1 #ifndef SECP256K1_H
2 #define SECP256K1_H
3 4 #ifdef __cplusplus
5 extern "C" {
6 #endif
7 8 #include <stddef.h>
9 10 /** Unless explicitly stated all pointer arguments must not be NULL.
11 *
12 * The following rules specify the order of arguments in API calls:
13 *
14 * 1. Context pointers go first, followed by output arguments, combined
15 * output/input arguments, and finally input-only arguments.
16 * 2. Array lengths always immediately follow the argument whose length
17 * they describe, even if this violates rule 1.
18 * 3. Within the OUT/OUTIN/IN groups, pointers to data that is typically generated
19 * later go first. This means: signatures, public nonces, secret nonces,
20 * messages, public keys, secret keys, tweaks.
21 * 4. Arguments that are not data pointers go last, from more complex to less
22 * complex: function pointers, algorithm names, messages, void pointers,
23 * counts, flags, booleans.
24 * 5. Opaque data pointers follow the function pointer they are to be passed to.
25 */
26 27 /** Opaque data structure that holds context information
28 *
29 * The primary purpose of context objects is to store randomization data for
30 * enhanced protection against side-channel leakage. This protection is only
31 * effective if the context is randomized after its creation. See
32 * secp256k1_context_create for creation of contexts and
33 * secp256k1_context_randomize for randomization.
34 *
35 * A secondary purpose of context objects is to store pointers to callback
36 * functions that the library will call when certain error states arise. See
37 * secp256k1_context_set_error_callback as well as
38 * secp256k1_context_set_illegal_callback for details. Future library versions
39 * may use context objects for additional purposes.
40 *
41 * A constructed context can safely be used from multiple threads
42 * simultaneously, but API calls that take a non-const pointer to a context
43 * need exclusive access to it. In particular this is the case for
44 * secp256k1_context_destroy, secp256k1_context_preallocated_destroy,
45 * and secp256k1_context_randomize.
46 *
47 * Regarding randomization, either do it once at creation time (in which case
48 * you do not need any locking for the other calls), or use a read-write lock.
49 */
50 typedef struct secp256k1_context_struct secp256k1_context;
51 52 /** Opaque data structure that holds a parsed and valid public key.
53 *
54 * The exact representation of data inside is implementation defined and not
55 * guaranteed to be portable between different platforms or versions. It is
56 * however guaranteed to be 64 bytes in size, and can be safely copied/moved.
57 * If you need to convert to a format suitable for storage or transmission,
58 * use secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse. To
59 * compare keys, use secp256k1_ec_pubkey_cmp.
60 */
61 typedef struct secp256k1_pubkey {
62 unsigned char data[64];
63 } secp256k1_pubkey;
64 65 /** Opaque data structure that holds a parsed ECDSA signature.
66 *
67 * The exact representation of data inside is implementation defined and not
68 * guaranteed to be portable between different platforms or versions. It is
69 * however guaranteed to be 64 bytes in size, and can be safely copied/moved.
70 * If you need to convert to a format suitable for storage, transmission, or
71 * comparison, use the secp256k1_ecdsa_signature_serialize_* and
72 * secp256k1_ecdsa_signature_parse_* functions.
73 */
74 typedef struct secp256k1_ecdsa_signature {
75 unsigned char data[64];
76 } secp256k1_ecdsa_signature;
77 78 /** A pointer to a function to deterministically generate a nonce.
79 *
80 * Returns: 1 if a nonce was successfully generated. 0 will cause signing to fail.
81 * Out: nonce32: pointer to a 32-byte array to be filled by the function.
82 * In: msg32: the 32-byte message hash being verified (will not be NULL)
83 * key32: pointer to a 32-byte secret key (will not be NULL)
84 * algo16: pointer to a 16-byte array describing the signature
85 * algorithm (will be NULL for ECDSA for compatibility).
86 * data: Arbitrary data pointer that is passed through.
87 * attempt: how many iterations we have tried to find a nonce.
88 * This will almost always be 0, but different attempt values
89 * are required to result in a different nonce.
90 *
91 * Except for test cases, this function should compute some cryptographic hash of
92 * the message, the algorithm, the key and the attempt.
93 */
94 typedef int (*secp256k1_nonce_function)(
95 unsigned char *nonce32,
96 const unsigned char *msg32,
97 const unsigned char *key32,
98 const unsigned char *algo16,
99 void *data,
100 unsigned int attempt
101 );
102 103 # if !defined(SECP256K1_GNUC_PREREQ)
104 # if defined(__GNUC__)&&defined(__GNUC_MINOR__)
105 # define SECP256K1_GNUC_PREREQ(_maj,_min) \
106 ((__GNUC__<<16)+__GNUC_MINOR__>=((_maj)<<16)+(_min))
107 # else
108 # define SECP256K1_GNUC_PREREQ(_maj,_min) 0
109 # endif
110 # endif
111 112 /* When this header is used at build-time the SECP256K1_BUILD define needs to be set
113 * to correctly setup export attributes and nullness checks. This is normally done
114 * by secp256k1.c but to guard against this header being included before secp256k1.c
115 * has had a chance to set the define (e.g. via test harnesses that just includes
116 * secp256k1.c) we set SECP256K1_NO_BUILD when this header is processed without the
117 * BUILD define so this condition can be caught.
