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diff --git a/src/openvpn/crypto_backend.h b/src/openvpn/crypto_backend.h
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+/*
+ *  OpenVPN -- An application to securely tunnel IP networks
+ *             over a single TCP/UDP port, with support for SSL/TLS-based
+ *             session authentication and key exchange,
+ *             packet encryption, packet authentication, and
+ *             packet compression.
+ *
+ *  Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net>
+ *  Copyright (C) 2010 Fox Crypto B.V. <openvpn@fox-it.com>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2
+ *  as published by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program (see the file COPYING included with this
+ *  distribution); if not, write to the Free Software Foundation, Inc.,
+ *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+/**
+ * @file Data Channel Cryptography SSL library-specific backend interface
+ */
+
+#ifndef CRYPTO_BACKEND_H_
+#define CRYPTO_BACKEND_H_
+
+#ifdef ENABLE_CRYPTO_OPENSSL
+#include "crypto_openssl.h"
+#endif
+#ifdef ENABLE_CRYPTO_POLARSSL
+#include "crypto_polarssl.h"
+#endif
+#include "basic.h"
+
+
+/*
+ * This routine should have additional OpenSSL crypto library initialisations
+ * used by both crypto and ssl components of OpenVPN.
+ */
+void crypto_init_lib (void);
+
+void crypto_uninit_lib (void);
+
+void crypto_clear_error (void);
+
+/*
+ * Initialise the given named crypto engine.
+ */
+void crypto_init_lib_engine (const char *engine_name);
+
+#ifdef DMALLOC
+/*
+ * OpenSSL memory debugging.  If dmalloc debugging is enabled, tell
+ * OpenSSL to use our private malloc/realloc/free functions so that
+ * we can dispatch them to dmalloc.
+ */
+void crypto_init_dmalloc (void);
+#endif /* DMALLOC */
+
+void show_available_ciphers (void);
+
+void show_available_digests (void);
+
+void show_available_engines (void);
+
+/*
+ *
+ * Random number functions, used in cases where we want
+ * reasonably strong cryptographic random number generation
+ * without depleting our entropy pool.  Used for random
+ * IV values and a number of other miscellaneous tasks.
+ *
+ */
+
+/**
+ * Wrapper for secure random number generator. Retrieves len bytes of random
+ * data, and places it in output.
+ *
+ * @param output	Output buffer
+ * @param len		Length of the output buffer, in bytes
+ *
+ * @return 		\c 1 on success, \c 0 on failure
+ */
+int rand_bytes (uint8_t *output, int len);
+
+/*
+ *
+ * Key functions, allow manipulation of keys.
+ *
+ */
+
+
+/**
+ * Return number of DES cblocks (1 cblock = length of a single-DES key) for the
+ * current key type or 0 if not a DES cipher.
+ *
+ * @param kt		Type of key
+ *
+ * @return 		Number of DES cblocks that the key consists of, or 0.
+ */
+int key_des_num_cblocks (const cipher_kt_t *kt);
+
+/*
+ * Check the given DES key. Checks the given key's length, weakness and parity.
+ *
+ * @param key		Key to check
+ * @param key_len	Length of the key, in bytes
+ * @param ndc		Number of DES cblocks that the key is made up of.
+ *
+ * @return 		\c true if the key is valid, \c false otherwise.
+ */
+bool key_des_check (uint8_t *key, int key_len, int ndc);
+
+/*
+ * Fix the given DES key, setting its parity to odd.
+ *
+ * @param key		Key to check
+ * @param key_len	Length of the key, in bytes
+ * @param ndc		Number of DES cblocks that the key is made up of.
+ */
+void key_des_fixup (uint8_t *key, int key_len, int ndc);
+
+/**
+ * Encrypt the given block, using DES ECB mode
+ *
+ * @param key		DES key to use.
+ * @param src		Buffer containing the 8-byte source.
