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4b48a43106
It's subtle, since it is actually only touched by hashfp (though we assert it's non-NULL), but give explicit advice in the default case. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
59 lines
2.2 KiB
C
59 lines
2.2 KiB
C
#ifndef SECP256K1_ECDH_H
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#define SECP256K1_ECDH_H
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#include "secp256k1.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/** A pointer to a function that applies hash function to a point
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*
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* Returns: 1 if a point was successfully hashed. 0 will cause ecdh to fail
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* Out: output: pointer to an array to be filled by the function
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* In: x: pointer to a 32-byte x coordinate
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* y: pointer to a 32-byte y coordinate
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* data: Arbitrary data pointer that is passed through
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*/
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typedef int (*secp256k1_ecdh_hash_function)(
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unsigned char *output,
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const unsigned char *x,
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const unsigned char *y,
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void *data
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);
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/** An implementation of SHA256 hash function that applies to compressed public key.
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* Populates the output parameter with 32 bytes. */
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SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256;
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/** A default ecdh hash function (currently equal to secp256k1_ecdh_hash_function_sha256).
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* Populates the output parameter with 32 bytes. */
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SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default;
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/** Compute an EC Diffie-Hellman secret in constant time
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* Returns: 1: exponentiation was successful
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* 0: scalar was invalid (zero or overflow)
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* Args: ctx: pointer to a context object (cannot be NULL)
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* Out: output: pointer to an array to be filled by hashfp
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* In: pubkey: a pointer to a secp256k1_pubkey containing an
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* initialized public key
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* privkey: a 32-byte scalar with which to multiply the point
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* hashfp: pointer to a hash function. If NULL, secp256k1_ecdh_hash_function_sha256 is used
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* (in which case, 32 bytes will be written to output)
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* data: Arbitrary data pointer that is passed through to hashfp
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh(
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const secp256k1_context* ctx,
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unsigned char *output,
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const secp256k1_pubkey *pubkey,
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const unsigned char *privkey,
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secp256k1_ecdh_hash_function hashfp,
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void *data
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
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#ifdef __cplusplus
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}
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#endif
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#endif /* SECP256K1_ECDH_H */
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