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/*
This file is part of TALER
Copyright (C) 2022-2023 Taler Systems SA
TALER is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation; either version 3, or (at your option) any later version.
TALER is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
TALER; see the file COPYING. If not, see <http://www.gnu.org/licenses/>
*/
/**
* @file util/age_restriction.c
* @brief Functions that are used for age restriction
* @author Özgür Kesim
*/
#include "platform.h"
#include "taler_util.h"
#include "taler_signatures.h"
#include <gnunet/gnunet_json_lib.h>
#include <gcrypt.h>
#include <stdint.h>
struct
#ifndef AGE_RESTRICTION_WITH_ECDSA
GNUNET_CRYPTO_Edx25519PublicKey
#else
GNUNET_CRYPTO_EcdsaPublicKey
#endif
TALER_age_commitment_base_public_key = {
.q_y = { 0x64, 0x41, 0xb9, 0xbd, 0xbf, 0x14, 0x39, 0x8e,
0x46, 0xeb, 0x5c, 0x1d, 0x34, 0xd3, 0x9b, 0x2f,
0x9b, 0x7d, 0xc8, 0x18, 0xeb, 0x9c, 0x09, 0xfb,
0x43, 0xad, 0x16, 0x64, 0xbc, 0x18, 0x49, 0xb5},
};
void
TALER_age_commitment_hash (
const struct TALER_AgeCommitment *commitment,
struct TALER_AgeCommitmentHash *ahash)
{
struct GNUNET_HashContext *hash_context;
struct GNUNET_HashCode hash;
GNUNET_assert (NULL != ahash);
if (NULL == commitment)
{
memset (ahash, 0, sizeof(struct TALER_AgeCommitmentHash));
return;
}
GNUNET_assert (__builtin_popcount (commitment->mask.bits) - 1 ==
(int) commitment->num);
hash_context = GNUNET_CRYPTO_hash_context_start ();
for (size_t i = 0; i < commitment->num; i++)
{
GNUNET_CRYPTO_hash_context_read (hash_context,
&commitment->keys[i],
sizeof(commitment->keys[i]));
}
GNUNET_CRYPTO_hash_context_finish (hash_context,
&hash);
GNUNET_memcpy (&ahash->shash.bits,
&hash.bits,
sizeof(ahash->shash.bits));
}
/* To a given age value between 0 and 31, returns the index of the age group
* defined by the given mask.
*/
uint8_t
TALER_get_age_group (
const struct TALER_AgeMask *mask,
uint8_t age)
{
uint32_t m = mask->bits;
uint8_t i = 0;
while (m > 0)
{
if (0 >= age)
break;
m = m >> 1;
i += m & 1;
age--;
}
return i;
}
uint8_t
TALER_get_lowest_age (
const struct TALER_AgeMask *mask,
uint8_t age)
{
uint32_t m = mask->bits;
uint8_t group = TALER_get_age_group (mask, age);
uint8_t lowest = 0;
while (group > 0)
{
m = m >> 1;
if (m & 1)
group--;
lowest++;
}
return lowest;
}
#ifdef AGE_RESTRICTION_WITH_ECDSA
/**
* @brief Helper function to generate a ECDSA private key
*
* @param seed Input seed
* @param size Size of the seed in bytes
* @param[out] pkey ECDSA private key
*/
static void
ecdsa_create_from_seed (
const void *seed,
size_t seed_size,
struct GNUNET_CRYPTO_EcdsaPrivateKey *key)
{
enum GNUNET_GenericReturnValue ret;
GNUNET_assert (
GNUNET_OK ==
GNUNET_CRYPTO_kdf (key,
sizeof (*key),
&seed,
seed_size,
"age commitment",
sizeof ("age commitment") - 1,
NULL, 0));
/* See GNUNET_CRYPTO_ecdsa_key_create */
key->d[0] &= 248;
key->d[31] &= 127;
key->d[31] |= 64;
}
#endif
void
TALER_age_restriction_commit (
const struct TALER_AgeMask *mask,
uint8_t age,
const struct GNUNET_HashCode *seed,
struct TALER_AgeCommitmentProof *ncp)
{
struct GNUNET_HashCode seed_i;
uint8_t num_pub;
uint8_t num_priv;
size_t i;
GNUNET_assert (NULL != mask);
GNUNET_assert (NULL != seed);
GNUNET_assert (NULL != ncp);
GNUNET_assert (mask->bits & 1); /* first bit must have been set */
num_pub = __builtin_popcount (mask->bits) - 1;
num_priv = TALER_get_age_group (mask, age);
GNUNET_assert (31 > num_priv);
GNUNET_assert (num_priv <= num_pub);
seed_i = *seed;
ncp->commitment.mask.bits = mask->bits;
ncp->commitment.num = num_pub;
ncp->proof.num = num_priv;
ncp->proof.keys = NULL;
ncp->commitment.keys = GNUNET_new_array (
num_pub,
struct TALER_AgeCommitmentPublicKeyP);
if (0 < num_priv)
ncp->proof.keys = GNUNET_new_array (
num_priv,
struct TALER_AgeCommitmentPrivateKeyP);
/* Create as many private keys as we need and fill the rest of the
* public keys with valid curve points.
