// SPDX-License-Identifier: GPL-2.0
  /*
   * Adiantum length-preserving encryption mode
   *
   * Copyright 2018 Google LLC
   */
  
  /*
   * Adiantum is a tweakable, length-preserving encryption mode designed for fast
   * and secure disk encryption, especially on CPUs without dedicated crypto
   * instructions.  Adiantum encrypts each sector using the XChaCha12 stream

   * cipher, two passes of an ε-almost-∆-universal (ε-∆U) hash function based on

   * NH and Poly1305, and an invocation of the AES-256 block cipher on a single
   * 16-byte block.  See the paper for details:
   *
   *	Adiantum: length-preserving encryption for entry-level processors
   *      (https://eprint.iacr.org/2018/720.pdf)
   *
   * For flexibility, this implementation also allows other ciphers:
   *
   *	- Stream cipher: XChaCha12 or XChaCha20
   *	- Block cipher: any with a 128-bit block size and 256-bit key
   *

   * This implementation doesn't currently allow other ε-∆U hash functions, i.e.

   * HPolyC is not supported.  This is because Adiantum is ~20% faster than HPolyC

   * but still provably as secure, and also the ε-∆U hash function of HBSH is

   * formally defined to take two inputs (tweak, message) which makes it difficult
   * to wrap with the crypto_shash API.  Rather, some details need to be handled

   * here.  Nevertheless, if needed in the future, support for other ε-∆U hash

   * functions could be added here.
   */
  
  #include <crypto/b128ops.h>
  #include <crypto/chacha.h>
  #include <crypto/internal/hash.h>

  #include <crypto/internal/poly1305.h>

  #include <crypto/internal/skcipher.h>
  #include <crypto/nhpoly1305.h>
  #include <crypto/scatterwalk.h>
  #include <linux/module.h>

  /*

   * Size of right-hand part of input data, in bytes; also the size of the block

   * cipher's block size and the hash function's output.
   */
  #define BLOCKCIPHER_BLOCK_SIZE		16
  
  /* Size of the block cipher key (K_E) in bytes */
  #define BLOCKCIPHER_KEY_SIZE		32
  
  /* Size of the hash key (K_H) in bytes */
  #define HASH_KEY_SIZE		(POLY1305_BLOCK_SIZE + NHPOLY1305_KEY_SIZE)
  
  /*
   * The specification allows variable-length tweaks, but Linux's crypto API
   * currently only allows algorithms to support a single length.  The "natural"
   * tweak length for Adiantum is 16, since that fits into one Poly1305 block for
   * the best performance.  But longer tweaks are useful for fscrypt, to avoid
   * needing to derive per-file keys.  So instead we use two blocks, or 32 bytes.
   */
  #define TWEAK_SIZE		32
  
  struct adiantum_instance_ctx {
  	struct crypto_skcipher_spawn streamcipher_spawn;

  	struct crypto_cipher_spawn blockcipher_spawn;

  	struct crypto_shash_spawn hash_spawn;
  };
  
  struct adiantum_tfm_ctx {
  	struct crypto_skcipher *streamcipher;
  	struct crypto_cipher *blockcipher;
  	struct crypto_shash *hash;

  	struct poly1305_core_key header_hash_key;

  };
  
  struct adiantum_request_ctx {
  
  	/*

  	 * Buffer for right-hand part of data, i.e.

  	 *
  	 *    P_L => P_M => C_M => C_R when encrypting, or
  	 *    C_R => C_M => P_M => P_L when decrypting.
  	 *
  	 * Also used to build the IV for the stream cipher.
  	 */
  	union {
  		u8 bytes[XCHACHA_IV_SIZE];
  		__le32 words[XCHACHA_IV_SIZE / sizeof(__le32)];
  		le128 bignum;	/* interpret as element of Z/(2^{128}Z) */
  	} rbuf;
  
  	bool enc; /* true if encrypting, false if decrypting */
  
  	/*

  	 * The result of the Poly1305 ε-∆U hash function applied to
  	 * (bulk length, tweak)

  	 */
  	le128 header_hash;
  
  	/* Sub-requests, must be last */
  	union {
  		struct shash_desc hash_desc;
  		struct skcipher_request streamcipher_req;
  	} u;
  };
  
