wg: support text-based ipc

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 101 insertions, 0 deletions

diff --git a/src/encoding.c b/src/encoding.c
new file mode 100644
index 0000000..389bbf7
--- /dev/null
+++ b/src/encoding.c
@@ -0,0 +1,101 @@
+/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * This is a specialized constant-time base64/hex implementation that resists side-channel attacks.
+ */
+
+#include <string.h>
+#include "encoding.h"
+
+static inline void encode_base64(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(&base64[i * 4], &key[i * 3]);
+	encode_base64(&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_base64(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(&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_base64((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;
+}
+
+void key_to_hex(char hex[static WG_KEY_LEN_HEX], const uint8_t key[static WG_KEY_LEN])
+{
+	unsigned int i;
+	for (i = 0; i < WG_KEY_LEN; ++i) {
+		hex[i * 2] = 87U + (key[i] >> 4) + ((((key[i] >> 4) - 10U) >> 8) & ~38U);
+		hex[i * 2 + 1] = 87U + (key[i] & 0xf) + ((((key[i] & 0xf) - 10U) >> 8) & ~38U);
+	}
+	hex[i * 2] = '\0';
+}
+
+bool key_from_hex(uint8_t key[static WG_KEY_LEN], const char *hex)
+{
+	uint8_t i, c, c_acc = 0, c_alpha0, c_alpha, c_num0, c_num, c_val, state = 0;
+
+	if (strlen(hex) != WG_KEY_LEN_HEX - 1)
+		return false;
+
+	for (i = 0; i < WG_KEY_LEN_HEX - 1; ++i) {
+		c = (uint8_t)hex[i];
+		c_num = c ^ 48U;
+		c_num0 = (c_num - 10U) >> 8;
+		c_alpha = (c & ~32U) - 55U;
+		c_alpha0 = ((c_alpha - 10U) ^ (c_alpha - 16U)) >> 8;
+		if (!(c_num0 | c_alpha0))
+			return false;
+		c_val = (c_num0 & c_num) | (c_alpha0 & c_alpha);
+		if (!state)
+			c_acc = c_val * 16U;
+		else
+			key[i / 2] = c_acc | c_val;
+		state = ~state;
+	}
+	return true;
+}