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test: Add modexp test vectors for even modulus and edge cases #1421

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chfast merged 1 commit into from
Jan 22, 2026
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test: Add modexp test vectors for even modulus and edge cases #1421

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38 changes: 38 additions & 0 deletions test/unittests/precompiles_expmod_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,12 @@ TEST(expmod, test_vectors)
{"03", "00", "06", "01"},
{"03", "01", "14", "03"},
{"03", "02", "14", "09"},
// Even modulus: 3^3 mod 12 = 27 mod 12 = 3.
{"03", "03", "0c", "03"},
// Even modulus: 2^5 mod 20 = 32 mod 20 = 12.
{"02", "05", "14", "0c"},
// Even modulus: 5^7 mod 24 = 78125 mod 24 = 5.
{"05", "07", "18", "05"},
{"03", "03", "03a0", "001b"},
{"09", "05", "10", "09"},
{"09", "05", "11", "08"},
Expand All @@ -41,6 +47,8 @@ TEST(expmod, test_vectors)
{"09", "05", "18", "09"},
{"03", "80", "ff", "ab"},
{"03", "1c93", "61", "5f"},
// Power-of-two modulus bigger than single word.
{"cc", "11", "00000001000000000000000000000000", "00000000fe8477d6c9cef3cc00000000"},
{
"03",
"fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2e",
Expand Down Expand Up @@ -100,6 +108,36 @@ TEST(expmod, test_vectors)
"e59e10c2a65950af0c4b047e185de46ee3d11f9b6b202d408bba3fa657dbb2cd49d4a1d329966c23e59e10"
"c2a65950af0c4b047e185de46ee3d11f9b6b20",
},
// Even modulus: (2^320 - 1) * 2^64.
{
"03",
"0300",
"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
"0000000000000000",
"52fb579ce1cc2f9ca0d054fc45bedb199389314a067aaff8f058864885f642c5acbbf6a3673585bb"
"442488538f42dc01",
},
// Even modulus: (2^768 - 1) * 2^320.
{
"03",
"0300",
"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
"ffffffffffffffffffffffffffffffff000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000",
"4059444789547ff685087bca8a144d32556b2251613171aa4cf05d8a005015d9b8408ba5f7c89595"
"e76d925173cf80e552a856b1ce217c1f33940f8241e6adcf76b672c4935a40f4bb36410ee24654c1"
"14cd718bea878742c703dc5abddbdbfa17d12328a2a6bb9d6e80dc0bc224eef03128625977a1e2c1"
"d189336e303567d7442488538f42dc01",
},
// Large base (48 bytes) with small even modulus (16 bytes).
{
"010101010101010101010101010101010101010101010101"
"010101010101010101010101010101010101010101010101",
"01",
"02020202020202020202020202020202",
"01010101010101010101010101010101",
},
};

for (const auto& [base_hex, exp_hex, mod_hex, expected_result_hex] : test_cases)
Expand Down