vendor libsecp256k1 so it doesn't depend on a shared library.

justfile

@@ -0,0 +1,23 @@
+list:
+    @just --list
+
+vendor-libsecp256k1:
+    #!/usr/bin/env fish
+    rm -r libsecp256k1
+    mkdir libsecp256k1
+    mkdir libsecp256k1/include
+    mkdir libsecp256k1/src
+    mkdir libsecp256k1/src/asm
+    mkdir libsecp256k1/src/modules
+    mkdir libsecp256k1/src/modules/extrakeys
+    mkdir libsecp256k1/src/modules/schnorrsig
+
+    wget https://api.github.com/repos/bitcoin-core/secp256k1/tarball/v0.6.0 -O libsecp256k1.tar.gz
+    tar -xvf libsecp256k1.tar.gz
+    rm libsecp256k1.tar.gz
+    cd bitcoin-core-secp256k1-*
+    for f in include/secp256k1.h include/secp256k1_ecdh.h include/secp256k1_ellswift.h include/secp256k1_extrakeys.h include/secp256k1_preallocated.h include/secp256k1_recovery.h include/secp256k1_schnorrsig.h src/asm/field_10x26_arm.s src/assumptions.h src/bench.c src/bench.h src/bench_ecmult.c src/bench_internal.c src/checkmem.h src/ecdsa.h src/ecdsa_impl.h src/eckey.h src/eckey_impl.h src/ecmult.h src/ecmult_compute_table.h src/ecmult_compute_table_impl.h src/ecmult_const.h src/ecmult_const_impl.h src/ecmult_gen.h src/ecmult_gen_compute_table.h src/ecmult_gen_compute_table_impl.h src/ecmult_gen_impl.h src/ecmult_impl.h src/field.h src/field_10x26.h src/field_10x26_impl.h src/field_5x52.h src/field_5x52_impl.h src/field_5x52_int128_impl.h src/field_impl.h src/group.h src/group_impl.h src/hash.h src/hash_impl.h src/hsort.h src/hsort_impl.h src/int128.h src/int128_impl.h src/int128_native.h src/int128_native_impl.h src/int128_struct.h src/int128_struct_impl.h src/modinv32.h src/modinv32_impl.h src/modinv64.h src/modinv64_impl.h src/modules/extrakeys/main_impl.h src/modules/schnorrsig/main_impl.h src/precompute_ecmult.c src/precompute_ecmult_gen.c src/precomputed_ecmult.c src/precomputed_ecmult.h src/precomputed_ecmult_gen.c src/precomputed_ecmult_gen.h src/scalar.h src/scalar_4x64.h src/scalar_4x64_impl.h src/scalar_8x32.h src/scalar_8x32_impl.h src/scalar_impl.h src/scalar_low.h src/scalar_low_impl.h src/scratch.h src/scratch_impl.h src/secp256k1.c src/selftest.h src/util.h
+        mv $f ../libsecp256k1/$f
+    end
+    cd ..
+    rm -r bitcoin-core-secp256k1-*

libsecp256k1/include/secp256k1_ecdh.h

@@ -0,0 +1,63 @@
+#ifndef SECP256K1_ECDH_H
+#define SECP256K1_ECDH_H
+
+#include "secp256k1.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** A pointer to a function that hashes an EC point to obtain an ECDH secret
+ *
+ *  Returns: 1 if the point was successfully hashed.
+ *           0 will cause secp256k1_ecdh to fail and return 0.
+ *           Other return values are not allowed, and the behaviour of
+ *           secp256k1_ecdh is undefined for other return values.
+ *  Out:     output:     pointer to an array to be filled by the function
+ *  In:      x32:        pointer to a 32-byte x coordinate
+ *           y32:        pointer to a 32-byte y coordinate
+ *           data:       arbitrary data pointer that is passed through
+ */
+typedef int (*secp256k1_ecdh_hash_function)(
+  unsigned char *output,
+  const unsigned char *x32,
+  const unsigned char *y32,
+  void *data
+);
+
+/** An implementation of SHA256 hash function that applies to compressed public key.
+ * Populates the output parameter with 32 bytes. */
+SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256;
+
+/** A default ECDH hash function (currently equal to secp256k1_ecdh_hash_function_sha256).
+ * Populates the output parameter with 32 bytes. */
+SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default;
+
+/** Compute an EC Diffie-Hellman secret in constant time
+ *
+ *  Returns: 1: exponentiation was successful
+ *           0: scalar was invalid (zero or overflow) or hashfp returned 0
+ *  Args:    ctx:        pointer to a context object.
+ *  Out:     output:     pointer to an array to be filled by hashfp.
+ *  In:      pubkey:     pointer to a secp256k1_pubkey containing an initialized public key.
+ *           seckey:     a 32-byte scalar with which to multiply the point.
+ *           hashfp:     pointer to a hash function. If NULL,
+ *                       secp256k1_ecdh_hash_function_sha256 is used
+ *                       (in which case, 32 bytes will be written to output).
+ *           data:       arbitrary data pointer that is passed through to hashfp
+ *                       (can be NULL for secp256k1_ecdh_hash_function_sha256).
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh(
+  const secp256k1_context *ctx,
+  unsigned char *output,
+  const secp256k1_pubkey *pubkey,
+  const unsigned char *seckey,
+  secp256k1_ecdh_hash_function hashfp,
+  void *data
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_ECDH_H */

