1 #ifndef SECP256K1_H
2 #define SECP256K1_H
3 4 #ifdef __cplusplus
5 extern "C" {
6 #endif
7 8 #include <stddef.h>
9 #include <stdint.h>
10 11 /** Unless explicitly stated all pointer arguments must not be NULL.
12 *
13 * The following rules specify the order of arguments in API calls:
14 *
15 * 1. Context pointers go first, followed by output arguments, combined
16 * output/input arguments, and finally input-only arguments.
17 * 2. Array lengths always immediately follow the argument whose length
18 * they describe, even if this violates rule 1.
19 * 3. Within the OUT/OUTIN/IN groups, pointers to data that is typically generated
20 * later go first. This means: signatures, public nonces, secret nonces,
21 * messages, public keys, secret keys, tweaks.
22 * 4. Arguments that are not data pointers go last, from more complex to less
23 * complex: function pointers, algorithm names, messages, void pointers,
24 * counts, flags, booleans.
25 * 5. Opaque data pointers follow the function pointer they are to be passed to.
26 */
27 28 /** Opaque data structure that holds context information
29 *
30 * The primary purpose of context objects is to store randomization data for
31 * enhanced protection against side-channel leakage. This protection is only
32 * effective if the context is randomized after its creation. See
33 * secp256k1_context_create for creation of contexts and
34 * secp256k1_context_randomize for randomization.
35 *
36 * A secondary purpose of context objects is to store pointers to callback
37 * functions that the library will call when certain error states arise. See
38 * secp256k1_context_set_error_callback as well as
39 * secp256k1_context_set_illegal_callback for details. Future library versions
40 * may use context objects for additional purposes.
41 *
42 * A constructed context can safely be used from multiple threads
43 * simultaneously, but API calls that take a non-const pointer to a context
44 * need exclusive access to it. In particular this is the case for
45 * secp256k1_context_destroy, secp256k1_context_preallocated_destroy,
46 * and secp256k1_context_randomize.
47 *
48 * Regarding randomization, either do it once at creation time (in which case
49 * you do not need any locking for the other calls), or use a read-write lock.
50 */
51 typedef struct secp256k1_context_struct secp256k1_context;
52 53 /** Opaque data structure that holds a parsed and valid public key.
54 *
55 * The exact representation of data inside is implementation defined and not
56 * guaranteed to be portable between different platforms or versions. It is
57 * however guaranteed to be 64 bytes in size, and can be safely copied/moved.
58 * If you need to convert to a format suitable for storage or transmission,
59 * use secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse. To
60 * compare keys, use secp256k1_ec_pubkey_cmp.
61 */
62 typedef struct secp256k1_pubkey {
63 unsigned char data[64];
64 } secp256k1_pubkey;
65 66 /** Opaque data structure that holds a parsed ECDSA signature.
67 *
68 * The exact representation of data inside is implementation defined and not
69 * guaranteed to be portable between different platforms or versions. It is
70 * however guaranteed to be 64 bytes in size, and can be safely copied/moved.
71 * If you need to convert to a format suitable for storage, transmission, or
72 * comparison, use the secp256k1_ecdsa_signature_serialize_* and
73 * secp256k1_ecdsa_signature_parse_* functions.
74 */
75 typedef struct secp256k1_ecdsa_signature {
76 unsigned char data[64];
77 } secp256k1_ecdsa_signature;
78 79 /** A pointer to a function to deterministically generate a nonce.
80 *
81 * Returns: 1 if a nonce was successfully generated. 0 will cause signing to fail.
82 * Out: nonce32: pointer to a 32-byte array to be filled by the function.
83 * In: msg32: the 32-byte message hash being verified (will not be NULL)
84 * key32: pointer to a 32-byte secret key (will not be NULL)
85 * algo16: pointer to a 16-byte array describing the signature
86 * algorithm (will be NULL for ECDSA for compatibility).
87 * data: Arbitrary data pointer that is passed through.
88 * attempt: how many iterations we have tried to find a nonce.
89 * This will almost always be 0, but different attempt values
90 * are required to result in a different nonce.
91 *
92 * Except for test cases, this function should compute some cryptographic hash of
93 * the message, the algorithm, the key and the attempt.
94 */
95 typedef int (*secp256k1_nonce_function)(
96 unsigned char *nonce32,
97 const unsigned char *msg32,
98 const unsigned char *key32,
99 const unsigned char *algo16,
100 void *data,
101 unsigned int attempt
102 );
103 104 # if !defined(SECP256K1_GNUC_PREREQ)
105 # if defined(__GNUC__)&&defined(__GNUC_MINOR__)
106 # define SECP256K1_GNUC_PREREQ(_maj,_min) \
107 ((__GNUC__<<16)+__GNUC_MINOR__>=((_maj)<<16)+(_min))
108 # else
109 # define SECP256K1_GNUC_PREREQ(_maj,_min) 0
110 # endif
111 # endif
112 113 /* When this header is used at build-time the SECP256K1_BUILD define needs to be set
114 * to correctly setup export attributes and nullness checks. This is normally done
115 * by secp256k1.c but to guard against this header being included before secp256k1.c
116 * has had a chance to set the define (e.g. via test harnesses that just includes
117 * secp256k1.c) we set SECP256K1_NO_BUILD when this header is processed without the
118 * BUILD define so this condition can be caught.
