studio/cli
2
0
Fork 0
Code Issues Pull Requests Actions Packages Releases 4 Wiki Activity
Files
9cd3c641da7d0aa929eba56f93c038c4d5126768
cli/vendor/aws-lc-sys/aws-lc/crypto/trust_token/voprf.c

1257 lines
40 KiB
C
Raw Blame History

// Copyright (c) 2020, Google Inc.
// SPDX-License-Identifier: ISC
#include <openssl/trust_token.h>
#include <openssl/bn.h>
#include <openssl/bytestring.h>
#include <openssl/ec.h>
#include <openssl/err.h>
#include <openssl/mem.h>
#include <openssl/nid.h>
#include <openssl/rand.h>
#include <openssl/sha.h>
#include "../ec_extra/internal.h"
#include "../fipsmodule/ec/internal.h"
#include "internal.h"
typedef int (*hash_to_group_func_t)(const EC_GROUP *group, EC_JACOBIAN *out,
const uint8_t t[TRUST_TOKEN_NONCE_SIZE]);
typedef int (*hash_to_scalar_func_t)(const EC_GROUP *group, EC_SCALAR *out,
uint8_t *buf, size_t len);
typedef struct {
const EC_GROUP *(*group_func)(void);
// hash_to_group implements the HashToGroup operation for VOPRFs. It returns
// one on success and zero on error.
hash_to_group_func_t hash_to_group;
// hash_to_scalar implements the HashToScalar operation for VOPRFs. It returns
// one on success and zero on error.
hash_to_scalar_func_t hash_to_scalar;
} VOPRF_METHOD;
static const uint8_t kDefaultAdditionalData[32] = {0};
static int cbb_add_point(CBB *out, const EC_GROUP *group,
const EC_AFFINE *point) {
uint8_t *p;
size_t len = ec_point_byte_len(group, POINT_CONVERSION_UNCOMPRESSED);
return CBB_add_space(out, &p, len) &&
ec_point_to_bytes(group, point, POINT_CONVERSION_UNCOMPRESSED, p,
len) == len &&
CBB_flush(out);
}
static int cbb_serialize_point(CBB *out, const EC_GROUP *group,
const EC_AFFINE *point) {
uint8_t *p;
size_t len = ec_point_byte_len(group, POINT_CONVERSION_COMPRESSED);
return CBB_add_u16(out, len) && CBB_add_space(out, &p, len) &&
ec_point_to_bytes(group, point, POINT_CONVERSION_COMPRESSED, p, len) ==
len &&
CBB_flush(out);
}
static int cbs_get_point(CBS *cbs, const EC_GROUP *group, EC_AFFINE *out) {
CBS child;
size_t plen = ec_point_byte_len(group, POINT_CONVERSION_UNCOMPRESSED);
if (!CBS_get_bytes(cbs, &child, plen) ||
!ec_point_from_uncompressed(group, out, CBS_data(&child),
CBS_len(&child))) {
return 0;
}
return 1;
}
static int scalar_to_cbb(CBB *out, const EC_GROUP *group,
const EC_SCALAR *scalar) {
uint8_t *buf;
size_t scalar_len = BN_num_bytes(EC_GROUP_get0_order(group));
if (!CBB_add_space(out, &buf, scalar_len)) {
return 0;
}
ec_scalar_to_bytes(group, buf, &scalar_len, scalar);
return 1;
}
static int scalar_from_cbs(CBS *cbs, const EC_GROUP *group, EC_SCALAR *out) {
size_t scalar_len = BN_num_bytes(EC_GROUP_get0_order(group));
CBS tmp;
if (!CBS_get_bytes(cbs, &tmp, scalar_len)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return 0;
}
ec_scalar_from_bytes(group, out, CBS_data(&tmp), CBS_len(&tmp));
return 1;
}
static int voprf_calculate_key(const VOPRF_METHOD *method, CBB *out_private,
CBB *out_public, const EC_SCALAR *priv) {
const EC_GROUP *group = method->group_func();
EC_JACOBIAN pub;
EC_AFFINE pub_affine;
if (!ec_point_mul_scalar_base(group, &pub, priv) ||
!ec_jacobian_to_affine(group, &pub_affine, &pub)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_KEYGEN_FAILURE);
return 0;
}
if (!scalar_to_cbb(out_private, group, priv) ||
!cbb_add_point(out_public, group, &pub_affine)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_BUFFER_TOO_SMALL);
return 0;
}
return 1;
}
static int voprf_generate_key(const VOPRF_METHOD *method, CBB *out_private,
CBB *out_public) {
EC_SCALAR priv;
if (!ec_random_nonzero_scalar(method->group_func(), &priv,
kDefaultAdditionalData)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_KEYGEN_FAILURE);
return 0;
}
return voprf_calculate_key(method, out_private, out_public, &priv);
}
static int voprf_derive_key_from_secret(const VOPRF_METHOD *method,
CBB *out_private, CBB *out_public,
const uint8_t *secret,
size_t secret_len) {
static const uint8_t kKeygenLabel[] = "TrustTokenVOPRFKeyGen";
EC_SCALAR priv;
int ok = 0;
CBB cbb;
CBB_zero(&cbb);
uint8_t *buf = NULL;
size_t len;
if (!CBB_init(&cbb, 0) ||
!CBB_add_bytes(&cbb, kKeygenLabel, sizeof(kKeygenLabel)) ||
!CBB_add_bytes(&cbb, secret, secret_len) ||
!CBB_finish(&cbb, &buf, &len) ||
!method->hash_to_scalar(method->group_func(), &priv, buf, len)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_KEYGEN_FAILURE);
goto err;
}
ok = voprf_calculate_key(method, out_private, out_public, &priv);
err:
CBB_cleanup(&cbb);
OPENSSL_free(buf);
return ok;
}
static int voprf_client_key_from_bytes(const VOPRF_METHOD *method,
TRUST_TOKEN_CLIENT_KEY *key,
const uint8_t *in, size_t len) {
const EC_GROUP *group = method->group_func();
if (!ec_point_from_uncompressed(group, &key->pubs, in, len)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return 0;
}
return 1;
}
static int voprf_issuer_key_from_bytes(const VOPRF_METHOD *method,
TRUST_TOKEN_ISSUER_KEY *key,
const uint8_t *in, size_t len) {
const EC_GROUP *group = method->group_func();
if (!ec_scalar_from_bytes(group, &key->xs, in, len)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return 0;
}
// Recompute the public key.
