Implement RFC 5297 AES-SIV

Add an implementation of Synthetic Initialization Vector (SIV)
Authenticated Encryption Using the Advanced Encryption Standard (AES).

This mode of AES is used to protect peering frames when using
the authenticated mesh peering exchange.

Signed-off-by: Javier Lopez <jlopex@gmail.com>
Signed-off-by: Jason Mobarak <x@jason.mobarak.name>
Signed-off-by: Bob Copeland <me@bobcopeland.com>

src/crypto/Makefile

@@ -26,6 +26,7 @@ LIB_OBJS= \
 	aes-internal-dec.o \
 	aes-internal-enc.o \
 	aes-omac1.o \
+	aes-siv.o \
 	aes-unwrap.o \
 	aes-wrap.o \
 	des-internal.o \

src/crypto/aes-siv.c

@@ -0,0 +1,187 @@
+/*
+ * AES SIV (RFC 5297)
+ * Copyright (c) 2013 Cozybit, Inc.
+ *
+ * This software may be distributed under the terms of the BSD license.
+ * See README for more details.
+ */
+
+#include "includes.h"
+
+#include "common.h"
+#include "aes.h"
+#include "aes_wrap.h"
+
+
+static const u8 zero[AES_BLOCK_SIZE];
+
+
+static void dbl(u8 *pad)
+{
+	int i, carry;
+
+	carry = pad[0] & 0x80;
+	for (i = 0; i < AES_BLOCK_SIZE - 1; i++)
+		pad[i] = (pad[i] << 1) | (pad[i + 1] >> 7);
+	pad[AES_BLOCK_SIZE - 1] <<= 1;
+	if (carry)
+		pad[AES_BLOCK_SIZE - 1] ^= 0x87;
+}
+
+
+static void xor(u8 *a, const u8 *b)
+{
+	int i;
+
+	for (i = 0; i < AES_BLOCK_SIZE; i++)
+		*a++ ^= *b++;
+}
+
+
+static void xorend(u8 *a, int alen, const u8 *b, int blen)
+{
+	int i;
+
+	if (alen < blen)
+		return;
+
+	for (i = 0; i < blen; i++)
+		a[alen - blen + i] ^= b[i];
+}
+
+
+static void pad(u8 *pad, const u8 *addr, size_t len)
+{
+	os_memset(pad, 0, AES_BLOCK_SIZE);
+	os_memcpy(pad, addr, len);
+
+	if (len < AES_BLOCK_SIZE)
+		pad[len] = 0x80;
+}
+
+
+int aes_s2v(const u8 *key, size_t num_elem, const u8 *addr[],
+	    size_t *len, u8 *mac)
+{
+	u8 tmp[AES_BLOCK_SIZE], tmp2[AES_BLOCK_SIZE];
+	u8 *buf = NULL;
+	int ret;
+	size_t i;
+
+	if (!num_elem) {
+		os_memcpy(tmp, zero, sizeof(zero));
+		tmp[AES_BLOCK_SIZE - 1] = 1;
+		return omac1_aes_128(key, tmp, sizeof(tmp), mac);
+	}
+
+	ret = omac1_aes_128(key, zero, sizeof(zero), tmp);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < num_elem - 1; i++) {
+		ret = omac1_aes_128(key, addr[i], len[i], tmp2);
+		if (ret)
+			return ret;
+
+		dbl(tmp);
+		xor(tmp, tmp2);
+	}
+	if (len[i] >= AES_BLOCK_SIZE) {
+		buf = os_malloc(len[i]);
+		if (!buf)
+			return -ENOMEM;
+
+		os_memcpy(buf, addr[i], len[i]);
+		xorend(buf, len[i], tmp, AES_BLOCK_SIZE);
+		ret = omac1_aes_128(key, buf, len[i], mac);
+		os_free(buf);
+		return ret;
+	}
+
+	dbl(tmp);
+	pad(tmp2, addr[i], len[i]);
+	xor(tmp, tmp2);
+
+	return omac1_aes_128(key, tmp, sizeof(tmp), mac);
+}
+
+
+int aes_siv_encrypt(const u8 *key, const u8 *pw,
+		    size_t pwlen, size_t num_elem,
+		    const u8 *addr[], const size_t *len, u8 *out)
+{
+	const u8 *_addr[6];
+	size_t _len[6];
+	const u8 *k1 = key, *k2 = key + 16;
+	u8 v[AES_BLOCK_SIZE];
+	size_t i;
+	u8 *iv, *crypt_pw;
+
+	if (num_elem > ARRAY_SIZE(_addr) - 1)
+		return -1;
+
+	for (i = 0; i < num_elem; i++) {
+		_addr[i] = addr[i];
+		_len[i] = len[i];
+	}
+	_addr[num_elem] = pw;
+	_len[num_elem] = pwlen;
+
+	if (aes_s2v(k1, num_elem + 1, _addr, _len, v))
+		return -1;
+
+	iv = out;
+	crypt_pw = out + AES_BLOCK_SIZE;
+
+	os_memcpy(iv, v, AES_BLOCK_SIZE);
+	os_memcpy(crypt_pw, pw, pwlen);
+
+	/* zero out 63rd and 31st bits of ctr (from right) */
+	v[8] &= 0x7f;
+	v[12] &= 0x7f;
+	return aes_128_ctr_encrypt(k2, v, crypt_pw, pwlen);
+}
+
+
+int aes_siv_decrypt(const u8 *key, const u8 *iv_crypt, size_t iv_c_len,
+		    size_t num_elem, const u8 *addr[], const size_t *len,
+		    u8 *out)
+{
+	const u8 *_addr[6];
+	size_t _len[6];
+	const u8 *k1 = key, *k2 = key + 16;
+	size_t crypt_len;
+	size_t i;
+	int ret;
+	u8 iv[AES_BLOCK_SIZE];
+	u8 check[AES_BLOCK_SIZE];
+
+	if (iv_c_len < AES_BLOCK_SIZE || num_elem > ARRAY_SIZE(_addr) - 1)
+		return -1;
+	crypt_len = iv_c_len - AES_BLOCK_SIZE;
+
+	for (i = 0; i < num_elem; i++) {
+		_addr[i] = addr[i];
+		_len[i] = len[i];
+	}
+	_addr[num_elem] = out;
+	_len[num_elem] = crypt_len;
+
+	os_memcpy(iv, iv_crypt, AES_BLOCK_SIZE);
+	os_memcpy(out, iv_crypt + AES_BLOCK_SIZE, crypt_len);
+
+	iv[8] &= 0x7f;
+	iv[12] &= 0x7f;
+
+	ret = aes_128_ctr_encrypt(k2, iv, out, crypt_len);
+	if (ret)
+		return ret;
+
+	ret = aes_s2v(k1, num_elem + 1, _addr, _len, check);
+	if (ret)
+		return ret;
+	if (os_memcmp(check, iv_crypt, AES_BLOCK_SIZE) == 0)
+		return 0;
+
+	return -1;
+}