119 */
120 #ifndef SECP256K1_BUILD
121 # define SECP256K1_NO_BUILD
122 #endif
123 124 /* Symbol visibility. */
125 #if !defined(SECP256K1_API) && defined(SECP256K1_NO_API_VISIBILITY_ATTRIBUTES)
126 /* The user has requested that we don't specify visibility attributes in
127 * the public API.
128 *
129 * Since all our non-API declarations use the static qualifier, this means
130 * that the user can use -fvisibility=<value> to set the visibility of the
131 * API symbols. For instance, -fvisibility=hidden can be useful *even for
132 * the API symbols*, e.g., when building a static library which is linked
133 * into a shared library, and the latter should not re-export the
134 * libsecp256k1 API.
135 *
136 * While visibility is a concept that applies only to shared libraries,
137 * setting visibility will still make a difference when building a static
138 * library: the visibility settings will be stored in the static library,
139 * solely for the potential case that the static library will be linked into
140 * a shared library. In that case, the stored visibility settings will
141 * resurface and be honored for the shared library. */
142 # define SECP256K1_API extern
143 #endif
144 #if !defined(SECP256K1_API)
145 # if defined(SECP256K1_BUILD)
146 /* On Windows, assume a shared library only if explicitly requested.
147 * 1. If using Libtool, it defines DLL_EXPORT automatically.
148 * 2. In other cases, SECP256K1_DLL_EXPORT must be defined. */
149 # if defined(_WIN32) && (defined(SECP256K1_DLL_EXPORT) || defined(DLL_EXPORT))
150 /* GCC for Windows (e.g., MinGW) accepts the __declspec syntax for
151 * MSVC compatibility. A __declspec declaration implies (but is not
152 * exactly equivalent to) __attribute__ ((visibility("default"))),
153 * and so we actually want __declspec even on GCC, see "Microsoft
154 * Windows Function Attributes" in the GCC manual and the
155 * recommendations in https://gcc.gnu.org/wiki/Visibility . */
156 # define SECP256K1_API extern __declspec(dllexport)
157 /* Avoid __attribute__ ((visibility("default"))) on Windows to get rid
158 * of warnings when compiling with -flto due to a bug in GCC, see
159 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116478 . */
160 # elif !defined(_WIN32) && defined (__GNUC__) && (__GNUC__ >= 4)
161 # define SECP256K1_API extern __attribute__ ((visibility("default")))
162 # else
163 # define SECP256K1_API extern
164 # endif
165 # else
166 /* On Windows, SECP256K1_STATIC must be defined when consuming
167 * libsecp256k1 as a static library. Note that SECP256K1_STATIC is a
168 * "consumer-only" macro, and it has no meaning when building
169 * libsecp256k1. */
170 # if defined(_WIN32) && !defined(SECP256K1_STATIC)
171 # define SECP256K1_API extern __declspec(dllimport)
172 # else
173 # define SECP256K1_API extern
174 # endif
175 # endif
176 #endif
177 178 /* Warning attributes
179 * NONNULL is not used if SECP256K1_BUILD is set to avoid the compiler optimizing out
180 * some paranoid null checks. */
181 # if defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
182 # define SECP256K1_WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
183 # else
184 # define SECP256K1_WARN_UNUSED_RESULT
185 # endif
186 # if !defined(SECP256K1_BUILD) && defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
187 # define SECP256K1_ARG_NONNULL(_x) __attribute__ ((__nonnull__(_x)))
188 # else
189 # define SECP256K1_ARG_NONNULL(_x)
190 # endif
191 192 /* Attribute for marking functions, types, and variables as deprecated */
193 #if !defined(SECP256K1_BUILD) && defined(__has_attribute)
194 # if __has_attribute(__deprecated__)
195 # define SECP256K1_DEPRECATED(_msg) __attribute__ ((__deprecated__(_msg)))
196 # else
197 # define SECP256K1_DEPRECATED(_msg)
198 # endif
199 #else
200 # define SECP256K1_DEPRECATED(_msg)
201 #endif
202 203 /* All flags' lower 8 bits indicate what they're for. Do not use directly. */
204 #define SECP256K1_FLAGS_TYPE_MASK ((1 << 8) - 1)
205 #define SECP256K1_FLAGS_TYPE_CONTEXT (1 << 0)
206 #define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
207 /* The higher bits contain the actual data. Do not use directly. */
208 #define SECP256K1_FLAGS_BIT_CONTEXT_VERIFY (1 << 8)
209 #define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9)
210 #define SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY (1 << 10)
211 #define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)
212 213 /** Context flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and
214 * secp256k1_context_preallocated_create. */
215 #define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)
216 217 /** Deprecated context flags. These flags are treated equivalent to SECP256K1_CONTEXT_NONE. */
218 #define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY)
219 #define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN)
220 221 /* Testing flag. Do not use. */
222 #define SECP256K1_CONTEXT_DECLASSIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY)
223 224 /** Flag to pass to secp256k1_ec_pubkey_serialize. */
225 #define SECP256K1_EC_COMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION | SECP256K1_FLAGS_BIT_COMPRESSION)
226 #define SECP256K1_EC_UNCOMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION)
227 228 /** Prefix byte used to tag various encoded curvepoints for specific purposes */
229 #define SECP256K1_TAG_PUBKEY_EVEN 0x02
230 #define SECP256K1_TAG_PUBKEY_ODD 0x03
231 #define SECP256K1_TAG_PUBKEY_UNCOMPRESSED 0x04
232 #define SECP256K1_TAG_PUBKEY_HYBRID_EVEN 0x06
233 #define SECP256K1_TAG_PUBKEY_HYBRID_ODD 0x07
234 235 /** A built-in constant secp256k1 context object with static storage duration, to be
236 * used in conjunction with secp256k1_selftest.
