-#ifndef _SECP256K1_
-# define _SECP256K1_
+#ifndef SECP256K1_H
+#define SECP256K1_H
-# ifdef __cplusplus
+#ifdef __cplusplus
extern "C" {
-# endif
+#endif
+
+#include <stddef.h>
+
+/* These 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 the 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, private 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 (precomputed tables etc.).
+ *
+ * The purpose of context structures is to cache large precomputed data tables
+ * that are expensive to construct, and also to maintain the randomization data
+ * for blinding.
+ *
+ * Do not create a new context object for each operation, as construction is
+ * far slower than all other API calls (~100 times slower than an ECDSA
+ * verification).
+ *
+ * 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 rewriteable "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, transmission, or
+ * comparison, use secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse.
+ */
+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_INLINE inline
# endif
+#ifndef SECP256K1_API
+# if defined(_WIN32)
+# ifdef SECP256K1_BUILD
+# define SECP256K1_API __declspec(dllexport)
+# else
+# define SECP256K1_API
+# endif
+# elif defined(__GNUC__) && defined(SECP256K1_BUILD)
+# define SECP256K1_API __attribute__ ((visibility ("default")))
+# else
+# define SECP256K1_API
+# endif
+#endif
+
/**Warning attributes
* NONNULL is not used if SECP256K1_BUILD is set to avoid the compiler optimizing out
* some paranoid null checks. */
# define SECP256K1_ARG_NONNULL(_x)
# endif
-/** Opaque data structure that holds context information (precomputed tables etc.).
- * Only functions that take a pointer to a non-const context require exclusive
- * access to it. Multiple functions that take a pointer to a const context may
- * run simultaneously.
+/** 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)
+
+/** Flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and
+ * secp256k1_context_preallocated_create. */
+#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)
+#define SECP256K1_CONTEXT_DECLASSIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_DECLASSIFY)
+#define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT)
+
+/** 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 simple secp256k1 context object with no precomputed tables. These are useful for
+ * type serialization/parsing functions which require a context object to maintain
+ * API consistency, but currently do not require expensive precomputations or dynamic
+ * allocations.
*/
-typedef struct secp256k1_context_struct secp256k1_context_t;
-
-/** Flags to pass to secp256k1_context_create. */
-# define SECP256K1_CONTEXT_VERIFY (1 << 0)
-# define SECP256K1_CONTEXT_SIGN (1 << 1)
+SECP256K1_API extern const secp256k1_context *secp256k1_context_no_precomp;
-/** Create a secp256k1 context object.
+/** 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 the functions in secp256k1_preallocated.h.
+ *
* Returns: a newly created context object.
* In: flags: which parts of the context to initialize.
+ *
+ * See also secp256k1_context_randomize.
*/
-secp256k1_context_t* secp256k1_context_create(
- int flags
+SECP256K1_API secp256k1_context* secp256k1_context_create(
+ unsigned int flags
) SECP256K1_WARN_UNUSED_RESULT;
-/** Copies a secp256k1 context object.
+/** Copy a secp256k1 context object (into dynamically allocated memory).
+ *
+ * This function uses malloc to allocate memory. It is guaranteed that malloc is
+ * called at most once for every call of this function. If you need to avoid dynamic
+ * memory allocation entirely, see the functions in secp256k1_preallocated.h.
+ *
* Returns: a newly created context object.
- * In: ctx: an existing context to copy
+ * Args: ctx: an existing context to copy (cannot be NULL)
*/
-secp256k1_context_t* secp256k1_context_clone(
- const secp256k1_context_t* ctx
-) SECP256K1_WARN_UNUSED_RESULT;
+SECP256K1_API secp256k1_context* secp256k1_context_clone(
+ const secp256k1_context* ctx
+) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT;
-/** Destroy a secp256k1 context object.
+/** Destroy a secp256k1 context object (created in dynamically allocated memory).
+ *
* The context pointer may not be used afterwards.