* We need to make sure that the public keys are proper points on the
* elliptic curve, so we can't simply fill the struct with random values. */
for (i = 0; i < num_pub; i++)
{
struct TALER_AgeCommitmentPrivateKeyP key = {0};
struct TALER_AgeCommitmentPrivateKeyP *pkey = &key;
/* Only save the private keys for age groups less than num_priv */
if (i < num_priv)
pkey = &ncp->proof.keys[i];
#ifndef AGE_RESTRICTION_WITH_ECDSA
GNUNET_CRYPTO_edx25519_key_create_from_seed (&seed_i,
sizeof(seed_i),
&pkey->priv);
GNUNET_CRYPTO_edx25519_key_get_public (&pkey->priv,
&ncp->commitment.keys[i].pub);
#else
ecdsa_create_from_seed (&seed_i,
sizeof(seed_i),
&pkey->priv);
GNUNET_CRYPTO_ecdsa_key_get_public (&pkey->priv,
&ncp->commitment.keys[i].pub);
#endif
seed_i.bits[0] += 1;
}
}
enum GNUNET_GenericReturnValue
TALER_age_commitment_derive (
const struct TALER_AgeCommitmentProof *orig,
const struct GNUNET_HashCode *salt,
struct TALER_AgeCommitmentProof *newacp)
{
GNUNET_assert (NULL != newacp);
GNUNET_assert (orig->proof.num <=
orig->commitment.num);
GNUNET_assert (((int) orig->commitment.num) ==
__builtin_popcount (orig->commitment.mask.bits) - 1);
newacp->commitment.mask = orig->commitment.mask;
newacp->commitment.num = orig->commitment.num;
newacp->commitment.keys = GNUNET_new_array (
newacp->commitment.num,
struct TALER_AgeCommitmentPublicKeyP);
newacp->proof.num = orig->proof.num;
newacp->proof.keys = NULL;
if (0 != newacp->proof.num)
newacp->proof.keys = GNUNET_new_array (
newacp->proof.num,
struct TALER_AgeCommitmentPrivateKeyP);
#ifndef AGE_RESTRICTION_WITH_ECDSA
/* 1. Derive the public keys */
for (size_t i = 0; i < orig->commitment.num; i++)
{
GNUNET_CRYPTO_edx25519_public_key_derive (
&orig->commitment.keys[i].pub,
salt,
sizeof(*salt),
&newacp->commitment.keys[i].pub);
}
/* 2. Derive the private keys */
for (size_t i = 0; i < orig->proof.num; i++)
{
GNUNET_CRYPTO_edx25519_private_key_derive (
&orig->proof.keys[i].priv,
salt,
sizeof(*salt),
&newacp->proof.keys[i].priv);
}
#else
{
const char *label = GNUNET_h2s (salt);
/* 1. Derive the public keys */
for (size_t i = 0; i < orig->commitment.num; i++)
{
GNUNET_CRYPTO_ecdsa_public_key_derive (
&orig->commitment.keys[i].pub,
label,
"age commitment derive",
&newacp->commitment.keys[i].pub);
}
/* 2. Derive the private keys */
for (size_t i = 0; i < orig->proof.num; i++)
{
struct GNUNET_CRYPTO_EcdsaPrivateKey *priv;
priv = GNUNET_CRYPTO_ecdsa_private_key_derive (
&orig->proof.keys[i].priv,
label,
"age commitment derive");
newacp->proof.keys[i].priv = *priv;
GNUNET_free (priv);
}
}
#endif
return GNUNET_OK;
}
GNUNET_NETWORK_STRUCT_BEGIN
/**
* Age group mask in network byte order.
