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rangeproof: several API changes

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* add summing function for blinded generators
* drop `excess` and `gen` from `verify_tally`
* add extra_commit to rangeproof sign and verify
This commit is contained in:
Andrew Poelstra
2016-07-06 15:44:09 +00:00
parent 21bfb3c91a
commit a2bc6604f9
11 changed files with 266 additions and 87 deletions
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88
include/secp256k1_rangeproof.h
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@@ -16,8 +16,7 @@ extern "C" {
* guaranteed to be portable between different platforms or versions. It is
* however guaranteed to be 33 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_pedersen_commitment_serialize_* and
* secp256k1_pedersen_commitment_serialize_* functions.
* secp256k1_pedersen_commitment_serialize and secp256k1_pedersen_commitment_parse.
*
* Furthermore, it is guaranteed to identical signatures will have identical
* representation, so they can be memcmp'ed.
@@ -71,7 +70,7 @@ void secp256k1_pedersen_context_initialize(secp256k1_context* ctx);
*
* Blinding factors can be generated and verified in the same way as secp256k1 private keys for ECDSA.
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_commit(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_commit(
const secp256k1_context* ctx,
secp256k1_pedersen_commitment *commit,
const unsigned char *blind,
@@ -88,7 +87,7 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_commit(
* nneg: how many of the initial factors should be treated with a positive sign.
* Out: blind_out: pointer to a 32-byte array for the sum (cannot be NULL)
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_blind_sum(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_blind_sum(
const secp256k1_context* ctx,
unsigned char *blind_out,
const unsigned char * const *blinds,
@@ -104,24 +103,57 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_blind_sum(
* pcnt: number of commitments pointed to by commits.
* ncommits: pointer to array of pointers to the negative commitments. (cannot be NULL if ncnt is non-zero)
* ncnt: number of commitments pointed to by ncommits.
* excess: signed 64bit amount to add to the total to bring it to zero, can be negative.
*
* This computes sum(commit[0..pcnt)) - sum(ncommit[0..ncnt)) - excess*H == 0.
* This computes sum(commit[0..pcnt)) - sum(ncommit[0..ncnt)) == 0.
*
* A pedersen commitment is xG + vH where G and H are generators for the secp256k1 group and x is a blinding factor,
* while v is the committed value. For a collection of commitments to sum to zero both their blinding factors and
* values must sum to zero.
* A pedersen commitment is xG + vA where G and A are generators for the secp256k1 group and x is a blinding factor,
* while v is the committed value. For a collection of commitments to sum to zero, for each distinct generator
* A all blinding factors and all values must sum to zero.
*
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_verify_tally(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_verify_tally(
const secp256k1_context* ctx,
const secp256k1_pedersen_commitment * const* commits,
size_t pcnt,
const secp256k1_pedersen_commitment * const* ncommits,
size_t ncnt,
int64_t excess,
const secp256k1_generator *gen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(7);
size_t ncnt
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4);
/** Sets the final Pedersen blinding factor correctly when the generators themselves
* have blinding factors.
*
* Consider a generator of the form A' = A + rG, where A is the "real" generator
* but A' is the generator provided to verifiers. Then a Pedersen commitment
* P = vA' + r'G really has the form vA + (vr + r')G. To get all these (vr + r')
* to sum to zero for multiple commitments, we take three arrays consisting of
* the `v`s, `r`s, and `r'`s, respectively called `value`s, `generator_blind`s
* and `blinding_factor`s, and sum them.
*
* The function then subtracts the sum of all (vr + r') from the last element
* of the `blinding_factor` array, setting the total sum to zero.
*
* Returns 1 always.
*
* In: ctx: pointer to a context object
* value: array of asset values, `v` in the above paragraph.
* May not be NULL unless `n_total` is 0.
* generator_blind: array of asset blinding factors, `r` in the above paragraph
* May not be NULL unless `n_total` is 0.
* n_total: Total size of the above arrays
* n_inputs: How many of the initial array elements represent commitments that
* will be negated in the final sum
* In/Out: blinding_factor: array of commitment blinding factors, `r'` in the above paragraph
* May not be NULL unless `n_total` is 0.
* the last value will be modified to get the total sum to zero.