+ *
+ * The context to destroy must have been created using secp256k1_context_create
+ * or secp256k1_context_clone. If the context has instead been created using
+ * secp256k1_context_preallocated_create or secp256k1_context_preallocated_clone, the
+ * behaviour is undefined. In that case, secp256k1_context_preallocated_destroy must
+ * be used instead.
+ *
+ * Args: ctx: an existing context to destroy, constructed using
+ * secp256k1_context_create or secp256k1_context_clone
*/
-void secp256k1_context_destroy(
- secp256k1_context_t* ctx
-) SECP256K1_ARG_NONNULL(1);
+SECP256K1_API void secp256k1_context_destroy(
+ secp256k1_context* ctx
+);
/** Set a callback function to be called when an illegal argument is passed to
- * an API call. The philosophy is that these shouldn't be dealt with through a
+ * an API call. It will only trigger for violations that are mentioned
+ * explicitly in the header.
+ *
+ * The philosophy is that these shouldn't be dealt with through a
* specific return value, as calling code should not have branches to deal with
* the case that this code itself is broken.
+ *
* On the other hand, during debug stage, one would want to be informed about
* such mistakes, and the default (crashing) may be inadvisable.
* When this callback is triggered, the API function called is guaranteed not
* to cause a crash, though its return value and output arguments are
* undefined.
+ *
+ * When this function has not been called (or called with fn==NULL), then the
+ * default handler will be used. The library provides a default handler which
+ * writes the message to stderr and calls abort. This default handler can be
+ * replaced at link time if the preprocessor macro
+ * USE_EXTERNAL_DEFAULT_CALLBACKS is defined, which is the case if the build
+ * has been configured with --enable-external-default-callbacks. Then the
+ * following two symbols must be provided to link against:
+ * - void secp256k1_default_illegal_callback_fn(const char* message, void* data);
+ * - void secp256k1_default_error_callback_fn(const char* message, void* data);
+ * The library can call these default handlers even before a proper callback data
+ * pointer could have been set using secp256k1_context_set_illegal_callback or
+ * secp256k1_context_set_error_callback, e.g., when the creation of a context
+ * fails. In this case, the corresponding default handler will be called with
+ * the data pointer argument set to NULL.
+ *
+ * Args: ctx: an existing context object (cannot be NULL)
+ * In: fun: a pointer to a function to call when an illegal argument is
+ * passed to the API, taking a message and an opaque pointer.
+ * (NULL restores the default handler.)
+ * data: the opaque pointer to pass to fun above.
+ *
+ * See also secp256k1_context_set_error_callback.
*/
-void secp256k1_context_set_illegal_callback(
- secp256k1_context_t* ctx,
- void (*fun)(const char* message, void* data),
- void* data
-) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
+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 is crashing.
+ *
* This can only trigger in case of a hardware failure, miscompilation,
* memory corruption, serious bug in the library, or other error would can
* otherwise result in undefined behaviour. It will not trigger due to mere
* incorrect usage of the API (see secp256k1_context_set_illegal_callback
* for that). After this callback returns, anything may happen, including
* crashing.
+ *
+ * Args: ctx: an existing context object (cannot be NULL)
+ * In: fun: a pointer to a function to call when an internal error occurs,
+ * taking a message and an opaque pointer (NULL restores the
+ * default handler, see secp256k1_context_set_illegal_callback
+ * for details).
+ * data: the opaque pointer to pass to fun above.
+ *
+ * See also secp256k1_context_set_illegal_callback.
*/
-void secp256k1_context_set_error_callback(
- secp256k1_context_t* ctx,
- void (*fun)(const char* message, void* data),
- void* data
-) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);
+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);
-/** Data type to hold a parsed and valid public key.
- This data type should be considered opaque to the user, and only created
- through API functions. It is not guaranteed to be compatible between
- different implementations. If you need to convert to a format suitable
- for storage or transmission, use secp256k1_ec_pubkey_serialize and
- secp256k1_ec_pubkey_parse.
+/** Create a secp256k1 scratch space object.
+ *
+ * Returns: a newly created scratch space.