237 *
238 * This context object offers *only limited functionality* , i.e., it cannot be used
239 * for API functions that perform computations involving secret keys, e.g., signing
240 * and public key generation. If this restriction applies to a specific API function,
241 * it is mentioned in its documentation. See secp256k1_context_create if you need a
242 * full context object that supports all functionality offered by the library.
243 *
244 * It is highly recommended to call secp256k1_selftest before using this context.
245 */
246 SECP256K1_API const secp256k1_context * const secp256k1_context_static;
247 248 /** Deprecated alias for secp256k1_context_static. */
249 SECP256K1_API const secp256k1_context * const secp256k1_context_no_precomp
250 SECP256K1_DEPRECATED("Use secp256k1_context_static instead");
251 252 /** Perform basic self tests (to be used in conjunction with secp256k1_context_static)
253 *
254 * This function performs self tests that detect some serious usage errors and
255 * similar conditions, e.g., when the library is compiled for the wrong endianness.
256 * This is a last resort measure to be used in production. The performed tests are
257 * very rudimentary and are not intended as a replacement for running the test
258 * binaries.
259 *
260 * It is highly recommended to call this before using secp256k1_context_static.
261 * It is not necessary to call this function before using a context created with
262 * secp256k1_context_create (or secp256k1_context_preallocated_create), which will
263 * take care of performing the self tests.
264 *
265 * If the tests fail, this function will call the default error callback to abort the
266 * program (see secp256k1_context_set_error_callback).
267 */
268 SECP256K1_API void secp256k1_selftest(void);
269 270 271 /** Create a secp256k1 context object (in dynamically allocated memory).
272 *
273 * This function uses malloc to allocate memory. It is guaranteed that malloc is
274 * called at most once for every call of this function. If you need to avoid dynamic
275 * memory allocation entirely, see secp256k1_context_static and the functions in
276 * secp256k1_preallocated.h.
277 *
278 * Returns: pointer to a newly created context object.
279 * In: flags: Always set to SECP256K1_CONTEXT_NONE (see below).
280 *
281 * The only valid non-deprecated flag in recent library versions is
282 * SECP256K1_CONTEXT_NONE, which will create a context sufficient for all functionality
283 * offered by the library. All other (deprecated) flags will be treated as equivalent
284 * to the SECP256K1_CONTEXT_NONE flag. Though the flags parameter primarily exists for
285 * historical reasons, future versions of the library may introduce new flags.
286 *
287 * If the context is intended to be used for API functions that perform computations
288 * involving secret keys, e.g., signing and public key generation, then it is highly
289 * recommended to call secp256k1_context_randomize on the context before calling
290 * those API functions. This will provide enhanced protection against side-channel
291 * leakage, see secp256k1_context_randomize for details.
292 *
293 * Do not create a new context object for each operation, as construction and
294 * randomization can take non-negligible time.
295 */
296 SECP256K1_API secp256k1_context *secp256k1_context_create(
297 unsigned int flags
298 ) SECP256K1_WARN_UNUSED_RESULT;
299 300 /** Copy a secp256k1 context object (into dynamically allocated memory).
301 *
302 * This function uses malloc to allocate memory. It is guaranteed that malloc is
303 * called at most once for every call of this function. If you need to avoid dynamic
304 * memory allocation entirely, see the functions in secp256k1_preallocated.h.
305 *
306 * Cloning secp256k1_context_static is not possible, and should not be emulated by
307 * the caller (e.g., using memcpy). Create a new context instead.
308 *
309 * Returns: pointer to a newly created context object.
310 * Args: ctx: pointer to a context to copy (not secp256k1_context_static).
311 */
312 SECP256K1_API secp256k1_context *secp256k1_context_clone(
313 const secp256k1_context *ctx
314 ) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT;
315 316 /** Destroy a secp256k1 context object (created in dynamically allocated memory).
317 *
318 * The context pointer may not be used afterwards.
319 *
320 * The context to destroy must have been created using secp256k1_context_create
321 * or secp256k1_context_clone. If the context has instead been created using
322 * secp256k1_context_preallocated_create or secp256k1_context_preallocated_clone, the
323 * behaviour is undefined. In that case, secp256k1_context_preallocated_destroy must
324 * be used instead.