libsecp256k1/include/secp256k1_ellswift.h

@@ -0,0 +1,200 @@
+#ifndef SECP256K1_ELLSWIFT_H
+#define SECP256K1_ELLSWIFT_H
+
+#include "secp256k1.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* This module provides an implementation of ElligatorSwift as well as a
+ * version of x-only ECDH using it (including compatibility with BIP324).
+ *
+ * ElligatorSwift is described in https://eprint.iacr.org/2022/759 by
+ * Chavez-Saab, Rodriguez-Henriquez, and Tibouchi. It permits encoding
+ * uniformly chosen public keys as 64-byte arrays which are indistinguishable
+ * from uniformly random arrays.
+ *
+ * Let f be the function from pairs of field elements to point X coordinates,
+ * defined as follows (all operations modulo p = 2^256 - 2^32 - 977)
+ * f(u,t):
+ * - Let C = 0xa2d2ba93507f1df233770c2a797962cc61f6d15da14ecd47d8d27ae1cd5f852,
+ *   a square root of -3.
+ * - If u=0, set u=1 instead.
+ * - If t=0, set t=1 instead.
+ * - If u^3 + t^2 + 7 = 0, multiply t by 2.
+ * - Let X = (u^3 + 7 - t^2) / (2 * t)
+ * - Let Y = (X + t) / (C * u)
+ * - Return the first in [u + 4 * Y^2, (-X/Y - u) / 2, (X/Y - u) / 2] that is an
+ *   X coordinate on the curve (at least one of them is, for any u and t).
+ *
+ * Then an ElligatorSwift encoding of x consists of the 32-byte big-endian
+ * encodings of field elements u and t concatenated, where f(u,t) = x.
+ * The encoding algorithm is described in the paper, and effectively picks a
+ * uniformly random pair (u,t) among those which encode x.
+ *
+ * If the Y coordinate is relevant, it is given the same parity as t.
+ *
+ * Changes w.r.t. the paper:
+ * - The u=0, t=0, and u^3+t^2+7=0 conditions result in decoding to the point
+ *   at infinity in the paper. Here they are remapped to finite points.
+ * - The paper uses an additional encoding bit for the parity of y. Here the
+ *   parity of t is used (negating t does not affect the decoded x coordinate,
+ *   so this is possible).
+ *
+ * For mathematical background about the scheme, see the doc/ellswift.md file.
+ */
+
+/** A pointer to a function used by secp256k1_ellswift_xdh to hash the shared X
+ *  coordinate along with the encoded public keys to a uniform shared secret.
+ *
+ *  Returns: 1 if a shared secret was successfully computed.
+ *           0 will cause secp256k1_ellswift_xdh to fail and return 0.
+ *           Other return values are not allowed, and the behaviour of
+ *           secp256k1_ellswift_xdh is undefined for other return values.
+ *  Out:     output:     pointer to an array to be filled by the function
+ *  In:      x32:        pointer to the 32-byte serialized X coordinate
+ *                       of the resulting shared point (will not be NULL)
+ *           ell_a64:    pointer to the 64-byte encoded public key of party A
+ *                       (will not be NULL)
+ *           ell_b64:    pointer to the 64-byte encoded public key of party B
+ *                       (will not be NULL)
+ *           data:       arbitrary data pointer that is passed through
+ */
+typedef int (*secp256k1_ellswift_xdh_hash_function)(
+    unsigned char *output,
+    const unsigned char *x32,
+    const unsigned char *ell_a64,
+    const unsigned char *ell_b64,
+    void *data
+);
+
+/** An implementation of an secp256k1_ellswift_xdh_hash_function which uses
+ *  SHA256(prefix64 || ell_a64 || ell_b64 || x32), where prefix64 is the 64-byte
+ *  array pointed to by data. */
+SECP256K1_API const secp256k1_ellswift_xdh_hash_function secp256k1_ellswift_xdh_hash_function_prefix;
+
+/** An implementation of an secp256k1_ellswift_xdh_hash_function compatible with
+ *  BIP324. It returns H_tag(ell_a64 || ell_b64 || x32), where H_tag is the
+ *  BIP340 tagged hash function with tag "bip324_ellswift_xonly_ecdh". Equivalent
+ *  to secp256k1_ellswift_xdh_hash_function_prefix with prefix64 set to
+ *  SHA256("bip324_ellswift_xonly_ecdh")||SHA256("bip324_ellswift_xonly_ecdh").
+ *  The data argument is ignored. */
+SECP256K1_API const secp256k1_ellswift_xdh_hash_function secp256k1_ellswift_xdh_hash_function_bip324;
+
+/** Construct a 64-byte ElligatorSwift encoding of a given pubkey.
+ *
+ *  Returns: 1 always.
+ *  Args:    ctx:        pointer to a context object
+ *  Out:     ell64:      pointer to a 64-byte array to be filled
+ *  In:      pubkey:     pointer to a secp256k1_pubkey containing an
+ *                       initialized public key
+ *           rnd32:      pointer to 32 bytes of randomness
+ *
+ * It is recommended that rnd32 consists of 32 uniformly random bytes, not
+ * known to any adversary trying to detect whether public keys are being
