bitcoin/include/secp256k1.h

#ifndef _SECP256K1_
# define _SECP256K1_

# ifdef __cplusplus
extern "C" {
# 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 call that take a non-const pointer to a context
 *  need exclusive access to it. In particular this is the case for
 *  secp256k1_context_destroy and secp256k1_context_randomize.
 *
 *  Regarding randomization, either do it once at creation time (in which case
 *  you do not need any locking for the other calls), or use a read-write lock.
 */
typedef struct secp256k1_context_struct secp256k1_context;

/** Opaque data structure that holds a parsed and valid public key.
 *
 *  The exact representation of data inside is implementation defined and not
 *  guaranteed to be portable between different platforms or versions. It is
 *  however guaranteed to be 64 bytes in size, and can be safely copied/moved.
 *  If you need to convert to a format suitable for storage or transmission, use
 *  secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse.
 *
 *  Furthermore, it is guaranteed that identical public keys (ignoring
 *  compression) will have identical representation, so they can be memcmp'ed.
 */
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 or transmission, use
 *  the secp256k1_ecdsa_signature_serialize_* and
 *  secp256k1_ecdsa_signature_serialize_* functions.
 *
 *  Furthermore, it is guaranteed to identical signatures will have identical
 *  representation, so they can be memcmp'ed.
 */
typedef struct {
    unsigned char data[64];
} secp256k1_ecdsa_signature;

/** A pointer to a function to deterministically generate a nonce.
 *
 * Returns: 1 if a nonce was successfully generated. 0 will cause signing to fail.
 * Out:     nonce32:   pointer to a 32-byte array to be filled by the function.
 * In:      msg32:     the 32-byte message hash being verified (will not be NULL)
 *          key32:     pointer to a 32-byte secret key (will not be NULL)
 *          algo16:    pointer to a 16-byte array describing the signature
 *                     algorithm (will be NULL for ECDSA for compatibility).
 *          data:      Arbitrary data pointer that is passed through.
 *          attempt:   how many iterations we have tried to find a nonce.
 *                     This will almost always be 0, but different attempt values
 *                     are required to result in a different nonce.
 *
 * Except for test cases, this function should compute some cryptographic hash of
 * the message, the algorithm, the key and the attempt.
 */
typedef int (*secp256k1_nonce_function)(
    unsigned char *nonce32,
    const unsigned char *msg32,
    const unsigned char *key32,
    const unsigned char *algo16,
    void *data,
    unsigned int attempt
);

# if !defined(SECP256K1_GNUC_PREREQ)
#  if defined(__GNUC__)&&defined(__GNUC_MINOR__)
#   define SECP256K1_GNUC_PREREQ(_maj,_min) \
 ((__GNUC__<<16)+__GNUC_MINOR__>=((_maj)<<16)+(_min))
#  else
#   define SECP256K1_GNUC_PREREQ(_maj,_min) 0
#  endif
# endif

# if (!defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L) )
#  if SECP256K1_GNUC_PREREQ(2,7)
#   define SECP256K1_INLINE __inline__
#  elif (defined(_MSC_VER))
#   define SECP256K1_INLINE __inline
#  else
#   define SECP256K1_INLINE
#  endif
# else
#  define SECP256K1_INLINE inline
# endif

/**Warning attributes
  * NONNULL is not used if SECP256K1_BUILD is set to avoid the compiler optimizing out
  * some paranoid null checks. */
# if defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
#  define SECP256K1_WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
# else
#  define SECP256K1_WARN_UNUSED_RESULT
# endif
# if !defined(SECP256K1_BUILD) && defined(__GNUC__) && SECP256K1_GNUC_PREREQ(3, 4)
#  define SECP256K1_ARG_NONNULL(_x)  __attribute__ ((__nonnull__(_x)))
# else
#  define SECP256K1_ARG_NONNULL(_x)
# endif

/** Flags to pass to secp256k1_context_create. */
# define SECP256K1_CONTEXT_VERIFY (1 << 0)
# define SECP256K1_CONTEXT_SIGN   (1 << 1)

/** Flag to pass to secp256k1_ec_pubkey_serialize and secp256k1_ec_privkey_export. */
# define SECP256K1_EC_COMPRESSED  (1 << 0)

/** Create a secp256k1 context object.
 *
 *  Returns: a newly created context object.
 *  In:      flags: which parts of the context to initialize.
 */
secp256k1_context* secp256k1_context_create(
    unsigned int flags
) SECP256K1_WARN_UNUSED_RESULT;

/** Copies a secp256k1 context object.
 *
 *  Returns: a newly created context object.
 *  Args:    ctx: an existing context to copy (cannot be NULL)
 */
secp256k1_context* secp256k1_context_clone(
    const secp256k1_context* ctx
) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT;

/** Destroy a secp256k1 context object.
 *
 *  The context pointer may not be used afterwards.
 *  Args:   ctx: an existing context to destroy (cannot be NULL)
 */
void secp256k1_context_destroy(
    secp256k1_context* ctx
);

