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secp256k1/include/secp256k1.h

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#ifndef SECP256K1_H
#define SECP256K1_H
#ifdef __cplusplus
extern "C" {
#endif
#include <stddef.h>
/** Unless explicitly stated all pointer arguments must not be NULL.
*
* The following rules specify the order of arguments in API calls:
*
* 1. Context pointers go first, followed by output arguments, combined
* output/input arguments, and finally input-only arguments.
* 2. Array lengths always immediately follow the argument whose length
* they describe, even if this violates rule 1.
* 3. Within the OUT/OUTIN/IN groups, pointers to data that is typically generated
* later go first. This means: signatures, public nonces, secret nonces,
* messages, public keys, secret keys, tweaks.
* 4. Arguments that are not data pointers go last, from more complex to less
* complex: function pointers, algorithm names, messages, void pointers,
* counts, flags, booleans.
* 5. Opaque data pointers follow the function pointer they are to be passed to.
*/
/** Opaque data structure that holds context information
*
* The primary purpose of context objects is to store randomization data for
* enhanced protection against side-channel leakage. This protection is only
* effective if the context is randomized after its creation. See
* secp256k1_context_create for creation of contexts and
* secp256k1_context_randomize for randomization.
*
* A secondary purpose of context objects is to store pointers to callback
* functions that the library will call when certain error states arise. See
* secp256k1_context_set_error_callback as well as
* secp256k1_context_set_illegal_callback for details. Future library versions
* may use context objects for additional purposes.
*
* A constructed context can safely be used from multiple threads
* simultaneously, but API calls that take a non-const pointer to a context
* need exclusive access to it. In particular this is the case for
* secp256k1_context_destroy, secp256k1_context_preallocated_destroy,
* and secp256k1_context_randomize.
*
* Regarding randomization, either do it once at creation time (in which case
* you do not need any locking for the other calls), or use a read-write lock.
*/
typedef struct secp256k1_context_struct secp256k1_context;
/** Opaque data structure that holds rewritable "scratch space"
*
* The purpose of this structure is to replace dynamic memory allocations,
* because we target architectures where this may not be available. It is
* essentially a resizable (within specified parameters) block of bytes,
* which is initially created either by memory allocation or TODO as a pointer
* into some fixed rewritable space.
*
* Unlike the context object, this cannot safely be shared between threads
* without additional synchronization logic.
*/
typedef struct secp256k1_scratch_space_struct secp256k1_scratch_space;
/** Opaque data structure that holds a parsed and valid public key.
*
* The exact representation of data inside is implementation defined and not
* guaranteed to be portable between different platforms or versions. It is
* however guaranteed to be 64 bytes in size, and can be safely copied/moved.
* If you need to convert to a format suitable for storage or transmission,
* use secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse. To
* compare keys, use secp256k1_ec_pubkey_cmp.
*/
typedef struct {
unsigned char data[64];
} secp256k1_pubkey;
/** Opaque data structured that holds a parsed ECDSA signature.
*
* The exact representation of data inside is implementation defined and not
* guaranteed to be portable between different platforms or versions. It is
* however guaranteed to be 64 bytes in size, and can be safely copied/moved.
* If you need to convert to a format suitable for storage, transmission, or
* comparison, use the secp256k1_ecdsa_signature_serialize_* and
* secp256k1_ecdsa_signature_parse_* functions.
*/
typedef struct {
unsigned char data[64];
} secp256k1_ecdsa_signature;
/** A pointer to a function to deterministically generate a nonce.
*
* Returns: 1 if a nonce was successfully generated. 0 will cause signing to fail.
* Out: nonce32: pointer to a 32-byte array to be filled by the function.
* In: msg32: the 32-byte message hash being verified (will not be NULL)
* key32: pointer to a 32-byte secret key (will not be NULL)
* algo16: pointer to a 16-byte array describing the signature
* algorithm (will be NULL for ECDSA for compatibility).
* data: Arbitrary data pointer that is passed through.
* attempt: how many iterations we have tried to find a nonce.
* This will almost always be 0, but different attempt values
* are required to result in a different nonce.
*
* Except for test cases, this function should compute some cryptographic hash of
* the message, the algorithm, the key and the attempt.
