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FelipeMdeOFelipeMdeO
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netutils/dropbear: back hmac-sha2-256 with NuttX /dev/crypto
Replace the bundled libtomcrypt HMAC modules with an adapter that computes the hmac-sha2-256 packet MAC through the NuttX crypto device using CRYPTO_SHA2_256_HMAC sessions. NETUTILS_DROPBEAR depends on CRYPTO_CRYPTODEV and CRYPTO_CRYPTODEV_SOFTWARE_CRYPTO instead of selecting them. Signed-off-by: Felipe Moura <moura.fmo@gmail.com>
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4 files changed

Lines changed: 255 additions & 1 deletion

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‎netutils/dropbear/CMakeLists.txt‎

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@@ -135,6 +135,13 @@ if(CONFIG_NETUTILS_DROPBEAR)
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file(GLOB_RECURSE LIBTOMCRYPT_SRCS CONFIGURE_DEPENDS
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"${CMAKE_CURRENT_SOURCE_DIR}/dropbear/libtomcrypt/src/*.c")
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list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/prngs/sober128tab\\.c$")
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# Drop the bundled libtomcrypt HMAC modules replaced by the NuttX adapter.
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list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/mac/hmac/hmac_init\\.c$")
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list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/mac/hmac/hmac_process\\.c$")
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list(FILTER LIBTOMCRYPT_SRCS EXCLUDE REGEX ".*/mac/hmac/hmac_done\\.c$")
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list(APPEND DROPBEAR_SRCS port/dropbear_ltc_hmac_sha256.c)
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list(APPEND DROPBEAR_SRCS ${LIBTOMCRYPT_SRCS})
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if(CONFIG_NETUTILS_DROPBEAR_SCP)

‎netutils/dropbear/Kconfig‎

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@@ -19,13 +19,23 @@ menuconfig NETUTILS_DROPBEAR
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depends on DEV_URANDOM
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depends on LIBC_NETDB
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depends on LIBC_GAISTRERROR
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select CRYPTO
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depends on ALLOW_BSD_COMPONENTS
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depends on CRYPTO_CRYPTODEV
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depends on CRYPTO_CRYPTODEV_SOFTWARE_CRYPTO
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select CRYPTO_RANDOM_POOL
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---help---
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Enable a minimal Dropbear SSH server port for NuttX. This initial
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port is based on the ESP-IDF MCU test port and provides a single
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foreground SSH server process with SSH sessions backed by NSH.
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The port computes the hmac-sha2-256 packet MAC through the NuttX
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crypto device (/dev/crypto, CRYPTO_SHA2_256_HMAC) instead of the
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bundled libtomcrypt implementation, which is dropped from the
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build. The SHA-256 hash descriptor itself stays in the
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application: Dropbear's key derivation clones partially-updated
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hash states (hashkeys() in common-kex.c), which cannot be
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represented by a kernel crypto session.
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if NETUTILS_DROPBEAR
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config NETUTILS_DROPBEAR_STACKSIZE

‎netutils/dropbear/Makefile‎

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@@ -119,6 +119,16 @@ CSRCS += \
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TOMMATH_SRCS = $(shell if [ -d "$(DROPBEAR_UNPACKNAME)/libtommath" ]; then find "$(DROPBEAR_UNPACKNAME)/libtommath" -name "*.c"; fi)
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TOMCRYPT_SRCS = $(shell if [ -d "$(DROPBEAR_UNPACKNAME)/libtomcrypt/src" ]; then find "$(DROPBEAR_UNPACKNAME)/libtomcrypt/src" -name "*.c" ! -name "sober128tab.c"; fi)
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# Drop the bundled libtomcrypt HMAC modules replaced by the NuttX adapter.
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TOMCRYPT_SRCS := $(filter-out \
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%/mac/hmac/hmac_init.c \
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%/mac/hmac/hmac_process.c \
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%/mac/hmac/hmac_done.c, \
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$(TOMCRYPT_SRCS))
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CSRCS += port/dropbear_ltc_hmac_sha256.c
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CSRCS += $(TOMMATH_SRCS)
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CSRCS += $(TOMCRYPT_SRCS)
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‎netutils/dropbear/port/dropbear_ltc_hmac_sha256.c‎