118 */
119 #ifndef SECP256K1_BUILD
120 # define SECP256K1_NO_BUILD
121 #endif
122 123 /* Symbol visibility. */
124 #if defined(_WIN32)
125 /* GCC for Windows (e.g., MinGW) accepts the __declspec syntax
126 * for MSVC compatibility. A __declspec declaration implies (but is not
127 * exactly equivalent to) __attribute__ ((visibility("default"))), and so we
128 * actually want __declspec even on GCC, see "Microsoft Windows Function
129 * Attributes" in the GCC manual and the recommendations in
130 * https://gcc.gnu.org/wiki/Visibility. */
131 # if defined(SECP256K1_BUILD)
132 # if defined(DLL_EXPORT) || defined(SECP256K1_DLL_EXPORT)
133 /* Building libsecp256k1 as a DLL.
134 * 1. If using Libtool, it defines DLL_EXPORT automatically.
135 * 2. In other cases, SECP256K1_DLL_EXPORT must be defined. */
136 # define SECP256K1_API extern __declspec (dllexport)
137 # else
138 /* Building libsecp256k1 as a static library on Windows.
139 * No declspec is needed, and so we would want the non-Windows-specific
140 * logic below take care of this case. However, this may result in setting
141 * __attribute__ ((visibility("default"))), which is supposed to be a noop
142 * on Windows but may trigger warnings when compiling with -flto due to a
143 * bug in GCC, see
144 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116478 . */
145 # define SECP256K1_API extern
146 # endif
147 /* The user must define SECP256K1_STATIC when consuming libsecp256k1 as a static
148 * library on Windows. */
149 # elif !defined(SECP256K1_STATIC)
150 /* Consuming libsecp256k1 as a DLL. */
151 # define SECP256K1_API extern __declspec (dllimport)
152 # endif
153 #endif
154 #ifndef SECP256K1_API
155 /* All cases not captured by the Windows-specific logic. */
156 # if defined(__GNUC__) && (__GNUC__ >= 4) && defined(SECP256K1_BUILD)
157 /* Building libsecp256k1 using GCC or compatible. */
158 # define SECP256K1_API extern __attribute__ ((visibility ("default")))
159 # else
160 /* Fall back to standard C's extern. */
161 # define SECP256K1_API extern
162 # endif
163 #endif
164 165 /* Warning attributes
166 * NONNULL is not used if SECP256K1_BUILD is set to avoid the compiler optimizing out
167 * some paranoid null checks. */
168 # if defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
169 # define SECP256K1_WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
170 # else
171 # define SECP256K1_WARN_UNUSED_RESULT
172 # endif
173 # if !defined(SECP256K1_BUILD) && defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
174 # define SECP256K1_ARG_NONNULL(_x) __attribute__ ((__nonnull__(_x)))
175 # else
176 # define SECP256K1_ARG_NONNULL(_x)
177 # endif
178 179 /* Attribute for marking functions, types, and variables as deprecated */
180 #if !defined(SECP256K1_BUILD) && defined(__has_attribute)
181 # if __has_attribute(__deprecated__)
182 # define SECP256K1_DEPRECATED(_msg) __attribute__ ((__deprecated__(_msg)))
183 # else
184 # define SECP256K1_DEPRECATED(_msg)
185 # endif
186 #else
187 # define SECP256K1_DEPRECATED(_msg)
188 #endif
189 190 /* All flags' lower 8 bits indicate what they're for. Do not use directly. */
191 #define SECP256K1_FLAGS_TYPE_MASK ((1 << 8) - 1)
192 #define SECP256K1_FLAGS_TYPE_CONTEXT (1 << 0)
193 #define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
194 /* The higher bits contain the actual data. Do not use directly. */
195 #define SECP256K1_FLAGS_BIT_CONTEXT_VERIFY (1 << 8)
196 #define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9)
197 #define SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY (1 << 10)
198 #define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)
199 200 /** Context flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and
201 * secp256k1_context_preallocated_create. */
202 #define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)
203 204 /** Deprecated context flags. These flags are treated equivalent to SECP256K1_CONTEXT_NONE. */
205 #define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY)
206 #define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN)
207 208 /* Testing flag. Do not use. */
209 #define SECP256K1_CONTEXT_DECLASSIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY)
210 211 /** Flag to pass to secp256k1_ec_pubkey_serialize. */
212 #define SECP256K1_EC_COMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION | SECP256K1_FLAGS_BIT_COMPRESSION)
213 #define SECP256K1_EC_UNCOMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION)
214 215 /** Prefix byte used to tag various encoded curvepoints for specific purposes */
216 #define SECP256K1_TAG_PUBKEY_EVEN 0x02
217 #define SECP256K1_TAG_PUBKEY_ODD 0x03
218 #define SECP256K1_TAG_PUBKEY_UNCOMPRESSED 0x04
219 #define SECP256K1_TAG_PUBKEY_HYBRID_EVEN 0x06
220 #define SECP256K1_TAG_PUBKEY_HYBRID_ODD 0x07
221 222 /** A built-in constant secp256k1 context object with static storage duration, to be
223 * used in conjunction with secp256k1_selftest.