src/crypto/aes_siv.h

@@ -0,0 +1,19 @@
+/*
+ * AES SIV (RFC 5297)
+ * Copyright (c) 2013 Cozybit, Inc.
+ *
+ * This software may be distributed under the terms of the BSD license.
+ * See README for more details.
+ */
+
+#ifndef AES_SIV_H
+#define AES_SIV_H
+
+int aes_siv_encrypt(const u8 *key, const u8 *pw,
+		    size_t pwlen, size_t num_elem,
+		    const u8 *addr[], const size_t *len, u8 *out);
+int aes_siv_decrypt(const u8 *key, const u8 *iv_crypt, size_t iv_c_len,
+		    size_t num_elem, const u8 *addr[], const size_t *len,
+		    u8 *out);
+
+#endif /* AES_SIV_H */

wpa_supplicant/Android.mk

@@ -1143,6 +1143,9 @@ ifdef CONFIG_INTERNAL_AES
 AESOBJS += src/crypto/aes-internal-enc.c
 endif
 endif
+ifdef NEED_AES_SIV
+AESOBJS += src/crypto/aes-siv.c
+endif
 ifdef NEED_AES
 OBJS += $(AESOBJS)
 endif

wpa_supplicant/Makefile

@@ -1145,6 +1145,9 @@ else
 AESOBJS += ../src/crypto/aes-omac1.o
 endif
 endif
+ifdef NEED_AES_SIV
+AESOBJS += ../src/crypto/aes-siv.o
+endif
 ifdef NEED_AES_WRAP
 NEED_AES_ENC=y
 AESOBJS += ../src/crypto/aes-wrap.o