Some work towards a composable GMAC method

src/methods/CMakeLists.txt

@@ -24,6 +24,7 @@ endmacro(fastd_method_require)
 
 add_subdirectory(null)
 add_subdirectory(generic_gcm)
+add_subdirectory(generic_gmac)
 add_subdirectory(xsalsa20_poly1305)
 
 

src/methods/generic_gmac/CMakeLists.txt

@@ -0,0 +1,4 @@
+fastd_method(generic-gmac
+  generic_gmac.c
+)
+fastd_method_link_libraries(generic-gmac method_common)

src/methods/generic_gmac/generic_gmac.c

@@ -0,0 +1,345 @@
+/*
+  Copyright (c) 2012-2013, Matthias Schiffer <mschiffer@universe-factory.net>
+  All rights reserved.
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+    1. Redistributions of source code must retain the above copyright notice,
+       this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright notice,
+       this list of conditions and the following disclaimer in the documentation
+       and/or other materials provided with the distribution.
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+
+#include "../../fastd.h"
+#include "../common.h"
+
+
+struct fastd_method_session_state {
+	fastd_method_common_t common;
+
+	const fastd_cipher_t *cipher;
+	const fastd_cipher_context_t *cipher_ctx;
+	fastd_cipher_state_t *cipher_state;
+	size_t ivlen;
+
+	const fastd_cipher_t *gmac_cipher;
+	const fastd_cipher_context_t *gmac_cipher_ctx;
+	fastd_cipher_state_t *gmac_cipher_state;
+	size_t gmac_ivlen;
+
+	const fastd_mac_t *ghash;
+	const fastd_mac_context_t *ghash_ctx;
+	fastd_mac_state_t *ghash_state;
+};
+
+
+static bool cipher_get(fastd_context_t *ctx, const char *name, const fastd_cipher_t **cipher, const fastd_cipher_context_t **cctx, const fastd_cipher_t **gmac_cipher, const fastd_cipher_context_t **gmac_cctx) {
+	if (!fastd_mac_available("ghash"))
+		return false;
+
+	size_t len = strlen(name);
+
+	if (len < 5)
+		return false;
+
+	if (strcmp(name+len-5, "-gmac"))
+		return false;
+
+	char cipher_name[len];
+	memcpy(cipher_name, name, len-4);
+	strncpy(cipher_name+len-4, "ctr", 4);
+
+	char *gmac_cipher_name = strchr(cipher_name, '+');
+
+	if (!gmac_cipher_name)
+		return false;
+
+	*gmac_cipher_name = 0;
+	gmac_cipher_name++;
+
+	if (ctx) {
+		*cipher = fastd_cipher_get_by_name(ctx, cipher_name, cctx);
+		*gmac_cipher = fastd_cipher_get_by_name(ctx, gmac_cipher_name, gmac_cctx);
+		return *cipher && *gmac_cipher;
+	}
+	else {
+		return fastd_cipher_available(cipher_name) && fastd_cipher_available(gmac_cipher_name);
+	}
+}
+
+
+static bool method_provides(const char *name) {
+	return cipher_get(NULL, name, NULL, NULL, NULL, NULL);
+}
+
+static size_t method_max_packet_size(fastd_context_t *ctx) {
+	return (fastd_max_packet_size(ctx) + COMMON_HEADBYTES + sizeof(fastd_block128_t));
+}
+
+
+static size_t method_min_encrypt_head_space(fastd_context_t *ctx UNUSED) {
+	return sizeof(fastd_block128_t);
+}
+
+static size_t method_min_decrypt_head_space(fastd_context_t *ctx UNUSED) {
+	return 0;
+}
+
+static size_t method_min_encrypt_tail_space(fastd_context_t *ctx UNUSED) {
+	return (sizeof(fastd_block128_t)-1);
+}
+
+static size_t method_min_decrypt_tail_space(fastd_context_t *ctx UNUSED) {
+	return (2*sizeof(fastd_block128_t)-1);
+}
+
+
+static size_t method_key_length(fastd_context_t *ctx, const char *name) {
+	const fastd_cipher_t *cipher = NULL;
+	const fastd_cipher_context_t *cctx;
+
+	const fastd_cipher_t *gmac_cipher = NULL;
+	const fastd_cipher_context_t *gmac_cctx;
+
+	if (!cipher_get(ctx, name, &cipher, &cctx, &gmac_cipher, &gmac_cctx))
+		exit_bug(ctx, "generic-gmac: can't get cipher key length");
+
+	return cipher->key_length(ctx, cctx) + gmac_cipher->key_length(ctx, gmac_cctx);
+}
+
+static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, const char *name, const uint8_t *secret, bool initiator) {
+	fastd_method_session_state_t *session = malloc(sizeof(fastd_method_session_state_t));