224 *
225 * This context object offers *only limited functionality* , i.e., it cannot be used
226 * for API functions that perform computations involving secret keys, e.g., signing
227 * and public key generation. If this restriction applies to a specific API function,
228 * it is mentioned in its documentation. See secp256k1_context_create if you need a
229 * full context object that supports all functionality offered by the library.
230 *
231 * It is highly recommended to call secp256k1_selftest before using this context.
232 */
233 SECP256K1_API const secp256k1_context *secp256k1_context_static;
234 235 /** Deprecated alias for secp256k1_context_static. */
236 SECP256K1_API const secp256k1_context *secp256k1_context_no_precomp
237 SECP256K1_DEPRECATED("Use secp256k1_context_static instead");
238 239 /** Perform basic self tests (to be used in conjunction with secp256k1_context_static)
240 *
241 * This function performs self tests that detect some serious usage errors and
242 * similar conditions, e.g., when the library is compiled for the wrong endianness.
243 * This is a last resort measure to be used in production. The performed tests are
244 * very rudimentary and are not intended as a replacement for running the test
245 * binaries.
246 *
247 * It is highly recommended to call this before using secp256k1_context_static.
248 * It is not necessary to call this function before using a context created with
249 * secp256k1_context_create (or secp256k1_context_preallocated_create), which will
250 * take care of performing the self tests.
251 *
252 * If the tests fail, this function will call the default error handler to abort the
253 * program (see secp256k1_context_set_error_callback).
254 */
255 SECP256K1_API void secp256k1_selftest(void);
256 257 258 /** Create a secp256k1 context object (in dynamically allocated memory).
259 *
260 * This function uses malloc to allocate memory. It is guaranteed that malloc is
261 * called at most once for every call of this function. If you need to avoid dynamic
262 * memory allocation entirely, see secp256k1_context_static and the functions in
263 * secp256k1_preallocated.h.
264 *
265 * Returns: pointer to a newly created context object.
266 * In: flags: Always set to SECP256K1_CONTEXT_NONE (see below).
267 *
268 * The only valid non-deprecated flag in recent library versions is
269 * SECP256K1_CONTEXT_NONE, which will create a context sufficient for all functionality
270 * offered by the library. All other (deprecated) flags will be treated as equivalent
271 * to the SECP256K1_CONTEXT_NONE flag. Though the flags parameter primarily exists for
272 * historical reasons, future versions of the library may introduce new flags.
273 *
274 * If the context is intended to be used for API functions that perform computations
275 * involving secret keys, e.g., signing and public key generation, then it is highly
276 * recommended to call secp256k1_context_randomize on the context before calling
277 * those API functions. This will provide enhanced protection against side-channel
278 * leakage, see secp256k1_context_randomize for details.
279 *
280 * Do not create a new context object for each operation, as construction and
281 * randomization can take non-negligible time.
282 */
283 SECP256K1_API secp256k1_context *secp256k1_context_create(
284 unsigned int flags
285 ) SECP256K1_WARN_UNUSED_RESULT;
286 287 /** Copy a secp256k1 context object (into dynamically allocated memory).
288 *
289 * This function uses malloc to allocate memory. It is guaranteed that malloc is
290 * called at most once for every call of this function. If you need to avoid dynamic
291 * memory allocation entirely, see the functions in secp256k1_preallocated.h.
292 *
293 * Cloning secp256k1_context_static is not possible, and should not be emulated by
294 * the caller (e.g., using memcpy). Create a new context instead.
295 *
296 * Returns: pointer to a newly created context object.
297 * Args: ctx: pointer to a context to copy (not secp256k1_context_static).
298 */
299 SECP256K1_API secp256k1_context *secp256k1_context_clone(
300 const secp256k1_context *ctx
301 ) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT;
302 303 /** Destroy a secp256k1 context object (created in dynamically allocated memory).
304 *
305 * The context pointer may not be used afterwards.
306 *
307 * The context to destroy must have been created using secp256k1_context_create
308 * or secp256k1_context_clone. If the context has instead been created using
309 * secp256k1_context_preallocated_create or secp256k1_context_preallocated_clone, the
310 * behaviour is undefined. In that case, secp256k1_context_preallocated_destroy must
311 * be used instead.