/** Set a callback function to be called when an illegal argument is passed to
 *  an API call. It will only trigger for violations that are mentioned
 *  explicitly in the header.
 *
 *  The philosophy is that these shouldn't be dealt with through a
 *  specific return value, as calling code should not have branches to deal with
 *  the case that this code itself is broken.
 *
 *  On the other hand, during debug stage, one would want to be informed about
 *  such mistakes, and the default (crashing) may be inadvisable.
 *  When this callback is triggered, the API function called is guaranteed not
 *  to cause a crash, though its return value and output arguments are
 *  undefined.
 *
 *  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 a default handler that calls abort).
 *        data: the opaque pointer to pass to fun above.
 */
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 interal error occurs,
 *              taking a message and an opaque pointer (NULL restores a default
 *              handler that calls abort).
 *        data: the opaque pointer to pass to fun above.
 */
void secp256k1_context_set_error_callback(
    secp256k1_context* ctx,
    void (*fun)(const char* message, void* data),
    const void* data
) SECP256K1_ARG_NONNULL(1);

/** Parse a variable-length public key into the pubkey object.
 *
 *  Returns: 1 if the public key was fully valid.
 *           0 if the public key could not be parsed or is invalid.
 *  Args: ctx:      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* ctx,
    secp256k1_pubkey* pubkey,
    const unsigned char *input,
    size_t inputlen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Serialize a pubkey object into a serialized byte sequence.
 *
 *  Returns: 1 always.
 *  Args: ctx:        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.
 *        outputlen:  a pointer to an integer which will contain the serialized
 *                    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.
 */
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);

/** 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
 *
 *  Note that this function also supports some violations of DER and even BER.
 */
int secp256k1_ecdsa_signature_parse_der(
    const secp256k1_context* ctx,
    secp256k1_ecdsa_signature* sig,
    const unsigned char *input,
    size_t inputlen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Serialize an ECDSA signature in DER format.
 *
 *  Returns: 1 if enough space was available to serialize, 0 otherwise
 *  Args:   ctx:       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* 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);

/** Verify an ECDSA signature.
 *
 *  Returns: 1: correct signature
 *           0: incorrect or unparseable signature
 *  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)
 *           pubkey:    pointer to an initialized public key to verify with (cannot be NULL)
 */
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);

/** 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 secp256k1_nonce_function_rfc6979;

/** A default safe nonce generation function (currently equal to secp256k1_nonce_function_rfc6979). */
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.
 *  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)
 *
 * 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* 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
 *  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* ctx,
    const unsigned char *seckey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);

/** Compute the public key for a secret key.
 *
 *  Returns: 1: secret was valid, public key stores
 *           0: secret was invalid, try again
 *  Args:   ctx:        pointer to a context object, 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* 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 BER format.
 *
 *  Returns: 1 if the private key was valid.
 *  Args: ctx:        pointer to a context object, initialized for signing (cannot
 *                    be NULL)
 *  Out: privkey:     pointer to an array for storing the private key in BER.
 *                    Should have space for 279 bytes, and cannot be NULL.
 *       privkeylen:  Pointer to an int where the length of the private key in
 *                    privkey will be stored.
 *  In:  seckey:      pointer to a 32-byte secret key to export.
 *       flags:       SECP256K1_EC_COMPRESSED if the key should be exported in
 *                    compressed format.
 *
 *  This function is purely meant for compatibility with applications that
 *  require BER encoded keys. When working with secp256k1-specific code, the
 *  simple 32-byte private keys are sufficient.
 *
 *  Note that this function does not guarantee correct DER output. It is
 *  guaranteed to be parsable by secp256k1_ec_privkey_import.
 */
SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_export(
    const secp256k1_context* ctx,
    unsigned char *privkey,
    size_t *privkeylen,
    const unsigned char *seckey,
    unsigned int flags
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

/** Import a private key in DER format.
 * Returns: 1 if a private key was extracted.
 * Args: ctx:        pointer to a context object (cannot be NULL).
 * Out:  seckey:     pointer to a 32-byte array for storing the private key.
 *                   (cannot be NULL).
 * In:   privkey:    pointer to a private key in DER format (cannot be NULL).
 *       privkeylen: length of the DER private key pointed to be privkey.
 *
 * This function will accept more than just strict DER, and even allow some BER
 * violations. The public key stored inside the DER-encoded private key is not
 * verified for correctness, nor are the curve parameters. Use this function
 * only if you know in advance it is supposed to contain a secp256k1 private
 * key.
 */
SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_import(
    const secp256k1_context* ctx,
    unsigned char *seckey,
    const unsigned char *privkey,
    size_t privkeylen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** 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_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.
 * 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* 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 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_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 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 obkect.
 * In:      tweak:  pointer to a 32-byte tweak.
 */
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
 *           0: error
 *  Args:    ctx:       pointer to a context object (cannot be NULL)
 *  In:      seed32:    pointer to a 32-byte random seed (NULL resets to initial state)
 */
SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize(
    secp256k1_context* ctx,
    const unsigned char *seed32
) SECP256K1_ARG_NONNULL(1);

/** Add a number of public keys together.
 *  Returns: 1: the sum of the public keys is valid.
 *           0: the sum of the public keys is not valid.
 *  Args:   ctx:        pointer to a context object
 *  Out:    out:        pointer to pubkey 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)
 *  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* ctx,
    secp256k1_pubkey *out,
    const secp256k1_pubkey * const * ins,
    int n
) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

# ifdef __cplusplus
}
# endif

#endif