ecdsa_impl.h File Reference

#include "scalar.h"
#include "field.h"
#include "group.h"
#include "ecmult.h"
#include "ecmult_gen.h"
#include "ecdsa.h"

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Functions
static int	secp256k1_der_read_len (size_t *len, const unsigned char **sigp, const unsigned char *sigend)
static int	secp256k1_der_parse_integer (secp256k1_scalar *r, const unsigned char **sig, const unsigned char *sigend)
static int	secp256k1_ecdsa_sig_parse (secp256k1_scalar *rr, secp256k1_scalar *rs, const unsigned char *sig, size_t size)
static int	secp256k1_ecdsa_sig_serialize (unsigned char *sig, size_t *size, const secp256k1_scalar *ar, const secp256k1_scalar *as)
static int	secp256k1_ecdsa_sig_verify (const secp256k1_scalar *sigr, const secp256k1_scalar *sigs, const secp256k1_ge *pubkey, const secp256k1_scalar *message)
static int	secp256k1_ecdsa_sig_sign (const secp256k1_ecmult_gen_context *ctx, secp256k1_scalar *sigr, secp256k1_scalar *sigs, const secp256k1_scalar *seckey, const secp256k1_scalar *message, const secp256k1_scalar *nonce, int *recid)

Variables
static const secp256k1_fe	secp256k1_ecdsa_const_order_as_fe
	Group order for secp256k1 defined as 'n' in "Standards for Efficient Cryptography" (SEC2) 2.7.1 $ sage -c 'load("secp256k1_params.sage"); print(hex(N))' 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141.
static const secp256k1_fe	secp256k1_ecdsa_const_p_minus_order
	Difference between field and order, values 'p' and 'n' values defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1.

Function Documentation

secp256k1_der_parse_integer()

int secp256k1_der_parse_integer ( secp256k1_scalar * r, const unsigned char ** sig, const unsigned char * sigend )

static

Definition at line 90 of file ecdsa_impl.h.

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secp256k1_der_read_len()

int secp256k1_der_read_len ( size_t * len, const unsigned char ** sigp, const unsigned char * sigend )

static

Definition at line 36 of file ecdsa_impl.h.

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secp256k1_ecdsa_sig_parse()

int secp256k1_ecdsa_sig_parse ( secp256k1_scalar * rr, secp256k1_scalar * rs, const unsigned char * sig, size_t size )

static

Definition at line 141 of file ecdsa_impl.h.

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secp256k1_ecdsa_sig_serialize()

int secp256k1_ecdsa_sig_serialize ( unsigned char * sig, size_t * size, const secp256k1_scalar * ar, const secp256k1_scalar * as )

static

Definition at line 171 of file ecdsa_impl.h.

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secp256k1_ecdsa_sig_sign()

int secp256k1_ecdsa_sig_sign ( const secp256k1_ecmult_gen_context * ctx, secp256k1_scalar * sigr, secp256k1_scalar * sigs, const secp256k1_scalar * seckey, const secp256k1_scalar * message, const secp256k1_scalar * nonce, int * recid )

static

Definition at line 266 of file ecdsa_impl.h.

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secp256k1_ecdsa_sig_verify()

int secp256k1_ecdsa_sig_verify ( const secp256k1_scalar * sigr, const secp256k1_scalar * sigs, const secp256k1_ge * pubkey, const secp256k1_scalar * message )

static

We now have the recomputed R point in pr, and its claimed x coordinate (modulo n) in xr. Naively, we would extract the x coordinate from pr (requiring a inversion modulo p), compute the remainder modulo n, and compare it to xr. However:

  xr == X(pr) mod n

<=> exists h. (xr + h * n < p && xr + h * n == X(pr)) [Since 2 * n > p, h can only be 0 or 1] <=> (xr == X(pr)) || (xr + n < p && xr + n == X(pr)) [In Jacobian coordinates, X(pr) is pr.x / pr.z^2 mod p] <=> (xr == pr.x / pr.z^2 mod p) || (xr + n < p && xr + n == pr.x / pr.z^2 mod p) [Multiplying both sides of the equations by pr.z^2 mod p] <=> (xr * pr.z^2 mod p == pr.x) || (xr + n < p && (xr + n) * pr.z^2 mod p == pr.x)

Thus, we can avoid the inversion, but we have to check both cases separately. secp256k1_gej_eq_x implements the (xr * pr.z^2 mod p == pr.x) test.

Definition at line 195 of file ecdsa_impl.h.

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Variable Documentation

secp256k1_ecdsa_const_order_as_fe

const secp256k1_fe secp256k1_ecdsa_const_order_as_fe

static

Initial value:

                                                            = SECP256K1_FE_CONST(
    0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL,
    0xBAAEDCE6UL, 0xAF48A03BUL, 0xBFD25E8CUL, 0xD0364141UL
)

Group order for secp256k1 defined as 'n' in "Standards for Efficient Cryptography" (SEC2) 2.7.1 $ sage -c 'load("secp256k1_params.sage"); print(hex(N))' 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141.

Definition at line 22 of file ecdsa_impl.h.

secp256k1_ecdsa_const_p_minus_order

const secp256k1_fe secp256k1_ecdsa_const_p_minus_order

static

Initial value:

                                                              = SECP256K1_FE_CONST(
    0, 0, 0, 1, 0x45512319UL, 0x50B75FC4UL, 0x402DA172UL, 0x2FC9BAEEUL
)

Difference between field and order, values 'p' and 'n' values defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1.

$ sage -c 'load("secp256k1_params.sage"); print(hex(P-N))' 0x14551231950b75fc4402da1722fc9baee

Definition at line 32 of file ecdsa_impl.h.