+ * Args: ctx: an existing context object (cannot be NULL)
+ * In: size: amount of memory to be available as scratch space. Some extra
+ * (<100 bytes) will be allocated for extra accounting.
*/
-typedef struct {
- unsigned char data[64];
-} secp256k1_pubkey_t;
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT secp256k1_scratch_space* secp256k1_scratch_space_create(
+ const secp256k1_context* ctx,
+ size_t size
+) SECP256K1_ARG_NONNULL(1);
+
+/** Destroy a secp256k1 scratch space.
+ *
+ * The pointer may not be used afterwards.
+ * Args: ctx: a secp256k1 context object.
+ * scratch: space to destroy
+ */
+SECP256K1_API void secp256k1_scratch_space_destroy(
+ const secp256k1_context* ctx,
+ secp256k1_scratch_space* scratch
+) SECP256K1_ARG_NONNULL(1);
/** Parse a variable-length public key into the pubkey object.
+ *
* Returns: 1 if the public key was fully valid.
* 0 if the public key could not be parsed or is invalid.
- * In: ctx: a secp256k1 context object.
- * input: pointer to a serialized public key
- * inputlen: length of the array pointed to by input
- * 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.
+ * Args: ctx: a secp256k1 context object.
+ * Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to a
+ * parsed version of input. If not, its value is undefined.
+ * In: input: pointer to a serialized public key
+ * inputlen: length of the array pointed to by input
+ *
* This function supports parsing compressed (33 bytes, header byte 0x02 or
* 0x03), uncompressed (65 bytes, header byte 0x04), or hybrid (65 bytes, header
* byte 0x06 or 0x07) format public keys.
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_parse(
- const secp256k1_context_t* ctx,
- secp256k1_pubkey_t* pubkey,
- const unsigned char *input,
- int inputlen
+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.
- * In: ctx: a secp256k1 context object.
- * pubkey: a pointer to a secp256k1_pubkey_t containing an initialized
- * public key.
- * compressed: whether to serialize in compressed format.
- * Out: output: a pointer to a 65-byte (if compressed==0) or 33-byte (if
- * compressed==1) byte array to place the serialized key in.
- * outputlen: a pointer to an integer which will contain the serialized
- * size.
- */
-int secp256k1_ec_pubkey_serialize(
- const secp256k1_context_t* ctx,
- unsigned char *output,
- int *outputlen,
- const secp256k1_pubkey_t* pubkey,
- int compressed
+ * Args: ctx: a secp256k1 context object.
+ * Out: output: a pointer to a 65-byte (if compressed==0) or 33-byte (if
+ * compressed==1) byte array to place the serialized key
+ * in.
+ * In/Out: outputlen: a pointer to an integer which is initially set to the
+ * size of output, and is overwritten with the written
+ * size.
+ * In: pubkey: a pointer to a secp256k1_pubkey containing an
+ * initialized public key.
+ * flags: SECP256K1_EC_COMPRESSED if serialization should be in
+ * compressed format, otherwise SECP256K1_EC_UNCOMPRESSED.
+ */
+SECP256K1_API int secp256k1_ec_pubkey_serialize(
+ const secp256k1_context* ctx,
+ unsigned char *output,
+ size_t *outputlen,
+ const secp256k1_pubkey* pubkey,
+ unsigned int flags
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
-/** Data type to hold a parsed ECDSA signature, optionally supporting pubkey
- * recovery.
- This data type should be considered opaque to the user, and only created
- through API functions. It is not guaranteed to be compatible between
- different implementations. If you need to convert to a format suitable
- for storage or transmission, use secp256k1_ecdsa_signature_serialize_* and
- secp256k1_ecdsa_signature_parse_* functions. */
-typedef struct {
- unsigned char data[65];
-} secp256k1_ecdsa_signature_t;
-
-/** Parse a DER ECDSA signature.
+/** Parse an ECDSA signature in compact (64 bytes) format.
+ *
* Returns: 1 when the signature could be parsed, 0 otherwise.
