1 /*############################################################################
2 # Copyright 2017 Intel Corporation
3 #
4 # Licensed under the Apache License, Version 2.0 (the "License");
5 # you may not use this file except in compliance with the License.
6 # You may obtain a copy of the License at
7 #
8 #     http://www.apache.org/licenses/LICENSE-2.0
9 #
10 # Unless required by applicable law or agreed to in writing, software
11 # distributed under the License is distributed on an "AS IS" BASIS,
12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 # See the License for the specific language governing permissions and
14 # limitations under the License.
15 ############################################################################*/
16 /// Basic signature computation.
17 /*! \file */
18 
19 #include "epid/member/tiny/src/signbasic.h"
20 
21 #include "epid/common/types.h"
22 #include "epid/member/tiny/math/efq.h"
23 #include "epid/member/tiny/math/fp.h"
24 #include "epid/member/tiny/math/hashwrap.h"
25 #include "epid/member/tiny/math/serialize.h"
26 #include "epid/member/tiny/src/context.h"
27 #include "epid/member/tiny/src/native_types.h"
28 #include "epid/member/tiny/src/presig_compute.h"
29 #include "epid/member/tiny/stdlib/tiny_stdlib.h"
30 
31 static const FpElemStr epid20_p_str = {
32     {{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFC, 0xF0, 0xCD, 0x46, 0xE5, 0xF2,
33       0x5E, 0xEE, 0x71, 0xA4, 0x9E, 0x0C, 0xDC, 0x65, 0xFB, 0x12, 0x99,
34       0x92, 0x1A, 0xF6, 0x2D, 0x53, 0x6C, 0xD1, 0x0B, 0x50, 0x0D}}};
35 
36 static const G2ElemStr epid20_g2_str = {
37     {{{{0xE2, 0x01, 0x71, 0xC5, 0x4A, 0xA3, 0xDA, 0x05, 0x21, 0x67, 0x04,
38         0x13, 0x74, 0x3C, 0xCF, 0x22, 0xD2, 0x5D, 0x52, 0x68, 0x3D, 0x32,
39         0x47, 0x0E, 0xF6, 0x02, 0x13, 0x43, 0xBF, 0x28, 0x23, 0x94}}},
40      {{{0x59, 0x2D, 0x1E, 0xF6, 0x53, 0xA8, 0x5A, 0x80, 0x46, 0xCC, 0xDC,
41         0x25, 0x4F, 0xBB, 0x56, 0x56, 0x43, 0x43, 0x3B, 0xF6, 0x28, 0x96,
42         0x53, 0xE2, 0x7D, 0xF7, 0xB2, 0x12, 0xBA, 0xA1, 0x89, 0xBE}}}},
43     {{{{0xAE, 0x60, 0xA4, 0xE7, 0x51, 0xFF, 0xD3, 0x50, 0xC6, 0x21, 0xE7,
44         0x03, 0x31, 0x28, 0x26, 0xBD, 0x55, 0xE8, 0xB5, 0x9A, 0x4D, 0x91,
45         0x68, 0x38, 0x41, 0x4D, 0xB8, 0x22, 0xDD, 0x23, 0x35, 0xAE}}},
46      {{{0x1A, 0xB4, 0x42, 0xF9, 0x89, 0xAF, 0xE5, 0xAD, 0xF8, 0x02, 0x74,
47         0xF8, 0x76, 0x45, 0xE2, 0x53, 0x2C, 0xDC, 0x61, 0x81, 0x90, 0x93,
48         0xD6, 0x13, 0x2C, 0x90, 0xFE, 0x89, 0x51, 0xB9, 0x24, 0x21}}}}};
49 
50 static const G1ElemStr epid20_g1_str = {
51     {{{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
52        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
53        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}}},
54     {{{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
55        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
56        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02}}}};
57 
EpidSignBasic(MemberCtx const * ctx,void const * msg,size_t msg_len,void const * basename,size_t basename_len,NativeBasicSignature * sig)58 EpidStatus EpidSignBasic(MemberCtx const* ctx, void const* msg, size_t msg_len,
59                          void const* basename, size_t basename_len,
60                          NativeBasicSignature* sig) {
61   EpidStatus sts = kEpidErr;
62   PreComputedSignatureData presig;
63   tiny_sha sha_state;
64   sha_digest digest;
65   G1ElemStr g1_str;
66   Fq12ElemStr fq12_str;
67   FpElemStr fp_str;
68   FpElem x;
69 
70   FpDeserialize(&x, &ctx->credential.x);
71   do {
72     sts = EpidMemberComputePreSig(ctx, &presig);
73     if (kEpidNoErr != sts) {
74       break;
75     }
76     // B <- random
77     if (basename) {
78       if (!IsBasenameAllowed(ctx->allowed_basenames, basename, basename_len)) {
79         sts = kEpidBadArgErr;
80         break;
81       }
82       /* Basename, K is linked to fixed B */
83       if (!EFqHash(&sig->B, (const unsigned char*)basename, basename_len,
84                    ctx->hash_alg)) {
85         break;
86       }
87     } else {
88       /* No basename, B is random */
89       if (!EFqRand(&sig->B, ctx->rnd_func, ctx->rnd_param)) {
90         break;
91       }
92     }
93     // K <- B^f
94     // guaranteed not to fail, based on f nonzero, B not identity
95     EFqAffineExp(&sig->K, &sig->B, &ctx->f);
96     EFqCp(&sig->T, &presig.T);
97 
98     // R1 = B^rf
99     // guaranteed not to fail, if rf != p or 0, but bad inputs could cause it to
100     // fail
101     if (!EFqAffineExp(&presig.R1, &sig->B, &presig.rf)) {
102       break;
103     }
104 
105     // 5.  The member computes
106     // t3 = Fp.hash(p || g1 || g2 || h1 || h2 || w || B || K || T || R1 || R2).
