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/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*
* This is a specialized constant-time base64 implementation that resists side-channel attacks.
*/
#include <string.h>
#include "base64.h"
static inline void encode(char dest[4], const uint8_t src[3])
{
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 };
for (unsigned int i = 0; i < 4; ++i)
dest[i] = input[i] + 'A'
+ (((25 - input[i]) >> 8) & 6)
- (((51 - input[i]) >> 8) & 75)
- (((61 - input[i]) >> 8) & 15)
+ (((62 - input[i]) >> 8) & 3);
}
void key_to_base64(char base64[static WG_KEY_LEN_BASE64], const uint8_t key[static WG_KEY_LEN])
{
unsigned int i;
for (i = 0; i < WG_KEY_LEN / 3; ++i)
encode(&base64[i * 4], &key[i * 3]);
encode(&base64[i * 4], (const uint8_t[]){ key[i * 3 + 0], key[i * 3 + 1], 0 });
base64[WG_KEY_LEN_BASE64 - 2] = '=';
base64[WG_KEY_LEN_BASE64 - 1] = '\0';
}
static inline int decode(const char src[4])
{
int val = 0;
for (unsigned int i = 0; i < 4; ++i)
val |= (-1
+ ((((('A' - 1) - src[i]) & (src[i] - ('Z' + 1))) >> 8) & (src[i] - 64))
+ ((((('a' - 1) - src[i]) & (src[i] - ('z' + 1))) >> 8) & (src[i] - 70))
+ ((((('0' - 1) - src[i]) & (src[i] - ('9' + 1))) >> 8) & (src[i] + 5))
+ ((((('+' - 1) - src[i]) & (src[i] - ('+' + 1))) >> 8) & 63)
+ ((((('/' - 1) - src[i]) & (src[i] - ('/' + 1))) >> 8) & 64)
) << (18 - 6 * i);
return val;
}
bool key_from_base64(uint8_t key[static WG_KEY_LEN], const char *base64)
{
unsigned int i;
int val;
if (strlen(base64) != WG_KEY_LEN_BASE64 - 1 || base64[WG_KEY_LEN_BASE64 - 2] != '=')
return false;
for (i = 0; i < WG_KEY_LEN / 3; ++i) {
val = decode(&base64[i * 4]);
if (val < 0)
return false;
key[i * 3 + 0] = (val >> 16) & 0xff;
key[i * 3 + 1] = (val >> 8) & 0xff;
key[i * 3 + 2] = val & 0xff;
}
val = decode((const char[]){ base64[i * 4 + 0], base64[i * 4 + 1], base64[i * 4 + 2], 'A' });
if (val < 0 || val & 0xff)
return false;
key[i * 3 + 0] = (val >> 16) & 0xff;
key[i * 3 + 1] = (val >> 8) & 0xff;
return true;
}
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