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Diffstat (limited to 'include/secp256k1.h')
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diff --git a/include/secp256k1.h b/include/secp256k1.h new file mode 100644 index 0000000..f4053f2 --- /dev/null +++ b/include/secp256k1.h @@ -0,0 +1,909 @@ +#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 + +/* 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) +# 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 +# if defined(__GNUC__) && (__GNUC__ >= 4) && defined(SECP256K1_BUILD) + /* Building libsecp256k1 on non-Windows using GCC or compatible. */ +# define SECP256K1_API extern __attribute__ ((visibility ("default"))) +# else + /* All cases not captured above. */ +# 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); + +/** Create a secp256k1 scratch space object. + * + * Returns: a newly created scratch space. + * Args: ctx: pointer to a 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: pointer to a 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: 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); + +/** 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 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, 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 */ |