EC_JACOBIAN pub;
if (!ec_point_mul_scalar_base(group, &pub, &key->xs) ||
!ec_jacobian_to_affine(group, &key->pubs, &pub)) {
return 0;
}
return 1;
}
static STACK_OF(TRUST_TOKEN_PRETOKEN) *voprf_blind(const VOPRF_METHOD *method,
CBB *cbb, size_t count,
int include_message,
const uint8_t *msg,
size_t msg_len) {
SHA512_CTX hash_ctx;
const EC_GROUP *group = method->group_func();
STACK_OF(TRUST_TOKEN_PRETOKEN) *pretokens =
sk_TRUST_TOKEN_PRETOKEN_new_null();
if (pretokens == NULL) {
goto err;
}
for (size_t i = 0; i < count; i++) {
// Insert |pretoken| into |pretokens| early to simplify error-handling.
TRUST_TOKEN_PRETOKEN *pretoken =
OPENSSL_malloc(sizeof(TRUST_TOKEN_PRETOKEN));
if (pretoken == NULL ||
!sk_TRUST_TOKEN_PRETOKEN_push(pretokens, pretoken)) {
TRUST_TOKEN_PRETOKEN_free(pretoken);
goto err;
}
AWSLC_ABORT_IF_NOT_ONE(RAND_bytes(pretoken->salt, sizeof(pretoken->salt)));
if (include_message) {
assert(SHA512_DIGEST_LENGTH == TRUST_TOKEN_NONCE_SIZE);
SHA512_Init(&hash_ctx);
SHA512_Update(&hash_ctx, pretoken->salt, sizeof(pretoken->salt));
SHA512_Update(&hash_ctx, msg, msg_len);
SHA512_Final(pretoken->t, &hash_ctx);
} else {
OPENSSL_memcpy(pretoken->t, pretoken->salt, TRUST_TOKEN_NONCE_SIZE);
}
// We sample r in Montgomery form to simplify inverting.
EC_SCALAR r;
if (!ec_random_nonzero_scalar(group, &r,
kDefaultAdditionalData)) {
goto err;
}
// pretoken->r is rinv.
ec_scalar_inv0_montgomery(group, &pretoken->r, &r);
// Convert both out of Montgomery form.
ec_scalar_from_montgomery(group, &r, &r);
ec_scalar_from_montgomery(group, &pretoken->r, &pretoken->r);
// Tp is the blinded token in the VOPRF protocol.
EC_JACOBIAN P, Tp;
if (!method->hash_to_group(group, &P, pretoken->t) ||
!ec_point_mul_scalar(group, &Tp, &P, &r) ||
!ec_jacobian_to_affine(group, &pretoken->Tp, &Tp)) {
goto err;
}
if (!cbb_add_point(cbb, group, &pretoken->Tp)) {
goto err;
}
}
return pretokens;
err:
sk_TRUST_TOKEN_PRETOKEN_pop_free(pretokens, TRUST_TOKEN_PRETOKEN_free);
return NULL;
}
static int hash_to_scalar_dleq(const VOPRF_METHOD *method, EC_SCALAR *out,
const EC_AFFINE *X, const EC_AFFINE *T,
const EC_AFFINE *W, const EC_AFFINE *K0,
const EC_AFFINE *K1) {
static const uint8_t kDLEQLabel[] = "DLEQ";
const EC_GROUP *group = method->group_func();
int ok = 0;
CBB cbb;
CBB_zero(&cbb);
uint8_t *buf = NULL;
size_t len;
if (!CBB_init(&cbb, 0) ||
!CBB_add_bytes(&cbb, kDLEQLabel, sizeof(kDLEQLabel)) ||
!cbb_add_point(&cbb, group, X) ||
!cbb_add_point(&cbb, group, T) ||
!cbb_add_point(&cbb, group, W) ||
!cbb_add_point(&cbb, group, K0) ||
!cbb_add_point(&cbb, group, K1) ||
!CBB_finish(&cbb, &buf, &len) ||
!method->hash_to_scalar(group, out, buf, len)) {
goto err;
}
ok = 1;
err:
CBB_cleanup(&cbb);
OPENSSL_free(buf);
return ok;
}
static int hash_to_scalar_challenge(const VOPRF_METHOD *method, EC_SCALAR *out,
const EC_AFFINE *Bm, const EC_AFFINE *a0,
const EC_AFFINE *a1, const EC_AFFINE *a2,
const EC_AFFINE *a3) {
static const uint8_t kChallengeLabel[] = "Challenge";
const EC_GROUP *group = method->group_func();
CBB cbb;
uint8_t transcript[5 * EC_MAX_COMPRESSED + 2 + sizeof(kChallengeLabel) - 1];
size_t len;
if (!CBB_init_fixed(&cbb, transcript, sizeof(transcript)) ||
!cbb_serialize_point(&cbb, group, Bm) ||
!cbb_serialize_point(&cbb, group, a0) ||
!cbb_serialize_point(&cbb, group, a1) ||
!cbb_serialize_point(&cbb, group, a2) ||
!cbb_serialize_point(&cbb, group, a3) ||
!CBB_add_bytes(&cbb, kChallengeLabel, sizeof(kChallengeLabel) - 1) ||
!CBB_finish(&cbb, NULL, &len) ||
!method->hash_to_scalar(group, out, transcript, len)) {
return 0;
}
return 1;
}
static int hash_to_scalar_batch(const VOPRF_METHOD *method, EC_SCALAR *out,
const CBB *points, size_t index) {
static const uint8_t kDLEQBatchLabel[] = "DLEQ BATCH";
if (index > 0xffff) {
// The protocol supports only two-byte batches.