*/
typedef int (*secp256k1_nonce_function)(
unsigned char *nonce32,
const unsigned char *msg32,
const unsigned char *key32,
const unsigned char *algo16,
void *data,
unsigned int attempt
);
# if !defined(SECP256K1_GNUC_PREREQ)
# if defined(__GNUC__)&&defined(__GNUC_MINOR__)
# define SECP256K1_GNUC_PREREQ(_maj,_min) \
((__GNUC__<<16)+__GNUC_MINOR__>=((_maj)<<16)+(_min))
# else
# define SECP256K1_GNUC_PREREQ(_maj,_min) 0
# endif
# endif
# if (!defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L) )
# if SECP256K1_GNUC_PREREQ(2,7)
# define SECP256K1_INLINE __inline__
# elif (defined(_MSC_VER))
# define SECP256K1_INLINE __inline
# else
# define SECP256K1_INLINE
# endif
# else
# define SECP256K1_INLINE inline
# endif
/* When this header is used at build-time the SECP256K1_BUILD define needs to be set
* to correctly setup export attributes and nullness checks. This is normally done
* by secp256k1.c but to guard against this header being included before secp256k1.c
* has had a chance to set the define (e.g. via test harnesses that just includes
* secp256k1.c) we set SECP256K1_NO_BUILD when this header is processed without the
* BUILD define so this condition can be caught.
*/
#ifndef SECP256K1_BUILD
# define SECP256K1_NO_BUILD
#endif
/** At secp256k1 build-time DLL_EXPORT is defined when building objects destined
* for a shared library, but not for those intended for static libraries.
*/
#ifndef SECP256K1_API
# if defined(_WIN32)
# if defined(SECP256K1_BUILD) && defined(DLL_EXPORT)
# define SECP256K1_API __declspec(dllexport)
# else
# define SECP256K1_API
# endif
# elif defined(__GNUC__) && (__GNUC__ >= 4) && defined(SECP256K1_BUILD)
# define SECP256K1_API __attribute__ ((visibility ("default")))
# else
# define SECP256K1_API
# endif
#endif
/* Warning attributes
* NONNULL is not used if SECP256K1_BUILD is set to avoid the compiler optimizing out
* some paranoid null checks. */
# if defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
# define SECP256K1_WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
# else
# define SECP256K1_WARN_UNUSED_RESULT
# endif
# if !defined(SECP256K1_BUILD) && defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
# define SECP256K1_ARG_NONNULL(_x) __attribute__ ((__nonnull__(_x)))
# else
# define SECP256K1_ARG_NONNULL(_x)
# endif
/* Attribute for marking functions, types, and variables as deprecated */
#if !defined(SECP256K1_BUILD) && defined(__has_attribute)
# if __has_attribute(__deprecated__)
# define SECP256K1_DEPRECATED(_msg) __attribute__ ((__deprecated__(_msg)))
# else
# define SECP256K1_DEPRECATED(_msg)
# endif
#else
# define SECP256K1_DEPRECATED(_msg)
#endif
/* All flags' lower 8 bits indicate what they're for. Do not use directly. */
#define SECP256K1_FLAGS_TYPE_MASK ((1 << 8) - 1)
#define SECP256K1_FLAGS_TYPE_CONTEXT (1 << 0)
#define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
/* The higher bits contain the actual data. Do not use directly. */
#define SECP256K1_FLAGS_BIT_CONTEXT_VERIFY (1 << 8)
#define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9)
#define SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY (1 << 10)
#define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)
/** Context flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and
* secp256k1_context_preallocated_create. */
#define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)
/** Deprecated context flags. These flags are treated equivalent to SECP256K1_CONTEXT_NONE. */
#define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY)
#define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN)
/* Testing flag. Do not use. */
#define SECP256K1_CONTEXT_DECLASSIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY)
/** Flag to pass to secp256k1_ec_pubkey_serialize. */
#define SECP256K1_EC_COMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION | SECP256K1_FLAGS_BIT_COMPRESSION)
#define SECP256K1_EC_UNCOMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION)
/** Prefix byte used to tag various encoded curvepoints for specific purposes */
#define SECP256K1_TAG_PUBKEY_EVEN 0x02
#define SECP256K1_TAG_PUBKEY_ODD 0x03
#define SECP256K1_TAG_PUBKEY_UNCOMPRESSED 0x04
#define SECP256K1_TAG_PUBKEY_HYBRID_EVEN 0x06
#define SECP256K1_TAG_PUBKEY_HYBRID_ODD 0x07
/** A built-in constant secp256k1 context object with static storage duration, to be
* used in conjunction with secp256k1_selftest.
