--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcm.c	Thu Oct 15 19:55:15 2020 +0800
@@ -0,0 +1,120 @@
+/*
+ * Dropbear SSH
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * Copyright (c) 2020 by Vladislav Grishenko
+ * All rights reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE. */
+
+#include "includes.h"
+#include "algo.h"
+#include "dbutil.h"
+#include "gcm.h"
+
+#if DROPBEAR_ENABLE_GCM_MODE
+
+#define GHASH_LEN 16
+
+static const struct dropbear_hash dropbear_ghash =
+	{NULL, 0, GHASH_LEN};
+
+static int dropbear_gcm_start(int cipher, const unsigned char *IV,
+			const unsigned char *key, int keylen,
+			int UNUSED(num_rounds), dropbear_gcm_state *state) {
+	int err;
+
+	TRACE2(("enter dropbear_gcm_start"))
+
+	if ((err = gcm_init(&state->gcm, cipher, key, keylen)) != CRYPT_OK) {
+		return err;
+	}
+	memcpy(state->iv, IV, GCM_NONCE_LEN);
+
+	TRACE2(("leave dropbear_gcm_start"))
+	return CRYPT_OK;
+}
+
+static int dropbear_gcm_crypt(unsigned int UNUSED(seq),
+			const unsigned char *in, unsigned char *out,
+			unsigned long len, unsigned long taglen,
+			dropbear_gcm_state *state, int direction) {
+	unsigned char *iv, tag[GHASH_LEN];
+	int i, err;
+
+	TRACE2(("enter dropbear_gcm_crypt"))
+
+	if (len < 4 || taglen != GHASH_LEN) {
+		return CRYPT_ERROR;
+	}
+
+	gcm_reset(&state->gcm);
+
+	if ((err = gcm_add_iv(&state->gcm,
+				state->iv, GCM_NONCE_LEN)) != CRYPT_OK) {
+		return err;
+	}
+
+	if ((err = gcm_add_aad(&state->gcm, in, 4)) != CRYPT_OK) {
+		return err;
+	}
+
+	if ((err = gcm_process(&state->gcm, (unsigned char *) in + 4,
+				len - 4, out + 4, direction)) != CRYPT_OK) {
+		return err;
+	}
+
+	if (direction == LTC_ENCRYPT) {
+		gcm_done(&state->gcm, out + len, &taglen);
+	} else {
+		gcm_done(&state->gcm, tag, &taglen);
+		if (constant_time_memcmp(in + len, tag, taglen) != 0) {
+			return CRYPT_ERROR;
+		}
+	}
+
+	/* increment invocation counter */
+	iv = state->iv + GCM_IVFIX_LEN;
+	for (i = GCM_IVCTR_LEN - 1; i >= 0 && ++iv[i] == 0; i--);
+
+	TRACE2(("leave dropbear_gcm_crypt"))
+	return CRYPT_OK;
+}
+
+static int dropbear_gcm_getlength(unsigned int UNUSED(seq),
+			const unsigned char *in, unsigned int *outlen,
+			unsigned long len, dropbear_gcm_state* UNUSED(state)) {
+	TRACE2(("enter dropbear_gcm_getlength"))
+
+	if (len < 4) {
+		return CRYPT_ERROR;
+	}
+
+	LOAD32H(*outlen, in);
+
+	TRACE2(("leave dropbear_gcm_getlength"))
+	return CRYPT_OK;
+}
+
+const struct dropbear_cipher_mode dropbear_mode_gcm =
+	{(void *)dropbear_gcm_start, NULL, NULL,
+	 (void *)dropbear_gcm_crypt,
+	 (void *)dropbear_gcm_getlength, &dropbear_ghash};
+
+#endif /* DROPBEAR_ENABLE_GCM_MODE */