OPENSSL_PUT_ERROR(TRUST_TOKEN, ERR_R_OVERFLOW);
return 0;
}
int ok = 0;
CBB cbb;
CBB_zero(&cbb);
uint8_t *buf = NULL;
size_t len;
if (!CBB_init(&cbb, 0) ||
!CBB_add_bytes(&cbb, kDLEQBatchLabel, sizeof(kDLEQBatchLabel)) ||
!CBB_add_bytes(&cbb, CBB_data(points), CBB_len(points)) ||
!CBB_add_u16(&cbb, (uint16_t)index) ||
!CBB_finish(&cbb, &buf, &len) ||
!method->hash_to_scalar(method->group_func(), out, buf, len)) {
goto err;
}
ok = 1;
err:
CBB_cleanup(&cbb);
OPENSSL_free(buf);
return ok;
}
static int dleq_generate(const VOPRF_METHOD *method, CBB *cbb,
const TRUST_TOKEN_ISSUER_KEY *priv,
const EC_JACOBIAN *T, const EC_JACOBIAN *W) {
const EC_GROUP *group = method->group_func();
enum {
idx_T,
idx_W,
idx_k0,
idx_k1,
num_idx,
};
EC_JACOBIAN jacobians[num_idx];
// Setup the DLEQ proof.
EC_SCALAR r;
if (// r <- Zp
!ec_random_nonzero_scalar(group, &r, kDefaultAdditionalData) ||
// k0;k1 = r*(G;T)
!ec_point_mul_scalar_base(group, &jacobians[idx_k0], &r) ||
!ec_point_mul_scalar(group, &jacobians[idx_k1], T, &r)) {
return 0;
}
EC_AFFINE affines[num_idx];
jacobians[idx_T] = *T;
jacobians[idx_W] = *W;
if (!ec_jacobian_to_affine_batch(group, affines, jacobians, num_idx)) {
return 0;
}
// Compute c = Hc(...).
EC_SCALAR c;
if (!hash_to_scalar_dleq(method, &c, &priv->pubs, &affines[idx_T],
&affines[idx_W], &affines[idx_k0],
&affines[idx_k1])) {
return 0;
}
EC_SCALAR c_mont;
ec_scalar_to_montgomery(group, &c_mont, &c);
// u = r + c*xs
EC_SCALAR u;
ec_scalar_mul_montgomery(group, &u, &priv->xs, &c_mont);
ec_scalar_add(group, &u, &r, &u);
// Store DLEQ proof in transcript.
if (!scalar_to_cbb(cbb, group, &c) ||
!scalar_to_cbb(cbb, group, &u)) {
return 0;
}
return 1;
}
static int mul_public_2(const EC_GROUP *group, EC_JACOBIAN *out,
const EC_JACOBIAN *p0, const EC_SCALAR *scalar0,
const EC_JACOBIAN *p1, const EC_SCALAR *scalar1) {
EC_JACOBIAN points[2] = {*p0, *p1};
EC_SCALAR scalars[2] = {*scalar0, *scalar1};
return ec_point_mul_scalar_public_batch(group, out, /*g_scalar=*/NULL, points,
scalars, 2);
}
static int dleq_verify(const VOPRF_METHOD *method, CBS *cbs,
const TRUST_TOKEN_CLIENT_KEY *pub, const EC_JACOBIAN *T,
const EC_JACOBIAN *W) {
const EC_GROUP *group = method->group_func();
enum {
idx_T,
idx_W,
idx_k0,
idx_k1,
num_idx,
};
EC_JACOBIAN jacobians[num_idx];
// Decode the DLEQ proof.
EC_SCALAR c, u;
if (!scalar_from_cbs(cbs, group, &c) ||
!scalar_from_cbs(cbs, group, &u)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return 0;
}
// k0;k1 = u*(G;T) - c*(pub;W)
EC_JACOBIAN pubs;
ec_affine_to_jacobian(group, &pubs, &pub->pubs);
EC_SCALAR minus_c;
ec_scalar_neg(group, &minus_c, &c);
if (!ec_point_mul_scalar_public(group, &jacobians[idx_k0], &u, &pubs,
&minus_c) ||
!mul_public_2(group, &jacobians[idx_k1], T, &u, W, &minus_c)) {
return 0;
}
// Check the DLEQ proof.
EC_AFFINE affines[num_idx];
jacobians[idx_T] = *T;
jacobians[idx_W] = *W;
if (!ec_jacobian_to_affine_batch(group, affines, jacobians, num_idx)) {
return 0;
}
// Compute c = Hc(...).
