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/*
This file is part of TALER
Copyright (C) 2020, 2022 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 auditor_signatures.c
* @brief Utility functions for Taler auditor signatures
* @author Christian Grothoff
*/
#include "platform.h"
#include "taler_util.h"
#include "taler_signatures.h"
/**
* @brief Information signed by an auditor affirming
* the master public key and the denomination keys
* of a exchange.
*/
struct TALER_ExchangeKeyValidityPS
{
/**
* Purpose is #TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS.
*/
struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
/**
* Hash of the auditor's URL (including 0-terminator).
*/
struct GNUNET_HashCode auditor_url_hash;
/**
* The long-term offline master key of the exchange, affirmed by the
* auditor.
*/
struct TALER_MasterPublicKeyP master;
/**
* Start time of the validity period for this key.
*/
struct GNUNET_TIME_TimestampNBO start;
/**
* The exchange will sign fresh coins between @e start and this time.
* @e expire_withdraw will be somewhat larger than @e start to
* ensure a sufficiently large anonymity set, while also allowing
* the Exchange to limit the financial damage in case of a key being
* compromised. Thus, exchanges with low volume are expected to have a
* longer withdraw period (@e expire_withdraw - @e start) than exchanges
* with high transaction volume. The period may also differ between
* types of coins. A exchange may also have a few denomination keys
* with the same value with overlapping validity periods, to address
* issues such as clock skew.
*/
struct GNUNET_TIME_TimestampNBO expire_withdraw;
/**
* Coins signed with the denomination key must be spent or refreshed
* between @e start and this expiration time. After this time, the
* exchange will refuse transactions involving this key as it will
* "drop" the table with double-spending information (shortly after)
* this time. Note that wallets should refresh coins significantly
* before this time to be on the safe side. @e expire_deposit must be
* significantly larger than @e expire_withdraw (by months or even
* years).
*/
struct GNUNET_TIME_TimestampNBO expire_deposit;
/**
* When do signatures with this denomination key become invalid?
* After this point, these signatures cannot be used in (legal)
* disputes anymore, as the Exchange is then allowed to destroy its side
* of the evidence. @e expire_legal is expected to be significantly
* larger than @e expire_deposit (by a year or more).
*/
struct GNUNET_TIME_TimestampNBO expire_legal;
/**
* The value of the coins signed with this denomination key.
*/
struct TALER_AmountNBO value;
/**
* Fees for the coin.
*/
struct TALER_DenomFeeSetNBOP fees;
/**
* Hash code of the denomination public key. (Used to avoid having
* the variable-size RSA key in this struct.)
*/
struct TALER_DenominationHashP denom_hash GNUNET_PACKED;
};
void
TALER_auditor_denom_validity_sign (
const char *auditor_url,
const struct TALER_DenominationHashP *h_denom_pub,
const struct TALER_MasterPublicKeyP *master_pub,
struct GNUNET_TIME_Timestamp stamp_start,
struct GNUNET_TIME_Timestamp stamp_expire_withdraw,
struct GNUNET_TIME_Timestamp stamp_expire_deposit,
struct GNUNET_TIME_Timestamp stamp_expire_legal,
const struct TALER_Amount *coin_value,
const struct TALER_DenomFeeSet *fees,
const struct TALER_AuditorPrivateKeyP *auditor_priv,
struct TALER_AuditorSignatureP *auditor_sig)
{
struct TALER_ExchangeKeyValidityPS kv = {
.purpose.purpose = htonl (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS),
.purpose.size = htonl (sizeof (kv)),
.start = GNUNET_TIME_timestamp_hton (stamp_start),
.expire_withdraw = GNUNET_TIME_timestamp_hton (stamp_expire_withdraw),
.expire_deposit = GNUNET_TIME_timestamp_hton (stamp_expire_deposit),
.expire_legal = GNUNET_TIME_timestamp_hton (stamp_expire_legal),
.denom_hash = *h_denom_pub,
.master = *master_pub,
};
TALER_amount_hton (&kv.value,
coin_value);
TALER_denom_fee_set_hton (&kv.fees,
fees);
GNUNET_CRYPTO_hash (auditor_url,
strlen (auditor_url) + 1,
&kv.auditor_url_hash);
GNUNET_CRYPTO_eddsa_sign (&auditor_priv->eddsa_priv,
&kv,
&auditor_sig->eddsa_sig);
}
enum GNUNET_GenericReturnValue
TALER_auditor_denom_validity_verify (
const char *auditor_url,
const struct TALER_DenominationHashP *h_denom_pub,
const struct TALER_MasterPublicKeyP *master_pub,
struct GNUNET_TIME_Timestamp stamp_start,
struct GNUNET_TIME_Timestamp stamp_expire_withdraw,
struct GNUNET_TIME_Timestamp stamp_expire_deposit,
struct GNUNET_TIME_Timestamp stamp_expire_legal,
const struct TALER_Amount *coin_value,
const struct TALER_DenomFeeSet *fees,
const struct TALER_AuditorPublicKeyP *auditor_pub,
const struct TALER_AuditorSignatureP *auditor_sig)
{
struct TALER_ExchangeKeyValidityPS kv = {
.purpose.purpose = htonl (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS),
.purpose.size = htonl (sizeof (kv)),
.start = GNUNET_TIME_timestamp_hton (stamp_start),
.expire_withdraw = GNUNET_TIME_timestamp_hton (stamp_expire_withdraw),
.expire_deposit = GNUNET_TIME_timestamp_hton (stamp_expire_deposit),
.expire_legal = GNUNET_TIME_timestamp_hton (stamp_expire_legal),
.denom_hash = *h_denom_pub,
.master = *master_pub,
};
TALER_amount_hton (&kv.value,
coin_value);
TALER_denom_fee_set_hton (&kv.fees,
fees);
GNUNET_CRYPTO_hash (auditor_url,
strlen (auditor_url) + 1,
&kv.auditor_url_hash);
return
GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS,
&kv,
&auditor_sig->eddsa_sig,
&auditor_pub->eddsa_pub);
}
/* end of auditor_signatures.c */
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