312 *
313 * Args: ctx: pointer to a context to destroy, constructed using
314 * secp256k1_context_create or secp256k1_context_clone
315 * (i.e., not secp256k1_context_static).
316 */
317 SECP256K1_API void secp256k1_context_destroy(
318 secp256k1_context *ctx
319 ) SECP256K1_ARG_NONNULL(1);
320 321 /** Set a callback function to be called when an illegal argument is passed to
322 * an API call. It will only trigger for violations that are mentioned
323 * explicitly in the header.
324 *
325 * The philosophy is that these shouldn't be dealt with through a
326 * specific return value, as calling code should not have branches to deal with
327 * the case that this code itself is broken.
328 *
329 * On the other hand, during debug stage, one would want to be informed about
330 * such mistakes, and the default (crashing) may be inadvisable.
331 * When this callback is triggered, the API function called is guaranteed not
332 * to cause a crash, though its return value and output arguments are
333 * undefined.
334 *
335 * When this function has not been called (or called with fn==NULL), then the
336 * default handler will be used. The library provides a default handler which
337 * writes the message to stderr and calls abort. This default handler can be
338 * replaced at link time if the preprocessor macro
339 * USE_EXTERNAL_DEFAULT_CALLBACKS is defined, which is the case if the build
340 * has been configured with --enable-external-default-callbacks. Then the
341 * following two symbols must be provided to link against:
342 * - void secp256k1_default_illegal_callback_fn(const char *message, void *data);
343 * - void secp256k1_default_error_callback_fn(const char *message, void *data);
344 * The library can call these default handlers even before a proper callback data
345 * pointer could have been set using secp256k1_context_set_illegal_callback or
346 * secp256k1_context_set_error_callback, e.g., when the creation of a context
347 * fails. In this case, the corresponding default handler will be called with
348 * the data pointer argument set to NULL.
349 *
350 * Args: ctx: pointer to a context object.
351 * In: fun: pointer to a function to call when an illegal argument is
352 * passed to the API, taking a message and an opaque pointer.
353 * (NULL restores the default handler.)
354 * data: the opaque pointer to pass to fun above, must be NULL for the default handler.
355 *
356 * See also secp256k1_context_set_error_callback.
357 */
358 SECP256K1_API void secp256k1_context_set_illegal_callback(
359 secp256k1_context *ctx,
360 void (*fun)(const char *message, void *data),
361 const void *data
362 ) SECP256K1_ARG_NONNULL(1);
363 364 /** Set a callback function to be called when an internal consistency check
365 * fails.
366 *
367 * The default callback writes an error message to stderr and calls abort
368 * to abort the program.
369 *
370 * This can only trigger in case of a hardware failure, miscompilation,
371 * memory corruption, serious bug in the library, or other error would can
372 * otherwise result in undefined behaviour. It will not trigger due to mere
373 * incorrect usage of the API (see secp256k1_context_set_illegal_callback
374 * for that). After this callback returns, anything may happen, including
375 * crashing.
376 *
377 * Args: ctx: pointer to a context object.
378 * In: fun: pointer to a function to call when an internal error occurs,
379 * taking a message and an opaque pointer (NULL restores the
380 * default handler, see secp256k1_context_set_illegal_callback
381 * for details).
382 * data: the opaque pointer to pass to fun above, must be NULL for the default handler.
383 *
384 * See also secp256k1_context_set_illegal_callback.
385 */
386 SECP256K1_API void secp256k1_context_set_error_callback(
387 secp256k1_context *ctx,
388 void (*fun)(const char *message, void *data),
389 const void *data
390 ) SECP256K1_ARG_NONNULL(1);
391 392 /** Parse a variable-length public key into the pubkey object.
393 *
394 * Returns: 1 if the public key was fully valid.
395 * 0 if the public key could not be parsed or is invalid.
396 * Args: ctx: pointer to a context object.
397 * Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to a
398 * parsed version of input. If not, its value is undefined.
399 * In: input: pointer to a serialized public key
400 * inputlen: length of the array pointed to by input
401 *
402 * This function supports parsing compressed (33 bytes, header byte 0x02 or
403 * 0x03), uncompressed (65 bytes, header byte 0x04), or hybrid (65 bytes, header
404 * byte 0x06 or 0x07) format public keys.
405 */
406 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_parse(
407 const secp256k1_context *ctx,
408 secp256k1_pubkey *pubkey,
409 const unsigned char *input,
410 size_t inputlen
411 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
412 413 /** Serialize a pubkey object into a serialized byte sequence.
414 *
415 * Returns: 1 always.
416 * Args: ctx: pointer to a context object.
417 * Out: output: pointer to a 65-byte (if compressed==0) or 33-byte (if
418 * compressed==1) byte array to place the serialized key
419 * in.
420 * In/Out: outputlen: pointer to an integer which is initially set to the
421 * size of output, and is overwritten with the written
422 * size.
423 * In: pubkey: pointer to a secp256k1_pubkey containing an
424 * initialized public key.