+
+	fastd_method_common_init(ctx, &session->common, initiator);
+
+	if (!cipher_get(ctx, name, &session->cipher, &session->cipher_ctx, &session->gmac_cipher, &session->gmac_cipher_ctx))
+		exit_bug(ctx, "generic-gmac: can't instanciate cipher");
+
+	session->cipher_state = session->cipher->init_state(ctx, session->cipher_ctx, secret);
+	session->ivlen = session->cipher->iv_length(ctx, session->cipher_state);
+	if (session->ivlen && session->ivlen <= COMMON_NONCEBYTES)
+		exit_bug(ctx, "generic-gmac: iv_length to small");
+
+	session->gmac_cipher_state = session->gmac_cipher->init_state(ctx, session->gmac_cipher_ctx, secret + session->cipher->key_length(ctx, session->cipher_ctx));
+	session->gmac_ivlen = session->gmac_cipher->iv_length(ctx, session->gmac_cipher_state);
+	if (session->gmac_ivlen <= COMMON_NONCEBYTES)
+		exit_bug(ctx, "generic-gmac: gmac cipher iv_length to small");
+
+	static const fastd_block128_t zeroblock = {};
+	fastd_block128_t H;
+
+	uint8_t zeroiv[session->gmac_ivlen];
+	memset(zeroiv, 0, session->gmac_ivlen);
+
+	session->gmac_cipher->crypt(ctx, session->gmac_cipher_state, &H, &zeroblock, sizeof(fastd_block128_t), zeroiv);
+
+	session->ghash = fastd_mac_get_by_name(ctx, "ghash", &session->ghash_ctx);
+	if (!session->ghash)
+		exit_bug(ctx, "generic-gmac: can't instanciate ghash mac");
+
+	session->ghash_state = session->ghash->init_state(ctx, session->ghash_ctx, H.b);
+
+	return session;
+}
+
+static bool method_session_is_valid(fastd_context_t *ctx, fastd_method_session_state_t *session) {
+	return (session && fastd_method_session_common_is_valid(ctx, &session->common));
+}
+
+static bool method_session_is_initiator(fastd_context_t *ctx UNUSED, fastd_method_session_state_t *session) {
+	return fastd_method_session_common_is_initiator(&session->common);
+}
+
+static bool method_session_want_refresh(fastd_context_t *ctx, fastd_method_session_state_t *session) {
+	return fastd_method_session_common_want_refresh(ctx, &session->common);
+}
+
+static void method_session_superseded(fastd_context_t *ctx, fastd_method_session_state_t *session) {
+	fastd_method_session_common_superseded(ctx, &session->common);
+}
+
+static void method_session_free(fastd_context_t *ctx, fastd_method_session_state_t *session) {
+	if (session) {
+		session->cipher->free_state(ctx, session->cipher_state);
+		session->gmac_cipher->free_state(ctx, session->gmac_cipher_state);
+		session->ghash->free_state(ctx, session->ghash_state);
+
+		free(session);
+	}
+}
+
+static inline void put_size(fastd_block128_t *out, size_t len) {
+	memset(out, 0, sizeof(fastd_block128_t));
+	out->b[3] = len >> 29;
+	out->b[4] = len >> 21;
+	out->b[5] = len >> 13;
+	out->b[6] = len >> 5;
+	out->b[7] = len << 3;
+}
+
+static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fastd_method_session_state_t *session, fastd_buffer_t *out, fastd_buffer_t in) {
+	fastd_buffer_pull_head(ctx, &in, sizeof(fastd_block128_t));
+	memset(in.data, 0, sizeof(fastd_block128_t));
+
+	size_t tail_len = alignto(in.len, sizeof(fastd_block128_t))-in.len;
+	*out = fastd_buffer_alloc(ctx, in.len, alignto(COMMON_HEADBYTES, 16), sizeof(fastd_block128_t)+tail_len);
+
+	if (tail_len)
+		memset(in.data+in.len, 0, tail_len);
+
+	int n_blocks = block_count(in.len, sizeof(fastd_block128_t));
+
+	fastd_block128_t *inblocks = in.data;
+	fastd_block128_t *outblocks = out->data;
+	fastd_block128_t sig;
+
+	uint8_t gmac_nonce[session->gmac_ivlen];
+	memset(gmac_nonce, 0, session->gmac_ivlen);
+	memcpy(gmac_nonce, session->common.send_nonce, COMMON_NONCEBYTES);
+	gmac_nonce[session->gmac_ivlen-1] = 1;
+
+	bool ok = session->gmac_cipher->crypt(ctx, session->gmac_cipher_state, outblocks, inblocks, sizeof(fastd_block128_t), gmac_nonce);
+
+	if (ok) {
+		uint8_t nonce[session->ivlen];
+		if (session->ivlen) {
