index; + memcpy(buf.salt, "view_tag", 8); // leave off null terminator + buf.derivation = derivation; + tools::write_varint(end, output_index); + assert(end <= buf.output_index + sizeof buf.output_index); + + // view_tag_full = H[salt|derivation|output_index] + hash view_tag_full; + cn_fast_hash(&buf, end - reinterpret_cast<char *>(&buf), view_tag_full); + + // only need a slice of view_tag_full to realize optimal perf/space efficiency + static_assert(sizeof(crypto::view_tag) <= sizeof(view_tag_full), "view tag should not be larger than hash result"); + memcpy(&view_tag, &view_tag_full, sizeof(crypto::view_tag)); + } } diff --git a/src/crypto/crypto.h b/src/crypto/crypto.h index 596090329..d8cd6c6a0 100644 --- a/src/crypto/crypto.h +++ b/src/crypto/crypto.h @@ -99,6 +99,10 @@ namespace crypto { ec_scalar c, r; friend class crypto_ops; }; + + POD_CLASS view_tag { + char data; + }; #pragma pack(pop) void hash_to_scalar(const void *data, size_t length, ec_scalar &res); @@ -107,7 +111,7 @@ namespace crypto { static_assert(sizeof(ec_point) == 32 && sizeof(ec_scalar) == 32 && sizeof(public_key) == 32 && sizeof(public_key_memsafe) == 32 && sizeof(secret_key) == 32 && sizeof(key_derivation) == 32 && sizeof(key_image) == 32 && - sizeof(signature) == 64, "Invalid structure size"); + sizeof(signature) == 64 && sizeof(view_tag) == 1, "Invalid structure size"); class crypto_ops { crypto_ops(); @@ -151,6 +155,8 @@ namespace crypto { const public_key *const *, std::size_t, const signature *); friend bool check_ring_signature(const hash &, const key_image &, const public_key *const *, std::size_t, const signature *); + static void derive_view_tag(const key_derivation &, std::size_t, view_tag &); + friend void derive_view_tag(const key_derivation &, std::size_t, view_tag &); }; void generate_random_bytes_thread_safe(size_t N, uint8_t *bytes); @@ -297,6 +303,14 @@ namespace crypto { return check_ring_signature(prefix_hash, image, pubs.data(), pubs.size(), sig); } + /* Derive a 1-byte view tag from the sender-receiver shared secret to reduce scanning time. + * When scanning outputs that were not sent to the user, checking the view tag for a match removes the need to proceed with expensive EC operations + * for an expected 99.6% of outputs (expected false positive rate = 1/2^8 = 1/256 = 0.4% = 100% - 99.6%). + */ + inline void derive_view_tag(const key_derivation &derivation, std::size_t output_index, view_tag &vt) { + crypto_ops::derive_view_tag(derivation, output_index, vt); + } + inline std::ostream &operator <<(std::ostream &o, const crypto::public_key &v) { epee::to_hex::formatted(o, epee::as_byte_span(v)); return o; } @@ -312,6 +326,9 @@ namespace crypto { inline std::ostream &operator <<(std::ostream &o, const crypto::signature &v) { epee::to_hex::formatted(o, epee::as_byte_span(v)); return o; } + inline std::ostream &operator <<(std::ostream &o, const crypto::view_tag &v) { + epee::to_hex::formatted(o, epee::as_byte_span(v)); return o; + } const extern crypto::public_key null_pkey; const extern crypto::secret_key null_skey; @@ -325,3 +342,4 @@ CRYPTO_MAKE_HASHABLE_CONSTANT_TIME(secret_key) CRYPTO_MAKE_HASHABLE_CONSTANT_TIME(public_key_memsafe) CRYPTO_MAKE_HASHABLE(key_image) CRYPTO_MAKE_COMPARABLE(signature) +CRYPTO_MAKE_COMPARABLE(view_tag) |