*
* This context object offers *only limited functionality* , i.e., it cannot be used
* for API functions that perform computations involving secret keys, e.g., signing
* and public key generation. If this restriction applies to a specific API function,
* it is mentioned in its documentation. See secp256k1_context_create if you need a
* full context object that supports all functionality offered by the library.
*
* It is highly recommended to call secp256k1_selftest before using this context.
*/
SECP256K1_API extern const secp256k1_context *secp256k1_context_static;
/** Deprecated alias for secp256k1_context_static. */
SECP256K1_API extern const secp256k1_context *secp256k1_context_no_precomp
SECP256K1_DEPRECATED("Use secp256k1_context_static instead");
/** Perform basic self tests (to be used in conjunction with secp256k1_context_static)
*
* This function performs self tests that detect some serious usage errors and
* similar conditions, e.g., when the library is compiled for the wrong endianness.
* This is a last resort measure to be used in production. The performed tests are
* very rudimentary and are not intended as a replacement for running the test
* binaries.
*
* It is highly recommended to call this before using secp256k1_context_static.
* It is not necessary to call this function before using a context created with
* secp256k1_context_create (or secp256k1_context_preallocated_create), which will
* take care of performing the self tests.
*
* If the tests fail, this function will call the default error handler to abort the
* program (see secp256k1_context_set_error_callback).
*/
SECP256K1_API void secp256k1_selftest(void);
/** Create a secp256k1 context object (in dynamically allocated memory).
*
* This function uses malloc to allocate memory. It is guaranteed that malloc is
* called at most once for every call of this function. If you need to avoid dynamic
* memory allocation entirely, see secp256k1_context_static and the functions in
* secp256k1_preallocated.h.
*
* Returns: a newly created context object.
* In: flags: Always set to SECP256K1_CONTEXT_NONE (see below).
*
* The only valid non-deprecated flag in recent library versions is
* SECP256K1_CONTEXT_NONE, which will create a context sufficient for all functionality
* offered by the library. All other (deprecated) flags will be treated as equivalent
* to the SECP256K1_CONTEXT_NONE flag. Though the flags parameter primarily exists for
* historical reasons, future versions of the library may introduce new flags.
*
* If the context is intended to be used for API functions that perform computations
* involving secret keys, e.g., signing and public key generation, then it is highly
* recommended to call secp256k1_context_randomize on the context before calling
* those API functions. This will provide enhanced protection against side-channel
* leakage, see secp256k1_context_randomize for details.
*
* Do not create a new context object for each operation, as construction and
* randomization can take non-negligible time.
*/
SECP256K1_API secp256k1_context* secp256k1_context_create(
unsigned int flags
) SECP256K1_WARN_UNUSED_RESULT;
/** Copy a secp256k1 context object (into dynamically allocated memory).
*
* This function uses malloc to allocate memory. It is guaranteed that malloc is
* called at most once for every call of this function. If you need to avoid dynamic
* memory allocation entirely, see the functions in secp256k1_preallocated.h.
*
* Returns: a newly created context object.
* Args: ctx: an existing context to copy
*/
SECP256K1_API secp256k1_context* secp256k1_context_clone(
const secp256k1_context* ctx
) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT;
/** Destroy a secp256k1 context object (created in dynamically allocated memory).
*
* The context pointer may not be used afterwards.
*
* The context to destroy must have been created using secp256k1_context_create
* or secp256k1_context_clone. If the context has instead been created using
* secp256k1_context_preallocated_create or secp256k1_context_preallocated_clone, the
* behaviour is undefined. In that case, secp256k1_context_preallocated_destroy must
* be used instead.
*
* Args: ctx: an existing context to destroy, constructed using
* secp256k1_context_create or secp256k1_context_clone
*/
SECP256K1_API void secp256k1_context_destroy(
secp256k1_context* ctx
) SECP256K1_ARG_NONNULL(1);
/** Set a callback function to be called when an illegal argument is passed to
* an API call. It will only trigger for violations that are mentioned
* explicitly in the header.