*/
struct TALER_AgeMaskNBO
{
uint32_t bits_nbo;
};
/**
* Used for attestation of a particular age
*/
struct TALER_AgeAttestationPS
{
/**
* Purpose must be #TALER_SIGNATURE_WALLET_AGE_ATTESTATION.
* (no GNUNET_PACKED here because the struct is already packed)
*/
struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
/**
* Age mask that defines the underlying age groups
*/
struct TALER_AgeMaskNBO mask GNUNET_PACKED;
/**
* The particular age that this attestation is for.
* We use uint32_t here for alignment.
*/
uint32_t age GNUNET_PACKED;
};
GNUNET_NETWORK_STRUCT_END
enum GNUNET_GenericReturnValue
TALER_age_commitment_attest (
const struct TALER_AgeCommitmentProof *cp,
uint8_t age,
struct TALER_AgeAttestation *attest)
{
uint8_t group;
GNUNET_assert (NULL != attest);
GNUNET_assert (NULL != cp);
group = TALER_get_age_group (&cp->commitment.mask,
age);
GNUNET_assert (group < 32);
if (0 == group)
{
/* Age group 0 means: no attestation necessary.
* We set the signature to zero and communicate success. */
memset (attest,
0,
sizeof(struct TALER_AgeAttestation));
return GNUNET_OK;
}
if (group > cp->proof.num)
return GNUNET_NO;
{
struct TALER_AgeAttestationPS at = {
.purpose.size = htonl (sizeof(at)),
.purpose.purpose = htonl (TALER_SIGNATURE_WALLET_AGE_ATTESTATION),
.mask.bits_nbo = htonl (cp->commitment.mask.bits),
.age = htonl (age),
};
#ifndef AGE_RESTRICTION_WITH_ECDSA
#define sign(a,b,c) GNUNET_CRYPTO_edx25519_sign (a,b,c)
#else
#define sign(a,b,c) GNUNET_CRYPTO_ecdsa_sign (a,b,c)
#endif
sign (&cp->proof.keys[group - 1].priv,
&at,
&attest->signature);
}
#undef sign
return GNUNET_OK;
}
enum GNUNET_GenericReturnValue
TALER_age_commitment_verify (
const struct TALER_AgeCommitment *comm,
uint8_t age,
const struct TALER_AgeAttestation *attest)
{
uint8_t group;
GNUNET_assert (NULL != attest);
GNUNET_assert (NULL != comm);
group = TALER_get_age_group (&comm->mask,
age);
GNUNET_assert (group < 32);
/* Age group 0 means: no attestation necessary. */
if (0 == group)
return GNUNET_OK;
if (group > comm->num)
{
GNUNET_break_op (0);
return GNUNET_NO;
}
{
struct TALER_AgeAttestationPS at = {
.purpose.size = htonl (sizeof(at)),
.purpose.purpose = htonl (TALER_SIGNATURE_WALLET_AGE_ATTESTATION),
.mask.bits_nbo = htonl (comm->mask.bits),
.age = htonl (age),
};
#ifndef AGE_RESTRICTION_WITH_ECDSA
#define verify(a,b,c,d) GNUNET_CRYPTO_edx25519_verify ((a),(b),(c),(d))
#else
#define verify(a,b,c,d) GNUNET_CRYPTO_ecdsa_verify ((a),(b),(c),(d))
#endif
return verify (TALER_SIGNATURE_WALLET_AGE_ATTESTATION,
&at,
&attest->signature,
&comm->keys[group - 1].pub);
}
#undef verify
}
void
TALER_age_commitment_free (
struct TALER_AgeCommitment *commitment)
{
if (NULL == commitment)
return;
if (NULL != commitment->keys)
{
GNUNET_free (commitment->keys);
commitment->keys = NULL;
}
GNUNET_free (commitment);
}
void
TALER_age_proof_free (
struct TALER_AgeProof *proof)
{
if (NULL == proof)
return;
if (NULL != proof->keys)
{
GNUNET_CRYPTO_zero_keys (
proof->keys,
sizeof(*proof->keys) * proof->num);
GNUNET_free (proof->keys);
proof->keys = NULL;
}
GNUNET_free (proof);
}
void
TALER_age_commitment_proof_free (
struct TALER_AgeCommitmentProof *acp)
{
if (NULL == acp)
return;
if (NULL != acp->proof.keys)