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_pedersen_blind_generator_blind_sum(
const secp256k1_context* ctx,
const uint64_t *value,
const unsigned char* const* generator_blind,
unsigned char* const* blinding_factor,
size_t n_total,
size_t n_inputs
);
/** Initialize a context for usage with Pedersen commitments. */
void secp256k1_rangeproof_context_initialize(secp256k1_context* ctx);
@@ -133,18 +165,22 @@ void secp256k1_rangeproof_context_initialize(secp256k1_context* ctx);
* commit: the commitment being proved. (cannot be NULL)
* proof: pointer to character array with the proof. (cannot be NULL)
* plen: length of proof in bytes.
* extra_commit: additional data covered in rangeproof signature
* extra_commit_len: length of extra_commit byte array (0 if NULL)
* Out: min_value: pointer to a unsigned int64 which will be updated with the minimum value that commit could have. (cannot be NULL)
* max_value: pointer to a unsigned int64 which will be updated with the maximum value that commit could have. (cannot be NULL)
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_verify(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_verify(
const secp256k1_context* ctx,
uint64_t *min_value,
uint64_t *max_value,
const secp256k1_pedersen_commitment *commit,
const unsigned char *proof,
size_t plen,
const unsigned char *extra_commit,
size_t extra_commit_len,
const secp256k1_generator* gen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5) SECP256K1_ARG_NONNULL(7);
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5) SECP256K1_ARG_NONNULL(9);
/** Verify a range proof proof and rewind the proof to recover information sent by its author.
* 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.
@@ -154,6 +190,8 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_verify(
* proof: pointer to character array with the proof. (cannot be NULL)
* plen: length of proof in bytes.
* nonce: 32-byte secret nonce used by the prover (cannot be NULL)
* extra_commit: additional data covered in rangeproof signature
* extra_commit_len: length of extra_commit byte array (0 if NULL)
* In/Out: blind_out: storage for the 32-byte blinding factor used for the commitment
* value_out: pointer to an unsigned int64 which has the exact value of the commitment.
* message_out: pointer to a 4096 byte character array to receive message data from the proof author.
@@ -161,7 +199,7 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_verify(
* min_value: pointer to an unsigned int64 which will be updated with the minimum value that commit could have. (cannot be NULL)
* max_value: pointer to an unsigned int64 which will be updated with the maximum value that commit could have. (cannot be NULL)
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_rewind(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_rewind(
const secp256k1_context* ctx,
unsigned char *blind_out,
uint64_t *value_out,
@@ -173,8 +211,10 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_rewind(
const secp256k1_pedersen_commitment *commit,
const unsigned char *proof,
size_t plen,
const unsigned char *extra_commit,
size_t extra_commit_len,
const secp256k1_generator *gen
) 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(12);
) 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);
/** Author a proof that a committed value is within a range.
* Returns 1: Proof successfully created.
@@ -189,6 +229,10 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_rewind(
* (-1 is a special case that makes the value public. 0 is the most private.)
* min_bits: Number of bits of the value to keep private. (0 = auto/minimal, - 64).
* value: Actual value of the commitment.
* message: pointer to a byte array of data to be embedded in the rangeproof that can be recovered by rewinding the proof
* msg_len: size of the message to be embedded in the rangeproof
* extra_commit: additional data to be covered in rangeproof signature
* extra_commit_len: length of extra_commit byte array (0 if NULL)
* In/out: plen: point to an integer with the size of the proof buffer and the size of the constructed proof.
*
* 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.
@@ -198,7 +242,7 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_rewind(
* 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.
*
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_sign(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_sign(
const secp256k1_context* ctx,
unsigned char *proof,
size_t *plen,
@@ -211,8 +255,10 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_sign(
uint64_t value,
const unsigned char *message,
size_t msg_len,
const unsigned char *extra_commit,
size_t extra_commit_len,
const secp256k1_generator *gen
) 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(13);
) 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);
/** Extract some basic information from a range-proof.
* Returns 1: Information successfully extracted.
@@ -225,7 +271,7 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_sign(
* min_value: pointer to an unsigned int64 which will be updated with the minimum value that commit could have. (cannot be NULL)
* max_value: pointer to an unsigned int64 which will be updated with the maximum value that commit could have. (cannot be NULL)
*/
SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_info(
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_rangeproof_info(
const secp256k1_context* ctx,
int *exp,
int *mantissa,