+			memset(nonce, 0, session->ivlen);
+			memcpy(nonce, session->common.send_nonce, COMMON_NONCEBYTES);
+			nonce[session->ivlen-1] = 1;
+		}
+
+		ok = session->cipher->crypt(ctx, session->cipher_state, outblocks+1, inblocks+1, (n_blocks-1)*sizeof(fastd_block128_t), nonce);
+	}
+
+	if (ok) {
+		if (tail_len)
+			memset(out->data+out->len, 0, tail_len);
+
+		put_size(&outblocks[n_blocks], in.len-sizeof(fastd_block128_t));
+
+		ok = session->ghash->hash(ctx, session->ghash_state, &sig, outblocks+1, n_blocks);
+	}
+
+	if (!ok) {
+		/* restore original buffer */
+		fastd_buffer_push_head(ctx, &in, sizeof(fastd_block128_t));
+		fastd_buffer_free(*out);
+		return false;
+	}
+
+	xor_a(&outblocks[0], &sig);
+
+	fastd_buffer_free(in);
+
+	fastd_buffer_pull_head(ctx, out, COMMON_HEADBYTES);
+
+	memcpy(out->data, session->common.send_nonce, COMMON_NONCEBYTES);
+	fastd_method_increment_nonce(&session->common);
+
+	((uint8_t*)out->data)[COMMON_NONCEBYTES] = 0; /* flags */
+
+	return true;
+}
+
+static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_method_session_state_t *session, fastd_buffer_t *out, fastd_buffer_t in) {
+	if (in.len < COMMON_HEADBYTES+sizeof(fastd_block128_t))
+		return false;
+
+	if (!method_session_is_valid(ctx, session))
+		return false;
+
+	if (((const uint8_t*)in.data)[COMMON_NONCEBYTES]) /* flags */
+		return false;
+
+	int64_t age;
+	if (!fastd_method_is_nonce_valid(ctx, &session->common, in.data, &age))
+		return false;
+
+	uint8_t gmac_nonce[session->gmac_ivlen];
+	memset(gmac_nonce, 0, session->gmac_ivlen);
+	memcpy(gmac_nonce, in.data, COMMON_NONCEBYTES);
+	gmac_nonce[session->gmac_ivlen-1] = 1;
+
+	uint8_t nonce[session->ivlen];
+	if (session->ivlen) {
+		memset(nonce, 0, session->ivlen);
+		memcpy(nonce, in.data, COMMON_NONCEBYTES);
+		nonce[session->ivlen-1] = 1;
+	}
+
+	fastd_buffer_push_head(ctx, &in, COMMON_HEADBYTES);
+
+	size_t tail_len = alignto(in.len, sizeof(fastd_block128_t))-in.len;
+	*out = fastd_buffer_alloc(ctx, in.len, 0, tail_len);
+
+	int n_blocks = block_count(in.len, sizeof(fastd_block128_t));
+
+	fastd_block128_t *inblocks = in.data;
+	fastd_block128_t *outblocks = out->data;
+	fastd_block128_t sig;
+
+	bool ok = session->gmac_cipher->crypt(ctx, session->gmac_cipher_state, outblocks, inblocks, sizeof(fastd_block128_t), gmac_nonce);
+
+	if (ok)
+		ok = session->cipher->crypt(ctx, session->cipher_state, outblocks+1, inblocks+1, (n_blocks-1)*sizeof(fastd_block128_t), nonce);
+
+	if (ok) {
+		if (tail_len)
+			memset(in.data+in.len, 0, tail_len);
+
+		put_size(&inblocks[n_blocks], in.len-sizeof(fastd_block128_t));
+
+		ok = session->ghash->hash(ctx, session->ghash_state, &sig, inblocks+1, n_blocks);
+	}
+
+	if (!ok || memcmp(&sig, &outblocks[0], sizeof(fastd_block128_t)) != 0) {
+		fastd_buffer_free(*out);
+		return false;
+	}
+
+	fastd_buffer_free(in);
+
+	fastd_buffer_push_head(ctx, out, sizeof(fastd_block128_t));
+
+	if (!fastd_method_reorder_check(ctx, peer, &session->common, nonce, age)) {
+		fastd_buffer_free(*out);
+		*out = fastd_buffer_alloc(ctx, 0, 0, 0);
+	}
+
+	return true;
+}
+
+const fastd_method_t fastd_method_generic_gmac = {
+	.provides = method_provides,
+
+	.max_packet_size = method_max_packet_size,
+	.min_encrypt_head_space = method_min_encrypt_head_space,
+	.min_decrypt_head_space = method_min_decrypt_head_space,
+	.min_encrypt_tail_space = method_min_encrypt_tail_space,
+	.min_decrypt_tail_space = method_min_decrypt_tail_space,
+
+	.key_length = method_key_length,
+	.session_init = method_session_init,
+	.session_is_valid = method_session_is_valid,
+	.session_is_initiator = method_session_is_initiator,
+	.session_want_refresh = method_session_want_refresh,
+	.session_superseded = method_session_superseded,
+	.session_free = method_session_free,
+
+	.encrypt = method_encrypt,
+	.decrypt = method_decrypt,
+};