425 * flags: SECP256K1_EC_COMPRESSED if serialization should be in
426 * compressed format, otherwise SECP256K1_EC_UNCOMPRESSED.
427 */
428 SECP256K1_API int secp256k1_ec_pubkey_serialize(
429 const secp256k1_context *ctx,
430 unsigned char *output,
431 size_t *outputlen,
432 const secp256k1_pubkey *pubkey,
433 unsigned int flags
434 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
435 436 /** Compare two public keys using lexicographic (of compressed serialization) order
437 *
438 * Returns: <0 if the first public key is less than the second
439 * >0 if the first public key is greater than the second
440 * 0 if the two public keys are equal
441 * Args: ctx: pointer to a context object
442 * In: pubkey1: first public key to compare
443 * pubkey2: second public key to compare
444 */
445 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_cmp(
446 const secp256k1_context *ctx,
447 const secp256k1_pubkey *pubkey1,
448 const secp256k1_pubkey *pubkey2
449 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
450 451 /** Sort public keys using lexicographic (of compressed serialization) order
452 *
453 * Returns: 0 if the arguments are invalid. 1 otherwise.
454 *
455 * Args: ctx: pointer to a context object
456 * In: pubkeys: array of pointers to pubkeys to sort
457 * n_pubkeys: number of elements in the pubkeys array
458 */
459 SECP256K1_API int secp256k1_ec_pubkey_sort(
460 const secp256k1_context *ctx,
461 const secp256k1_pubkey **pubkeys,
462 size_t n_pubkeys
463 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
464 465 /** Parse an ECDSA signature in compact (64 bytes) format.
466 *
467 * Returns: 1 when the signature could be parsed, 0 otherwise.
468 * Args: ctx: pointer to a context object
469 * Out: sig: pointer to a signature object
470 * In: input64: pointer to the 64-byte array to parse
471 *
472 * The signature must consist of a 32-byte big endian R value, followed by a
473 * 32-byte big endian S value. If R or S fall outside of [0..order-1], the
474 * encoding is invalid. R and S with value 0 are allowed in the encoding.
475 *
476 * After the call, sig will always be initialized. If parsing failed or R or
477 * S are zero, the resulting sig value is guaranteed to fail verification for
478 * any message and public key.
479 */
480 SECP256K1_API int secp256k1_ecdsa_signature_parse_compact(
481 const secp256k1_context *ctx,
482 secp256k1_ecdsa_signature *sig,
483 const unsigned char *input64
484 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
485 486 /** Parse a DER ECDSA signature.
487 *
488 * Returns: 1 when the signature could be parsed, 0 otherwise.
489 * Args: ctx: pointer to a context object
490 * Out: sig: pointer to a signature object
491 * In: input: pointer to the signature to be parsed
492 * inputlen: the length of the array pointed to be input
493 *
494 * This function will accept any valid DER encoded signature, even if the
495 * encoded numbers are out of range.
496 *
497 * After the call, sig will always be initialized. If parsing failed or the
498 * encoded numbers are out of range, signature verification with it is
499 * guaranteed to fail for every message and public key.
500 */
501 SECP256K1_API int secp256k1_ecdsa_signature_parse_der(
502 const secp256k1_context *ctx,
503 secp256k1_ecdsa_signature *sig,
504 const unsigned char *input,
505 size_t inputlen
506 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
507 508 /** Serialize an ECDSA signature in DER format.
509 *
510 * Returns: 1 if enough space was available to serialize, 0 otherwise
511 * Args: ctx: pointer to a context object
512 * Out: output: pointer to an array to store the DER serialization
513 * In/Out: outputlen: pointer to a length integer. Initially, this integer
514 * should be set to the length of output. After the call
515 * it will be set to the length of the serialization (even
516 * if 0 was returned).
517 * In: sig: pointer to an initialized signature object
518 */
519 SECP256K1_API int secp256k1_ecdsa_signature_serialize_der(
520 const secp256k1_context *ctx,
521 unsigned char *output,
522 size_t *outputlen,
523 const secp256k1_ecdsa_signature *sig
524 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
525 526 /** Serialize an ECDSA signature in compact (64 byte) format.
527 *
528 * Returns: 1
529 * Args: ctx: pointer to a context object
530 * Out: output64: pointer to a 64-byte array to store the compact serialization
531 * In: sig: pointer to an initialized signature object
532 *
533 * See secp256k1_ecdsa_signature_parse_compact for details about the encoding.
534 */
535 SECP256K1_API int secp256k1_ecdsa_signature_serialize_compact(
536 const secp256k1_context *ctx,
537 unsigned char *output64,
538 const secp256k1_ecdsa_signature *sig
539 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
540 541 /** Verify an ECDSA signature.
542 *
543 * Returns: 1: correct signature
544 * 0: incorrect or unparseable signature
545 * Args: ctx: pointer to a context object
546 * In: sig: the signature being verified.