*
* The philosophy is that these shouldn't be dealt with through a
* specific return value, as calling code should not have branches to deal with
* the case that this code itself is broken.
*
* On the other hand, during debug stage, one would want to be informed about
* such mistakes, and the default (crashing) may be inadvisable.
* When this callback is triggered, the API function called is guaranteed not
* to cause a crash, though its return value and output arguments are
* undefined.
*
* When this function has not been called (or called with fn==NULL), then the
* default handler will be used. The library provides a default handler which
* writes the message to stderr and calls abort. This default handler can be
* replaced at link time if the preprocessor macro
* USE_EXTERNAL_DEFAULT_CALLBACKS is defined, which is the case if the build
* has been configured with --enable-external-default-callbacks. Then the
* following two symbols must be provided to link against:
* - void secp256k1_default_illegal_callback_fn(const char* message, void* data);
* - void secp256k1_default_error_callback_fn(const char* message, void* data);
* The library can call these default handlers even before a proper callback data
* pointer could have been set using secp256k1_context_set_illegal_callback or
* secp256k1_context_set_error_callback, e.g., when the creation of a context
* fails. In this case, the corresponding default handler will be called with
* the data pointer argument set to NULL.
*
* Args: ctx: an existing context object.
* In: fun: a pointer to a function to call when an illegal argument is
* passed to the API, taking a message and an opaque pointer.
* (NULL restores the default handler.)
* data: the opaque pointer to pass to fun above, must be NULL for the default handler.
*
* See also secp256k1_context_set_error_callback.
*/
SECP256K1_API void secp256k1_context_set_illegal_callback(
secp256k1_context* ctx,
void (*fun)(const char* message, void* data),
const void* data
) SECP256K1_ARG_NONNULL(1);
/** Set a callback function to be called when an internal consistency check
* fails.
*
* The default callback writes an error message to stderr and calls abort
* to abort the program.
*
* This can only trigger in case of a hardware failure, miscompilation,
* memory corruption, serious bug in the library, or other error would can
* otherwise result in undefined behaviour. It will not trigger due to mere
* incorrect usage of the API (see secp256k1_context_set_illegal_callback
* for that). After this callback returns, anything may happen, including
* crashing.
*
* Args: ctx: an existing context object.
* In: fun: a pointer to a function to call when an internal error occurs,
* taking a message and an opaque pointer (NULL restores the
* default handler, see secp256k1_context_set_illegal_callback
* for details).
* data: the opaque pointer to pass to fun above, must be NULL for the default handler.
*
* See also secp256k1_context_set_illegal_callback.
*/
SECP256K1_API void secp256k1_context_set_error_callback(
secp256k1_context* ctx,
void (*fun)(const char* message, void* data),
const void* data
) SECP256K1_ARG_NONNULL(1);
/** Create a secp256k1 scratch space object.
*
* Returns: a newly created scratch space.
* Args: ctx: an existing context object.
* In: size: amount of memory to be available as scratch space. Some extra
* (<100 bytes) will be allocated for extra accounting.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT secp256k1_scratch_space* secp256k1_scratch_space_create(
const secp256k1_context* ctx,
size_t size
) SECP256K1_ARG_NONNULL(1);
/** Destroy a secp256k1 scratch space.
*
* The pointer may not be used afterwards.
* Args: ctx: a secp256k1 context object.
* scratch: space to destroy
*/
SECP256K1_API void secp256k1_scratch_space_destroy(
const secp256k1_context* ctx,
secp256k1_scratch_space* scratch
) SECP256K1_ARG_NONNULL(1);
/** Parse a variable-length public key into the pubkey object.
*
* Returns: 1 if the public key was fully valid.
* 0 if the public key could not be parsed or is invalid.
* Args: ctx: a secp256k1 context object.
* Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to a
* parsed version of input. If not, its value is undefined.
* In: input: pointer to a serialized public key
* inputlen: length of the array pointed to by input
*
* This function supports parsing compressed (33 bytes, header byte 0x02 or
* 0x03), uncompressed (65 bytes, header byte 0x04), or hybrid (65 bytes, header
* byte 0x06 or 0x07) format public keys.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_parse(
const secp256k1_context* ctx,
secp256k1_pubkey* pubkey,
const unsigned char *input,
size_t inputlen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Serialize a pubkey object into a serialized byte sequence.
