#ifndef SECP256K1_H #define SECP256K1_H #ifdef __cplusplus extern "C" { #endif #include /** 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 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 secp256k1_pubkey { unsigned char data[64]; } secp256k1_pubkey; /** Opaque data structure 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 secp256k1_ecdsa_signature { 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 /* 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 /* Symbol visibility. */ #if defined(_WIN32) /* GCC for Windows (e.g., MinGW) accepts the __declspec syntax * for MSVC compatibility. A __declspec declaration implies (but is not * exactly equivalent to) __attribute__ ((visibility("default"))), and so we * actually want __declspec even on GCC, see "Microsoft Windows Function * Attributes" in the GCC manual and the recommendations in * https://gcc.gnu.org/wiki/Visibility. */ # if defined(SECP256K1_BUILD) # if defined(DLL_EXPORT) || defined(SECP256K1_DLL_EXPORT) /* Building libsecp256k1 as a DLL. * 1. If using Libtool, it defines DLL_EXPORT automatically. * 2. In other cases, SECP256K1_DLL_EXPORT must be defined. */ # define SECP256K1_API extern __declspec (dllexport) # else /* Building libsecp256k1 as a static library on Windows. * No declspec is needed, and so we would want the non-Windows-specific * logic below take care of this case. However, this may result in setting * __attribute__ ((visibility("default"))), which is supposed to be a noop * on Windows but may trigger warnings when compiling with -flto due to a * bug in GCC, see * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116478 . */ # define SECP256K1_API extern # endif /* The user must define SECP256K1_STATIC when consuming libsecp256k1 as a static * library on Windows. */ # elif !defined(SECP256K1_STATIC) /* Consuming libsecp256k1 as a DLL. */ # define SECP256K1_API extern __declspec (dllimport) # endif #endif #ifndef SECP256K1_API /* All cases not captured by the Windows-specific logic. */ # if defined(__GNUC__) && (__GNUC__ >= 4) && defined(SECP256K1_BUILD) /* Building libsecp256k1 using GCC or compatible. */ # define SECP256K1_API extern __attribute__ ((visibility ("default"))) # else /* Fall back to standard C's extern. */ # define SECP256K1_API extern # 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 const secp256k1_context *secp256k1_context_static; /** Deprecated alias for secp256k1_context_static. */ SECP256K1_API 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: pointer to 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. * * Cloning secp256k1_context_static is not possible, and should not be emulated by * the caller (e.g., using memcpy). Create a new context instead. * * Returns: pointer to a newly created context object. * Args: ctx: pointer to a context to copy (not secp256k1_context_static). */ 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: pointer to a context to destroy, constructed using * secp256k1_context_create or secp256k1_context_clone * (i.e., not secp256k1_context_static). */ 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: pointer to a context object. * In: fun: 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: pointer to a context object. * In: fun: 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); /** 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: pointer to a 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: pointer to a context object. * Out: output: 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: pointer to an integer which is initially set to the * size of output, and is overwritten with the written * size. * In: pubkey: 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: pointer to a 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); /** Sort public keys using lexicographic (of compressed serialization) order * * Returns: 0 if the arguments are invalid. 1 otherwise. * * Args: ctx: pointer to a context object * In: pubkeys: array of pointers to pubkeys to sort * n_pubkeys: number of elements in the pubkeys array */ SECP256K1_API int secp256k1_ec_pubkey_sort( const secp256k1_context *ctx, const secp256k1_pubkey **pubkeys, size_t n_pubkeys ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2); /** Parse an ECDSA signature in compact (64 bytes) format. * * Returns: 1 when the signature could be parsed, 0 otherwise. * Args: ctx: pointer to a context object * Out: sig: pointer to a signature object * In: input64: 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: pointer to a context object * Out: sig: pointer to a signature object * In: input: 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: pointer to a context object * Out: output: pointer to an array to store the DER serialization * In/Out: outputlen: 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: 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: pointer to a context object * Out: output64: pointer to a 64-byte array to store the compact serialization * In: sig: 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: pointer to a 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: pointer to a context object * Out: sigout: 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: 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 const secp256k1_nonce_function secp256k1_nonce_function_rfc6979; /** A default safe nonce generation function (currently equal to secp256k1_nonce_function_rfc6979). */ SECP256K1_API 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 elliptic curve 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. However, if it does happen it should * be assumed that the randomness source is severely broken and there should * be no retry. * * 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, which must be valid according to * secp256k1_ec_seckey_verify or 32 zero bytes. For uniformly * random 32-byte tweaks, 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, which must be valid according to * secp256k1_ec_seckey_verify or 32 zero bytes. For uniformly * random 32-byte tweaks, 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 * 0: error * Args: ctx: pointer to a context object (not secp256k1_context_static). * 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. Randomization of the static * context secp256k1_context_static is not supported. * * 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 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. */ 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 */