Line data Source code
1 : /*
2 : This file is part of TALER
3 : Copyright (C) 2020, 2022 Taler Systems SA
4 :
5 : TALER is free software; you can redistribute it and/or modify it under the
6 : terms of the GNU General Public License as published by the Free Software
7 : Foundation; either version 3, or (at your option) any later version.
8 :
9 : TALER is distributed in the hope that it will be useful, but WITHOUT ANY
10 : WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
11 : A PARTICULAR PURPOSE. See the GNU General Public License for more details.
12 :
13 : You should have received a copy of the GNU General Public License along with
14 : TALER; see the file COPYING. If not, see <http://www.gnu.org/licenses/>
15 : */
16 : /**
17 : * @file auditor_signatures.c
18 : * @brief Utility functions for Taler auditor signatures
19 : * @author Christian Grothoff
20 : */
21 : #include "taler/taler_util.h"
22 : #include "taler/taler_signatures.h"
23 :
24 :
25 : /**
26 : * @brief Information signed by an auditor affirming
27 : * the master public key and the denomination keys
28 : * of a exchange.
29 : */
30 : struct TALER_ExchangeKeyValidityPS
31 : {
32 :
33 : /**
34 : * Purpose is #TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS.
35 : */
36 : struct GNUNET_CRYPTO_SignaturePurpose purpose;
37 :
38 : /**
39 : * Hash of the auditor's URL (including 0-terminator).
40 : */
41 : struct GNUNET_HashCode auditor_url_hash;
42 :
43 : /**
44 : * The long-term offline master key of the exchange, affirmed by the
45 : * auditor.
46 : */
47 : struct TALER_MasterPublicKeyP master;
48 :
49 : /**
50 : * Start time of the validity period for this key.
51 : */
52 : struct GNUNET_TIME_TimestampNBO start;
53 :
54 : /**
55 : * The exchange will sign fresh coins between @e start and this time.
56 : * @e expire_withdraw will be somewhat larger than @e start to
57 : * ensure a sufficiently large anonymity set, while also allowing
58 : * the Exchange to limit the financial damage in case of a key being
59 : * compromised. Thus, exchanges with low volume are expected to have a
60 : * longer withdraw period (@e expire_withdraw - @e start) than exchanges
61 : * with high transaction volume. The period may also differ between
62 : * types of coins. A exchange may also have a few denomination keys
63 : * with the same value with overlapping validity periods, to address
64 : * issues such as clock skew.
65 : */
66 : struct GNUNET_TIME_TimestampNBO expire_withdraw;
67 :
68 : /**
69 : * Coins signed with the denomination key must be spent or refreshed
70 : * between @e start and this expiration time. After this time, the
71 : * exchange will refuse transactions involving this key as it will
72 : * "drop" the table with double-spending information (shortly after)
73 : * this time. Note that wallets should refresh coins significantly
74 : * before this time to be on the safe side. @e expire_deposit must be
75 : * significantly larger than @e expire_withdraw (by months or even
76 : * years).
77 : */
78 : struct GNUNET_TIME_TimestampNBO expire_deposit;
79 :
80 : /**
81 : * When do signatures with this denomination key become invalid?
82 : * After this point, these signatures cannot be used in (legal)
83 : * disputes anymore, as the Exchange is then allowed to destroy its side
84 : * of the evidence. @e expire_legal is expected to be significantly
85 : * larger than @e expire_deposit (by a year or more).
86 : */
87 : struct GNUNET_TIME_TimestampNBO expire_legal;
88 :
89 : /**
90 : * The value of the coins signed with this denomination key.
91 : */
92 : struct TALER_AmountNBO value;
93 :
94 : /**
95 : * Fees for the coin.
96 : */
97 : struct TALER_DenomFeeSetNBOP fees;
98 :
99 : /**
100 : * Hash code of the denomination public key. (Used to avoid having
101 : * the variable-size RSA key in this struct.)