*
* Returns: 1 always.
* Args: ctx: a secp256k1 context object.
* Out: output: a pointer to a 65-byte (if compressed==0) or 33-byte (if
* compressed==1) byte array to place the serialized key
* in.
* In/Out: outputlen: a pointer to an integer which is initially set to the
* size of output, and is overwritten with the written
* size.
* In: pubkey: a pointer to a secp256k1_pubkey containing an
* initialized public key.
* flags: SECP256K1_EC_COMPRESSED if serialization should be in
* compressed format, otherwise SECP256K1_EC_UNCOMPRESSED.
*/
SECP256K1_API int secp256k1_ec_pubkey_serialize(
const secp256k1_context* ctx,
unsigned char *output,
size_t *outputlen,
const secp256k1_pubkey* pubkey,
unsigned int flags
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
/** Compare two public keys using lexicographic (of compressed serialization) order
*
* Returns: <0 if the first public key is less than the second
* >0 if the first public key is greater than the second
* 0 if the two public keys are equal
* Args: ctx: a secp256k1 context object.
* In: pubkey1: first public key to compare
* pubkey2: second public key to compare
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_cmp(
const secp256k1_context* ctx,
const secp256k1_pubkey* pubkey1,
const secp256k1_pubkey* pubkey2
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Parse an ECDSA signature in compact (64 bytes) format.
*
* Returns: 1 when the signature could be parsed, 0 otherwise.
* Args: ctx: a secp256k1 context object
* Out: sig: a pointer to a signature object
* In: input64: a pointer to the 64-byte array to parse
*
* The signature must consist of a 32-byte big endian R value, followed by a
* 32-byte big endian S value. If R or S fall outside of [0..order-1], the
* encoding is invalid. R and S with value 0 are allowed in the encoding.
*
* After the call, sig will always be initialized. If parsing failed or R or
* S are zero, the resulting sig value is guaranteed to fail verification for
* any message and public key.
*/
SECP256K1_API int secp256k1_ecdsa_signature_parse_compact(
const secp256k1_context* ctx,
secp256k1_ecdsa_signature* sig,
const unsigned char *input64
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Parse a DER ECDSA signature.
*
* Returns: 1 when the signature could be parsed, 0 otherwise.
* Args: ctx: a secp256k1 context object
* Out: sig: a pointer to a signature object
* In: input: a pointer to the signature to be parsed
* inputlen: the length of the array pointed to be input
*
* This function will accept any valid DER encoded signature, even if the
* encoded numbers are out of range.
*
* After the call, sig will always be initialized. If parsing failed or the
* encoded numbers are out of range, signature verification with it is
* guaranteed to fail for every message and public key.
*/
SECP256K1_API int secp256k1_ecdsa_signature_parse_der(
const secp256k1_context* ctx,
secp256k1_ecdsa_signature* sig,
const unsigned char *input,
size_t inputlen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Serialize an ECDSA signature in DER format.
*
* Returns: 1 if enough space was available to serialize, 0 otherwise
* Args: ctx: a secp256k1 context object
* Out: output: a pointer to an array to store the DER serialization
* In/Out: outputlen: a pointer to a length integer. Initially, this integer
* should be set to the length of output. After the call
* it will be set to the length of the serialization (even
* if 0 was returned).
* In: sig: a pointer to an initialized signature object
*/
SECP256K1_API int secp256k1_ecdsa_signature_serialize_der(
const secp256k1_context* ctx,
unsigned char *output,
size_t *outputlen,
const secp256k1_ecdsa_signature* sig
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
/** Serialize an ECDSA signature in compact (64 byte) format.
*
* Returns: 1
* Args: ctx: a secp256k1 context object
* Out: output64: a pointer to a 64-byte array to store the compact serialization
* In: sig: a pointer to an initialized signature object
*
* See secp256k1_ecdsa_signature_parse_compact for details about the encoding.
*/
SECP256K1_API int secp256k1_ecdsa_signature_serialize_compact(
const secp256k1_context* ctx,
unsigned char *output64,
const secp256k1_ecdsa_signature* sig
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Verify an ECDSA signature.