547 * msghash32: the 32-byte message hash being verified.
548 * The verifier must make sure to apply a cryptographic
549 * hash function to the message by itself and not accept an
550 * msghash32 value directly. Otherwise, it would be easy to
551 * create a "valid" signature without knowledge of the
552 * secret key. See also
553 * https://bitcoin.stackexchange.com/a/81116/35586 for more
554 * background on this topic.
555 * pubkey: pointer to an initialized public key to verify with.
556 *
557 * To avoid accepting malleable signatures, only ECDSA signatures in lower-S
558 * form are accepted.
559 *
560 * If you need to accept ECDSA signatures from sources that do not obey this
561 * rule, apply secp256k1_ecdsa_signature_normalize to the signature prior to
562 * verification, but be aware that doing so results in malleable signatures.
563 *
564 * For details, see the comments for that function.
565 */
566 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify(
567 const secp256k1_context *ctx,
568 const secp256k1_ecdsa_signature *sig,
569 const unsigned char *msghash32,
570 const secp256k1_pubkey *pubkey
571 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
572 573 /** Convert a signature to a normalized lower-S form.
574 *
575 * Returns: 1 if sigin was not normalized, 0 if it already was.
576 * Args: ctx: pointer to a context object
577 * Out: sigout: pointer to a signature to fill with the normalized form,
578 * or copy if the input was already normalized. (can be NULL if
579 * you're only interested in whether the input was already
580 * normalized).
581 * In: sigin: pointer to a signature to check/normalize (can be identical to sigout)
582 *
583 * With ECDSA a third-party can forge a second distinct signature of the same
584 * message, given a single initial signature, but without knowing the key. This
585 * is done by negating the S value modulo the order of the curve, 'flipping'
586 * the sign of the random point R which is not included in the signature.
587 *
588 * Forgery of the same message isn't universally problematic, but in systems
589 * where message malleability or uniqueness of signatures is important this can
590 * cause issues. This forgery can be blocked by all verifiers forcing signers
591 * to use a normalized form.
592 *
593 * The lower-S form reduces the size of signatures slightly on average when
594 * variable length encodings (such as DER) are used and is cheap to verify,
595 * making it a good choice. Security of always using lower-S is assured because
596 * anyone can trivially modify a signature after the fact to enforce this
597 * property anyway.
598 *
599 * The lower S value is always between 0x1 and
600 * 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0,
601 * inclusive.
602 *
603 * No other forms of ECDSA malleability are known and none seem likely, but
604 * there is no formal proof that ECDSA, even with this additional restriction,
605 * is free of other malleability. Commonly used serialization schemes will also
606 * accept various non-unique encodings, so care should be taken when this
607 * property is required for an application.
608 *
609 * The secp256k1_ecdsa_sign function will by default create signatures in the
610 * lower-S form, and secp256k1_ecdsa_verify will not accept others. In case
611 * signatures come from a system that cannot enforce this property,
612 * secp256k1_ecdsa_signature_normalize must be called before verification.
613 */
614 SECP256K1_API int secp256k1_ecdsa_signature_normalize(
615 const secp256k1_context *ctx,
616 secp256k1_ecdsa_signature *sigout,
617 const secp256k1_ecdsa_signature *sigin
618 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(3);
619 620 /** An implementation of RFC6979 (using HMAC-SHA256) as nonce generation function.
621 * If a data pointer is passed, it is assumed to be a pointer to 32 bytes of
622 * extra entropy.
623 */
624 SECP256K1_API const secp256k1_nonce_function secp256k1_nonce_function_rfc6979;
625 626 /** A default safe nonce generation function (currently equal to secp256k1_nonce_function_rfc6979). */
627 SECP256K1_API const secp256k1_nonce_function secp256k1_nonce_function_default;
628 629 /** Create an ECDSA signature.
630 *
631 * Returns: 1: signature created
632 * 0: the nonce generation function failed, or the secret key was invalid.
633 * Args: ctx: pointer to a context object (not secp256k1_context_static).
634 * Out: sig: pointer to an array where the signature will be placed.
635 * In: msghash32: the 32-byte message hash being signed.
636 * seckey: pointer to a 32-byte secret key.
637 * noncefp: pointer to a nonce generation function. If NULL,
638 * secp256k1_nonce_function_default is used.
639 * ndata: pointer to arbitrary data used by the nonce generation function
640 * (can be NULL). If it is non-NULL and
641 * secp256k1_nonce_function_default is used, then ndata must be a
642 * pointer to 32-bytes of additional data.
643 *
644 * The created signature is always in lower-S form. See
645 * secp256k1_ecdsa_signature_normalize for more details.
646 */
647 SECP256K1_API int secp256k1_ecdsa_sign(
648 const secp256k1_context *ctx,
649 secp256k1_ecdsa_signature *sig,
650 const unsigned char *msghash32,
651 const unsigned char *seckey,
652 secp256k1_nonce_function noncefp,
653 const void *ndata
654 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
655 656 /** Verify an elliptic curve secret key.