EC_SCALAR calculated;
if (!hash_to_scalar_dleq(method, &calculated, &pub->pubs, &affines[idx_T],
&affines[idx_W], &affines[idx_k0],
&affines[idx_k1])) {
return 0;
}
// c == calculated
if (!ec_scalar_equal_vartime(group, &c, &calculated)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_INVALID_PROOF);
return 0;
}
return 1;
}
static int voprf_sign_tt(const VOPRF_METHOD *method,
const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
size_t num_requested, size_t num_to_issue) {
const EC_GROUP *group = method->group_func();
if (num_requested < num_to_issue) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, ERR_R_INTERNAL_ERROR);
return 0;
}
int ret = 0;
EC_JACOBIAN *BTs = OPENSSL_calloc(num_to_issue, sizeof(EC_JACOBIAN));
EC_JACOBIAN *Zs = OPENSSL_calloc(num_to_issue, sizeof(EC_JACOBIAN));
EC_SCALAR *es = OPENSSL_calloc(num_to_issue, sizeof(EC_SCALAR));
CBB batch_cbb;
CBB_zero(&batch_cbb);
if (!BTs ||
!Zs ||
!es ||
!CBB_init(&batch_cbb, 0) ||
!cbb_add_point(&batch_cbb, group, &key->pubs)) {
goto err;
}
for (size_t i = 0; i < num_to_issue; i++) {
EC_AFFINE BT_affine, Z_affine;
EC_JACOBIAN BT, Z;
if (!cbs_get_point(cbs, group, &BT_affine)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
goto err;
}
ec_affine_to_jacobian(group, &BT, &BT_affine);
if (!ec_point_mul_scalar(group, &Z, &BT, &key->xs) ||
!ec_jacobian_to_affine(group, &Z_affine, &Z) ||
!cbb_add_point(cbb, group, &Z_affine)) {
goto err;
}
if (!cbb_add_point(&batch_cbb, group, &BT_affine) ||
!cbb_add_point(&batch_cbb, group, &Z_affine)) {
goto err;
}
BTs[i] = BT;
Zs[i] = Z;
if (!CBB_flush(cbb)) {
goto err;
}
}
// The DLEQ batching construction is described in appendix B of
// https://eprint.iacr.org/2020/072/20200324:214215. Note the additional
// computations all act on public inputs.
for (size_t i = 0; i < num_to_issue; i++) {
if (!hash_to_scalar_batch(method, &es[i], &batch_cbb, i)) {
goto err;
}
}
EC_JACOBIAN BT_batch, Z_batch;
if (!ec_point_mul_scalar_public_batch(group, &BT_batch,
/*g_scalar=*/NULL, BTs, es,
num_to_issue) ||
!ec_point_mul_scalar_public_batch(group, &Z_batch,
/*g_scalar=*/NULL, Zs, es,
num_to_issue)) {
goto err;
}
CBB proof;
if (!CBB_add_u16_length_prefixed(cbb, &proof) ||
!dleq_generate(method, &proof, key, &BT_batch, &Z_batch) ||
!CBB_flush(cbb)) {
goto err;
}
// Skip over any unused requests.
size_t point_len = ec_point_byte_len(group, POINT_CONVERSION_UNCOMPRESSED);
if (!CBS_skip(cbs, point_len * (num_requested - num_to_issue))) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
goto err;
}
ret = 1;
err:
OPENSSL_free(BTs);
OPENSSL_free(Zs);
OPENSSL_free(es);
CBB_cleanup(&batch_cbb);
return ret;
}
static STACK_OF(TRUST_TOKEN) *voprf_unblind_tt(
const VOPRF_METHOD *method, const TRUST_TOKEN_CLIENT_KEY *key,
const STACK_OF(TRUST_TOKEN_PRETOKEN) *pretokens, CBS *cbs, size_t count,
uint32_t key_id) {
const EC_GROUP *group = method->group_func();
if (count > sk_TRUST_TOKEN_PRETOKEN_num(pretokens)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return NULL;
}
int ok = 0;
STACK_OF(TRUST_TOKEN) *ret = sk_TRUST_TOKEN_new_null();
EC_JACOBIAN *BTs = OPENSSL_calloc(count, sizeof(EC_JACOBIAN));
EC_JACOBIAN *Zs = OPENSSL_calloc(count, sizeof(EC_JACOBIAN));
EC_SCALAR *es = OPENSSL_calloc(count, sizeof(EC_SCALAR));
CBB batch_cbb;
CBB_zero(&batch_cbb);
if (ret == NULL ||
BTs == NULL ||
Zs == NULL ||
es == NULL ||
!CBB_init(&batch_cbb, 0) ||
!cbb_add_point(&batch_cbb, group, &key->pubs)) {
goto err;
}
for (size_t i = 0; i < count; i++) {
const TRUST_TOKEN_PRETOKEN *pretoken =
sk_TRUST_TOKEN_PRETOKEN_value(pretokens, i);
EC_AFFINE Z_affine;
if (!cbs_get_point(cbs, group, &Z_affine)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
goto err;
}
ec_affine_to_jacobian(group, &BTs[i], &pretoken->Tp);
ec_affine_to_jacobian(group, &Zs[i], &Z_affine);
if (!cbb_add_point(&batch_cbb, group, &pretoken->Tp) ||
!cbb_add_point(&batch_cbb, group, &Z_affine)) {
goto err;
}
// Unblind the token.
// pretoken->r is rinv.
EC_JACOBIAN N;
EC_AFFINE N_affine;
if (!ec_point_mul_scalar(group, &N, &Zs[i], &pretoken->r) ||
!ec_jacobian_to_affine(group, &N_affine, &N)) {
goto err;
}
// Serialize the token. Include |key_id| to avoid an extra copy in the layer
// above.
CBB token_cbb;
size_t point_len = ec_point_byte_len(group, POINT_CONVERSION_UNCOMPRESSED);
if (!CBB_init(&token_cbb, 4 + TRUST_TOKEN_NONCE_SIZE + (2 + point_len)) ||
!CBB_add_u32(&token_cbb, key_id) ||
!CBB_add_bytes(&token_cbb, pretoken->salt, TRUST_TOKEN_NONCE_SIZE) ||
!cbb_add_point(&token_cbb, group, &N_affine) ||
!CBB_flush(&token_cbb)) {
CBB_cleanup(&token_cbb);
goto err;
}
TRUST_TOKEN *token =
TRUST_TOKEN_new(CBB_data(&token_cbb), CBB_len(&token_cbb));
CBB_cleanup(&token_cbb);
if (token == NULL ||
!sk_TRUST_TOKEN_push(ret, token)) {
TRUST_TOKEN_free(token);
goto err;
}
}
// The DLEQ batching construction is described in appendix B of
// https://eprint.iacr.org/2020/072/20200324:214215. Note the additional
// computations all act on public inputs.