  /*
   * Given the XChaCha stream key K_S, derive the block cipher key K_E and the
   * hash key K_H as follows:
   *
   *     K_E || K_H || ... = XChaCha(key=K_S, nonce=1||0^191)
   *
   * Note that this denotes using bits from the XChaCha keystream, which here we
   * get indirectly by encrypting a buffer containing all 0's.
   */
  static int adiantum_setkey(struct crypto_skcipher *tfm, const u8 *key,
  			   unsigned int keylen)
  {
  	struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  	struct {
  		u8 iv[XCHACHA_IV_SIZE];
  		u8 derived_keys[BLOCKCIPHER_KEY_SIZE + HASH_KEY_SIZE];
  		struct scatterlist sg;
  		struct crypto_wait wait;
  		struct skcipher_request req; /* must be last */
  	} *data;
  	u8 *keyp;
  	int err;
  
  	/* Set the stream cipher key (K_S) */
  	crypto_skcipher_clear_flags(tctx->streamcipher, CRYPTO_TFM_REQ_MASK);
  	crypto_skcipher_set_flags(tctx->streamcipher,
  				  crypto_skcipher_get_flags(tfm) &
  				  CRYPTO_TFM_REQ_MASK);
  	err = crypto_skcipher_setkey(tctx->streamcipher, key, keylen);

  	if (err)
  		return err;
  
  	/* Derive the subkeys */
  	data = kzalloc(sizeof(*data) +
  		       crypto_skcipher_reqsize(tctx->streamcipher), GFP_KERNEL);
  	if (!data)
  		return -ENOMEM;
  	data->iv[0] = 1;
  	sg_init_one(&data->sg, data->derived_keys, sizeof(data->derived_keys));
  	crypto_init_wait(&data->wait);
  	skcipher_request_set_tfm(&data->req, tctx->streamcipher);
  	skcipher_request_set_callback(&data->req, CRYPTO_TFM_REQ_MAY_SLEEP |
  						  CRYPTO_TFM_REQ_MAY_BACKLOG,
  				      crypto_req_done, &data->wait);
  	skcipher_request_set_crypt(&data->req, &data->sg, &data->sg,
  				   sizeof(data->derived_keys), data->iv);
  	err = crypto_wait_req(crypto_skcipher_encrypt(&data->req), &data->wait);
  	if (err)
  		goto out;
  	keyp = data->derived_keys;
  
  	/* Set the block cipher key (K_E) */
  	crypto_cipher_clear_flags(tctx->blockcipher, CRYPTO_TFM_REQ_MASK);
  	crypto_cipher_set_flags(tctx->blockcipher,
  				crypto_skcipher_get_flags(tfm) &
  				CRYPTO_TFM_REQ_MASK);
  	err = crypto_cipher_setkey(tctx->blockcipher, keyp,
  				   BLOCKCIPHER_KEY_SIZE);

  	if (err)
  		goto out;
  	keyp += BLOCKCIPHER_KEY_SIZE;
  
  	/* Set the hash key (K_H) */
  	poly1305_core_setkey(&tctx->header_hash_key, keyp);
  	keyp += POLY1305_BLOCK_SIZE;
  
  	crypto_shash_clear_flags(tctx->hash, CRYPTO_TFM_REQ_MASK);
  	crypto_shash_set_flags(tctx->hash, crypto_skcipher_get_flags(tfm) &
  					   CRYPTO_TFM_REQ_MASK);
  	err = crypto_shash_setkey(tctx->hash, keyp, NHPOLY1305_KEY_SIZE);

  	keyp += NHPOLY1305_KEY_SIZE;
  	WARN_ON(keyp != &data->derived_keys[ARRAY_SIZE(data->derived_keys)]);
  out:

  	kfree_sensitive(data);

  	return err;
  }
  
  /* Addition in Z/(2^{128}Z) */
  static inline void le128_add(le128 *r, const le128 *v1, const le128 *v2)
  {
  	u64 x = le64_to_cpu(v1->b);
  	u64 y = le64_to_cpu(v2->b);
  
  	r->b = cpu_to_le64(x + y);
  	r->a = cpu_to_le64(le64_to_cpu(v1->a) + le64_to_cpu(v2->a) +
  			   (x + y < x));
  }
  