{
GNUNET_CRYPTO_zero_keys (
acp->proof.keys,
sizeof(*acp->proof.keys) * acp->proof.num);
GNUNET_free (acp->proof.keys);
acp->proof.keys = NULL;
}
if (NULL != acp->commitment.keys)
{
GNUNET_free (acp->commitment.keys);
acp->commitment.keys = NULL;
}
}
struct TALER_AgeCommitmentProof *
TALER_age_commitment_proof_duplicate (
const struct TALER_AgeCommitmentProof *acp)
{
struct TALER_AgeCommitmentProof *nacp;
GNUNET_assert (NULL != acp);
GNUNET_assert (__builtin_popcount (acp->commitment.mask.bits) - 1 ==
(int) acp->commitment.num);
nacp = GNUNET_new (struct TALER_AgeCommitmentProof);
TALER_age_commitment_proof_deep_copy (acp,nacp);
return nacp;
}
void
TALER_age_commitment_proof_deep_copy (
const struct TALER_AgeCommitmentProof *acp,
struct TALER_AgeCommitmentProof *nacp)
{
GNUNET_assert (NULL != acp);
GNUNET_assert (__builtin_popcount (acp->commitment.mask.bits) - 1 ==
(int) acp->commitment.num);
*nacp = *acp;
nacp->commitment.keys =
GNUNET_new_array (acp->commitment.num,
struct TALER_AgeCommitmentPublicKeyP);
nacp->proof.keys =
GNUNET_new_array (acp->proof.num,
struct TALER_AgeCommitmentPrivateKeyP);
for (size_t i = 0; i < acp->commitment.num; i++)
nacp->commitment.keys[i] = acp->commitment.keys[i];
for (size_t i = 0; i < acp->proof.num; i++)
nacp->proof.keys[i] = acp->proof.keys[i];
}
enum GNUNET_GenericReturnValue
TALER_JSON_parse_age_groups (const json_t *root,
struct TALER_AgeMask *mask)
{
enum GNUNET_GenericReturnValue ret;
const char *str;
struct GNUNET_JSON_Specification spec[] = {
GNUNET_JSON_spec_string ("age_groups",
&str),
GNUNET_JSON_spec_end ()
};
ret = GNUNET_JSON_parse (root,
spec,
NULL,
NULL);
if (GNUNET_OK == ret)
TALER_parse_age_group_string (str, mask);
GNUNET_JSON_parse_free (spec);
return ret;
}
enum GNUNET_GenericReturnValue
TALER_parse_age_group_string (
const char *groups,
struct TALER_AgeMask *mask)
{
const char *pos = groups;
unsigned int prev = 0;
unsigned int val = 0;
char c;
/* reset mask */
mask->bits = 0;
while (*pos)
{
c = *pos++;
if (':' == c)
{
if (prev >= val)
return GNUNET_SYSERR;
mask->bits |= 1 << val;
prev = val;
val = 0;
continue;
}
if ('0'>c || '9'<c)
return GNUNET_SYSERR;
val = 10 * val + c - '0';
if (0>=val || 32<=val)
return GNUNET_SYSERR;
}
if (32<=val || prev>=val)
return GNUNET_SYSERR;
mask->bits |= (1 << val);
mask->bits |= 1; // mark zeroth group, too
return GNUNET_OK;
}
const char *
TALER_age_mask_to_string (
const struct TALER_AgeMask *mask)
{
static char buf[256] = {0};
uint32_t bits = mask->bits;
unsigned int n = 0;
char *pos = buf;
memset (buf, 0, sizeof(buf));
while (bits != 0)
{
bits >>= 1;
n++;
if (0 == (bits & 1))
{
continue;
}
if (n > 9)
{
*(pos++) = '0' + n / 10;
}
*(pos++) = '0' + n % 10;
if (0 != (bits >> 1))
{
*(pos++) = ':';
}
}
return buf;
}
void
TALER_age_restriction_from_secret (
const struct TALER_PlanchetMasterSecretP *secret,
const struct TALER_AgeMask *mask,
const uint8_t max_age,
struct TALER_AgeCommitmentProof *ncp)
{
struct GNUNET_HashCode seed_i = {0};
uint8_t num_pub;
uint8_t num_priv;
GNUNET_assert (NULL != mask);
GNUNET_assert (NULL != secret);
GNUNET_assert (NULL != ncp);
GNUNET_assert (mask->bits & 1); /* fist bit must have been set */
