102 lines
3.1 KiB
C
102 lines
3.1 KiB
C
/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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*
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* This is a specialized constant-time base64/hex implementation that resists side-channel attacks.
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*/
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#include <string.h>
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#include "encoding.h"
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static inline void encode_base64(char dest[4], const uint8_t src[3])
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{
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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 };
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for (unsigned int i = 0; i < 4; ++i)
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dest[i] = input[i] + 'A'
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+ (((25 - input[i]) >> 8) & 6)
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- (((51 - input[i]) >> 8) & 75)
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- (((61 - input[i]) >> 8) & 15)
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+ (((62 - input[i]) >> 8) & 3);
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}
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void key_to_base64(char base64[static WG_KEY_LEN_BASE64], const uint8_t key[static WG_KEY_LEN])
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{
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unsigned int i;
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for (i = 0; i < WG_KEY_LEN / 3; ++i)
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encode_base64(&base64[i * 4], &key[i * 3]);
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encode_base64(&base64[i * 4], (const uint8_t[]){ key[i * 3 + 0], key[i * 3 + 1], 0 });
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base64[WG_KEY_LEN_BASE64 - 2] = '=';
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base64[WG_KEY_LEN_BASE64 - 1] = '\0';
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}
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static inline int decode_base64(const char src[4])
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{
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int val = 0;
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for (unsigned int i = 0; i < 4; ++i)
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val |= (-1
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+ ((((('A' - 1) - src[i]) & (src[i] - ('Z' + 1))) >> 8) & (src[i] - 64))
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+ ((((('a' - 1) - src[i]) & (src[i] - ('z' + 1))) >> 8) & (src[i] - 70))
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+ ((((('0' - 1) - src[i]) & (src[i] - ('9' + 1))) >> 8) & (src[i] + 5))
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+ ((((('+' - 1) - src[i]) & (src[i] - ('+' + 1))) >> 8) & 63)
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+ ((((('/' - 1) - src[i]) & (src[i] - ('/' + 1))) >> 8) & 64)
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) << (18 - 6 * i);
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return val;
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}
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bool key_from_base64(uint8_t key[static WG_KEY_LEN], const char *base64)
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{
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unsigned int i;
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int val;
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if (strlen(base64) != WG_KEY_LEN_BASE64 - 1 || base64[WG_KEY_LEN_BASE64 - 2] != '=')
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return false;
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for (i = 0; i < WG_KEY_LEN / 3; ++i) {
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val = decode_base64(&base64[i * 4]);
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if (val < 0)
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return false;
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key[i * 3 + 0] = (val >> 16) & 0xff;
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key[i * 3 + 1] = (val >> 8) & 0xff;
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key[i * 3 + 2] = val & 0xff;
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}
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val = decode_base64((const char[]){ base64[i * 4 + 0], base64[i * 4 + 1], base64[i * 4 + 2], 'A' });
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if (val < 0 || val & 0xff)
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return false;
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key[i * 3 + 0] = (val >> 16) & 0xff;
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key[i * 3 + 1] = (val >> 8) & 0xff;
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return true;
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}
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void key_to_hex(char hex[static WG_KEY_LEN_HEX], const uint8_t key[static WG_KEY_LEN])
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{
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unsigned int i;
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for (i = 0; i < WG_KEY_LEN; ++i) {
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hex[i * 2] = 87U + (key[i] >> 4) + ((((key[i] >> 4) - 10U) >> 8) & ~38U);
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hex[i * 2 + 1] = 87U + (key[i] & 0xf) + ((((key[i] & 0xf) - 10U) >> 8) & ~38U);
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}
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hex[i * 2] = '\0';
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}
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bool key_from_hex(uint8_t key[static WG_KEY_LEN], const char *hex)
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{
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uint8_t i, c, c_acc = 0, c_alpha0, c_alpha, c_num0, c_num, c_val, state = 0;
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if (strlen(hex) != WG_KEY_LEN_HEX - 1)
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return false;
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for (i = 0; i < WG_KEY_LEN_HEX - 1; ++i) {
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c = (uint8_t)hex[i];
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c_num = c ^ 48U;
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c_num0 = (c_num - 10U) >> 8;
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c_alpha = (c & ~32U) - 55U;
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c_alpha0 = ((c_alpha - 10U) ^ (c_alpha - 16U)) >> 8;
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if (!(c_num0 | c_alpha0))
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return false;
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c_val = (c_num0 & c_num) | (c_alpha0 & c_alpha);
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if (!state)
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c_acc = c_val * 16U;
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else
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key[i / 2] = c_acc | c_val;
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state = ~state;
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}
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return true;
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}
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