  /* Subtraction in Z/(2^{128}Z) */
  static inline void le128_sub(le128 *r, const le128 *v1, const le128 *v2)
  {
  	u64 x = le64_to_cpu(v1->b);
  	u64 y = le64_to_cpu(v2->b);
  
  	r->b = cpu_to_le64(x - y);
  	r->a = cpu_to_le64(le64_to_cpu(v1->a) - le64_to_cpu(v2->a) -
  			   (x - y > x));
  }
  
  /*

   * Apply the Poly1305 ε-∆U hash function to (bulk length, tweak) and save the
   * result to rctx->header_hash.  This is the calculation

   *

   *	H_T ← Poly1305_{K_T}(bin_{128}(|L|) || T)
   *
   * from the procedure in section 6.4 of the Adiantum paper.  The resulting value
   * is reused in both the first and second hash steps.  Specifically, it's added
   * to the result of an independently keyed ε-∆U hash function (for equal length
   * inputs only) taken over the left-hand part (the "bulk") of the message, to
   * give the overall Adiantum hash of the (tweak, left-hand part) pair.

   */
  static void adiantum_hash_header(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
  	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
  	struct {
  		__le64 message_bits;
  		__le64 padding;
  	} header = {
  		.message_bits = cpu_to_le64((u64)bulk_len * 8)
  	};
  	struct poly1305_state state;
  
  	poly1305_core_init(&state);
  
  	BUILD_BUG_ON(sizeof(header) % POLY1305_BLOCK_SIZE != 0);
  	poly1305_core_blocks(&state, &tctx->header_hash_key,

  			     &header, sizeof(header) / POLY1305_BLOCK_SIZE, 1);

  
  	BUILD_BUG_ON(TWEAK_SIZE % POLY1305_BLOCK_SIZE != 0);
  	poly1305_core_blocks(&state, &tctx->header_hash_key, req->iv,

  			     TWEAK_SIZE / POLY1305_BLOCK_SIZE, 1);

  	poly1305_core_emit(&state, NULL, &rctx->header_hash);

  }

  /* Hash the left-hand part (the "bulk") of the message using NHPoly1305 */

  static int adiantum_hash_message(struct skcipher_request *req,
  				 struct scatterlist *sgl, le128 *digest)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
  	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
  	struct shash_desc *hash_desc = &rctx->u.hash_desc;
  	struct sg_mapping_iter miter;
  	unsigned int i, n;
  	int err;
  
  	hash_desc->tfm = tctx->hash;

  
  	err = crypto_shash_init(hash_desc);
  	if (err)
  		return err;
  
  	sg_miter_start(&miter, sgl, sg_nents(sgl),
  		       SG_MITER_FROM_SG | SG_MITER_ATOMIC);
  	for (i = 0; i < bulk_len; i += n) {
  		sg_miter_next(&miter);
  		n = min_t(unsigned int, miter.length, bulk_len - i);
  		err = crypto_shash_update(hash_desc, miter.addr, n);
  		if (err)
  			break;
  	}
  	sg_miter_stop(&miter);
  	if (err)
  		return err;
  
  	return crypto_shash_final(hash_desc, (u8 *)digest);
  }
  
  /* Continue Adiantum encryption/decryption after the stream cipher step */
  static int adiantum_finish(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
  	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
  	le128 digest;
  	int err;
  
  	/* If decrypting, decrypt C_M with the block cipher to get P_M */
  	if (!rctx->enc)
  		crypto_cipher_decrypt_one(tctx->blockcipher, rctx->rbuf.bytes,
  					  rctx->rbuf.bytes);
  