- * In: ctx: a secp256k1 context object
- * input: a pointer to the signature to be parsed
- * inputlen: the length of the array pointed to be input
- * Out: sig: a pointer to a signature object
+ * Args: ctx: a secp256k1 context object
+ * Out: sig: a pointer to a signature object
+ * In: input64: a pointer to the 64-byte array to parse
*
- * Note that this function also supports some violations of DER.
+ * 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.
*
- * The resulting signature object will not support pubkey recovery.
+ * 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 validation for any
+ * message and public key.
*/
-int secp256k1_ecdsa_signature_parse_der(
- const secp256k1_context_t* ctx,
- secp256k1_ecdsa_signature_t* sig,
- const unsigned char *input,
- int inputlen
+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 compact ECDSA signature (64 bytes + recovery id).
- * Returns: 1 when the signature could be parsed, 0 otherwise
- * In: ctx: a secp256k1 context object
- * input64: a pointer to a 64-byte compact signature
- * recid: the recovery id (0, 1, 2 or 3, or -1 for unknown)
- * Out: sig: a pointer to a signature object
- *
- * If recid is not -1, the resulting signature object will support pubkey
- * recovery.
- */
-int secp256k1_ecdsa_signature_parse_compact(
- const secp256k1_context_t* ctx,
- secp256k1_ecdsa_signature_t* sig,
- const unsigned char *input64,
- int recid
+/** Parse a DER ECDSA signature.
+ *
+ * Returns: 1 when the signature could be parsed, 0 otherwise.
+ * Args: ctx: a secp256k1 context object
+ * Out: sig: a pointer to a signature object
+ * In: input: a pointer to the signature to be parsed
+ * inputlen: the length of the array pointed to be input
+ *
+ * This function will accept any valid DER encoded signature, even if the
+ * encoded numbers are out of range.
+ *
+ * After the call, sig will always be initialized. If parsing failed or the
+ * encoded numbers are out of range, signature validation 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
- * In: ctx: a secp256k1 context object
- * sig: a pointer to an initialized signature object
+ * Args: ctx: a secp256k1 context object
* Out: output: a pointer to an array to store the DER serialization
* In/Out: outputlen: a pointer to a length integer. Initially, this integer
* should be set to the length of output. After the call
* it will be set to the length of the serialization (even
* if 0 was returned).
+ * In: sig: a pointer to an initialized signature object
*/
-int secp256k1_ecdsa_signature_serialize_der(
- const secp256k1_context_t* ctx,
- unsigned char *output,
- int *outputlen,
- const secp256k1_ecdsa_signature_t* sig
+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 format (64 bytes + recovery id).
+/** Serialize an ECDSA signature in compact (64 byte) format.
+ *
* Returns: 1
- * In: ctx: a secp256k1 context object
- * sig: a pointer to an initialized signature object (cannot be NULL)
- * Out: output64: a pointer to a 64-byte array of the compact signature (cannot be NULL)
- * recid: a pointer to an integer to hold the recovery id (can be NULL).
+ * Args: ctx: a secp256k1 context object
+ * Out: output64: a pointer to a 64-byte array to store the compact serialization
+ * In: sig: a pointer to an initialized signature object
*
- * If recid is not NULL, the signature must support pubkey recovery.
+ * See secp256k1_ecdsa_signature_parse_compact for details about the encoding.
*/
-int secp256k1_ecdsa_signature_serialize_compact(
- const secp256k1_context_t* ctx,
- unsigned char *output64,
- int *recid,
- const secp256k1_ecdsa_signature_t* sig
-) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4);
+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
- * In: ctx: a secp256k1 context object, initialized for verification.
+ * Args: ctx: a secp256k1 context object, initialized for verification.
+ * In: sig: the signature being verified (cannot be NULL)
* msg32: the 32-byte message hash being verified (cannot be NULL)
- * sig: the signature being verified (cannot be NULL)
* pubkey: pointer to an initialized public key to verify with (cannot be NULL)
+ *
+ * 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
+ * validation, but be aware that doing so results in malleable signatures.
+ *
+ * For details, see the comments for that function.