107     tinysha_init(ctx->hash_alg, &sha_state);
108 
109     tinysha_update(&sha_state, (void const*)&epid20_p_str,
110                    sizeof(epid20_p_str));
111     tinysha_update(&sha_state, (void const*)&epid20_g1_str,
112                    sizeof(epid20_g1_str));
113     tinysha_update(&sha_state, (void const*)&epid20_g2_str,
114                    sizeof(epid20_g2_str));
115     tinysha_update(&sha_state, (void const*)&ctx->pub_key.h1,
116                    sizeof(ctx->pub_key.h1));
117     tinysha_update(&sha_state, (void const*)&ctx->pub_key.h2,
118                    sizeof(ctx->pub_key.h2));
119     tinysha_update(&sha_state, (void const*)&ctx->pub_key.w,
120                    sizeof(ctx->pub_key.w));
121     EFqSerialize(&g1_str, &sig->B);
122     tinysha_update(&sha_state, (void const*)&g1_str, sizeof(g1_str));
123     EFqSerialize(&g1_str, &sig->K);
124     tinysha_update(&sha_state, (void const*)&g1_str, sizeof(g1_str));
125     EFqSerialize(&g1_str, &sig->T);
126     tinysha_update(&sha_state, (void const*)&g1_str, sizeof(g1_str));
127     EFqSerialize(&g1_str, &presig.R1);
128     tinysha_update(&sha_state, (void const*)&g1_str, sizeof(g1_str));
129     Fq12Serialize(&fq12_str, &presig.R2);
130     tinysha_update(&sha_state, (void const*)&fq12_str, sizeof(fq12_str));
131     tinysha_final(digest.digest, &sha_state);
132     FpFromHash(&sig->c, digest.digest, tinysha_digest_size(&sha_state));
133 
134     // 6.  The member computes c = Fp.hash(t3 || m).
135     tinysha_init(ctx->hash_alg, &sha_state);
136     FpSerialize(&fp_str, &sig->c);
137     tinysha_update(&sha_state, (void const*)&fp_str, sizeof(fp_str));
138     tinysha_update(&sha_state, msg, msg_len);
139     tinysha_final(digest.digest, &sha_state);
140 
141     FpFromHash(&sig->c, digest.digest, tinysha_digest_size(&sha_state));
142     // The variables sx, sf, sa, sb are computed from x, f, a, b with random
143     // elements
144     // This randomness allows verification but means that the s variables reveal
145     // no secret information
146     FpMul(&sig->sx, &sig->c, &x);
147     FpMul(&sig->sf, &sig->c, &ctx->f);
148     FpMul(&sig->sa, &sig->c, &presig.a);
149     FpMul(&sig->sb, &sig->c, &presig.b);
150     FpAdd(&sig->sx, &sig->sx, &presig.rx);
151     FpAdd(&sig->sf, &sig->sf, &presig.rf);
152     FpAdd(&sig->sa, &sig->sa, &presig.ra);
153     FpAdd(&sig->sb, &sig->sb, &presig.rb);
154     sts = kEpidNoErr;
155   } while (0);
156   // clearing stack-allocated variables before function return
157   (void)memset(&presig, 0, sizeof(presig));
158   return sts;
159 }
160