for (size_t i = 0; i < count; i++) {
if (!hash_to_scalar_batch(method, &es[i], &batch_cbb, i)) {
goto err;
}
}
EC_JACOBIAN BT_batch, Z_batch;
if (!ec_point_mul_scalar_public_batch(group, &BT_batch,
/*g_scalar=*/NULL, BTs, es, count) ||
!ec_point_mul_scalar_public_batch(group, &Z_batch,
/*g_scalar=*/NULL, Zs, es, count)) {
goto err;
}
CBS proof;
if (!CBS_get_u16_length_prefixed(cbs, &proof) ||
!dleq_verify(method, &proof, key, &BT_batch, &Z_batch) ||
CBS_len(&proof) != 0) {
goto err;
}
ok = 1;
err:
OPENSSL_free(BTs);
OPENSSL_free(Zs);
OPENSSL_free(es);
CBB_cleanup(&batch_cbb);
if (!ok) {
sk_TRUST_TOKEN_pop_free(ret, TRUST_TOKEN_free);
ret = NULL;
}
return ret;
}
static void sha384_update_u16(SHA512_CTX *ctx, uint16_t v) {
uint8_t buf[2] = {v >> 8, v & 0xff};
SHA384_Update(ctx, buf, 2);
}
static void sha384_update_point_with_length(
SHA512_CTX *ctx, const EC_GROUP *group, const EC_AFFINE *point) {
uint8_t buf[EC_MAX_COMPRESSED];
size_t len = ec_point_to_bytes(group, point, POINT_CONVERSION_COMPRESSED,
buf, sizeof(buf));
assert(len > 0);
sha384_update_u16(ctx, (uint16_t)len);
SHA384_Update(ctx, buf, len);
}
static int compute_composite_seed(const VOPRF_METHOD *method,
uint8_t out[SHA384_DIGEST_LENGTH],
const EC_AFFINE *pub) {
const EC_GROUP *group = method->group_func();
static const uint8_t kSeedDST[] = "Seed-OPRFV1-\x01-P384-SHA384";
SHA512_CTX hash_ctx;
SHA384_Init(&hash_ctx);
sha384_update_point_with_length(&hash_ctx, group, pub);
sha384_update_u16(&hash_ctx, sizeof(kSeedDST) - 1);
SHA384_Update(&hash_ctx, kSeedDST, sizeof(kSeedDST) - 1);
SHA384_Final(out, &hash_ctx);
return 1;
}
static int compute_composite_element(const VOPRF_METHOD *method,
uint8_t seed[SHA384_DIGEST_LENGTH],
EC_SCALAR *di, size_t index,
const EC_AFFINE *C, const EC_AFFINE *D) {
static const uint8_t kCompositeLabel[] = "Composite";
const EC_GROUP *group = method->group_func();
if (index > UINT16_MAX) {
return 0;
}
CBB cbb;
uint8_t transcript[2 + SHA384_DIGEST_LENGTH + 2 + 2 * EC_MAX_COMPRESSED +
sizeof(kCompositeLabel) - 1];
size_t len;
if (!CBB_init_fixed(&cbb, transcript, sizeof(transcript)) ||
!CBB_add_u16(&cbb, SHA384_DIGEST_LENGTH) ||
!CBB_add_bytes(&cbb, seed, SHA384_DIGEST_LENGTH) ||
!CBB_add_u16(&cbb, index) ||
!cbb_serialize_point(&cbb, group, C) ||
!cbb_serialize_point(&cbb, group, D) ||
!CBB_add_bytes(&cbb, kCompositeLabel,
sizeof(kCompositeLabel) - 1) ||
!CBB_finish(&cbb, NULL, &len) ||
!method->hash_to_scalar(group, di, transcript, len)) {
return 0;
}
return 1;
}
static int generate_proof(const VOPRF_METHOD *method, CBB *cbb,
const TRUST_TOKEN_ISSUER_KEY *priv,
const EC_SCALAR *r, const EC_JACOBIAN *M,
const EC_JACOBIAN *Z) {
const EC_GROUP *group = method->group_func();
enum {
idx_M,
idx_Z,
idx_t2,
idx_t3,
num_idx,
};
EC_JACOBIAN jacobians[num_idx];
if (!ec_point_mul_scalar_base(group, &jacobians[idx_t2], r) ||
!ec_point_mul_scalar(group, &jacobians[idx_t3], M, r)) {
return 0;
}
EC_AFFINE affines[num_idx];
jacobians[idx_M] = *M;
jacobians[idx_Z] = *Z;
if (!ec_jacobian_to_affine_batch(group, affines, jacobians, num_idx)) {
return 0;
}
EC_SCALAR c;
if (!hash_to_scalar_challenge(method, &c, &priv->pubs, &affines[idx_M],
&affines[idx_Z], &affines[idx_t2],
&affines[idx_t3])) {
return 0;
}
EC_SCALAR c_mont;
ec_scalar_to_montgomery(group, &c_mont, &c);
// s = r - c*xs
EC_SCALAR s;
ec_scalar_mul_montgomery(group, &s, &priv->xs, &c_mont);
ec_scalar_sub(group, &s, r, &s);
// Store DLEQ proof in transcript.