num_pub = __builtin_popcount (mask->bits) - 1;
num_priv = TALER_get_age_group (mask, max_age);
GNUNET_assert (31 > num_priv);
GNUNET_assert (num_priv <= num_pub);
ncp->commitment.mask.bits = mask->bits;
ncp->commitment.num = num_pub;
ncp->proof.num = num_priv;
ncp->proof.keys = NULL;
ncp->commitment.keys = GNUNET_new_array (
num_pub,
struct TALER_AgeCommitmentPublicKeyP);
if (0 < num_priv)
ncp->proof.keys = GNUNET_new_array (
num_priv,
struct TALER_AgeCommitmentPrivateKeyP);
/* Create as many private keys as allow with max_age and derive the
* corresponding public keys. The rest of the needed public keys are created
* by scalar mulitplication with the TALER_age_commitment_base_public_key. */
for (size_t i = 0; i < num_pub; i++)
{
enum GNUNET_GenericReturnValue ret;
const char *label = i < num_priv ? "age-commitment" : "age-factor";
ret = GNUNET_CRYPTO_kdf (&seed_i, sizeof(seed_i),
secret, sizeof(*secret),
label, strlen (label),
&i, sizeof(i),
NULL, 0);
GNUNET_assert (GNUNET_OK == ret);
/* Only generate and save the private keys and public keys for age groups
* less than num_priv */
if (i < num_priv)
{
struct TALER_AgeCommitmentPrivateKeyP *pkey = &ncp->proof.keys[i];
#ifndef AGE_RESTRICTION_WITH_ECDSA
GNUNET_CRYPTO_edx25519_key_create_from_seed (&seed_i,
sizeof(seed_i),
&pkey->priv);
GNUNET_CRYPTO_edx25519_key_get_public (&pkey->priv,
&ncp->commitment.keys[i].pub);
#else
ecdsa_create_from_seed (&seed_i,
sizeof(seed_i),
&pkey->priv);
GNUNET_CRYPTO_ecdsa_key_get_public (&pkey->priv,
&ncp->commitment.keys[i].pub);
#endif
}
else
{
/* For all indices larger than num_priv, derive a public key from
* TALER_age_commitment_base_public_key by scalar multiplication */
#ifndef AGE_RESTRICTION_WITH_ECDSA
GNUNET_CRYPTO_edx25519_public_key_derive (
&TALER_age_commitment_base_public_key,
&seed_i,
sizeof(seed_i),
&ncp->commitment.keys[i].pub);
#else
GNUNET_CRYPTO_ecdsa_public_key_derive (
&TALER_age_commitment_base_public_key,
GNUNET_h2s (&seed_i),
"age withdraw",
&ncp->commitment.keys[i].pub);
#endif
}
}
}
enum GNUNET_GenericReturnValue
TALER_parse_coarse_date (
const char *in,
const struct TALER_AgeMask *mask,
uint32_t *out)
{
struct tm date = {0};
struct tm limit = {0};
time_t seconds;
if (NULL == in)
{
/* FIXME[oec]: correct behaviour? */
*out = 0;
return GNUNET_OK;
}
GNUNET_assert (NULL !=mask);
GNUNET_assert (NULL !=out);
if (NULL == strptime (in, "%Y-%m-%d", &date))
{
if (NULL == strptime (in, "%Y-%m-00", &date))
if (NULL == strptime (in, "%Y-00-00", &date))
return GNUNET_SYSERR;
/* turns out that the day is off by one in the last two cases */
date.tm_mday += 1;
}
seconds = timegm (&date);
if (-1 == seconds)
return GNUNET_SYSERR;
/* calculate the limit date for the largest age group */
{
time_t l = time (NULL);
localtime_r (&l, &limit);
}
limit.tm_year -= TALER_adult_age (mask);
GNUNET_assert (-1 != timegm (&limit));
if ((limit.tm_year < date.tm_year)
|| ((limit.tm_year == date.tm_year)
&& (limit.tm_mon < date.tm_mon))
|| ((limit.tm_year == date.tm_year)
&& (limit.tm_mon == date.tm_mon)
&& (limit.tm_mday < date.tm_mday)))
*out = seconds / 60 / 60 / 24;
else
*out = 0;
return GNUNET_OK;
}
/* end util/age_restriction.c */
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