*
* Returns: 1: correct signature
* 0: incorrect or unparseable signature
* Args: ctx: a secp256k1 context object.
* In: sig: the signature being verified.
* msghash32: the 32-byte message hash being verified.
* The verifier must make sure to apply a cryptographic
* hash function to the message by itself and not accept an
* msghash32 value directly. Otherwise, it would be easy to
* create a "valid" signature without knowledge of the
* secret key. See also
* https://bitcoin.stackexchange.com/a/81116/35586 for more
* background on this topic.
* pubkey: pointer to an initialized public key to verify with.
*
* To avoid accepting malleable signatures, only ECDSA signatures in lower-S
* form are accepted.
*
* If you need to accept ECDSA signatures from sources that do not obey this
* rule, apply secp256k1_ecdsa_signature_normalize to the signature prior to
* verification, but be aware that doing so results in malleable signatures.
*
* For details, see the comments for that function.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify(
const secp256k1_context* ctx,
const secp256k1_ecdsa_signature *sig,
const unsigned char *msghash32,
const secp256k1_pubkey *pubkey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
/** Convert a signature to a normalized lower-S form.
*
* Returns: 1 if sigin was not normalized, 0 if it already was.
* Args: ctx: a secp256k1 context object
* Out: sigout: a pointer to a signature to fill with the normalized form,
* or copy if the input was already normalized. (can be NULL if
* you're only interested in whether the input was already
* normalized).
* In: sigin: a pointer to a signature to check/normalize (can be identical to sigout)
*
* With ECDSA a third-party can forge a second distinct signature of the same
* message, given a single initial signature, but without knowing the key. This
* is done by negating the S value modulo the order of the curve, 'flipping'
* the sign of the random point R which is not included in the signature.
*
* Forgery of the same message isn't universally problematic, but in systems
* where message malleability or uniqueness of signatures is important this can
* cause issues. This forgery can be blocked by all verifiers forcing signers
* to use a normalized form.
*
* The lower-S form reduces the size of signatures slightly on average when
* variable length encodings (such as DER) are used and is cheap to verify,
* making it a good choice. Security of always using lower-S is assured because
* anyone can trivially modify a signature after the fact to enforce this
* property anyway.
*
* The lower S value is always between 0x1 and
* 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0,
* inclusive.
*
* No other forms of ECDSA malleability are known and none seem likely, but
* there is no formal proof that ECDSA, even with this additional restriction,
* is free of other malleability. Commonly used serialization schemes will also
* accept various non-unique encodings, so care should be taken when this
* property is required for an application.
*
* The secp256k1_ecdsa_sign function will by default create signatures in the
* lower-S form, and secp256k1_ecdsa_verify will not accept others. In case
* signatures come from a system that cannot enforce this property,
* secp256k1_ecdsa_signature_normalize must be called before verification.
*/
SECP256K1_API int secp256k1_ecdsa_signature_normalize(
const secp256k1_context* ctx,
secp256k1_ecdsa_signature *sigout,
const secp256k1_ecdsa_signature *sigin
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(3);
/** An implementation of RFC6979 (using HMAC-SHA256) as nonce generation function.
* If a data pointer is passed, it is assumed to be a pointer to 32 bytes of
* extra entropy.
*/
SECP256K1_API extern const secp256k1_nonce_function secp256k1_nonce_function_rfc6979;
/** A default safe nonce generation function (currently equal to secp256k1_nonce_function_rfc6979). */
SECP256K1_API extern const secp256k1_nonce_function secp256k1_nonce_function_default;
/** Create an ECDSA signature.
*
* Returns: 1: signature created
* 0: the nonce generation function failed, or the secret key was invalid.
* Args: ctx: pointer to a context object (not secp256k1_context_static).
* Out: sig: pointer to an array where the signature will be placed.
* In: msghash32: the 32-byte message hash being signed.
* seckey: pointer to a 32-byte secret key.
* noncefp: pointer to a nonce generation function. If NULL,
* secp256k1_nonce_function_default is used.
* ndata: pointer to arbitrary data used by the nonce generation function
* (can be NULL). If it is non-NULL and
* secp256k1_nonce_function_default is used, then ndata must be a
* pointer to 32-bytes of additional data.
*
* The created signature is always in lower-S form. See
* secp256k1_ecdsa_signature_normalize for more details.