if (!scalar_to_cbb(cbb, group, &c) ||
!scalar_to_cbb(cbb, group, &s)) {
return 0;
}
return 1;
}
static int verify_proof(const VOPRF_METHOD *method, CBS *cbs,
const TRUST_TOKEN_CLIENT_KEY *pub,
const EC_JACOBIAN *M, const EC_JACOBIAN *Z) {
const EC_GROUP *group = method->group_func();
enum {
idx_M,
idx_Z,
idx_t2,
idx_t3,
num_idx,
};
EC_JACOBIAN jacobians[num_idx];
EC_SCALAR c, s;
if (!scalar_from_cbs(cbs, group, &c) ||
!scalar_from_cbs(cbs, group, &s)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return 0;
}
EC_JACOBIAN pubs;
ec_affine_to_jacobian(group, &pubs, &pub->pubs);
if (!ec_point_mul_scalar_public(group, &jacobians[idx_t2], &s, &pubs,
&c) ||
!mul_public_2(group, &jacobians[idx_t3], M, &s, Z, &c)) {
return 0;
}
EC_AFFINE affines[num_idx];
jacobians[idx_M] = *M;
jacobians[idx_Z] = *Z;
if (!ec_jacobian_to_affine_batch(group, affines, jacobians, num_idx)) {
return 0;
}
EC_SCALAR expected_c;
if (!hash_to_scalar_challenge(method, &expected_c, &pub->pubs,
&affines[idx_M], &affines[idx_Z],
&affines[idx_t2], &affines[idx_t3])) {
return 0;
}
// c == expected_c
if (!ec_scalar_equal_vartime(group, &c, &expected_c)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_INVALID_PROOF);
return 0;
}
return 1;
}
static int voprf_sign_impl(const VOPRF_METHOD *method,
const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb,
CBS *cbs, size_t num_requested, size_t num_to_issue,
const EC_SCALAR *proof_scalar) {
const EC_GROUP *group = method->group_func();
if (num_requested < num_to_issue) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, ERR_R_INTERNAL_ERROR);
return 0;
}
int ret = 0;
EC_JACOBIAN *BTs = OPENSSL_calloc(num_to_issue, sizeof(EC_JACOBIAN));
EC_JACOBIAN *Zs = OPENSSL_calloc(num_to_issue, sizeof(EC_JACOBIAN));
EC_SCALAR *dis = OPENSSL_calloc(num_to_issue, sizeof(EC_SCALAR));
if (!BTs || !Zs || !dis) {
goto err;
}
uint8_t seed[SHA384_DIGEST_LENGTH];
if (!compute_composite_seed(method, seed, &key->pubs)) {
goto err;
}
// This implements the BlindEvaluateBatch as defined in section 4 of
// draft-robert-privacypass-batched-tokens-01, based on the constructions
// in draft-irtf-cfrg-voprf-21. To optimize the computation of the proof,
// the computation of di is done during the token signing and passed into
// the proof generation.
for (size_t i = 0; i < num_to_issue; i++) {
EC_AFFINE BT_affine, Z_affine;
EC_JACOBIAN BT, Z;
if (!cbs_get_point(cbs, group, &BT_affine)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
goto err;
}
ec_affine_to_jacobian(group, &BT, &BT_affine);
if (!ec_point_mul_scalar(group, &Z, &BT, &key->xs) ||
!ec_jacobian_to_affine(group, &Z_affine, &Z) ||
!cbb_add_point(cbb, group, &Z_affine)) {
goto err;
}
BTs[i] = BT;
Zs[i] = Z;
if (!compute_composite_element(method, seed, &dis[i], i, &BT_affine,
&Z_affine)) {
goto err;
}
if (!CBB_flush(cbb)) {
goto err;
}
}
EC_JACOBIAN M, Z;
if (!ec_point_mul_scalar_public_batch(group, &M,
/*g_scalar=*/NULL, BTs, dis,
num_to_issue) ||
!ec_point_mul_scalar(group, &Z, &M, &key->xs)) {
goto err;
}
CBB proof;
if (!CBB_add_u16_length_prefixed(cbb, &proof) ||
!generate_proof(method, &proof, key, proof_scalar, &M, &Z) ||
!CBB_flush(cbb)) {
goto err;
}
// Skip over any unused requests.
size_t point_len = ec_point_byte_len(group, POINT_CONVERSION_UNCOMPRESSED);
if (!CBS_skip(cbs, point_len * (num_requested - num_to_issue))) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
goto err;
}
ret = 1;
err:
OPENSSL_free(BTs);
OPENSSL_free(Zs);
OPENSSL_free(dis);
return ret;
}
static int voprf_sign(const VOPRF_METHOD *method,
const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
size_t num_requested, size_t num_to_issue) {
EC_SCALAR proof_scalar;
if (!ec_random_nonzero_scalar(method->group_func(), &proof_scalar,
kDefaultAdditionalData)) {
return 0;
}
return voprf_sign_impl(method, key, cbb, cbs, num_requested, num_to_issue,
&proof_scalar);
}
static int voprf_sign_with_proof_scalar_for_testing(
const VOPRF_METHOD *method, const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb,
CBS *cbs, size_t num_requested, size_t num_to_issue,
const uint8_t *proof_scalar_buf, size_t proof_scalar_len) {
EC_SCALAR proof_scalar;
if (!ec_scalar_from_bytes(method->group_func(), &proof_scalar,
proof_scalar_buf, proof_scalar_len)) {
return 0;
}
return voprf_sign_impl(method, key, cbb, cbs, num_requested, num_to_issue,
&proof_scalar);
}
static STACK_OF(TRUST_TOKEN) *voprf_unblind(
const VOPRF_METHOD *method, const TRUST_TOKEN_CLIENT_KEY *key,
const STACK_OF(TRUST_TOKEN_PRETOKEN) *pretokens, CBS *cbs, size_t count,
uint32_t key_id) {
const EC_GROUP *group = method->group_func();
if (count > sk_TRUST_TOKEN_PRETOKEN_num(pretokens)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
return NULL;
}
int ok = 0;
STACK_OF(TRUST_TOKEN) *ret = sk_TRUST_TOKEN_new_null();
EC_JACOBIAN *BTs = OPENSSL_calloc(count, sizeof(EC_JACOBIAN));
EC_JACOBIAN *Zs = OPENSSL_calloc(count, sizeof(EC_JACOBIAN));
EC_SCALAR *dis = OPENSSL_calloc(count, sizeof(EC_SCALAR));
if (ret == NULL || !BTs || !Zs || !dis) {
goto err;
}
uint8_t seed[SHA384_DIGEST_LENGTH];
if (!compute_composite_seed(method, seed, &key->pubs)) {
goto err;
}
for (size_t i = 0; i < count; i++) {
const TRUST_TOKEN_PRETOKEN *pretoken =
sk_TRUST_TOKEN_PRETOKEN_value(pretokens, i);
EC_AFFINE Z_affine;
if (!cbs_get_point(cbs, group, &Z_affine)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_DECODE_FAILURE);
goto err;
}
ec_affine_to_jacobian(group, &BTs[i], &pretoken->Tp);
ec_affine_to_jacobian(group, &Zs[i], &Z_affine);
if (!compute_composite_element(method, seed, &dis[i], i, &pretoken->Tp,
&Z_affine)) {
goto err;
}
// Unblind the token.
