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Split ecdsa_sign logic into a new function and use it from ecdsa_sign…
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… and recovery
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@elichai
elichai committed May 27, 2020
1 parent 05d315a commit 9b3c6e8
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Showing 3 changed files with 38 additions and 46 deletions.
39 changes: 3 additions & 36 deletions src/modules/recovery/main_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -122,48 +122,15 @@ static int secp256k1_ecdsa_sig_recover(const secp256k1_ecmult_context *ctx, cons

int secp256k1_ecdsa_sign_recoverable(const secp256k1_context* ctx, secp256k1_ecdsa_recoverable_signature *signature, const unsigned char *msg32, const unsigned char *seckey, secp256k1_nonce_function noncefp, const void* noncedata) {
secp256k1_scalar r, s;
secp256k1_scalar sec, non, msg;
int recid;
int ret = 0;
int overflow = 0;
int ret, recid;
VERIFY_CHECK(ctx != NULL);
ARG_CHECK(secp256k1_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx));
ARG_CHECK(msg32 != NULL);
ARG_CHECK(signature != NULL);
ARG_CHECK(seckey != NULL);
if (noncefp == NULL) {
noncefp = secp256k1_nonce_function_default;
}

secp256k1_scalar_set_b32(&sec, seckey, &overflow);
/* Fail if the secret key is invalid. */
if (!overflow && !secp256k1_scalar_is_zero(&sec)) {
unsigned char nonce32[32];
unsigned int count = 0;
secp256k1_scalar_set_b32(&msg, msg32, NULL);
while (1) {
ret = noncefp(nonce32, msg32, seckey, NULL, (void*)noncedata, count);
if (!ret) {
break;
}
secp256k1_scalar_set_b32(&non, nonce32, &overflow);
if (!overflow && !secp256k1_scalar_is_zero(&non)) {
if (secp256k1_ecdsa_sig_sign(&ctx->ecmult_gen_ctx, &r, &s, &sec, &msg, &non, &recid)) {
break;
}
}
count++;
}
memset(nonce32, 0, 32);
secp256k1_scalar_clear(&msg);
secp256k1_scalar_clear(&non);
secp256k1_scalar_clear(&sec);
}
if (ret) {
secp256k1_ecdsa_recoverable_signature_save(signature, &r, &s, recid);
} else {
memset(signature, 0, sizeof(*signature));
}
ret = secp256k1_ecdsa_sign_inner(ctx, &r, &s, &recid, msg32, seckey, noncefp, noncedata);
secp256k1_ecdsa_recoverable_signature_save(signature, &r, &s, recid);
return ret;
}

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37 changes: 27 additions & 10 deletions src/secp256k1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -467,18 +467,18 @@ static int nonce_function_rfc6979(unsigned char *nonce32, const unsigned char *m
const secp256k1_nonce_function secp256k1_nonce_function_rfc6979 = nonce_function_rfc6979;
const secp256k1_nonce_function secp256k1_nonce_function_default = nonce_function_rfc6979;

int secp256k1_ecdsa_sign(const secp256k1_context* ctx, secp256k1_ecdsa_signature *signature, const unsigned char *msg32, const unsigned char *seckey, secp256k1_nonce_function noncefp, const void* noncedata) {
secp256k1_scalar r, s;
static int secp256k1_ecdsa_sign_inner(const secp256k1_context* ctx, secp256k1_scalar* r, secp256k1_scalar* s, int* recid, const unsigned char *msg32, const unsigned char *seckey, secp256k1_nonce_function noncefp, const void* noncedata) {
secp256k1_scalar sec, non, msg;
int ret = 0;
int is_sec_valid;
unsigned char nonce32[32];
unsigned int count = 0;
VERIFY_CHECK(ctx != NULL);
ARG_CHECK(secp256k1_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx));
ARG_CHECK(msg32 != NULL);
ARG_CHECK(signature != NULL);
ARG_CHECK(seckey != NULL);
/* Default initialization here is important so we won't pass uninit values to the cmov in the end */
*r = secp256k1_scalar_zero;
*s = secp256k1_scalar_zero;
if (recid) {
*recid = 0;
}
if (noncefp == NULL) {
noncefp = secp256k1_nonce_function_default;
}
Expand All @@ -497,7 +497,7 @@ int secp256k1_ecdsa_sign(const secp256k1_context* ctx, secp256k1_ecdsa_signature
/* The nonce is still secret here, but it being invalid is is less likely than 1:2^255. */
secp256k1_declassify(ctx, &is_nonce_valid, sizeof(is_nonce_valid));
if (is_nonce_valid) {
ret = secp256k1_ecdsa_sig_sign(&ctx->ecmult_gen_ctx, &r, &s, &sec, &msg, &non, NULL);
ret = secp256k1_ecdsa_sig_sign(&ctx->ecmult_gen_ctx, r, s, &sec, &msg, &non, recid);
/* The final signature is no longer a secret, nor is the fact that we were successful or not. */
secp256k1_declassify(ctx, &ret, sizeof(ret));
if (ret) {
Expand All @@ -514,8 +514,25 @@ int secp256k1_ecdsa_sign(const secp256k1_context* ctx, secp256k1_ecdsa_signature
secp256k1_scalar_clear(&msg);
secp256k1_scalar_clear(&non);
secp256k1_scalar_clear(&sec);
secp256k1_scalar_cmov(&r, &secp256k1_scalar_zero, !ret);
secp256k1_scalar_cmov(&s, &secp256k1_scalar_zero, !ret);
secp256k1_scalar_cmov(r, &secp256k1_scalar_zero, !ret);
secp256k1_scalar_cmov(s, &secp256k1_scalar_zero, !ret);
if (recid) {
const int zero = 0;
secp256k1_int_cmov(recid, &zero, !ret);
}
return ret;
}

int secp256k1_ecdsa_sign(const secp256k1_context* ctx, secp256k1_ecdsa_signature *signature, const unsigned char *msg32, const unsigned char *seckey, secp256k1_nonce_function noncefp, const void* noncedata) {
secp256k1_scalar r, s;
int ret;
VERIFY_CHECK(ctx != NULL);
ARG_CHECK(secp256k1_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx));
ARG_CHECK(msg32 != NULL);
ARG_CHECK(signature != NULL);
ARG_CHECK(seckey != NULL);

ret = secp256k1_ecdsa_sign_inner(ctx, &r, &s, NULL, msg32, seckey, noncefp, noncedata);
secp256k1_ecdsa_signature_save(signature, &r, &s);
return ret;
}
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8 changes: 8 additions & 0 deletions src/util.h
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Original file line number Diff line number Diff line change
Expand Up @@ -175,4 +175,12 @@ static SECP256K1_INLINE void memczero(void *s, size_t len, int flag) {
}
}

/** If flag is true, set *r equal to *a; otherwise leave it. Constant-time. Both *r and *a must be initialized.*/
static SECP256K1_INLINE void secp256k1_int_cmov(int *r, const int *a, int flag) {
uint32_t mask0, mask1;
mask0 = flag + ~((uint32_t)0);
mask1 = ~mask0;
*r = (*r & mask0) | (*a & mask1);
}

#endif /* SECP256K1_UTIL_H */

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