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crypto: add FSChaCha20, a rekeying wrapper around ChaCha20

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This adds the FSChaCha20 stream cipher as specified in BIP324, a
wrapper around the ChaCha20 stream cipher (specified in RFC8439
section 2.4) which automatically rekeys every N messages, and
manages the nonces used for encryption.

Co-authored-by: dhruv <856960+dhruv@users.noreply.github.com>
This commit is contained in:
Pieter Wuille
2023-06-28 18:20:30 -04:00
parent 9ff0768bdc
commit 0fee267792
4 changed files with 164 additions and 0 deletions
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54
src/test/crypto_tests.cpp
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@@ -182,6 +182,46 @@ static void TestChaCha20(const std::string &hex_message, const std::string &hexk
}
}
static void TestFSChaCha20(const std::string& hex_plaintext, const std::string& hexkey, uint32_t rekey_interval, const std::string& ciphertext_after_rotation)
{
auto key = ParseHex<std::byte>(hexkey);
BOOST_CHECK_EQUAL(FSChaCha20::KEYLEN, key.size());
auto plaintext = ParseHex<std::byte>(hex_plaintext);
auto fsc20 = FSChaCha20{key, rekey_interval};
auto c20 = ChaCha20{UCharCast(key.data())};
std::vector<std::byte> fsc20_output;
fsc20_output.resize(plaintext.size());
std::vector<std::byte> c20_output;
c20_output.resize(plaintext.size());
for (size_t i = 0; i < rekey_interval; i++) {
fsc20.Crypt(plaintext, fsc20_output);
c20.Crypt(UCharCast(plaintext.data()), UCharCast(c20_output.data()), plaintext.size());
BOOST_CHECK(c20_output == fsc20_output);
}
// At the rotation interval, the outputs will no longer match
fsc20.Crypt(plaintext, fsc20_output);
auto c20_copy = c20;
c20.Crypt(UCharCast(plaintext.data()), UCharCast(c20_output.data()), plaintext.size());
BOOST_CHECK(c20_output != fsc20_output);
std::byte new_key[FSChaCha20::KEYLEN];
c20_copy.Keystream(UCharCast(new_key), sizeof(new_key));
c20.SetKey32(UCharCast(new_key));
c20.Seek64({0, 1}, 0);
// Outputs should match again after simulating key rotation
c20.Crypt(UCharCast(plaintext.data()), UCharCast(c20_output.data()), plaintext.size());
BOOST_CHECK(c20_output == fsc20_output);
BOOST_CHECK_EQUAL(HexStr(fsc20_output), ciphertext_after_rotation);
}
static void TestPoly1305(const std::string &hexmessage, const std::string &hexkey, const std::string& hextag)
{
auto key = ParseHex<std::byte>(hexkey);
@@ -696,6 +736,20 @@ BOOST_AUTO_TEST_CASE(chacha20_testvector)
"fd565dea5addbdb914208fde7950f23e0385f9a727143f6a6ac51d84b1c0fb3e"
"2e3b00b63d6841a1cc6d1538b1d3a74bef1eb2f54c7b7281e36e484dba89b351"
"c8f572617e61e342879f211b0e4c515df50ea9d0771518fad96cd0baee62deb6");
// Forward secure ChaCha20
TestFSChaCha20("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
"0000000000000000000000000000000000000000000000000000000000000000",
256,
"a93df4ef03011f3db95f60d996e1785df5de38fc39bfcb663a47bb5561928349");
TestFSChaCha20("01",
"000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
5,
"ea");
TestFSChaCha20("e93fdb5c762804b9a706816aca31e35b11d2aa3080108ef46a5b1f1508819c0a",
"8ec4c3ccdaea336bdeb245636970be01266509b33f3d2642504eaf412206207a",
4096,
"8bfaa4eacff308fdb4a94a5ff25bd9d0c1f84b77f81239f67ff39d6e1ac280c9");
}
BOOST_AUTO_TEST_CASE(chacha20_midblock)