// pretoken->r is rinv.
EC_JACOBIAN N;
EC_AFFINE N_affine;
if (!ec_point_mul_scalar(group, &N, &Zs[i], &pretoken->r) ||
!ec_jacobian_to_affine(group, &N_affine, &N)) {
goto err;
}
// Serialize the token. Include |key_id| to avoid an extra copy in the layer
// above.
CBB token_cbb;
size_t point_len = ec_point_byte_len(group, POINT_CONVERSION_UNCOMPRESSED);
if (!CBB_init(&token_cbb, 4 + TRUST_TOKEN_NONCE_SIZE + (2 + point_len)) ||
!CBB_add_u32(&token_cbb, key_id) ||
!CBB_add_bytes(&token_cbb, pretoken->salt, TRUST_TOKEN_NONCE_SIZE) ||
!cbb_add_point(&token_cbb, group, &N_affine) ||
!CBB_flush(&token_cbb)) {
CBB_cleanup(&token_cbb);
goto err;
}
TRUST_TOKEN *token =
TRUST_TOKEN_new(CBB_data(&token_cbb), CBB_len(&token_cbb));
CBB_cleanup(&token_cbb);
if (token == NULL ||
!sk_TRUST_TOKEN_push(ret, token)) {
TRUST_TOKEN_free(token);
goto err;
}
}
EC_JACOBIAN M, Z;
if (!ec_point_mul_scalar_public_batch(group, &M,
/*g_scalar=*/NULL, BTs, dis,
count) ||
!ec_point_mul_scalar_public_batch(group, &Z,
/*g_scalar=*/NULL, Zs, dis,
count)) {
goto err;
}
CBS proof;
if (!CBS_get_u16_length_prefixed(cbs, &proof) ||
!verify_proof(method, &proof, key, &M, &Z) ||
CBS_len(&proof) != 0) {
goto err;
}
ok = 1;
err:
OPENSSL_free(BTs);
OPENSSL_free(Zs);
OPENSSL_free(dis);
if (!ok) {
sk_TRUST_TOKEN_pop_free(ret, TRUST_TOKEN_free);
ret = NULL;
}
return ret;
}
static int voprf_read(const VOPRF_METHOD *method,
const TRUST_TOKEN_ISSUER_KEY *key,
uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
const uint8_t *token, size_t token_len,
int include_message, const uint8_t *msg, size_t msg_len) {
const EC_GROUP *group = method->group_func();
CBS cbs, salt;
CBS_init(&cbs, token, token_len);
EC_AFFINE Ws;
if (!CBS_get_bytes(&cbs, &salt, TRUST_TOKEN_NONCE_SIZE) ||
!cbs_get_point(&cbs, group, &Ws) ||
CBS_len(&cbs) != 0) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_INVALID_TOKEN);
return 0;
}
if (include_message) {
SHA512_CTX hash_ctx;
assert(SHA512_DIGEST_LENGTH == TRUST_TOKEN_NONCE_SIZE);
SHA512_Init(&hash_ctx);
SHA512_Update(&hash_ctx, CBS_data(&salt), CBS_len(&salt));
SHA512_Update(&hash_ctx, msg, msg_len);
SHA512_Final(out_nonce, &hash_ctx);
} else {
OPENSSL_memcpy(out_nonce, CBS_data(&salt), CBS_len(&salt));
}
EC_JACOBIAN T;
if (!method->hash_to_group(group, &T, out_nonce)) {
return 0;
}
EC_JACOBIAN Ws_calculated;
if (!ec_point_mul_scalar(group, &Ws_calculated, &T, &key->xs) ||
!ec_affine_jacobian_equal(group, &Ws, &Ws_calculated)) {
OPENSSL_PUT_ERROR(TRUST_TOKEN, TRUST_TOKEN_R_BAD_VALIDITY_CHECK);
return 0;
}
return 1;
}
// VOPRF experiment v2.