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify(
- const secp256k1_context_t* ctx,
- const unsigned char *msg32,
- const secp256k1_ecdsa_signature_t *sig,
- const secp256k1_pubkey_t *pubkey
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify(
+ const secp256k1_context* ctx,
+ const secp256k1_ecdsa_signature *sig,
+ const unsigned char *msg32,
+ const secp256k1_pubkey *pubkey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
-/** A pointer to a function to deterministically generate a nonce.
- * Returns: 1 if a nonce was successfully generated. 0 will cause signing to fail.
- * 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).
- * 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.
- * data: Arbitrary data pointer that is passed through.
- * Out: nonce32: pointer to a 32-byte array to be filled by the function.
- * Except for test cases, this function should compute some cryptographic hash of
- * the message, the key and the attempt.
- */
-typedef int (*secp256k1_nonce_function_t)(
- unsigned char *nonce32,
- const unsigned char *msg32,
- const unsigned char *key32,
- const unsigned char *algo16,
- unsigned int attempt,
- const void *data
-);
+/** Convert a signature to a normalized lower-S form.
+ *
+ * Returns: 1 if sigin was not normalized, 0 if it already was.
+ * Args: ctx: a secp256k1 context object
+ * Out: sigout: a pointer to a signature to fill with the normalized form,
+ * or copy if the input was already normalized. (can be NULL if
+ * you're only interested in whether the input was already
+ * normalized).
+ * In: sigin: a pointer to a signature to check/normalize (cannot be NULL,
+ * 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.
*/
-extern const secp256k1_nonce_function_t secp256k1_nonce_function_rfc6979;
+SECP256K1_API extern const secp256k1_nonce_function secp256k1_nonce_function_rfc6979;
/** A default safe nonce generation function (currently equal to secp256k1_nonce_function_rfc6979). */
-extern const secp256k1_nonce_function_t secp256k1_nonce_function_default;
+SECP256K1_API extern const secp256k1_nonce_function secp256k1_nonce_function_default;
/** Create an ECDSA signature.
+ *
* Returns: 1: signature created
* 0: the nonce generation function failed, or the private key was invalid.
- * In: ctx: pointer to a context object, initialized for signing (cannot be NULL)
- * msg32: the 32-byte message hash being signed (cannot be NULL)
+ * Args: ctx: pointer to a context object, initialized for signing (cannot be NULL)
+ * Out: sig: pointer to an array where the signature will be placed (cannot be NULL)
+ * In: msg32: the 32-byte message hash being signed (cannot be NULL)
* seckey: pointer to a 32-byte secret key (cannot be NULL)
* 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)
- * Out: sig: pointer to an array where the signature will be placed (cannot be NULL)
*
- * The resulting signature will support pubkey recovery.
- *
- * The sig always has an s value in the lower half of the range (From 0x1
- * to 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0,
- * inclusive), unlike many other implementations.
- * With ECDSA a third-party can can forge a second distinct signature
- * of the same message given a single initial signature without knowing
- * the key by setting s to its additive inverse mod-order, 'flipping' the
- * sign of the random point R which is not included in the signature.
- * Since the forgery is of the same message this 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 canonical 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. Adjusting it inside the signing
- * function avoids the need to re-serialize or have curve specific
- * constants outside of the library. By always using a canonical form
- * even in applications where it isn't needed it becomes possible to
- * impose a requirement later if a need is discovered.
- * 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.
- */
-int secp256k1_ecdsa_sign(
- const secp256k1_context_t* ctx,
- const unsigned char *msg32,
- secp256k1_ecdsa_signature_t *sig,
- const unsigned char *seckey,
- secp256k1_nonce_function_t noncefp,
- const void *ndata
-) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
-
-/** Recover an ECDSA public key from a signature.
- * Returns: 1: public key successfully recovered (which guarantees a correct signature).
- * 0: otherwise.