325 *
326 * Args: ctx: pointer to a context to destroy, constructed using
327 * secp256k1_context_create or secp256k1_context_clone
328 * (i.e., not secp256k1_context_static).
329 */
330 SECP256K1_API void secp256k1_context_destroy(
331 secp256k1_context *ctx
332 ) SECP256K1_ARG_NONNULL(1);
333 334 /** Set a callback function to be called when an illegal argument is passed to
335 * an API call. It will only trigger for violations that are mentioned
336 * explicitly in the header.
337 *
338 * The philosophy is that these shouldn't be dealt with through a specific
339 * return value, as calling code should not have branches to deal with the case
340 * that this code itself is broken.
341 *
342 * On the other hand, during debug stage, one would want to be informed about
343 * such mistakes, and the default (crashing) may be inadvisable. Should this
344 * callback return instead of crashing, the return value and output arguments
345 * of the API function call are undefined. Moreover, the same API call may
346 * trigger the callback again in this case.
347 *
348 * When this function has not been called (or called with fun==NULL), then the
349 * default callback will be used. The library provides a default callback which
350 * writes the message to stderr and calls abort. This default callback can be
351 * replaced at link time if the preprocessor macro
352 * USE_EXTERNAL_DEFAULT_CALLBACKS is defined, which is the case if the build
353 * has been configured with --enable-external-default-callbacks (GNU Autotools) or
354 * -DSECP256K1_USE_EXTERNAL_DEFAULT_CALLBACKS=ON (CMake). Then the
355 * following two symbols must be provided to link against:
356 * - void secp256k1_default_illegal_callback_fn(const char *message, void *data);
357 * - void secp256k1_default_error_callback_fn(const char *message, void *data);
358 * The library may call a default callback even before a proper callback data
359 * pointer could have been set using secp256k1_context_set_illegal_callback or
360 * secp256k1_context_set_error_callback, e.g., when the creation of a context
361 * fails. In this case, the corresponding default callback will be called with
362 * the data pointer argument set to NULL.
363 *
364 * Args: ctx: pointer to a context object.
365 * In: fun: pointer to a function to call when an illegal argument is
366 * passed to the API, taking a message and an opaque pointer.
367 * (NULL restores the default callback.)
368 * data: the opaque pointer to pass to fun above, must be NULL for the
369 * default callback.
370 *
371 * See also secp256k1_context_set_error_callback.
372 */
373 SECP256K1_API void secp256k1_context_set_illegal_callback(
374 secp256k1_context *ctx,
375 void (*fun)(const char *message, void *data),
376 const void *data
377 ) SECP256K1_ARG_NONNULL(1);
378 379 /** Set a callback function to be called when an internal consistency check
380 * fails.
381 *
382 * The default callback writes an error message to stderr and calls abort
383 * to abort the program.
384 *
385 * This can only trigger in case of a hardware failure, miscompilation,
386 * memory corruption, serious bug in the library, or other error that would
387 * result in undefined behaviour. It will not trigger due to mere
388 * incorrect usage of the API (see secp256k1_context_set_illegal_callback
389 * for that). After this callback returns, anything may happen, including
390 * crashing.
391 *
392 * Args: ctx: pointer to a context object.
393 * In: fun: pointer to a function to call when an internal error occurs,
394 * taking a message and an opaque pointer (NULL restores the
395 * default callback, see secp256k1_context_set_illegal_callback
396 * for details).
397 * data: the opaque pointer to pass to fun above, must be NULL for the
398 * default callback.
399 *
400 * See also secp256k1_context_set_illegal_callback.
401 */
402 SECP256K1_API void secp256k1_context_set_error_callback(
403 secp256k1_context *ctx,
404 void (*fun)(const char *message, void *data),
405 const void *data
406 ) SECP256K1_ARG_NONNULL(1);
407 408 /** A pointer to a function implementing SHA256's internal compression function.
409 *
410 * This function processes one or more contiguous 64-byte message blocks and
411 * updates the internal SHA256 state accordingly. The function is not responsible
412 * for counting consumed blocks or bytes, nor for performing padding.
413 *
414 * In/Out: state: pointer to eight 32-bit words representing the current internal state;
415 * the state is updated in place.
416 * In: blocks64: pointer to concatenation of n_blocks blocks, of 64 bytes each.
417 * no alignment guarantees are made for this pointer.
418 * n_blocks: number of contiguous 64-byte blocks to process.
419 */
420 typedef void (*secp256k1_sha256_compression_function)(
421 uint32_t *state,
422 const unsigned char *blocks64,
423 size_t n_blocks
424 );
425 426 /**
427 * Set a callback function to override the internal SHA256 compression function.
428 *
429 * This installs a function to replace the built-in block-compression
430 * step used by the library's internal SHA256 implementation.
431 * The provided callback must exactly implement the effect of n_blocks
432 * repeated applications of the SHA256 compression function.
433 *
434 * This API exists to support environments that wish to route the
435 * SHA256 compression step through a hardware-accelerated or otherwise
436 * specialized implementation. It is NOT meant for replacing SHA256
437 * with a different hash function.