*/
SECP256K1_API int secp256k1_ecdsa_sign(
const secp256k1_context* ctx,
secp256k1_ecdsa_signature *sig,
const unsigned char *msghash32,
const unsigned char *seckey,
secp256k1_nonce_function noncefp,
const void *ndata
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
/** Verify an ECDSA secret key.
*
* A secret key is valid if it is not 0 and less than the secp256k1 curve order
* when interpreted as an integer (most significant byte first). The
* probability of choosing a 32-byte string uniformly at random which is an
* invalid secret key is negligible.
*
* Returns: 1: secret key is valid
* 0: secret key is invalid
* Args: ctx: pointer to a context object.
* In: seckey: pointer to a 32-byte secret key.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_verify(
const secp256k1_context* ctx,
const unsigned char *seckey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
/** Compute the public key for a secret key.
*
* Returns: 1: secret was valid, public key stores.
* 0: secret was invalid, try again.
* Args: ctx: pointer to a context object (not secp256k1_context_static).
* Out: pubkey: pointer to the created public key.
* In: seckey: pointer to a 32-byte secret key.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_create(
const secp256k1_context* ctx,
secp256k1_pubkey *pubkey,
const unsigned char *seckey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Negates a secret key in place.
*
* Returns: 0 if the given secret key is invalid according to
* secp256k1_ec_seckey_verify. 1 otherwise
* Args: ctx: pointer to a context object
* In/Out: seckey: pointer to the 32-byte secret key to be negated. If the
* secret key is invalid according to
* secp256k1_ec_seckey_verify, this function returns 0 and
* seckey will be set to some unspecified value.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_negate(
const secp256k1_context* ctx,
unsigned char *seckey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
/** Same as secp256k1_ec_seckey_negate, but DEPRECATED. Will be removed in
* future versions. */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_negate(
const secp256k1_context* ctx,
unsigned char *seckey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2)
SECP256K1_DEPRECATED("Use secp256k1_ec_seckey_negate instead");
/** Negates a public key in place.
*
* Returns: 1 always
* Args: ctx: pointer to a context object
* In/Out: pubkey: pointer to the public key to be negated.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_negate(
const secp256k1_context* ctx,
secp256k1_pubkey *pubkey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
/** Tweak a secret key by adding tweak to it.
*
* Returns: 0 if the arguments are invalid or the resulting secret key would be
* invalid (only when the tweak is the negation of the secret key). 1
* otherwise.
* Args: ctx: pointer to a context object.
* In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
* invalid according to secp256k1_ec_seckey_verify, this
* function returns 0. seckey will be set to some unspecified
* value if this function returns 0.
* In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
* secp256k1_ec_seckey_verify, this function returns 0. For
* uniformly random 32-byte arrays the chance of being invalid
* is negligible (around 1 in 2^128).
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_add(
const secp256k1_context* ctx,
unsigned char *seckey,
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Same as secp256k1_ec_seckey_tweak_add, but DEPRECATED. Will be removed in
* future versions. */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_add(
const secp256k1_context* ctx,
unsigned char *seckey,
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3)
SECP256K1_DEPRECATED("Use secp256k1_ec_seckey_tweak_add instead");
/** Tweak a public key by adding tweak times the generator to it.
*
* Returns: 0 if the arguments are invalid or the resulting public key would be
* invalid (only when the tweak is the negation of the corresponding
* secret key). 1 otherwise.
* Args: ctx: pointer to a context object.
* In/Out: pubkey: pointer to a public key object. pubkey will be set to an
* invalid value if this function returns 0.
* In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
* secp256k1_ec_seckey_verify, this function returns 0. For
* uniformly random 32-byte arrays the chance of being invalid
* is negligible (around 1 in 2^128).
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
const secp256k1_context* ctx,
secp256k1_pubkey *pubkey,
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Tweak a secret key by multiplying it by a tweak.
*
* Returns: 0 if the arguments are invalid. 1 otherwise.
* Args: ctx: pointer to a context object.
* In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
* invalid according to secp256k1_ec_seckey_verify, this
* function returns 0. seckey will be set to some unspecified
* value if this function returns 0.
* In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
* secp256k1_ec_seckey_verify, this function returns 0. For
* uniformly random 32-byte arrays the chance of being invalid
* is negligible (around 1 in 2^128).