+ * @param dst		Buffer containing the 8-byte destination
+ */
+void cipher_des_encrypt_ecb (const unsigned char key[DES_KEY_LENGTH],
+    unsigned char src[DES_KEY_LENGTH],
+    unsigned char dst[DES_KEY_LENGTH]);
+
+/*
+ *
+ * Generic cipher key type functions
+ *
+ */
+/*
+ * Max size in bytes of any cipher key that might conceivably be used.
+ *
+ * This value is checked at compile time in crypto.c to make sure
+ * it is always at least EVP_MAX_KEY_LENGTH.
+ *
+ * We define our own value, since this parameter
+ * is used to control the size of static key files.
+ * If the OpenSSL library increases EVP_MAX_KEY_LENGTH,
+ * we don't want our key files to be suddenly rendered
+ * unusable.
+ */
+#define MAX_CIPHER_KEY_LENGTH 64
+
+/**
+ * Return cipher parameters, based on the given cipher name. The
+ * contents of these parameters are library-specific, and can be used to
+ * initialise encryption/decryption.
+ *
+ * @param ciphername 	Name of the cipher to retrieve parameters for (e.g.
+ * 			\c AES-128-CBC).
+ *
+ * @return		A statically allocated structure containing parameters
+ * 			for the given cipher.
+ */
+const cipher_kt_t * cipher_kt_get (const char *ciphername);
+
+/**
+ * Retrieve a string describing the cipher (e.g. \c AES-128-CBC).
+ *
+ * @param cipher_kt 	Static cipher parameters
+ *
+ * @return a statically allocated string describing the cipher.
+ */
+const char * cipher_kt_name (const cipher_kt_t *cipher_kt);
+
+/**
+ * Returns the size of keys used by the cipher, in bytes. If the cipher has a
+ * variable key size, return the default key size.
+ *
+ * @param cipher_kt 	Static cipher parameters
+ *
+ * @return 		(Default) size of keys used by the cipher, in bytes.
+ */
+int cipher_kt_key_size (const cipher_kt_t *cipher_kt);
+
+/**
+ * Returns the size of the IV used by the cipher, in bytes, or 0 if no IV is
+ * used.
+ *
+ * @param cipher_kt 	Static cipher parameters
+ *
+ * @return 		Size of the IV, in bytes, or 0 if the cipher does not
+ * 			use an IV.
+ */
+int cipher_kt_iv_size (const cipher_kt_t *cipher_kt);
+
+/**
+ * Returns the block size of the cipher, in bytes.
+ *
+ * @param cipher_kt 	Static cipher parameters
+ *
+ * @return 		Block size, in bytes.
+ */
+int cipher_kt_block_size (const cipher_kt_t *cipher_kt);
+
+/**
+ * Returns the mode that the cipher runs in.
+ *
+ * @param cipher_kt 	Static cipher parameters
+ *
+ * @return 		Cipher mode, either \c OPENVPN_MODE_CBC, \c
+ * 			OPENVPN_MODE_OFB or \c OPENVPN_MODE_CFB
+ */
+int cipher_kt_mode (const cipher_kt_t *cipher_kt);
+
+
+/**
+ *
+ * Generic cipher functions
+ *
+ */
+
+/**
+ * Initialise a cipher context, based on the given key and key type.
+ *
+ * @param ctx		Cipher context. May not be NULL
+ * @param key		Buffer containing the key to use
+ * @param key_len 	Length of the key, in bytes
+ * @param kt		Static cipher parameters to use
+ * @param enc		Whether to encrypt or decrypt (either
+ * 			\c POLARSSL_OP_ENCRYPT or \c POLARSSL_OP_DECRYPT).
+ */
+void cipher_ctx_init (cipher_ctx_t *ctx, uint8_t *key, int key_len,
+    const cipher_kt_t *kt, int enc);
+
+/**
+ * Cleanup the specified context.
+ *
+ * @param ctx	Cipher context to cleanup.
+ */
+void cipher_ctx_cleanup (cipher_ctx_t *ctx);
+
+/**
+ * Returns the size of the IV used by the cipher, in bytes, or 0 if no IV is
+ * used.