657 *
658 * A secret key is valid if it is not 0 and less than the secp256k1 curve order
659 * when interpreted as an integer (most significant byte first). The
660 * probability of choosing a 32-byte string uniformly at random which is an
661 * invalid secret key is negligible. However, if it does happen it should
662 * be assumed that the randomness source is severely broken and there should
663 * be no retry.
664 *
665 * Returns: 1: secret key is valid
666 * 0: secret key is invalid
667 * Args: ctx: pointer to a context object.
668 * In: seckey: pointer to a 32-byte secret key.
669 */
670 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_verify(
671 const secp256k1_context *ctx,
672 const unsigned char *seckey
673 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
674 675 /** Compute the public key for a secret key.
676 *
677 * Returns: 1: secret was valid, public key stores.
678 * 0: secret was invalid, try again.
679 * Args: ctx: pointer to a context object (not secp256k1_context_static).
680 * Out: pubkey: pointer to the created public key.
681 * In: seckey: pointer to a 32-byte secret key.
682 */
683 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_create(
684 const secp256k1_context *ctx,
685 secp256k1_pubkey *pubkey,
686 const unsigned char *seckey
687 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
688 689 /** Negates a secret key in place.
690 *
691 * Returns: 0 if the given secret key is invalid according to
692 * secp256k1_ec_seckey_verify. 1 otherwise
693 * Args: ctx: pointer to a context object
694 * In/Out: seckey: pointer to the 32-byte secret key to be negated. If the
695 * secret key is invalid according to
696 * secp256k1_ec_seckey_verify, this function returns 0 and
697 * seckey will be set to some unspecified value.
698 */
699 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_negate(
700 const secp256k1_context *ctx,
701 unsigned char *seckey
702 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
703 704 /** Same as secp256k1_ec_seckey_negate, but DEPRECATED. Will be removed in
705 * future versions. */
706 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_negate(
707 const secp256k1_context *ctx,
708 unsigned char *seckey
709 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2)
710 SECP256K1_DEPRECATED("Use secp256k1_ec_seckey_negate instead");
711 712 /** Negates a public key in place.
713 *
714 * Returns: 1 always
715 * Args: ctx: pointer to a context object
716 * In/Out: pubkey: pointer to the public key to be negated.
717 */
718 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_negate(
719 const secp256k1_context *ctx,
720 secp256k1_pubkey *pubkey
721 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
722 723 /** Tweak a secret key by adding tweak to it.
724 *
725 * Returns: 0 if the arguments are invalid or the resulting secret key would be
726 * invalid (only when the tweak is the negation of the secret key). 1
727 * otherwise.
728 * Args: ctx: pointer to a context object.
729 * In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
730 * invalid according to secp256k1_ec_seckey_verify, this
731 * function returns 0. seckey will be set to some unspecified
732 * value if this function returns 0.
733 * In: tweak32: pointer to a 32-byte tweak, which must be valid according to
734 * secp256k1_ec_seckey_verify or 32 zero bytes. For uniformly
735 * random 32-byte tweaks, the chance of being invalid is
736 * negligible (around 1 in 2^128).
737 */
738 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_add(
739 const secp256k1_context *ctx,
740 unsigned char *seckey,
741 const unsigned char *tweak32
742 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
743 744 /** Same as secp256k1_ec_seckey_tweak_add, but DEPRECATED. Will be removed in
745 * future versions. */
746 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_add(
747 const secp256k1_context *ctx,
748 unsigned char *seckey,
749 const unsigned char *tweak32
750 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3)
751 SECP256K1_DEPRECATED("Use secp256k1_ec_seckey_tweak_add instead");
752 753 /** Tweak a public key by adding tweak times the generator to it.
754 *
755 * Returns: 0 if the arguments are invalid or the resulting public key would be
756 * invalid (only when the tweak is the negation of the corresponding
757 * secret key). 1 otherwise.
758 * Args: ctx: pointer to a context object.
759 * In/Out: pubkey: pointer to a public key object. pubkey will be set to an
760 * invalid value if this function returns 0.
761 * In: tweak32: pointer to a 32-byte tweak, which must be valid according to
762 * secp256k1_ec_seckey_verify or 32 zero bytes. For uniformly
763 * random 32-byte tweaks, the chance of being invalid is
764 * negligible (around 1 in 2^128).
765 */
766 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
767 const secp256k1_context *ctx,
768 secp256k1_pubkey *pubkey,
769 const unsigned char *tweak32
770 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
771 772 /** Tweak a secret key by multiplying it by a tweak.
773 *
774 * Returns: 0 if the arguments are invalid. 1 otherwise.
775 * Args: ctx: pointer to a context object.
776 * In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
777 * invalid according to secp256k1_ec_seckey_verify, this
778 * function returns 0. seckey will be set to some unspecified
779 * value if this function returns 0.