static int voprf_exp2_hash_to_group(const EC_GROUP *group, EC_JACOBIAN *out,
const uint8_t t[TRUST_TOKEN_NONCE_SIZE]) {
const uint8_t kHashTLabel[] = "TrustToken VOPRF Experiment V2 HashToGroup";
return ec_hash_to_curve_p384_xmd_sha512_sswu_draft07(
group, out, kHashTLabel, sizeof(kHashTLabel), t, TRUST_TOKEN_NONCE_SIZE);
}
static int voprf_exp2_hash_to_scalar(const EC_GROUP *group, EC_SCALAR *out,
uint8_t *buf, size_t len) {
const uint8_t kHashCLabel[] = "TrustToken VOPRF Experiment V2 HashToScalar";
return ec_hash_to_scalar_p384_xmd_sha512_draft07(
group, out, kHashCLabel, sizeof(kHashCLabel), buf, len);
}
static VOPRF_METHOD voprf_exp2_method = {
EC_group_p384, voprf_exp2_hash_to_group, voprf_exp2_hash_to_scalar};
int voprf_exp2_generate_key(CBB *out_private, CBB *out_public) {
return voprf_generate_key(&voprf_exp2_method, out_private, out_public);
}
int voprf_exp2_derive_key_from_secret(CBB *out_private, CBB *out_public,
const uint8_t *secret,
size_t secret_len) {
return voprf_derive_key_from_secret(&voprf_exp2_method, out_private,
out_public, secret, secret_len);
}
int voprf_exp2_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
const uint8_t *in, size_t len) {
return voprf_client_key_from_bytes(&voprf_exp2_method, key, in, len);
}
int voprf_exp2_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
const uint8_t *in, size_t len) {
return voprf_issuer_key_from_bytes(&voprf_exp2_method, key, in, len);
}
STACK_OF(TRUST_TOKEN_PRETOKEN) *voprf_exp2_blind(CBB *cbb, size_t count,
int include_message,
const uint8_t *msg,
size_t msg_len) {
return voprf_blind(&voprf_exp2_method, cbb, count, include_message, msg,
msg_len);
}
int voprf_exp2_sign(const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
size_t num_requested, size_t num_to_issue,
uint8_t private_metadata) {
if (private_metadata != 0) {
return 0;
}
return voprf_sign_tt(&voprf_exp2_method, key, cbb, cbs, num_requested,
num_to_issue);
}
STACK_OF(TRUST_TOKEN) *voprf_exp2_unblind(
const TRUST_TOKEN_CLIENT_KEY *key,
const STACK_OF(TRUST_TOKEN_PRETOKEN) *pretokens, CBS *cbs, size_t count,
uint32_t key_id) {
return voprf_unblind_tt(&voprf_exp2_method, key, pretokens, cbs, count,
key_id);
}
int voprf_exp2_read(const TRUST_TOKEN_ISSUER_KEY *key,
uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
uint8_t *out_private_metadata, const uint8_t *token,
size_t token_len, int include_message, const uint8_t *msg,
size_t msg_len) {
return voprf_read(&voprf_exp2_method, key, out_nonce, token, token_len,
include_message, msg, msg_len);
}
// VOPRF PST v1.
static int voprf_pst1_hash_to_group(const EC_GROUP *group, EC_JACOBIAN *out,
const uint8_t t[TRUST_TOKEN_NONCE_SIZE]) {
const uint8_t kHashTLabel[] = "HashToGroup-OPRFV1-\x01-P384-SHA384";
return ec_hash_to_curve_p384_xmd_sha384_sswu(group, out, kHashTLabel,
sizeof(kHashTLabel) - 1, t,
TRUST_TOKEN_NONCE_SIZE);
}
static int voprf_pst1_hash_to_scalar(const EC_GROUP *group, EC_SCALAR *out,
uint8_t *buf, size_t len) {
const uint8_t kHashCLabel[] = "HashToScalar-OPRFV1-\x01-P384-SHA384";
return ec_hash_to_scalar_p384_xmd_sha384(group, out, kHashCLabel,
sizeof(kHashCLabel) - 1, buf, len);
}
static VOPRF_METHOD voprf_pst1_method = {
EC_group_p384, voprf_pst1_hash_to_group, voprf_pst1_hash_to_scalar};
int voprf_pst1_generate_key(CBB *out_private, CBB *out_public) {
return voprf_generate_key(&voprf_pst1_method, out_private, out_public);
}
int voprf_pst1_derive_key_from_secret(CBB *out_private, CBB *out_public,
const uint8_t *secret,
size_t secret_len) {
return voprf_derive_key_from_secret(&voprf_pst1_method, out_private,
out_public, secret, secret_len);
}
int voprf_pst1_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
const uint8_t *in, size_t len) {
return voprf_client_key_from_bytes(&voprf_pst1_method, key, in, len);
}
int voprf_pst1_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
const uint8_t *in, size_t len) {
return voprf_issuer_key_from_bytes(&voprf_pst1_method, key, in, len);
}
STACK_OF(TRUST_TOKEN_PRETOKEN) *voprf_pst1_blind(CBB *cbb, size_t count,
int include_message,
const uint8_t *msg,
size_t msg_len) {
return voprf_blind(&voprf_pst1_method, cbb, count, include_message, msg,
msg_len);
}
int voprf_pst1_sign(const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
size_t num_requested, size_t num_to_issue,
uint8_t private_metadata) {
if (private_metadata != 0) {
return 0;
}
return voprf_sign(&voprf_pst1_method, key, cbb, cbs, num_requested,
num_to_issue);
}
int voprf_pst1_sign_with_proof_scalar_for_testing(
const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs, size_t num_requested,
size_t num_to_issue, uint8_t private_metadata,
const uint8_t *proof_scalar_buf, size_t proof_scalar_len) {
if (private_metadata != 0) {
return 0;
}
return voprf_sign_with_proof_scalar_for_testing(
&voprf_pst1_method, key, cbb, cbs, num_requested, num_to_issue,
proof_scalar_buf, proof_scalar_len);
}
STACK_OF(TRUST_TOKEN) *voprf_pst1_unblind(
const TRUST_TOKEN_CLIENT_KEY *key,
const STACK_OF(TRUST_TOKEN_PRETOKEN) *pretokens, CBS *cbs, size_t count,
uint32_t key_id) {
return voprf_unblind(&voprf_pst1_method, key, pretokens, cbs, count, key_id);
}
int voprf_pst1_read(const TRUST_TOKEN_ISSUER_KEY *key,
uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
uint8_t *out_private_metadata, const uint8_t *token,
size_t token_len, int include_message, const uint8_t *msg,
size_t msg_len) {
return voprf_read(&voprf_pst1_method, key, out_nonce, token, token_len,
include_message, msg, msg_len);
}
Reference in New Issue View Git Blame Copy Permalink