438 *
439 * Args: ctx: pointer to a context object.
440 * In: fn_compression: pointer to a function implementing the compression function;
441 * passing NULL restores the default implementation.
442 */
443 SECP256K1_API void secp256k1_context_set_sha256_compression(
444 secp256k1_context *ctx,
445 secp256k1_sha256_compression_function fn_compression
446 ) SECP256K1_ARG_NONNULL(1);
447 448 /** Parse a variable-length public key into the pubkey object.
449 *
450 * Returns: 1 if the public key was fully valid.
451 * 0 if the public key could not be parsed or is invalid.
452 * Args: ctx: pointer to a context object.
453 * Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to a
454 * parsed version of input. If not, its value is undefined.
455 * In: input: pointer to a serialized public key
456 * inputlen: length of the array pointed to by input
457 *
458 * This function supports parsing compressed (33 bytes, header byte 0x02 or
459 * 0x03), uncompressed (65 bytes, header byte 0x04), or hybrid (65 bytes, header
460 * byte 0x06 or 0x07) format public keys.
461 */
462 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_parse(
463 const secp256k1_context *ctx,
464 secp256k1_pubkey *pubkey,
465 const unsigned char *input,
466 size_t inputlen
467 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
468 469 /** Serialize a pubkey object into a serialized byte sequence.
470 *
471 * Returns: 1 always.
472 * Args: ctx: pointer to a context object.
473 * Out: output: pointer to a 65-byte (if compressed==0) or 33-byte (if
474 * compressed==1) byte array to place the serialized key
475 * in.
476 * In/Out: outputlen: pointer to an integer which is initially set to the
477 * size of output, and is overwritten with the written
478 * size.
479 * In: pubkey: pointer to a secp256k1_pubkey containing an
480 * initialized public key.
481 * flags: SECP256K1_EC_COMPRESSED if serialization should be in
482 * compressed format, otherwise SECP256K1_EC_UNCOMPRESSED.
483 */
484 SECP256K1_API int secp256k1_ec_pubkey_serialize(
485 const secp256k1_context *ctx,
486 unsigned char *output,
487 size_t *outputlen,
488 const secp256k1_pubkey *pubkey,
489 unsigned int flags
490 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
491 492 /** Compare two public keys using lexicographic (of compressed serialization) order
493 *
494 * Returns: <0 if the first public key is less than the second
495 * >0 if the first public key is greater than the second
496 * 0 if the two public keys are equal
497 * Args: ctx: pointer to a context object
498 * In: pubkey1: first public key to compare
499 * pubkey2: second public key to compare
500 */
501 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_cmp(
502 const secp256k1_context *ctx,
503 const secp256k1_pubkey *pubkey1,
504 const secp256k1_pubkey *pubkey2
505 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
506 507 /** Sort public keys using lexicographic (of compressed serialization) order
508 *
509 * Returns: 0 if the arguments are invalid. 1 otherwise.
510 *
511 * Args: ctx: pointer to a context object
512 * In: pubkeys: array of pointers to pubkeys to sort
513 * n_pubkeys: number of elements in the pubkeys array
514 */
515 SECP256K1_API int secp256k1_ec_pubkey_sort(
516 const secp256k1_context *ctx,
517 const secp256k1_pubkey **pubkeys,
518 size_t n_pubkeys
519 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
520 521 /** Parse an ECDSA signature in compact (64 bytes) format.
522 *
523 * Returns: 1 when the signature could be parsed, 0 otherwise.
524 * Args: ctx: pointer to a context object
525 * Out: sig: pointer to a signature object
526 * In: input64: pointer to the 64-byte array to parse
527 *
528 * The signature must consist of a 32-byte big endian R value, followed by a
529 * 32-byte big endian S value. If R or S fall outside of [0..order-1], the
530 * encoding is invalid. R and S with value 0 are allowed in the encoding.
531 *
532 * After the call, sig will always be initialized. If parsing failed or R or
533 * S are zero, the resulting sig value is guaranteed to fail verification for
534 * any message and public key.
535 */
536 SECP256K1_API int secp256k1_ecdsa_signature_parse_compact(
537 const secp256k1_context *ctx,
538 secp256k1_ecdsa_signature *sig,
539 const unsigned char *input64
540 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
541 542 /** Parse a DER ECDSA signature.
543 *
544 * Returns: 1 when the signature could be parsed, 0 otherwise.
545 * Args: ctx: pointer to a context object
546 * Out: sig: pointer to a signature object
547 * In: input: pointer to the signature to be parsed
548 * inputlen: the length of the array pointed to be input
549 *
550 * This function will accept any valid DER encoded signature, even if the
551 * encoded numbers are out of range.
552 *
553 * After the call, sig will always be initialized. If parsing failed or the
554 * encoded numbers are out of range, signature verification with it is
555 * guaranteed to fail for every message and public key.
556 */
557 SECP256K1_API int secp256k1_ecdsa_signature_parse_der(
558 const secp256k1_context *ctx,
559 secp256k1_ecdsa_signature *sig,
560 const unsigned char *input,
561 size_t inputlen
562 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
563 564 /** Serialize an ECDSA signature in DER format.