+ *
+ * @param ctx	 	The cipher's context
+ *
+ * @return 		Size of the IV, in bytes, or \c 0 if the cipher does not
+ * 			use an IV or ctx was NULL.
+ */
+int cipher_ctx_iv_length (const cipher_ctx_t *ctx);
+
+/**
+ * Returns the block size of the cipher, in bytes.
+ *
+ * @param ctx	 	The cipher's context
+ *
+ * @return 		Block size, in bytes, or 0 if ctx was NULL.
+ */
+int cipher_ctx_block_size (const cipher_ctx_t *ctx);
+
+/**
+ * Returns the mode that the cipher runs in.
+ *
+ * @param ctx 		Cipher's context. May not be NULL.
+ *
+ * @return 		Cipher mode, either \c OPENVPN_MODE_CBC, \c
+ * 			OPENVPN_MODE_OFB or \c OPENVPN_MODE_CFB
+ */
+int cipher_ctx_mode (const cipher_ctx_t *ctx);
+
+/**
+ * Resets the given cipher context, setting the IV to the specified value.
+ * Preserves the associated key information.
+ *
+ * @param ctx 		Cipher's context. May not be NULL.
+ * @param iv_buf	The IV to use.
+ *
+ * @return 		\c 0 on failure, \c 1 on success.
+ */
+int cipher_ctx_reset (cipher_ctx_t *ctx, uint8_t *iv_buf);
+
+/**
+ * Updates the given cipher context, encrypting data in the source buffer, and
+ * placing any complete blocks in the destination buffer.
+ *
+ * Note that if a complete block cannot be written, data is cached in the
+ * context, and emitted at a later call to \c cipher_ctx_update, or by a call
+ * to \c cipher_ctx_final(). This implies that dst should have enough room for
+ * src_len + \c cipher_ctx_block_size() - 1.
+ *
+ * @param ctx 		Cipher's context. May not be NULL.
+ * @param dst		Destination buffer
+ * @param dst_len	Length of the destination buffer, in bytes
+ * @param src		Source buffer
+ * @param src_len	Length of the source buffer, in bytes
+ *
+ * @return 		\c 0 on failure, \c 1 on success.
+ */
+int cipher_ctx_update (cipher_ctx_t *ctx, uint8_t *dst, int *dst_len,
+    uint8_t *src, int src_len);
+
+/**
+ * Pads the final cipher block using PKCS padding, and output to the destination
+ * buffer.
+ *
+ * @param ctx 		Cipher's context. May not be NULL.
+ * @param dst		Destination buffer
+ * @param dst_len	Length of the destination buffer, in bytes
+ *
+ * @return 		\c 0 on failure, \c 1 on success.
+ */
+int cipher_ctx_final (cipher_ctx_t *ctx, uint8_t *dst, int *dst_len);
+
+/*
+ *
+ * Generic message digest information functions
+ *
+ */
+
+/*
+ * Max size in bytes of any HMAC key that might conceivably be used.
+ *
+ * This value is checked at compile time in crypto.c to make sure
+ * it is always at least EVP_MAX_MD_SIZE.  We define our own value
+ * for the same reason as above.
+ */
+#define MAX_HMAC_KEY_LENGTH 64
+
+/**
+ * Return message digest parameters, based on the given digest name. The
+ * contents of these parameters are library-specific, and can be used to
+ * initialise HMAC or message digest operations.
+ *
+ * @param digest	Name of the digest to retrieve parameters for (e.g.
+ * 			\c MD5).
+ *
+ * @return		A statically allocated structure containing parameters
+ * 			for the given message digest.
+ */
+const md_kt_t * md_kt_get (const char *digest);
+
+/**
+ * Retrieve a string describing the digest digest (e.g. \c SHA1).
+ *
+ * @param kt 		Static message digest parameters
+ *
+ * @return 		Statically allocated string describing the message
+ * 			digest.
+ */
+const char * md_kt_name (const md_kt_t *kt);
+
+/**
+ * Returns the size of the message digest, in bytes.
