294 lines
15 KiB
C
294 lines
15 KiB
C
#ifndef _SECP256K1_RANGEPROOF_
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# define _SECP256K1_RANGEPROOF_
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# include "secp256k1.h"
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# include "secp256k1_generator.h"
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# ifdef __cplusplus
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extern "C" {
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# endif
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#include <stdint.h>
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/** Opaque data structure that stores a Pedersen commitment
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*
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* The exact representation of data inside is implementation defined and not
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* guaranteed to be portable between different platforms or versions. It is
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* however guaranteed to be 64 bytes in size, and can be safely copied/moved.
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* If you need to convert to a format suitable for storage, transmission, or
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* comparison, use secp256k1_pedersen_commitment_serialize and
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* secp256k1_pedersen_commitment_parse.
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*/
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typedef struct {
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unsigned char data[64];
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} secp256k1_pedersen_commitment;
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/**
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* Static constant generator 'h' maintained for historical reasons.
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*/
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SECP256K1_API extern const secp256k1_generator *secp256k1_generator_h;
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/** Parse a 33-byte commitment into a commitment object.
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*
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* Returns: 1 if input contains a valid commitment.
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* Args: ctx: a secp256k1 context object.
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* Out: commit: pointer to the output commitment object
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* In: input: pointer to a 33-byte serialized commitment key
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_commitment_parse(
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const secp256k1_context* ctx,
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secp256k1_pedersen_commitment* commit,
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const unsigned char *input
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
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/** Serialize a commitment object into a serialized byte sequence.
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*
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* Returns: 1 always.
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* Args: ctx: a secp256k1 context object.
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* Out: output: a pointer to a 33-byte byte array
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* In: commit: a pointer to a secp256k1_pedersen_commitment containing an
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* initialized commitment
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*/
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SECP256K1_API int secp256k1_pedersen_commitment_serialize(
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const secp256k1_context* ctx,
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unsigned char *output,
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const secp256k1_pedersen_commitment* commit
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
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/** Generate a pedersen commitment.
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* Returns 1: Commitment successfully created.
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* 0: Error. The blinding factor is larger than the group order
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* (probability for random 32 byte number < 2^-127) or results in the
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* point at infinity. Retry with a different factor.
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* In: ctx: pointer to a context object, initialized for signing and Pedersen commitment (cannot be NULL)
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* blind: pointer to a 32-byte blinding factor (cannot be NULL)
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* value: unsigned 64-bit integer value to commit to.
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* gen: additional generator 'h'
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* Out: commit: pointer to the commitment (cannot be NULL)
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*
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* Blinding factors can be generated and verified in the same way as secp256k1 private keys for ECDSA.
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_commit(
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const secp256k1_context* ctx,
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secp256k1_pedersen_commitment *commit,
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const unsigned char *blind,
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uint64_t value,
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const secp256k1_generator *gen
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(5);
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/** Computes the sum of multiple positive and negative blinding factors.
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* Returns 1: Sum successfully computed.
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* 0: Error. A blinding factor is larger than the group order
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* (probability for random 32 byte number < 2^-127). Retry with
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* different factors.
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* In: ctx: pointer to a context object (cannot be NULL)
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* blinds: pointer to pointers to 32-byte character arrays for blinding factors. (cannot be NULL)
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* n: number of factors pointed to by blinds.
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* npositive: how many of the initial factors should be treated with a positive sign.
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* Out: blind_out: pointer to a 32-byte array for the sum (cannot be NULL)
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_blind_sum(
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const secp256k1_context* ctx,
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unsigned char *blind_out,
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const unsigned char * const *blinds,
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size_t n,
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size_t npositive
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
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/** Verify a tally of pedersen commitments
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* Returns 1: commitments successfully sum to zero.
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* 0: Commitments do not sum to zero or other error.
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* In: ctx: pointer to a context object (cannot be NULL)
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* commits: pointer to array of pointers to the commitments. (cannot be NULL if pcnt is non-zero)
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* pcnt: number of commitments pointed to by commits.
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* ncommits: pointer to array of pointers to the negative commitments. (cannot be NULL if ncnt is non-zero)
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* ncnt: number of commitments pointed to by ncommits.
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*
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* This computes sum(commit[0..pcnt)) - sum(ncommit[0..ncnt)) == 0.