102 : */
103 : struct TALER_DenominationHashP denom_hash GNUNET_PACKED;
104 :
105 : };
106 :
107 :
108 : void
109 240 : TALER_auditor_denom_validity_sign (
110 : const char *auditor_url,
111 : const struct TALER_DenominationHashP *h_denom_pub,
112 : const struct TALER_MasterPublicKeyP *master_pub,
113 : struct GNUNET_TIME_Timestamp stamp_start,
114 : struct GNUNET_TIME_Timestamp stamp_expire_withdraw,
115 : struct GNUNET_TIME_Timestamp stamp_expire_deposit,
116 : struct GNUNET_TIME_Timestamp stamp_expire_legal,
117 : const struct TALER_Amount *coin_value,
118 : const struct TALER_DenomFeeSet *fees,
119 : const struct TALER_AuditorPrivateKeyP *auditor_priv,
120 : struct TALER_AuditorSignatureP *auditor_sig)
121 : {
122 480 : struct TALER_ExchangeKeyValidityPS kv = {
123 240 : .purpose.purpose = htonl (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS),
124 240 : .purpose.size = htonl (sizeof (kv)),
125 240 : .start = GNUNET_TIME_timestamp_hton (stamp_start),
126 240 : .expire_withdraw = GNUNET_TIME_timestamp_hton (stamp_expire_withdraw),
127 240 : .expire_deposit = GNUNET_TIME_timestamp_hton (stamp_expire_deposit),
128 240 : .expire_legal = GNUNET_TIME_timestamp_hton (stamp_expire_legal),
129 : .denom_hash = *h_denom_pub,
130 : .master = *master_pub,
131 : };
132 :
133 240 : TALER_amount_hton (&kv.value,
134 : coin_value);
135 240 : TALER_denom_fee_set_hton (&kv.fees,
136 : fees);
137 240 : GNUNET_CRYPTO_hash (auditor_url,
138 240 : strlen (auditor_url) + 1,
139 : &kv.auditor_url_hash);
140 240 : GNUNET_CRYPTO_eddsa_sign (&auditor_priv->eddsa_priv,
141 : &kv,
142 : &auditor_sig->eddsa_sig);
143 240 : }
144 :
145 :
146 : enum GNUNET_GenericReturnValue
147 400 : TALER_auditor_denom_validity_verify (
148 : const char *auditor_url,
149 : const struct TALER_DenominationHashP *h_denom_pub,
150 : const struct TALER_MasterPublicKeyP *master_pub,
151 : struct GNUNET_TIME_Timestamp stamp_start,
152 : struct GNUNET_TIME_Timestamp stamp_expire_withdraw,
153 : struct GNUNET_TIME_Timestamp stamp_expire_deposit,
154 : struct GNUNET_TIME_Timestamp stamp_expire_legal,
155 : const struct TALER_Amount *coin_value,
156 : const struct TALER_DenomFeeSet *fees,
157 : const struct TALER_AuditorPublicKeyP *auditor_pub,
158 : const struct TALER_AuditorSignatureP *auditor_sig)
159 : {
160 800 : struct TALER_ExchangeKeyValidityPS kv = {
161 400 : .purpose.purpose = htonl (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS),
162 400 : .purpose.size = htonl (sizeof (kv)),
163 400 : .start = GNUNET_TIME_timestamp_hton (stamp_start),
164 400 : .expire_withdraw = GNUNET_TIME_timestamp_hton (stamp_expire_withdraw),
165 400 : .expire_deposit = GNUNET_TIME_timestamp_hton (stamp_expire_deposit),
166 400 : .expire_legal = GNUNET_TIME_timestamp_hton (stamp_expire_legal),
167 : .denom_hash = *h_denom_pub,
168 : .master = *master_pub,
169 : };
170 :
171 400 : TALER_amount_hton (&kv.value,
172 : coin_value);
173 400 : TALER_denom_fee_set_hton (&kv.fees,
174 : fees);
175 400 : GNUNET_CRYPTO_hash (auditor_url,
176 400 : strlen (auditor_url) + 1,
177 : &kv.auditor_url_hash);
178 : return
179 400 : GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS,
180 : &kv,
181 : &auditor_sig->eddsa_sig,
182 : &auditor_pub->eddsa_pub);
183 : }
184 :
185 :
186 : /* end of auditor_signatures.c */
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