/*-
 * Copyright (c) 2014-2015 MongoDB, Inc.
 * Copyright (c) 2008-2014 WiredTiger, Inc.
 *	All rights reserved.
 *
 * See the file LICENSE for redistribution information.
 */

#include "wt_internal.h"

/*
 * __wt_decrypt --
 *	Common code to decrypt and verify the encrypted data in a
 *	WT_ITEM and return the decrypted buffer.
 */
int
__wt_decrypt(WT_SESSION_IMPL *session,
    WT_ENCRYPTOR *encryptor, size_t skip, WT_ITEM *in, WT_ITEM *out)
{
	size_t encryptor_data_len, result_len;
	uint32_t encrypt_len;
	uint8_t *dst, *src;

	encrypt_len = WT_STORE_SIZE(*((uint32_t *)
	    ((uint8_t *)in->data + skip)));
	if (encrypt_len > in->size)
		WT_RET_MSG(session, WT_ERROR,
		    "corrupted encrypted item: padded size less than "
		    "actual size");
	/*
	 * We're allocating the number of bytes we're expecting
	 * from decryption plus the unencrypted header.
	 */
	WT_RET(__wt_buf_initsize(session, out, encrypt_len));

	src = (uint8_t *)in->data + skip + WT_ENCRYPT_LEN_SIZE;
	encryptor_data_len = encrypt_len - (skip + WT_ENCRYPT_LEN_SIZE);
	dst = (uint8_t *)out->mem + skip;

	WT_RET(encryptor->decrypt(encryptor, &session->iface,
	    src, encryptor_data_len, dst, encryptor_data_len, &result_len));
	/*
	 * We require encryption to be byte for byte.  It should not expand
	 * the data.
	 */
	WT_ASSERT(session, result_len <= encryptor_data_len);

	/*
	 * Copy in the skipped header bytes.
	 */
	memcpy(out->mem, in->data, skip);

	/*
	 * Set the real result length in the output buffer including the skipped
	 * header size. The encryptor may have done its own padding so the
	 * returned result length is the real data length after decryption
	 * removes any of its padding.
	 */
	out->size = result_len + skip;

	return (0);
}

/*
 * __wt_encrypt --
 *	Common code to encrypt a WT_ITEM and return the encrypted buffer.
 */
int
__wt_encrypt(WT_SESSION_IMPL *session,
    WT_KEYED_ENCRYPTOR *kencryptor, size_t skip, WT_ITEM *in, WT_ITEM *out)
{
	size_t dst_len, result_len, src_len;
	uint32_t *unpadded_lenp;
	uint8_t *dst, *src;

	/* Skip the header bytes of the source data. */
	src = (uint8_t *)in->mem + skip;
	src_len = in->size - skip;

	unpadded_lenp = (uint32_t *)((uint8_t *)out->mem + skip);

	/*
	 * Skip the header bytes and the length we store in the destination
	 * data. Add in the encryptor size constant to the expected destination
	 * length.
	 */
	dst = (uint8_t *)out->mem + skip + WT_ENCRYPT_LEN_SIZE;
	dst_len = src_len + kencryptor->size_const;

	WT_RET(kencryptor->encryptor->encrypt(kencryptor->encryptor,
	    &session->iface, src, src_len, dst, dst_len, &result_len));
	/*
	 * We require encryption to be byte for byte.  It should never expand
	 * the data.
	 */
	WT_ASSERT(session, result_len <= dst_len);

	/*
	 * The final result length includes the skipped lengths.
	 */
	result_len += skip + WT_ENCRYPT_LEN_SIZE;
	/*
	 * Store original size so we know how much space is needed on the
	 * decryption side.
	 */
	*unpadded_lenp = WT_STORE_SIZE(result_len);
	/*
	 * Copy in the skipped header bytes, set the final data size.
	 */
	memcpy(out->mem, in->mem, skip);
	out->size = result_len;
	return (0);
}

/*
 * __wt_encrypt_size --
 *	Return the size needed for the destination buffer.
 */
void
__wt_encrypt_size(WT_SESSION_IMPL *session,
    WT_KEYED_ENCRYPTOR *kencryptor, size_t incoming_size, size_t *sizep)
{
	WT_UNUSED(session);

	if (sizep == NULL)
		return;

	*sizep = incoming_size + kencryptor->size_const + WT_ENCRYPT_LEN_SIZE;
	return;
}