- * In: ctx: pointer to a context object, initialized for verification (cannot be NULL)
- * msg32: the 32-byte message hash assumed to be signed (cannot be NULL)
- * sig64: pointer to initialized signature that supports pubkey recovery (cannot be NULL)
- * Out: pubkey: pointer to the recoved public key (cannot be NULL)
- */
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_recover(
- const secp256k1_context_t* ctx,
- const unsigned char *msg32,
- const secp256k1_ecdsa_signature_t *sig,
- secp256k1_pubkey_t *pubkey
+ * 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 *msg32,
+ 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.
+ *
* Returns: 1: secret key is valid
* 0: secret key is invalid
- * In: ctx: pointer to a context object (cannot be NULL)
- * seckey: pointer to a 32-byte secret key (cannot be NULL)
+ * Args: ctx: pointer to a context object (cannot be NULL)
+ * In: seckey: pointer to a 32-byte secret key (cannot be NULL)
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_verify(
- const secp256k1_context_t* ctx,
- const unsigned char *seckey
+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.
- * In: ctx: pointer to a context object, initialized for signing (cannot be NULL)
- * seckey: pointer to a 32-byte private key (cannot be NULL)
- * Out: pubkey: pointer to the created public key (cannot be NULL)
+ *
* Returns: 1: secret was valid, public key stores
* 0: secret was invalid, try again
+ * Args: ctx: pointer to a context object, initialized for signing (cannot be NULL)
+ * Out: pubkey: pointer to the created public key (cannot be NULL)
+ * In: seckey: pointer to a 32-byte private key (cannot be NULL)
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_create(
- const secp256k1_context_t* ctx,
- secp256k1_pubkey_t *pubkey,
- const unsigned char *seckey
+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);
-/** Export a private key in DER format.
- * In: ctx: pointer to a context object, initialized for signing (cannot be NULL)
+/** Negates a private key in place.
+ *
+ * Returns: 1 always
+ * Args: ctx: pointer to a context object
+ * In/Out: seckey: pointer to the 32-byte private key to be negated (cannot be NULL)
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_export(
- const secp256k1_context_t* ctx,
- const unsigned char *seckey,
- unsigned char *privkey,
- int *privkeylen,
- int compressed
-) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
+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);
-/** Import a private key in DER format. */
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_import(
- const secp256k1_context_t* ctx,
- unsigned char *seckey,
- const unsigned char *privkey,
- int privkeylen
-) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
+/** 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 (cannot be NULL)
+ */
+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 private key by adding tweak to it. */
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_add(
- const secp256k1_context_t* ctx,
- unsigned char *seckey,
- const unsigned char *tweak
+/** Tweak a private key by adding tweak to it.
+ * Returns: 0 if the tweak was out of range (chance of around 1 in 2^128 for
+ * uniformly random 32-byte arrays, or if the resulting private key
+ * would be invalid (only when the tweak is the complement of the
+ * private key). 1 otherwise.
+ * Args: ctx: pointer to a context object (cannot be NULL).
+ * In/Out: seckey: pointer to a 32-byte private key.
+ * In: tweak: pointer to a 32-byte tweak.
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_add(
+ const secp256k1_context* ctx,
+ unsigned char *seckey,
+ const unsigned char *tweak
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Tweak a public key by adding tweak times the generator to it.
- * In: ctx: pointer to a context object, initialized for verification (cannot be NULL)
+ * Returns: 0 if the tweak was out of range (chance of around 1 in 2^128 for
+ * uniformly random 32-byte arrays, or if the resulting public key
+ * would be invalid (only when the tweak is the complement of the
+ * corresponding private key). 1 otherwise.
+ * Args: ctx: pointer to a context object initialized for validation
+ * (cannot be NULL).
+ * In/Out: pubkey: pointer to a public key object.
+ * In: tweak: pointer to a 32-byte tweak.
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
- const secp256k1_context_t* ctx,
- secp256k1_pubkey_t *pubkey,
- const unsigned char *tweak
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
+ const secp256k1_context* ctx,
+ secp256k1_pubkey *pubkey,
+ const unsigned char *tweak
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
-/** Tweak a private key by multiplying it with tweak. */
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_mul(
- const secp256k1_context_t* ctx,
- unsigned char *seckey,
- const unsigned char *tweak
+/** Tweak a private key by multiplying it by a tweak.