780 * In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
781 * secp256k1_ec_seckey_verify, this function returns 0. For
782 * uniformly random 32-byte arrays the chance of being invalid
783 * is negligible (around 1 in 2^128).
784 */
785 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_mul(
786 const secp256k1_context *ctx,
787 unsigned char *seckey,
788 const unsigned char *tweak32
789 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
790 791 /** Same as secp256k1_ec_seckey_tweak_mul, but DEPRECATED. Will be removed in
792 * future versions. */
793 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_mul(
794 const secp256k1_context *ctx,
795 unsigned char *seckey,
796 const unsigned char *tweak32
797 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3)
798 SECP256K1_DEPRECATED("Use secp256k1_ec_seckey_tweak_mul instead");
799 800 /** Tweak a public key by multiplying it by a tweak value.
801 *
802 * Returns: 0 if the arguments are invalid. 1 otherwise.
803 * Args: ctx: pointer to a context object.
804 * In/Out: pubkey: pointer to a public key object. pubkey will be set to an
805 * invalid value if this function returns 0.
806 * In: tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
807 * secp256k1_ec_seckey_verify, this function returns 0. For
808 * uniformly random 32-byte arrays the chance of being invalid
809 * is negligible (around 1 in 2^128).
810 */
811 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
812 const secp256k1_context *ctx,
813 secp256k1_pubkey *pubkey,
814 const unsigned char *tweak32
815 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
816 817 /** Randomizes the context to provide enhanced protection against side-channel leakage.
818 *
819 * Returns: 1: randomization successful
820 * 0: error
821 * Args: ctx: pointer to a context object (not secp256k1_context_static).
822 * In: seed32: pointer to a 32-byte random seed (NULL resets to initial state).
823 *
824 * While secp256k1 code is written and tested to be constant-time no matter what
825 * secret values are, it is possible that a compiler may output code which is not,
826 * and also that the CPU may not emit the same radio frequencies or draw the same
827 * amount of power for all values. Randomization of the context shields against
828 * side-channel observations which aim to exploit secret-dependent behaviour in
829 * certain computations which involve secret keys.
830 *
831 * It is highly recommended to call this function on contexts returned from
832 * secp256k1_context_create or secp256k1_context_clone (or from the corresponding
833 * functions in secp256k1_preallocated.h) before using these contexts to call API
834 * functions that perform computations involving secret keys, e.g., signing and
835 * public key generation. It is possible to call this function more than once on
836 * the same context, and doing so before every few computations involving secret
837 * keys is recommended as a defense-in-depth measure. Randomization of the static
838 * context secp256k1_context_static is not supported.
839 *
840 * Currently, the random seed is mainly used for blinding multiplications of a
841 * secret scalar with the elliptic curve base point. Multiplications of this
842 * kind are performed by exactly those API functions which are documented to
843 * require a context that is not secp256k1_context_static. As a rule of thumb,
844 * these are all functions which take a secret key (or a keypair) as an input.
845 * A notable exception to that rule is the ECDH module, which relies on a different
846 * kind of elliptic curve point multiplication and thus does not benefit from
847 * enhanced protection against side-channel leakage currently.
848 */
849 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize(
850 secp256k1_context *ctx,
851 const unsigned char *seed32
852 ) SECP256K1_ARG_NONNULL(1);
853 854 /** Add a number of public keys together.
855 *
856 * Returns: 1: the sum of the public keys is valid.
857 * 0: the sum of the public keys is not valid.
858 * Args: ctx: pointer to a context object.
859 * Out: out: pointer to a public key object for placing the resulting public key.
860 * In: ins: pointer to array of pointers to public keys.
861 * n: the number of public keys to add together (must be at least 1).
862 */
863 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_combine(
864 const secp256k1_context *ctx,
865 secp256k1_pubkey *out,
866 const secp256k1_pubkey * const *ins,
867 size_t n
868 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
869 870 /** Compute a tagged hash as defined in BIP-340.
871 *
872 * This is useful for creating a message hash and achieving domain separation
873 * through an application-specific tag. This function returns
874 * SHA256(SHA256(tag)||SHA256(tag)||msg). Therefore, tagged hash
875 * implementations optimized for a specific tag can precompute the SHA256 state
876 * after hashing the tag hashes.
877 *
878 * Returns: 1 always.
879 * Args: ctx: pointer to a context object
880 * Out: hash32: pointer to a 32-byte array to store the resulting hash
881 * In: tag: pointer to an array containing the tag
882 * taglen: length of the tag array
883 * msg: pointer to an array containing the message
884 * msglen: length of the message array
885 */
886 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_tagged_sha256(
887 const secp256k1_context *ctx,
888 unsigned char *hash32,
889 const unsigned char *tag,
890 size_t taglen,
891 const unsigned char *msg,
892 size_t msglen
893 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(5);
894 895 #ifdef __cplusplus
896 }
897 #endif
898 899 #endif /* SECP256K1_H */
900