565 *
566 * Returns: 1 if enough space was available to serialize, 0 otherwise
567 * Args: ctx: pointer to a context object
568 * Out: output: pointer to an array to store the DER serialization
569 * In/Out: outputlen: pointer to a length integer. Initially, this integer
570 * should be set to the length of output. After the call
571 * it will be set to the length of the serialization (even
572 * if 0 was returned).
573 * In: sig: pointer to an initialized signature object
574 */
575 SECP256K1_API int secp256k1_ecdsa_signature_serialize_der(
576 const secp256k1_context *ctx,
577 unsigned char *output,
578 size_t *outputlen,
579 const secp256k1_ecdsa_signature *sig
580 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
581 582 /** Serialize an ECDSA signature in compact (64 byte) format.
583 *
584 * Returns: 1
585 * Args: ctx: pointer to a context object
586 * Out: output64: pointer to a 64-byte array to store the compact serialization
587 * In: sig: pointer to an initialized signature object
588 *
589 * See secp256k1_ecdsa_signature_parse_compact for details about the encoding.
590 */
591 SECP256K1_API int secp256k1_ecdsa_signature_serialize_compact(
592 const secp256k1_context *ctx,
593 unsigned char *output64,
594 const secp256k1_ecdsa_signature *sig
595 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
596 597 /** Verify an ECDSA signature.
598 *
599 * Returns: 1: correct signature
600 * 0: incorrect or unparseable signature
601 * Args: ctx: pointer to a context object
602 * In: sig: the signature being verified.
603 * msghash32: the 32-byte message hash being verified.
604 * The verifier must make sure to apply a cryptographic
605 * hash function to the message by itself and not accept an
606 * msghash32 value directly. Otherwise, it would be easy to
607 * create a "valid" signature without knowledge of the
608 * secret key. See also
609 * https://bitcoin.stackexchange.com/a/81116/35586 for more
610 * background on this topic.
611 * pubkey: pointer to an initialized public key to verify with.
612 *
613 * To avoid accepting malleable signatures, only ECDSA signatures in lower-S
614 * form are accepted.
615 *
616 * If you need to accept ECDSA signatures from sources that do not obey this
617 * rule, apply secp256k1_ecdsa_signature_normalize to the signature prior to
618 * verification, but be aware that doing so results in malleable signatures.
619 *
620 * For details, see the comments for that function.
621 */
622 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify(
623 const secp256k1_context *ctx,
624 const secp256k1_ecdsa_signature *sig,
625 const unsigned char *msghash32,
626 const secp256k1_pubkey *pubkey
627 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
628 629 /** Convert a signature to a normalized lower-S form.
630 *
631 * Returns: 1 if sigin was not normalized, 0 if it already was.
632 * Args: ctx: pointer to a context object
633 * Out: sigout: pointer to a signature to fill with the normalized form,
634 * or copy if the input was already normalized. (can be NULL if
635 * you're only interested in whether the input was already
636 * normalized).
637 * In: sigin: pointer to a signature to check/normalize (can be identical to sigout)
638 *
639 * With ECDSA a third-party can forge a second distinct signature of the same
640 * message, given a single initial signature, but without knowing the key. This
641 * is done by negating the S value modulo the order of the curve, 'flipping'
642 * the sign of the random point R which is not included in the signature.
643 *
644 * Forgery of the same message isn't universally problematic, but in systems
645 * where message malleability or uniqueness of signatures is important this can
646 * cause issues. This forgery can be blocked by all verifiers forcing signers
647 * to use a normalized form.
648 *
649 * The lower-S form reduces the size of signatures slightly on average when
650 * variable length encodings (such as DER) are used and is cheap to verify,
651 * making it a good choice. Security of always using lower-S is assured because
652 * anyone can trivially modify a signature after the fact to enforce this
653 * property anyway.
654 *
655 * The lower S value is always between 0x1 and
656 * 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0,
657 * inclusive.
658 *
659 * No other forms of ECDSA malleability are known and none seem likely, but
660 * there is no formal proof that ECDSA, even with this additional restriction,
661 * is free of other malleability. Commonly used serialization schemes will also
662 * accept various non-unique encodings, so care should be taken when this
663 * property is required for an application.
664 *
665 * The secp256k1_ecdsa_sign function will by default create signatures in the
666 * lower-S form, and secp256k1_ecdsa_verify will not accept others. In case
667 * signatures come from a system that cannot enforce this property,
668 * secp256k1_ecdsa_signature_normalize must be called before verification.
669 */
670 SECP256K1_API int secp256k1_ecdsa_signature_normalize(
671 const secp256k1_context *ctx,
672 secp256k1_ecdsa_signature *sigout,
673 const secp256k1_ecdsa_signature *sigin
674 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(3);
675 676 /** An implementation of RFC6979 (using HMAC-SHA256) as nonce generation function.
677 * If a data pointer is passed, it is assumed to be a pointer to 32 bytes of
678 * extra entropy.