+ *
+ * @param kt 		Static message digest parameters
+ *
+ * @return 		Message digest size, in bytes, or 0 if ctx was NULL.
+ */
+int md_kt_size (const md_kt_t *kt);
+
+
+/*
+ *
+ * Generic message digest functions
+ *
+ */
+
+/*
+ * Calculates the message digest for the given buffer.
+ *
+ * @param kt 		Static message digest parameters
+ * @param src		Buffer to digest. May not be NULL.
+ * @param src_len	The length of the incoming buffer.
+ * @param dst		Buffer to write the message digest to. May not be NULL.
+ *
+ * @return		\c 1 on success, \c 0 on failure
+ */
+int md_full (const md_kt_t *kt, const uint8_t *src, int src_len, uint8_t *dst);
+
+/*
+ * Initialises the given message digest context.
+ *
+ * @param ctx		Message digest context
+ * @param kt 		Static message digest parameters
+ */
+void md_ctx_init (md_ctx_t *ctx, const md_kt_t *kt);
+
+/*
+ * Free the given message digest context.
+ *
+ * @param ctx		Message digest context
+ */
+void md_ctx_cleanup(md_ctx_t *ctx);
+
+/*
+ * Returns the size of the message digest output by the given context
+ *
+ * @param ctx 		Message digest context.
+ *
+ * @return 		Size of the message digest, or \0 if ctx is NULL.
+ */
+int md_ctx_size (const md_ctx_t *ctx);
+
+/*
+ * Process the given data for use in the message digest.
+ *
+ * @param ctx		Message digest context. May not be NULL.
+ * @param src		Buffer to digest. May not be NULL.
+ * @param src_len	The length of the incoming buffer.
+ */
+void md_ctx_update (md_ctx_t *ctx, const uint8_t *src, int src_len);
+
+/*
+ * Output the message digest to the given buffer.
+ *
+ * @param ctx		Message digest context. May not be NULL.
+ * @param dst		Buffer to write the message digest to. May not be NULL.
+ */
+void md_ctx_final (md_ctx_t *ctx, uint8_t *dst);
+
+
+/*
+ *
+ * Generic HMAC functions
+ *
+ */
+
+/*
+ * Initialises the given HMAC context, using the given digest
+ * and key.
+ *
+ * @param ctx		HMAC context to intialise
+ * @param key		The key to use for the HMAC
+ * @param key_len	The key length to use
+ * @param kt 		Static message digest parameters
+ *
+ */
+void hmac_ctx_init (hmac_ctx_t *ctx, const uint8_t *key, int key_length,
+    const md_kt_t *kt);
+
+/*
+ * Free the given HMAC context.
+ *
+ * @param ctx		HMAC context
+ */
+void hmac_ctx_cleanup(hmac_ctx_t *ctx);
+
+/*
+ * Returns the size of the HMAC output by the given HMAC Context
+ *
+ * @param ctx 		HMAC context.
+ *
+ * @return 		Size of the HMAC, or \0 if ctx is NULL.
+ */
+int hmac_ctx_size (const hmac_ctx_t *ctx);
+
+/*
+ * Resets the given HMAC context, preserving the associated key information
+ *
+ * @param ctx 		HMAC context. May not be NULL.
+ */
+void hmac_ctx_reset (hmac_ctx_t *ctx);
+
+/*
+ * Process the given data for use in the HMAC.
+ *
+ * @param ctx		HMAC context. May not be NULL.
+ * @param src		The buffer to HMAC. May not be NULL.
+ * @param src_len	The length of the incoming buffer.
+ */
+void hmac_ctx_update (hmac_ctx_t *ctx, const uint8_t *src, int src_len);
+
+/*
+ * Output the HMAC to the given buffer.
+ *
+ * @param ctx		HMAC context. May not be NULL.
+ * @param dst		buffer to write the HMAC to. May not be NULL.
+ */
+void hmac_ctx_final (hmac_ctx_t *ctx, uint8_t *dst);
+
+#endif /* CRYPTO_BACKEND_H_ */