linux/include/crypto/xts.h

#ifndef _CRYPTO_XTS_H
#define _CRYPTO_XTS_H

#include <crypto/b128ops.h>
#include <crypto/internal/skcipher.h>
#include <linux/fips.h>

struct scatterlist;
struct blkcipher_desc;

#define XTS_BLOCK_SIZE 16

struct xts_crypt_req {
	be128 *tbuf;
	unsigned int tbuflen;

	void *tweak_ctx;
	void (*tweak_fn)(void *ctx, u8* dst, const u8* src);
	void *crypt_ctx;
	void (*crypt_fn)(void *ctx, u8 *blks, unsigned int nbytes);
};

#define XTS_TWEAK_CAST(x) ((void (*)(void *, u8*, const u8*))(x))

int xts_crypt(struct blkcipher_desc *desc, struct scatterlist *dst,
	      struct scatterlist *src, unsigned int nbytes,
	      struct xts_crypt_req *req);

static inline int xts_check_key(struct crypto_tfm *tfm,
				const u8 *key, unsigned int keylen)
{
	u32 *flags = &tfm->crt_flags;

	/*
	 * key consists of keys of equal size concatenated, therefore
	 * the length must be even.
	 */
	if (keylen % 2) {
		*flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
		return -EINVAL;
	}

	/* ensure that the AES and tweak key are not identical */
	if (fips_enabled &&
	    !crypto_memneq(key, key + (keylen / 2), keylen / 2)) {
		*flags |= CRYPTO_TFM_RES_WEAK_KEY;
		return -EINVAL;
	}

	return 0;
}

static inline int xts_verify_key(struct crypto_skcipher *tfm,
				 const u8 *key, unsigned int keylen)
{
	/*
	 * key consists of keys of equal size concatenated, therefore
	 * the length must be even.
	 */
	if (keylen % 2) {
		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
		return -EINVAL;
	}

	/* ensure that the AES and tweak key are not identical */
	if ((fips_enabled || crypto_skcipher_get_flags(tfm) &
			     CRYPTO_TFM_REQ_WEAK_KEY) &&
	    !crypto_memneq(key, key + (keylen / 2), keylen / 2)) {
		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_WEAK_KEY);
		return -EINVAL;
	}

	return 0;
}

#endif  /* _CRYPTO_XTS_H */