679 */
680 SECP256K1_API const secp256k1_nonce_function secp256k1_nonce_function_rfc6979;
681 682 /** A default safe nonce generation function (currently equal to secp256k1_nonce_function_rfc6979). */
683 SECP256K1_API const secp256k1_nonce_function secp256k1_nonce_function_default;
684 685 /** Create an ECDSA signature.
686 *
687 * Returns: 1: signature created
688 * 0: the nonce generation function failed, or the secret key was invalid.
689 * Args: ctx: pointer to a context object (not secp256k1_context_static).
690 * Out: sig: pointer to a signature object.
691 * In: msghash32: the 32-byte message hash being signed.
692 * seckey: pointer to a 32-byte secret key.
693 * noncefp: pointer to a nonce generation function. If NULL,
694 * secp256k1_nonce_function_default is used.
695 * ndata: pointer to arbitrary data used by the nonce generation function
696 * (can be NULL). If it is non-NULL and
697 * secp256k1_nonce_function_default is used, then ndata must be a
698 * pointer to 32-bytes of additional data.
699 *
700 * The created signature is always in lower-S form. See
701 * secp256k1_ecdsa_signature_normalize for more details.
702 */
703 SECP256K1_API int secp256k1_ecdsa_sign(
704 const secp256k1_context *ctx,
705 secp256k1_ecdsa_signature *sig,
706 const unsigned char *msghash32,
707 const unsigned char *seckey,
708 secp256k1_nonce_function noncefp,
709 const void *ndata
710 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
711 712 /** Verify an elliptic curve secret key.
713 *
714 * A secret key is valid if it is not 0 and less than the secp256k1 curve order
715 * when interpreted as an integer (most significant byte first). The
716 * probability of choosing a 32-byte string uniformly at random which is an
717 * invalid secret key is negligible. However, if it does happen it should
718 * be assumed that the randomness source is severely broken and there should
719 * be no retry.
720 *
721 * Returns: 1: secret key is valid
722 * 0: secret key is invalid
723 * Args: ctx: pointer to a context object.
724 * In: seckey: pointer to a 32-byte secret key.
725 */
726 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_verify(
727 const secp256k1_context *ctx,
728 const unsigned char *seckey
729 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
730 731 /** Compute the public key for a secret key.
732 *
733 * Returns: 1: secret was valid, public key stores.
734 * 0: secret was invalid, try again.
735 * Args: ctx: pointer to a context object (not secp256k1_context_static).
736 * Out: pubkey: pointer to the created public key.
737 * In: seckey: pointer to a 32-byte secret key.
738 */
739 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_create(
740 const secp256k1_context *ctx,
741 secp256k1_pubkey *pubkey,
742 const unsigned char *seckey
743 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
744 745 /** Negates a secret key in place.
746 *
747 * Returns: 0 if the given secret key is invalid according to
748 * secp256k1_ec_seckey_verify. 1 otherwise
749 * Args: ctx: pointer to a context object
750 * In/Out: seckey: pointer to the 32-byte secret key to be negated. If the
751 * secret key is invalid according to
752 * secp256k1_ec_seckey_verify, this function returns 0 and
753 * seckey will be set to some unspecified value.
754 */
755 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_negate(
756 const secp256k1_context *ctx,
757 unsigned char *seckey
758 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
759 760 /** Negates a public key in place.
761 *
762 * Returns: 1 always
763 * Args: ctx: pointer to a context object
764 * In/Out: pubkey: pointer to the public key to be negated.
765 */
766 SECP256K1_API int secp256k1_ec_pubkey_negate(
767 const secp256k1_context *ctx,
768 secp256k1_pubkey *pubkey
769 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
770 771 /** Tweak a secret key by adding tweak to it.
772 *
773 * Returns: 0 if the arguments are invalid or the resulting secret key would be
774 * invalid (only when the tweak is the negation of the secret key). 1
775 * otherwise.
776 * Args: ctx: pointer to a context object.
777 * In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
778 * invalid according to secp256k1_ec_seckey_verify, this
779 * function returns 0. seckey will be set to some unspecified
780 * value if this function returns 0.
781 * In: tweak32: pointer to a 32-byte tweak, which must be valid according to
782 * secp256k1_ec_seckey_verify or 32 zero bytes. For uniformly
783 * random 32-byte tweaks, the chance of being invalid is
784 * negligible (around 1 in 2^128).
785 */
786 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_add(
787 const secp256k1_context *ctx,
788 unsigned char *seckey,
789 const unsigned char *tweak32
790 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
791 792 /** Tweak a public key by adding tweak times the generator to it.
793 *
794 * Returns: 0 if the arguments are invalid or the resulting public key would be
795 * invalid (only when the tweak is the negation of the corresponding
796 * secret key). 1 otherwise.
797 * Args: ctx: pointer to a context object.
798 * In/Out: pubkey: pointer to a public key object. pubkey will be set to an
799 * invalid value if this function returns 0.
800 * In: tweak32: pointer to a 32-byte tweak, which must be valid according to
801 * secp256k1_ec_seckey_verify or 32 zero bytes. For uniformly
802 * random 32-byte tweaks, the chance of being invalid is
803 * negligible (around 1 in 2^128).