+ * Returns: 0 if the tweak was out of range (chance of around 1 in 2^128 for
+ * uniformly random 32-byte arrays, or equal to zero. 1 otherwise.
+ * Args: ctx: pointer to a context object (cannot be NULL).
+ * In/Out: seckey: pointer to a 32-byte private key.
+ * In: tweak: pointer to a 32-byte tweak.
+ */
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_mul(
+ const secp256k1_context* ctx,
+ unsigned char *seckey,
+ const unsigned char *tweak
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
-/** Tweak a public key by multiplying it with tweak.
- * In: ctx: pointer to a context object, initialized for verification (cannot be NULL)
+/** Tweak a public key by multiplying it by a tweak value.
+ * Returns: 0 if the tweak was out of range (chance of around 1 in 2^128 for
+ * uniformly random 32-byte arrays, or equal to zero. 1 otherwise.
+ * Args: ctx: pointer to a context object initialized for validation
+ * (cannot be NULL).
+ * In/Out: pubkey: pointer to a public key object.
+ * In: tweak: pointer to a 32-byte tweak.
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
- const secp256k1_context_t* ctx,
- secp256k1_pubkey_t *pubkey,
- const unsigned char *tweak
+SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
+ const secp256k1_context* ctx,
+ secp256k1_pubkey *pubkey,
+ const unsigned char *tweak
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
-/** Updates the context randomization.
- * Returns: 1: randomization successfully updated
+/** Updates the context randomization to protect against side-channel leakage.
+ * Returns: 1: randomization successfully updated or nothing to randomize
* 0: error
- * In: ctx: pointer to a context object (cannot be NULL)
- * seed32: pointer to a 32-byte random seed (NULL resets to initial state)
+ * Args: ctx: pointer to a context object (cannot be NULL)
+ * In: seed32: pointer to a 32-byte random seed (NULL resets to initial state)
+ *
+ * While secp256k1 code is written to be constant-time no matter what secret
+ * values are, it's possible that a future compiler may output code which isn't,
+ * and also that the CPU may not emit the same radio frequencies or draw the same
+ * amount power for all values.
+ *
+ * This function provides a seed which is combined into the blinding value: that
+ * blinding value is added before each multiplication (and removed afterwards) so
+ * that it does not affect function results, but shields against attacks which
+ * rely on any input-dependent behaviour.
+ *
+ * This function has currently an effect only on contexts initialized for signing
+ * because randomization is currently used only for signing. However, this is not
+ * guaranteed and may change in the future. It is safe to call this function on
+ * contexts not initialized for signing; then it will have no effect and return 1.
+ *
+ * You should call this after secp256k1_context_create or
+ * secp256k1_context_clone (and secp256k1_context_preallocated_create or
+ * secp256k1_context_clone, resp.), and you may call this repeatedly afterwards.
*/
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize(
- secp256k1_context_t* ctx,
- const unsigned char *seed32
+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.
- * In: ctx: pointer to a context object
- * out: pointer to pubkey for placing the resulting public key
+ * Args: ctx: pointer to a context object
+ * Out: out: pointer to a public key object for placing the resulting public key
* (cannot be NULL)
+ * In: ins: pointer to array of pointers to public keys (cannot be NULL)
* n: the number of public keys to add together (must be at least 1)
- * ins: pointer to array of pointers to public keys (cannot be NULL)
- * Use secp256k1_ec_pubkey_compress and secp256k1_ec_pubkey_decompress if the
- * uncompressed format is needed.
- */
-SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_combine(
- const secp256k1_context_t* ctx,
- secp256k1_pubkey_t *out,
- int n,
- const secp256k1_pubkey_t * const * ins
-) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4);
-
-# ifdef __cplusplus
+ */
+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(2) SECP256K1_ARG_NONNULL(3);
+
+#ifdef __cplusplus
}
-# endif
-
#endif
+
+#endif /* SECP256K1_H */
projects / secp256k1.git / blobdiff