  	/*
  	 * Second hash step
  	 *	enc: C_R = C_M - H_{K_H}(T, C_L)
  	 *	dec: P_R = P_M - H_{K_H}(T, P_L)
  	 */
  	err = adiantum_hash_message(req, req->dst, &digest);
  	if (err)
  		return err;
  	le128_add(&digest, &digest, &rctx->header_hash);
  	le128_sub(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
  	scatterwalk_map_and_copy(&rctx->rbuf.bignum, req->dst,
  				 bulk_len, BLOCKCIPHER_BLOCK_SIZE, 1);
  	return 0;
  }
  
  static void adiantum_streamcipher_done(struct crypto_async_request *areq,
  				       int err)
  {
  	struct skcipher_request *req = areq->data;
  
  	if (!err)
  		err = adiantum_finish(req);
  
  	skcipher_request_complete(req, err);
  }
  
  static int adiantum_crypt(struct skcipher_request *req, bool enc)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
  	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
  	unsigned int stream_len;
  	le128 digest;
  	int err;
  
  	if (req->cryptlen < BLOCKCIPHER_BLOCK_SIZE)
  		return -EINVAL;
  
  	rctx->enc = enc;
  
  	/*
  	 * First hash step
  	 *	enc: P_M = P_R + H_{K_H}(T, P_L)
  	 *	dec: C_M = C_R + H_{K_H}(T, C_L)
  	 */
  	adiantum_hash_header(req);
  	err = adiantum_hash_message(req, req->src, &digest);
  	if (err)
  		return err;
  	le128_add(&digest, &digest, &rctx->header_hash);
  	scatterwalk_map_and_copy(&rctx->rbuf.bignum, req->src,
  				 bulk_len, BLOCKCIPHER_BLOCK_SIZE, 0);
  	le128_add(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
  
  	/* If encrypting, encrypt P_M with the block cipher to get C_M */
  	if (enc)
  		crypto_cipher_encrypt_one(tctx->blockcipher, rctx->rbuf.bytes,
  					  rctx->rbuf.bytes);
  
  	/* Initialize the rest of the XChaCha IV (first part is C_M) */
  	BUILD_BUG_ON(BLOCKCIPHER_BLOCK_SIZE != 16);
  	BUILD_BUG_ON(XCHACHA_IV_SIZE != 32);	/* nonce || stream position */
  	rctx->rbuf.words[4] = cpu_to_le32(1);
  	rctx->rbuf.words[5] = 0;
  	rctx->rbuf.words[6] = 0;
  	rctx->rbuf.words[7] = 0;
  
  	/*
  	 * XChaCha needs to be done on all the data except the last 16 bytes;
  	 * for disk encryption that usually means 4080 or 496 bytes.  But ChaCha
  	 * implementations tend to be most efficient when passed a whole number
  	 * of 64-byte ChaCha blocks, or sometimes even a multiple of 256 bytes.
  	 * And here it doesn't matter whether the last 16 bytes are written to,
  	 * as the second hash step will overwrite them.  Thus, round the XChaCha
  	 * length up to the next 64-byte boundary if possible.
  	 */
  	stream_len = bulk_len;
  	if (round_up(stream_len, CHACHA_BLOCK_SIZE) <= req->cryptlen)
  		stream_len = round_up(stream_len, CHACHA_BLOCK_SIZE);
  
  	skcipher_request_set_tfm(&rctx->u.streamcipher_req, tctx->streamcipher);
  	skcipher_request_set_crypt(&rctx->u.streamcipher_req, req->src,
  				   req->dst, stream_len, &rctx->rbuf);
  	skcipher_request_set_callback(&rctx->u.streamcipher_req,
  				      req->base.flags,
  				      adiantum_streamcipher_done, req);
  	return crypto_skcipher_encrypt(&rctx->u.streamcipher_req) ?:
  		adiantum_finish(req);
  }
  
  static int adiantum_encrypt(struct skcipher_request *req)
  {
  	return adiantum_crypt(req, true);
  }
  
  static int adiantum_decrypt(struct skcipher_request *req)
  {
  	return adiantum_crypt(req, false);
  }
  
  static int adiantum_init_tfm(struct crypto_skcipher *tfm)
  {
  	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
  	struct adiantum_instance_ctx *ictx = skcipher_instance_ctx(inst);
  	struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  	struct crypto_skcipher *streamcipher;
  	struct crypto_cipher *blockcipher;
  	struct crypto_shash *hash;
  	unsigned int subreq_size;
  	int err;
  
  	streamcipher = crypto_spawn_skcipher(&ictx->streamcipher_spawn);
  	if (IS_ERR(streamcipher))
  		return PTR_ERR(streamcipher);
  
  	blockcipher = crypto_spawn_cipher(&ictx->blockcipher_spawn);
  	if (IS_ERR(blockcipher)) {
  		err = PTR_ERR(blockcipher);
  		goto err_free_streamcipher;
  	}
  
  	hash = crypto_spawn_shash(&ictx->hash_spawn);
  	if (IS_ERR(hash)) {
  		err = PTR_ERR(hash);
  		goto err_free_blockcipher;
  	}
  
  	tctx->streamcipher = streamcipher;
  	tctx->blockcipher = blockcipher;
  	tctx->hash = hash;
  