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*
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* A pedersen commitment is xG + vA where G and A are generators for the secp256k1 group and x is a blinding factor,
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* while v is the committed value. For a collection of commitments to sum to zero, for each distinct generator
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* A all blinding factors and all values must sum to zero.
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*
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_verify_tally(
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const secp256k1_context* ctx,
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const secp256k1_pedersen_commitment * const* commits,
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size_t pcnt,
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const secp256k1_pedersen_commitment * const* ncommits,
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size_t ncnt
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4);
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/** Sets the final Pedersen blinding factor correctly when the generators themselves
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* have blinding factors.
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*
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* Consider a generator of the form A' = A + rG, where A is the "real" generator
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* but A' is the generator provided to verifiers. Then a Pedersen commitment
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* P = vA' + r'G really has the form vA + (vr + r')G. To get all these (vr + r')
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* to sum to zero for multiple commitments, we take three arrays consisting of
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* the `v`s, `r`s, and `r'`s, respectively called `value`s, `generator_blind`s
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* and `blinding_factor`s, and sum them.
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*
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* The function then subtracts the sum of all (vr + r') from the last element
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* of the `blinding_factor` array, setting the total sum to zero.
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*
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* Returns 1: Blinding factor successfully computed.
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* 0: Error. A blinding_factor or generator_blind are larger than the group
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* order (probability for random 32 byte number < 2^-127). Retry with
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* different values.
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*
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* In: ctx: pointer to a context object
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* value: array of asset values, `v` in the above paragraph.
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* May not be NULL unless `n_total` is 0.
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* generator_blind: array of asset blinding factors, `r` in the above paragraph
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* May not be NULL unless `n_total` is 0.
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* n_total: Total size of the above arrays
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* n_inputs: How many of the initial array elements represent commitments that
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* will be negated in the final sum
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* In/Out: blinding_factor: array of commitment blinding factors, `r'` in the above paragraph
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* May not be NULL unless `n_total` is 0.
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* the last value will be modified to get the total sum to zero.
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_blind_generator_blind_sum(
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const secp256k1_context* ctx,
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const uint64_t *value,
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const unsigned char* const* generator_blind,
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unsigned char* const* blinding_factor,
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size_t n_total,
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size_t n_inputs
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);
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/** Verify a proof that a committed value is within a range.
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* Returns 1: Value is within the range [0..2^64), the specifically proven range is in the min/max value outputs.
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* 0: Proof failed or other error.
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* In: ctx: pointer to a context object, initialized for range-proof and commitment (cannot be NULL)
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* commit: the commitment being proved. (cannot be NULL)
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* proof: pointer to character array with the proof. (cannot be NULL)
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* plen: length of proof in bytes.
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* extra_commit: additional data covered in rangeproof signature
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* extra_commit_len: length of extra_commit byte array (0 if NULL)
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* gen: additional generator 'h'
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* Out: min_value: pointer to a unsigned int64 which will be updated with the minimum value that commit could have. (cannot be NULL)
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* max_value: pointer to a unsigned int64 which will be updated with the maximum value that commit could have. (cannot be NULL)
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_verify(
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const secp256k1_context* ctx,
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uint64_t *min_value,
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uint64_t *max_value,
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const secp256k1_pedersen_commitment *commit,
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const unsigned char *proof,
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size_t plen,
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const unsigned char *extra_commit,
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size_t extra_commit_len,
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const secp256k1_generator* gen
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5) SECP256K1_ARG_NONNULL(9);
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/** Verify a range proof proof and rewind the proof to recover information sent by its author.
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* Returns 1: Value is within the range [0..2^64), the specifically proven range is in the min/max value outputs, and the value and blinding were recovered.
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* 0: Proof failed, rewind failed, or other error.
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* In: ctx: pointer to a context object, initialized for range-proof and Pedersen commitment (cannot be NULL)
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* commit: the commitment being proved. (cannot be NULL)
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* proof: pointer to character array with the proof. (cannot be NULL)
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* plen: length of proof in bytes.
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* nonce: 32-byte secret nonce used by the prover (cannot be NULL)
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* extra_commit: additional data covered in rangeproof signature
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* extra_commit_len: length of extra_commit byte array (0 if NULL)
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* gen: additional generator 'h'
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* In/Out: blind_out: storage for the 32-byte blinding factor used for the commitment
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* value_out: pointer to an unsigned int64 which has the exact value of the commitment.
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* message_out: pointer to a 4096 byte character array to receive message data from the proof author.
