Alien-libsecp256k1

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libsecp256k1/doc/safegcd_implementation.md  view on Meta::CPAN

    # always odd, so its inverse modulo a power of two always exists.
    w = (g * NEGINV16[(f & 15) // 2]) % (2**limit)
    # As w = -g/f mod (2**limit), g+w*f mod 2**limit = 0 mod 2**limit.
    g += w * f
    assert g % (2**limit) == 0
    # The next iteration will now shift out at least limit bottom zero bits from g.
```

By using a bigger table more bits can be cancelled at once. The table can also be implemented
as a formula. Several formulas are known for computing modular inverses modulo powers of two;
some can be found in Hacker's Delight second edition by Henry S. Warren, Jr. pages 245-247.
Here we need the negated modular inverse, which is a simple transformation of those:

- Instead of a 3-bit table:
  - *-f* or *f ^ 6*
- Instead of a 4-bit table:
  - *1 - f(f + 1)*
  - *-(f + (((f + 1) & 4) << 1))*
- For larger tables the following technique can be used: if *w=-1/f mod 2<sup>L</sup>*, then *w(w&thinsp;f+2)* is
  *-1/f mod 2<sup>2L</sup>*. This allows extending the previous formulas (or tables). In particular we
  have this 6-bit function (based on the 3-bit function above):

libsecp256k1/src/tests.c  view on Meta::CPAN

    memcpy(msg, "msg", 3);
    CHECK(secp256k1_tagged_sha256(CTX, hash32, tag, 3, msg, 3) == 1);
    CHECK(secp256k1_memcmp_var(hash32, hash_expected, sizeof(hash32)) == 0);
}

/***** MODINV TESTS *****/

/* Compute the modular inverse of (odd) x mod 2^64. */
static uint64_t modinv2p64(uint64_t x) {
    /* If w = 1/x mod 2^(2^L), then w*(2 - w*x) = 1/x mod 2^(2^(L+1)). See
     * Hacker's Delight second edition, Henry S. Warren, Jr., pages 245-247 for
     * why. Start with L=0, for which it is true for every odd x that
     * 1/x=1 mod 2. Iterating 6 times gives us 1/x mod 2^64. */
    int l;
    uint64_t w = 1;
    CHECK(x & 1);
    for (l = 0; l < 6; ++l) w *= (2 - w*x);
    return w;
}

libsecp256k1/src/wycheproof/WYCHEPROOF_COPYING  view on Meta::CPAN

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libsecp256k1/src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.h  view on Meta::CPAN

/* Note: this file was autogenerated using tests_wycheproof_generate.py. Do not edit. */
#define SECP256K1_ECDSA_WYCHEPROOF_NUMBER_TESTVECTORS (463)

typedef struct {
    size_t pk_offset;
    size_t msg_offset;
    size_t msg_len;
    size_t sig_offset;
    size_t sig_len;
    int expected_verify;
} wycheproof_ecdsa_testvector;

libsecp256k1/tools/tests_wycheproof_generate.py  view on Meta::CPAN

    size_t pk_offset;
    size_t msg_offset;
    size_t msg_len;
    size_t sig_offset;
    size_t sig_len;
    int expected_verify;
} wycheproof_ecdsa_testvector;
"""


print("/* Note: this file was autogenerated using tests_wycheproof_generate.py. Do not edit. */")
print(f"#define SECP256K1_ECDSA_WYCHEPROOF_NUMBER_TESTVECTORS ({num_vectors})")

print(struct_definition)

print("static const unsigned char wycheproof_ecdsa_messages[]    = { " + messages + "};\n")
print("static const unsigned char wycheproof_ecdsa_public_keys[] = { " + public_keys + "};\n")
print("static const unsigned char wycheproof_ecdsa_signatures[]  = { " + signatures + "};\n")

print("static const wycheproof_ecdsa_testvector testvectors[SECP256K1_ECDSA_WYCHEPROOF_NUMBER_TESTVECTORS] = {")
print(out)