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_mul(
const secp256k1_context* ctx,
unsigned char *seckey,
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Same as secp256k1_ec_seckey_tweak_mul, but DEPRECATED. Will be removed in
* future versions. */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_mul(
const secp256k1_context* ctx,
unsigned char *seckey,
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3)
SECP256K1_DEPRECATED("Use secp256k1_ec_seckey_tweak_mul instead");
/** Tweak a public key by multiplying it by a tweak value.
*
* Returns: 0 if the arguments are invalid. 1 otherwise.
* Args: ctx: pointer to a context object.
* In/Out: pubkey: pointer to a public key object. pubkey will be set to an
* invalid value if this function returns 0.
* In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
* secp256k1_ec_seckey_verify, this function returns 0. For
* uniformly random 32-byte arrays the chance of being invalid
* is negligible (around 1 in 2^128).
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
const secp256k1_context* ctx,
secp256k1_pubkey *pubkey,
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Randomizes the context to provide enhanced protection against side-channel leakage.
*
* Returns: 1: randomization successful (or called on copy of secp256k1_context_static)
* 0: error
* Args: ctx: pointer to a context object.
* In: seed32: pointer to a 32-byte random seed (NULL resets to initial state)
*
* While secp256k1 code is written and tested to be constant-time no matter what
* secret values are, it is possible that a compiler may output code which is not,
* and also that the CPU may not emit the same radio frequencies or draw the same
* amount of power for all values. Randomization of the context shields against
* side-channel observations which aim to exploit secret-dependent behaviour in
* certain computations which involve secret keys.
*
* It is highly recommended to call this function on contexts returned from
* secp256k1_context_create or secp256k1_context_clone (or from the corresponding
* functions in secp256k1_preallocated.h) before using these contexts to call API
* functions that perform computations involving secret keys, e.g., signing and
* public key generation. It is possible to call this function more than once on
* the same context, and doing so before every few computations involving secret
* keys is recommended as a defense-in-depth measure.
*
* Currently, the random seed is mainly used for blinding multiplications of a
* secret scalar with the elliptic curve base point. Multiplications of this
* kind are performed by exactly those API functions which are documented to
* require a context that is not the secp256k1_context_static. As a rule of thumb,
* these are all functions which take a secret key (or a keypair) as an input.
* A notable exception to that rule is the ECDH module, which relies on a different
* kind of elliptic curve point multiplication and thus does not benefit from
* enhanced protection against side-channel leakage currently.
*
* It is safe to call this function on a copy of secp256k1_context_static in writable
* memory (e.g., obtained via secp256k1_context_clone). In that case, this
* function is guaranteed to return 1, but the call will have no effect because
* the static context (or a copy thereof) is not meant to be randomized.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize(
secp256k1_context* ctx,
const unsigned char *seed32
) SECP256K1_ARG_NONNULL(1);
/** Add a number of public keys together.
*
* Returns: 1: the sum of the public keys is valid.
* 0: the sum of the public keys is not valid.
* Args: ctx: pointer to a context object.
* Out: out: pointer to a public key object for placing the resulting public key.
* In: ins: pointer to array of pointers to public keys.
* n: the number of public keys to add together (must be at least 1).
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_combine(
const secp256k1_context* ctx,
secp256k1_pubkey *out,
const secp256k1_pubkey * const * ins,
size_t n
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Compute a tagged hash as defined in BIP-340.
*
* This is useful for creating a message hash and achieving domain separation
* through an application-specific tag. This function returns
* SHA256(SHA256(tag)||SHA256(tag)||msg). Therefore, tagged hash
* implementations optimized for a specific tag can precompute the SHA256 state
* after hashing the tag hashes.
*
* Returns: 1 always.
* Args: ctx: pointer to a context object
* Out: hash32: pointer to a 32-byte array to store the resulting hash
* In: tag: pointer to an array containing the tag
* taglen: length of the tag array
* msg: pointer to an array containing the message
* msglen: length of the message array
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_tagged_sha256(
const secp256k1_context* ctx,
unsigned char *hash32,
const unsigned char *tag,
size_t taglen,
const unsigned char *msg,
size_t msglen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(5);
#ifdef __cplusplus
}
#endif
#endif /* SECP256K1_H */
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