804 */
805 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
806 const secp256k1_context *ctx,
807 secp256k1_pubkey *pubkey,
808 const unsigned char *tweak32
809 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
810 811 /** Tweak a secret key by multiplying it by a tweak.
812 *
813 * Returns: 0 if the arguments are invalid. 1 otherwise.
814 * Args: ctx: pointer to a context object.
815 * In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
816 * invalid according to secp256k1_ec_seckey_verify, this
817 * function returns 0. seckey will be set to some unspecified
818 * value if this function returns 0.
819 * In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
820 * secp256k1_ec_seckey_verify, this function returns 0. For
821 * uniformly random 32-byte arrays the chance of being invalid
822 * is negligible (around 1 in 2^128).
823 */
824 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_mul(
825 const secp256k1_context *ctx,
826 unsigned char *seckey,
827 const unsigned char *tweak32
828 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
829 830 /** Tweak a public key by multiplying it by a tweak value.
831 *
832 * Returns: 0 if the arguments are invalid. 1 otherwise.
833 * Args: ctx: pointer to a context object.
834 * In/Out: pubkey: pointer to a public key object. pubkey will be set to an
835 * invalid value if this function returns 0.
836 * In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
837 * secp256k1_ec_seckey_verify, this function returns 0. For
838 * uniformly random 32-byte arrays the chance of being invalid
839 * is negligible (around 1 in 2^128).
840 */
841 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
842 const secp256k1_context *ctx,
843 secp256k1_pubkey *pubkey,
844 const unsigned char *tweak32
845 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
846 847 /** Randomizes the context to provide enhanced protection against side-channel leakage.
848 *
849 * Returns: 1: randomization successful
850 * 0: error
851 * Args: ctx: pointer to a context object (not secp256k1_context_static).
852 * In: seed32: pointer to a 32-byte random seed (NULL resets to initial state).
853 *
854 * While secp256k1 code is written and tested to be constant-time no matter what
855 * secret values are, it is possible that a compiler may output code which is not,
856 * and also that the CPU may not emit the same radio frequencies or draw the same
857 * amount of power for all values. Randomization of the context shields against
858 * side-channel observations which aim to exploit secret-dependent behaviour in
859 * certain computations which involve secret keys.
860 *
861 * It is highly recommended to call this function on contexts returned from
862 * secp256k1_context_create or secp256k1_context_clone (or from the corresponding
863 * functions in secp256k1_preallocated.h) before using these contexts to call API
864 * functions that perform computations involving secret keys, e.g., signing and
865 * public key generation. It is possible to call this function more than once on
866 * the same context, and doing so before every few computations involving secret
867 * keys is recommended as a defense-in-depth measure. Randomization of the static
868 * context secp256k1_context_static is not supported.
869 *
870 * Currently, the random seed is mainly used for blinding multiplications of a
871 * secret scalar with the elliptic curve base point. Multiplications of this
872 * kind are performed by exactly those API functions which are documented to
873 * require a context that is not secp256k1_context_static. As a rule of thumb,
874 * these are all functions which take a secret key (or a keypair) as an input.
875 * A notable exception to that rule is the ECDH module, which relies on a different
876 * kind of elliptic curve point multiplication and thus does not benefit from
877 * enhanced protection against side-channel leakage currently.
878 */
879 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize(
880 secp256k1_context *ctx,
881 const unsigned char *seed32
882 ) SECP256K1_ARG_NONNULL(1);
883 884 /** Add a number of public keys together.
885 *
886 * Returns: 1: the sum of the public keys is valid.
887 * 0: the sum of the public keys is not valid.
888 * Args: ctx: pointer to a context object.
889 * Out: out: pointer to a public key object for placing the resulting public key.
890 * In: ins: pointer to array of pointers to public keys.
891 * n: the number of public keys to add together (must be at least 1).
892 */
893 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_combine(
894 const secp256k1_context *ctx,
895 secp256k1_pubkey *out,
896 const secp256k1_pubkey * const *ins,
897 size_t n
898 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
899 900 /** Compute a tagged hash as defined in BIP-340.
901 *
902 * This is useful for creating a message hash and achieving domain separation
903 * through an application-specific tag. This function returns
904 * SHA256(SHA256(tag)||SHA256(tag)||msg). Therefore, tagged hash
905 * implementations optimized for a specific tag can precompute the SHA256 state
906 * after hashing the tag hashes.
907 *
908 * Returns: 1 always.
909 * Args: ctx: pointer to a context object
910 * Out: hash32: pointer to a 32-byte array to store the resulting hash
911 * In: tag: pointer to an array containing the tag
912 * taglen: length of the tag array
913 * msg: pointer to an array containing the message
914 * msglen: length of the message array
915 */
916 SECP256K1_API int secp256k1_tagged_sha256(
917 const secp256k1_context *ctx,
918 unsigned char *hash32,
919 const unsigned char *tag,
920 size_t taglen,
921 const unsigned char *msg,
922 size_t msglen
923 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(5);
924 925 #ifdef __cplusplus
926 }
927 #endif
928 929 #endif /* SECP256K1_H */
930