+ * encoded, though 16 bytes of randomness (padded to an array of 32 bytes,
+ * e.g., with zeros) suffice to make the result indistinguishable from
+ * uniform. The randomness in rnd32 must not be a deterministic function of
+ * the pubkey (it can be derived from the private key, though).
+ *
+ * It is not guaranteed that the computed encoding is stable across versions
+ * of the library, even if all arguments to this function (including rnd32)
+ * are the same.
+ *
+ * This function runs in variable time.
+ */
+SECP256K1_API int secp256k1_ellswift_encode(
+    const secp256k1_context *ctx,
+    unsigned char *ell64,
+    const secp256k1_pubkey *pubkey,
+    const unsigned char *rnd32
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
+
+/** Decode a 64-bytes ElligatorSwift encoded public key.
+ *
+ *  Returns: always 1
+ *  Args:    ctx:        pointer to a context object
+ *  Out:     pubkey:     pointer to a secp256k1_pubkey that will be filled
+ *  In:      ell64:      pointer to a 64-byte array to decode
+ *
+ * This function runs in variable time.
+ */
+SECP256K1_API int secp256k1_ellswift_decode(
+    const secp256k1_context *ctx,
+    secp256k1_pubkey *pubkey,
+    const unsigned char *ell64
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
+
+/** Compute an ElligatorSwift public key for a secret key.
+ *
+ *  Returns: 1: secret was valid, public key was stored.
+ *           0: secret was invalid, try again.
+ *  Args:    ctx:        pointer to a context object
+ *  Out:     ell64:      pointer to a 64-byte array to receive the ElligatorSwift
+ *                       public key
+ *  In:      seckey32:   pointer to a 32-byte secret key
+ *           auxrnd32:   (optional) pointer to 32 bytes of randomness
+ *
+ * Constant time in seckey and auxrnd32, but not in the resulting public key.
+ *
+ * It is recommended that auxrnd32 contains 32 uniformly random bytes, though
+ * it is optional (and does result in encodings that are indistinguishable from
+ * uniform even without any auxrnd32). It differs from the (mandatory) rnd32
+ * argument to secp256k1_ellswift_encode in this regard.
+ *
+ * This function can be used instead of calling secp256k1_ec_pubkey_create
+ * followed by secp256k1_ellswift_encode. It is safer, as it uses the secret
+ * key as entropy for the encoding (supplemented with auxrnd32, if provided).
+ *
+ * Like secp256k1_ellswift_encode, this function does not guarantee that the
+ * computed encoding is stable across versions of the library, even if all
+ * arguments (including auxrnd32) are the same.
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ellswift_create(
+    const secp256k1_context *ctx,
+    unsigned char *ell64,
+    const unsigned char *seckey32,
+    const unsigned char *auxrnd32
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
+
+/** Given a private key, and ElligatorSwift public keys sent in both directions,
+ *  compute a shared secret using x-only Elliptic Curve Diffie-Hellman (ECDH).
+ *
+ *  Returns: 1: shared secret was successfully computed
+ *           0: secret was invalid or hashfp returned 0
+ *  Args:    ctx:       pointer to a context object.
+ *  Out:     output:    pointer to an array to be filled by hashfp.
+ *  In:      ell_a64:   pointer to the 64-byte encoded public key of party A
+ *                      (will not be NULL)
+ *           ell_b64:   pointer to the 64-byte encoded public key of party B
+ *                      (will not be NULL)
+ *           seckey32:  pointer to our 32-byte secret key
+ *           party:     boolean indicating which party we are: zero if we are
+ *                      party A, non-zero if we are party B. seckey32 must be
+ *                      the private key corresponding to that party's ell_?64.
+ *                      This correspondence is not checked.
+ *           hashfp:    pointer to a hash function.
+ *           data:      arbitrary data pointer passed through to hashfp.
+ *
+ * Constant time in seckey32.
+ *
+ * This function is more efficient than decoding the public keys, and performing
+ * ECDH on them.
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ellswift_xdh(
+  const secp256k1_context *ctx,
+  unsigned char *output,
+  const unsigned char *ell_a64,
+  const unsigned char *ell_b64,
+  const unsigned char *seckey32,
+  int party,
+  secp256k1_ellswift_xdh_hash_function hashfp,
+  void *data
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5) SECP256K1_ARG_NONNULL(7);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_ELLSWIFT_H */