  	BUILD_BUG_ON(offsetofend(struct adiantum_request_ctx, u) !=
  		     sizeof(struct adiantum_request_ctx));

  	subreq_size = max(sizeof_field(struct adiantum_request_ctx,

  				       u.hash_desc) +
  			  crypto_shash_descsize(hash),

  			  sizeof_field(struct adiantum_request_ctx,

  				       u.streamcipher_req) +
  			  crypto_skcipher_reqsize(streamcipher));
  
  	crypto_skcipher_set_reqsize(tfm,
  				    offsetof(struct adiantum_request_ctx, u) +
  				    subreq_size);
  	return 0;
  
  err_free_blockcipher:
  	crypto_free_cipher(blockcipher);
  err_free_streamcipher:
  	crypto_free_skcipher(streamcipher);
  	return err;
  }
  
  static void adiantum_exit_tfm(struct crypto_skcipher *tfm)
  {
  	struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
  
  	crypto_free_skcipher(tctx->streamcipher);
  	crypto_free_cipher(tctx->blockcipher);
  	crypto_free_shash(tctx->hash);
  }
  
  static void adiantum_free_instance(struct skcipher_instance *inst)
  {
  	struct adiantum_instance_ctx *ictx = skcipher_instance_ctx(inst);
  
  	crypto_drop_skcipher(&ictx->streamcipher_spawn);

  	crypto_drop_cipher(&ictx->blockcipher_spawn);

  	crypto_drop_shash(&ictx->hash_spawn);
  	kfree(inst);
  }
  
  /*
   * Check for a supported set of inner algorithms.
   * See the comment at the beginning of this file.
   */
  static bool adiantum_supported_algorithms(struct skcipher_alg *streamcipher_alg,
  					  struct crypto_alg *blockcipher_alg,
  					  struct shash_alg *hash_alg)
  {
  	if (strcmp(streamcipher_alg->base.cra_name, "xchacha12") != 0 &&
  	    strcmp(streamcipher_alg->base.cra_name, "xchacha20") != 0)
  		return false;
  
  	if (blockcipher_alg->cra_cipher.cia_min_keysize > BLOCKCIPHER_KEY_SIZE ||
  	    blockcipher_alg->cra_cipher.cia_max_keysize < BLOCKCIPHER_KEY_SIZE)
  		return false;
  	if (blockcipher_alg->cra_blocksize != BLOCKCIPHER_BLOCK_SIZE)
  		return false;
  
  	if (strcmp(hash_alg->base.cra_name, "nhpoly1305") != 0)
  		return false;
  
  	return true;
  }
  
  static int adiantum_create(struct crypto_template *tmpl, struct rtattr **tb)
  {

  	u32 mask;

  	const char *nhpoly1305_name;
  	struct skcipher_instance *inst;
  	struct adiantum_instance_ctx *ictx;
  	struct skcipher_alg *streamcipher_alg;
  	struct crypto_alg *blockcipher_alg;

  	struct shash_alg *hash_alg;
  	int err;

  	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
  	if (err)
  		return err;

  
  	inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL);
  	if (!inst)
  		return -ENOMEM;
  	ictx = skcipher_instance_ctx(inst);
  
  	/* Stream cipher, e.g. "xchacha12" */

  	err = crypto_grab_skcipher(&ictx->streamcipher_spawn,
  				   skcipher_crypto_instance(inst),

  				   crypto_attr_alg_name(tb[1]), 0, mask);

  	if (err)

  		goto err_free_inst;

  	streamcipher_alg = crypto_spawn_skcipher_alg(&ictx->streamcipher_spawn);
  