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@@ -0,0 +1,227 @@
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/****************************************************************************
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* apps/netutils/dropbear/port/dropbear_ltc_hmac_sha256.c
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/* LibTomCrypt-compatible incremental HMAC API backed by a
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* CRYPTO_SHA2_256_HMAC /dev/crypto session (hmac-sha2-256, the only MAC the
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* NuttX Dropbear configuration enables): init opens the session, process
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* feeds data with COP_FLAG_UPDATE, done reads the tag and frees the session.
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*/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include "includes.h"
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#include <sys/ioctl.h>
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#include <fcntl.h>
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#include <string.h>
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#include <unistd.h>
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#include <crypto/cryptodev.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define DROPBEAR_HMAC_SHA256_DIGESTLEN 32
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#define DROPBEAR_HMAC_SHA256_BLOCKLEN 64
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/* Stash the /dev/crypto session id in the unused md hash-state buffer so the
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* upstream hmac_state needs no patch (hash index uses the existing field).
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*/
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#define HMAC_SES(h) (*(FAR unsigned int *)&(h)->md)
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/****************************************************************************
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* Private Data
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****************************************************************************/
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static int g_dropbear_hmac_cryptofd = -1;
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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static int dropbear_hmac_cryptodev_fd(void)
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{
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int fd;
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int cfd;
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if (g_dropbear_hmac_cryptofd >= 0)
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{
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return g_dropbear_hmac_cryptofd;
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}
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fd = open("/dev/crypto", O_RDWR);
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if (fd < 0)
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{
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return -1;
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}
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if (ioctl(fd, CRIOGET, &cfd) < 0)
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{
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close(fd);
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return -1;
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}
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close(fd);
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g_dropbear_hmac_cryptofd = cfd;
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return g_dropbear_hmac_cryptofd;
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}
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static int dropbear_hmac_hash_is_sha256(int hash)
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{
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int ret;
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ret = hash_is_valid(hash);
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if (ret != CRYPT_OK)
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{
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return ret;
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}
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if (hash_descriptor[hash].hashsize != DROPBEAR_HMAC_SHA256_DIGESTLEN ||
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hash_descriptor[hash].blocksize != DROPBEAR_HMAC_SHA256_BLOCKLEN)
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{
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return CRYPT_INVALID_HASH;
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}
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return CRYPT_OK;
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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int hmac_init(hmac_state *hmac, int hash, const unsigned char *key,
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unsigned long keylen)
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{
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struct session_op session;
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int cfd;
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int ret;
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LTC_ARGCHK(hmac != NULL);
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LTC_ARGCHK(key != NULL);
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if (keylen == 0)
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{
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return CRYPT_INVALID_KEYSIZE;
128+
}
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ret = dropbear_hmac_hash_is_sha256(hash);
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if (ret != CRYPT_OK)
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{
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return ret;
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}
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cfd = dropbear_hmac_cryptodev_fd();
137+
if (cfd < 0)
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{
139+
return CRYPT_ERROR;
140+
}
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142+
memset(&session, 0, sizeof(session));
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session.mac = CRYPTO_SHA2_256_HMAC;
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session.mackey = (caddr_t)key;
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session.mackeylen = keylen;
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if (ioctl(cfd, CIOCGSESSION, &session) < 0)
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{
148+
return CRYPT_ERROR;
149+
}
150+
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hmac->hash = hash;
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HMAC_SES(hmac) = session.ses;
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return CRYPT_OK;
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}
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int hmac_process(hmac_state *hmac, const unsigned char *in,
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unsigned long inlen)
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{
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struct crypt_op cryp;
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int cfd;
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LTC_ARGCHK(hmac != NULL);
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LTC_ARGCHK(in != NULL || inlen == 0);
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cfd = dropbear_hmac_cryptodev_fd();
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if (cfd < 0)
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{
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return CRYPT_ERROR;
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}
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memset(&cryp, 0, sizeof(cryp));
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cryp.ses = HMAC_SES(hmac);
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cryp.op = COP_ENCRYPT;
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cryp.flags = COP_FLAG_UPDATE;
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cryp.len = inlen;
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cryp.src = (caddr_t)in;
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if (ioctl(cfd, CIOCCRYPT, &cryp) < 0)
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{
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return CRYPT_ERROR;
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}
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return CRYPT_OK;
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}
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int hmac_done(hmac_state *hmac, unsigned char *out, unsigned long *outlen)
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{
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unsigned char digest[DROPBEAR_HMAC_SHA256_DIGESTLEN];
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struct crypt_op cryp;
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unsigned long copylen;
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int cfd;
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int ret = CRYPT_ERROR;
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LTC_ARGCHK(hmac != NULL);
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LTC_ARGCHK(out != NULL);
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LTC_ARGCHK(outlen != NULL);
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cfd = dropbear_hmac_cryptodev_fd();
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if (cfd < 0)
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{
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goto out;
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}
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memset(&cryp, 0, sizeof(cryp));
204+
cryp.ses = HMAC_SES(hmac);
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cryp.op = COP_ENCRYPT;
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cryp.len = 0;
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cryp.mac = (caddr_t)digest;
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if (ioctl(cfd, CIOCCRYPT, &cryp) < 0)
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{
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goto out;
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}
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copylen = MIN(*outlen, DROPBEAR_HMAC_SHA256_DIGESTLEN);
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memcpy(out, digest, copylen);
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*outlen = copylen;
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ret = CRYPT_OK;
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out:
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if (cfd >= 0)
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{
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ioctl(cfd, CIOCFSESSION, &HMAC_SES(hmac));
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}
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zeromem(digest, sizeof(digest));
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zeromem(hmac, sizeof(*hmac));
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return ret;
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}

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