1 // SPDX-License-Identifier: GPL-2.0 OR MIT
2 /*
3 * Copyright (C) 2015-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 *
5 * This is a specialized constant-time base64/hex implementation that resists side-channel attacks.
6 */
7
8 #include <string.h>
9 #include "encoding.h"
10
encode_base64(char dest[static4],const uint8_t src[static3])11 static inline void encode_base64(char dest[static 4], const uint8_t src[static 3])
12 {
13 const uint8_t input[] = { (src[0] >> 2) & 63, ((src[0] << 4) | (src[1] >> 4)) & 63, ((src[1] << 2) | (src[2] >> 6)) & 63, src[2] & 63 };
14
15 for (unsigned int i = 0; i < 4; ++i)
16 dest[i] = input[i] + 'A'
17 + (((25 - input[i]) >> 8) & 6)
18 - (((51 - input[i]) >> 8) & 75)
19 - (((61 - input[i]) >> 8) & 15)
20 + (((62 - input[i]) >> 8) & 3);
21
22 }
23
key_to_base64(char base64[static WG_KEY_LEN_BASE64],const uint8_t key[static WG_KEY_LEN])24 void key_to_base64(char base64[static WG_KEY_LEN_BASE64], const uint8_t key[static WG_KEY_LEN])
25 {
26 unsigned int i;
27
28 for (i = 0; i < WG_KEY_LEN / 3; ++i)
29 encode_base64(&base64[i * 4], &key[i * 3]);
30 encode_base64(&base64[i * 4], (const uint8_t[]){ key[i * 3 + 0], key[i * 3 + 1], 0 });
31 base64[WG_KEY_LEN_BASE64 - 2] = '=';
32 base64[WG_KEY_LEN_BASE64 - 1] = '\0';
33 }
34
decode_base64(const char src[static4])35 static inline int decode_base64(const char src[static 4])
36 {
37 int val = 0;
38
39 for (unsigned int i = 0; i < 4; ++i)
40 val |= (-1
41 + ((((('A' - 1) - src[i]) & (src[i] - ('Z' + 1))) >> 8) & (src[i] - 64))
42 + ((((('a' - 1) - src[i]) & (src[i] - ('z' + 1))) >> 8) & (src[i] - 70))
43 + ((((('0' - 1) - src[i]) & (src[i] - ('9' + 1))) >> 8) & (src[i] + 5))
44 + ((((('+' - 1) - src[i]) & (src[i] - ('+' + 1))) >> 8) & 63)
45 + ((((('/' - 1) - src[i]) & (src[i] - ('/' + 1))) >> 8) & 64)
46 ) << (18 - 6 * i);
47 return val;
48 }
49
key_from_base64(uint8_t key[static WG_KEY_LEN],const char * base64)50 bool key_from_base64(uint8_t key[static WG_KEY_LEN], const char *base64)
51 {
52 unsigned int i;
53 volatile uint8_t ret = 0;
54 int val;
55
56 if (strlen(base64) != WG_KEY_LEN_BASE64 - 1 || base64[WG_KEY_LEN_BASE64 - 2] != '=')
57 return false;
58
59 for (i = 0; i < WG_KEY_LEN / 3; ++i) {
60 val = decode_base64(&base64[i * 4]);
61 ret |= (uint32_t)val >> 31;
62 key[i * 3 + 0] = (val >> 16) & 0xff;
63 key[i * 3 + 1] = (val >> 8) & 0xff;
64 key[i * 3 + 2] = val & 0xff;
65 }
66 val = decode_base64((const char[]){ base64[i * 4 + 0], base64[i * 4 + 1], base64[i * 4 + 2], 'A' });
67 ret |= ((uint32_t)val >> 31) | (val & 0xff);
68 key[i * 3 + 0] = (val >> 16) & 0xff;
69 key[i * 3 + 1] = (val >> 8) & 0xff;
70
71 return 1 & ((ret - 1) >> 8);
72 }
73
key_to_hex(char hex[static WG_KEY_LEN_HEX],const uint8_t key[static WG_KEY_LEN])74 void key_to_hex(char hex[static WG_KEY_LEN_HEX], const uint8_t key[static WG_KEY_LEN])
75 {
76 unsigned int i;
77
78 for (i = 0; i < WG_KEY_LEN; ++i) {
79 hex[i * 2] = 87U + (key[i] >> 4) + ((((key[i] >> 4) - 10U) >> 8) & ~38U);
80 hex[i * 2 + 1] = 87U + (key[i] & 0xf) + ((((key[i] & 0xf) - 10U) >> 8) & ~38U);
81 }
82 hex[i * 2] = '\0';
83 }
84
key_from_hex(uint8_t key[static WG_KEY_LEN],const char * hex)85 bool key_from_hex(uint8_t key[static WG_KEY_LEN], const char *hex)
86 {
87 uint8_t c, c_acc, c_alpha0, c_alpha, c_num0, c_num, c_val;
88 volatile uint8_t ret = 0;
89
90 if (strlen(hex) != WG_KEY_LEN_HEX - 1)
91 return false;
92
93 for (unsigned int i = 0; i < WG_KEY_LEN_HEX - 1; i += 2) {
94 c = (uint8_t)hex[i];
95 c_num = c ^ 48U;
96 c_num0 = (c_num - 10U) >> 8;
97 c_alpha = (c & ~32U) - 55U;
98 c_alpha0 = ((c_alpha - 10U) ^ (c_alpha - 16U)) >> 8;
99 ret |= ((c_num0 | c_alpha0) - 1) >> 8;
100 c_val = (c_num0 & c_num) | (c_alpha0 & c_alpha);
101 c_acc = c_val * 16U;
102
103 c = (uint8_t)hex[i + 1];
104 c_num = c ^ 48U;
105 c_num0 = (c_num - 10U) >> 8;
106 c_alpha = (c & ~32U) - 55U;
107 c_alpha0 = ((c_alpha - 10U) ^ (c_alpha - 16U)) >> 8;
108 ret |= ((c_num0 | c_alpha0) - 1) >> 8;
109 c_val = (c_num0 & c_num) | (c_alpha0 & c_alpha);
110 key[i / 2] = c_acc | c_val;
111 }
112
113 return 1 & ((ret - 1) >> 8);
114 }
115
key_is_zero(const uint8_t key[static WG_KEY_LEN])116 bool key_is_zero(const uint8_t key[static WG_KEY_LEN])
117 {
118 volatile uint8_t acc = 0;
119
120 for (unsigned int i = 0; i < WG_KEY_LEN; ++i) {
121 acc |= key[i];
122 asm volatile("" : "=r"(acc) : "0"(acc));
123 }
124 return 1 & ((acc - 1) >> 8);
125 }
126