  	/* Block cipher, e.g. "aes" */

  	err = crypto_grab_cipher(&ictx->blockcipher_spawn,
  				 skcipher_crypto_instance(inst),
  				 crypto_attr_alg_name(tb[2]), 0, mask);

  	if (err)

  		goto err_free_inst;
  	blockcipher_alg = crypto_spawn_cipher_alg(&ictx->blockcipher_spawn);

  	/* NHPoly1305 ε-∆U hash function */

  	nhpoly1305_name = crypto_attr_alg_name(tb[3]);
  	if (nhpoly1305_name == ERR_PTR(-ENOENT))
  		nhpoly1305_name = "nhpoly1305";
  	err = crypto_grab_shash(&ictx->hash_spawn,
  				skcipher_crypto_instance(inst),
  				nhpoly1305_name, 0, mask);

  	if (err)

  		goto err_free_inst;
  	hash_alg = crypto_spawn_shash_alg(&ictx->hash_spawn);

  
  	/* Check the set of algorithms */
  	if (!adiantum_supported_algorithms(streamcipher_alg, blockcipher_alg,
  					   hash_alg)) {
  		pr_warn("Unsupported Adiantum instantiation: (%s,%s,%s)
  ",
  			streamcipher_alg->base.cra_name,
  			blockcipher_alg->cra_name, hash_alg->base.cra_name);
  		err = -EINVAL;

  		goto err_free_inst;

  	}
  
  	/* Instance fields */
  
  	err = -ENAMETOOLONG;
  	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
  		     "adiantum(%s,%s)", streamcipher_alg->base.cra_name,
  		     blockcipher_alg->cra_name) >= CRYPTO_MAX_ALG_NAME)

  		goto err_free_inst;

  	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
  		     "adiantum(%s,%s,%s)",
  		     streamcipher_alg->base.cra_driver_name,
  		     blockcipher_alg->cra_driver_name,
  		     hash_alg->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)

  		goto err_free_inst;

  
  	inst->alg.base.cra_blocksize = BLOCKCIPHER_BLOCK_SIZE;
  	inst->alg.base.cra_ctxsize = sizeof(struct adiantum_tfm_ctx);
  	inst->alg.base.cra_alignmask = streamcipher_alg->base.cra_alignmask |
  				       hash_alg->base.cra_alignmask;
  	/*
  	 * The block cipher is only invoked once per message, so for long
  	 * messages (e.g. sectors for disk encryption) its performance doesn't
  	 * matter as much as that of the stream cipher and hash function.  Thus,
  	 * weigh the block cipher's ->cra_priority less.
  	 */
  	inst->alg.base.cra_priority = (4 * streamcipher_alg->base.cra_priority +
  				       2 * hash_alg->base.cra_priority +
  				       blockcipher_alg->cra_priority) / 7;
  
  	inst->alg.setkey = adiantum_setkey;
  	inst->alg.encrypt = adiantum_encrypt;
  	inst->alg.decrypt = adiantum_decrypt;
  	inst->alg.init = adiantum_init_tfm;
  	inst->alg.exit = adiantum_exit_tfm;
  	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(streamcipher_alg);
  	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(streamcipher_alg);
  	inst->alg.ivsize = TWEAK_SIZE;
  
  	inst->free = adiantum_free_instance;
  
  	err = skcipher_register_instance(tmpl, inst);

  	if (err) {
  err_free_inst:
  		adiantum_free_instance(inst);
  	}

  	return err;
  }
  
  /* adiantum(streamcipher_name, blockcipher_name [, nhpoly1305_name]) */
  static struct crypto_template adiantum_tmpl = {
  	.name = "adiantum",
  	.create = adiantum_create,
  	.module = THIS_MODULE,
  };
  
  static int __init adiantum_module_init(void)
  {
  	return crypto_register_template(&adiantum_tmpl);
  }
  
  static void __exit adiantum_module_exit(void)
  {
  	crypto_unregister_template(&adiantum_tmpl);
  }

  subsys_initcall(adiantum_module_init);

  module_exit(adiantum_module_exit);
  
  MODULE_DESCRIPTION("Adiantum length-preserving encryption mode");
  MODULE_LICENSE("GPL v2");
  MODULE_AUTHOR("Eric Biggers <ebiggers@google.com>");
  MODULE_ALIAS_CRYPTO("adiantum");