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* outlen: length of message data written to message_out. This is generally not equal to the
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* msg_len used by the signer. However, for all i with msg_len <= i < outlen, it is
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* guaranteed that message_out[i] == 0.
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* min_value: pointer to an unsigned int64 which will be updated with the minimum value that commit could have. (cannot be NULL)
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* max_value: pointer to an unsigned int64 which will be updated with the maximum value that commit could have. (cannot be NULL)
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_rewind(
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const secp256k1_context* ctx,
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unsigned char *blind_out,
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uint64_t *value_out,
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unsigned char *message_out,
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size_t *outlen,
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const unsigned char *nonce,
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uint64_t *min_value,
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uint64_t *max_value,
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const secp256k1_pedersen_commitment *commit,
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const unsigned char *proof,
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size_t plen,
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const unsigned char *extra_commit,
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size_t extra_commit_len,
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const secp256k1_generator *gen
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(6) SECP256K1_ARG_NONNULL(7) SECP256K1_ARG_NONNULL(8) SECP256K1_ARG_NONNULL(9) SECP256K1_ARG_NONNULL(10) SECP256K1_ARG_NONNULL(14);
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/** Author a proof that a committed value is within a range.
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* Returns 1: Proof successfully created.
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* 0: Error
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* In: ctx: pointer to a context object, initialized for range-proof, signing, and Pedersen commitment (cannot be NULL)
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* proof: pointer to array to receive the proof, can be up to 5134 bytes. (cannot be NULL)
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* min_value: constructs a proof where the verifer can tell the minimum value is at least the specified amount.
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* commit: the commitment being proved.
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* blind: 32-byte blinding factor used by commit.
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* nonce: 32-byte secret nonce used to initialize the proof (value can be reverse-engineered out of the proof if this secret is known.)
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* exp: Base-10 exponent. Digits below above will be made public, but the proof will be made smaller. Allowed range is -1 to 18.
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* (-1 is a special case that makes the value public. 0 is the most private.)
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* min_bits: Number of bits of the value to keep private. (0 = auto/minimal, - 64).
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* value: Actual value of the commitment.
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* message: pointer to a byte array of data to be embedded in the rangeproof that can be recovered by rewinding the proof
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* msg_len: size of the message to be embedded in the rangeproof
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* extra_commit: additional data to be covered in rangeproof signature
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* extra_commit_len: length of extra_commit byte array (0 if NULL)
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* gen: additional generator 'h'
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* In/out: plen: point to an integer with the size of the proof buffer and the size of the constructed proof.
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*
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* If min_value or exp is non-zero then the value must be on the range [0, 2^63) to prevent the proof range from spanning past 2^64.
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*
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* If exp is -1 the value is revealed by the proof (e.g. it proves that the proof is a blinding of a specific value, without revealing the blinding key.)
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*
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* This can randomly fail with probability around one in 2^100. If this happens, buy a lottery ticket and retry with a different nonce or blinding.
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*
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_sign(
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const secp256k1_context* ctx,
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unsigned char *proof,
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size_t *plen,
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uint64_t min_value,
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const secp256k1_pedersen_commitment *commit,
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const unsigned char *blind,
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const unsigned char *nonce,
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int exp,
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int min_bits,
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uint64_t value,
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const unsigned char *message,
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size_t msg_len,
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const unsigned char *extra_commit,
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size_t extra_commit_len,
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const secp256k1_generator *gen
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(5) SECP256K1_ARG_NONNULL(6) SECP256K1_ARG_NONNULL(7) SECP256K1_ARG_NONNULL(15);
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/** Extract some basic information from a range-proof.
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* Returns 1: Information successfully extracted.
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* 0: Decode failed.
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* In: ctx: pointer to a context object
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* proof: pointer to character array with the proof.
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* plen: length of proof in bytes.
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* Out: exp: Exponent used in the proof (-1 means the value isn't private).
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* mantissa: Number of bits covered by the proof.
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* min_value: pointer to an unsigned int64 which will be updated with the minimum value that commit could have. (cannot be NULL)
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* max_value: pointer to an unsigned int64 which will be updated with the maximum value that commit could have. (cannot be NULL)
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_info(
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const secp256k1_context* ctx,
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int *exp,
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int *mantissa,
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uint64_t *min_value,
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uint64_t *max_value,
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const unsigned char *proof,
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size_t plen
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5);
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# ifdef __cplusplus
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}
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# endif
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#endif
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