crypto: drbg - Export CTR DRBG DF functions

Export drbg_ctr_df() derivative function to new module df_sp80090.

Signed-off-by: Harsh Jain <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

crypto/Kconfig

···
 
 config CRYPTO_DRBG_CTR
 	bool "CTR_DRBG"
-	select CRYPTO_AES
-	select CRYPTO_CTR
+	select CRYPTO_DF80090A
 	help
 	  CTR_DRBG variant as defined in NIST SP800-90A.
 
···
 	tristate
 	select CRYPTO_HMAC
 	select CRYPTO_SHA256
+
+config CRYPTO_DF80090A
+	tristate
+	select CRYPTO_AES
+	select CRYPTO_CTR
 
 endmenu
 menu "Userspace interface"

crypto/Makefile

···
 #
 obj-$(CONFIG_CRYPTO_KDF800108_CTR) += kdf_sp800108.o
 
+obj-$(CONFIG_CRYPTO_DF80090A) += df_sp80090a.o
+
 obj-$(CONFIG_CRYPTO_KRB5) += krb5/

crypto/df_sp80090a.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * NIST SP800-90A DRBG derivation function
+ *
+ * Copyright (C) 2014, Stephan Mueller <[e-mail]>
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <crypto/df_sp80090a.h>
+#include <crypto/internal/drbg.h>
+
+static void drbg_kcapi_symsetkey(struct crypto_cipher *tfm,
+				 const unsigned char *key,
+				 u8 keylen);
+static int drbg_kcapi_sym(struct crypto_cipher *tfm, unsigned char *outval,
+			  const struct drbg_string *in, u8 blocklen_bytes);
+
+static void drbg_kcapi_symsetkey(struct crypto_cipher *tfm,
+				 const unsigned char *key, u8 keylen)
+{
+	crypto_cipher_setkey(tfm, key, keylen);
+}
+
+static int drbg_kcapi_sym(struct crypto_cipher *tfm, unsigned char *outval,
+			  const struct drbg_string *in, u8 blocklen_bytes)
+{
+	/* there is only component in *in */
+	BUG_ON(in->len < blocklen_bytes);
+	crypto_cipher_encrypt_one(tfm, outval, in->buf);
+	return 0;
+}
+
+/* BCC function for CTR DRBG as defined in 10.4.3 */
+
+static int drbg_ctr_bcc(struct crypto_cipher *tfm,
+			unsigned char *out, const unsigned char *key,
+			struct list_head *in,
+			u8 blocklen_bytes,
+			u8 keylen)
+{
+	int ret = 0;
+	struct drbg_string *curr = NULL;
+	struct drbg_string data;
+	short cnt = 0;
+
+	drbg_string_fill(&data, out, blocklen_bytes);
+
+	/* 10.4.3 step 2 / 4 */
+	drbg_kcapi_symsetkey(tfm, key, keylen);
+	list_for_each_entry(curr, in, list) {
+		const unsigned char *pos = curr->buf;
+		size_t len = curr->len;
+		/* 10.4.3 step 4.1 */
+		while (len) {
+			/* 10.4.3 step 4.2 */
+			if (blocklen_bytes == cnt) {
+				cnt = 0;
+				ret = drbg_kcapi_sym(tfm, out, &data, blocklen_bytes);
+				if (ret)
+					return ret;
+			}
+			out[cnt] ^= *pos;
+			pos++;
+			cnt++;
+			len--;
+		}
+	}
+	/* 10.4.3 step 4.2 for last block */
+	if (cnt)
+		ret = drbg_kcapi_sym(tfm, out, &data, blocklen_bytes);
+
+	return ret;
+}
+
+/*
+ * scratchpad usage: drbg_ctr_update is interlinked with crypto_drbg_ctr_df
+ * (and drbg_ctr_bcc, but this function does not need any temporary buffers),
+ * the scratchpad is used as follows:
+ * drbg_ctr_update:
+ *	temp
+ *		start: drbg->scratchpad
+ *		length: drbg_statelen(drbg) + drbg_blocklen(drbg)
+ *			note: the cipher writing into this variable works
+ *			blocklen-wise. Now, when the statelen is not a multiple
+ *			of blocklen, the generateion loop below "spills over"
+ *			by at most blocklen. Thus, we need to give sufficient
+ *			memory.
+ *	df_data
+ *		start: drbg->scratchpad +
+ *				drbg_statelen(drbg) + drbg_blocklen(drbg)
+ *		length: drbg_statelen(drbg)
+ *
+ * crypto_drbg_ctr_df:
+ *	pad
+ *		start: df_data + drbg_statelen(drbg)
+ *		length: drbg_blocklen(drbg)
+ *	iv
+ *		start: pad + drbg_blocklen(drbg)
+ *		length: drbg_blocklen(drbg)
+ *	temp
+ *		start: iv + drbg_blocklen(drbg)
+ *		length: drbg_satelen(drbg) + drbg_blocklen(drbg)
+ *			note: temp is the buffer that the BCC function operates
+ *			on. BCC operates blockwise. drbg_statelen(drbg)
+ *			is sufficient when the DRBG state length is a multiple
+ *			of the block size. For AES192 (and maybe other ciphers)
+ *			this is not correct and the length for temp is
+ *			insufficient (yes, that also means for such ciphers,
+ *			the final output of all BCC rounds are truncated).
+ *			Therefore, add drbg_blocklen(drbg) to cover all
+ *			possibilities.
+ * refer to crypto_drbg_ctr_df_datalen() to get required length
+ */
+
+/* Derivation Function for CTR DRBG as defined in 10.4.2 */
+int crypto_drbg_ctr_df(struct crypto_cipher *tfm,
+		       unsigned char *df_data, size_t bytes_to_return,
+		       struct list_head *seedlist,
+		       u8 blocklen_bytes,
+		       u8 statelen)
+{
+	int ret = -EFAULT;
+	unsigned char L_N[8];
+	/* S3 is input */
+	struct drbg_string S1, S2, S4, cipherin;
+	LIST_HEAD(bcc_list);
+	unsigned char *pad = df_data + statelen;
+	unsigned char *iv = pad + blocklen_bytes;
+	unsigned char *temp = iv + blocklen_bytes;
+	size_t padlen = 0;
+	unsigned int templen = 0;
+	/* 10.4.2 step 7 */
+	unsigned int i = 0;
+	/* 10.4.2 step 8 */
+	const unsigned char *K = (unsigned char *)
+			   "\x00\x01\x02\x03\x04\x05\x06\x07"
+			   "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f"
+			   "\x10\x11\x12\x13\x14\x15\x16\x17"
+			   "\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f";
+	unsigned char *X;
+	size_t generated_len = 0;
+	size_t inputlen = 0;
+	struct drbg_string *seed = NULL;
+	u8 keylen;
+
+	memset(pad, 0, blocklen_bytes);
+	memset(iv, 0, blocklen_bytes);
+	keylen = statelen - blocklen_bytes;
+	/* 10.4.2 step 1 is implicit as we work byte-wise */
+
+	/* 10.4.2 step 2 */
+	if ((512 / 8) < bytes_to_return)
+		return -EINVAL;
+
+	/* 10.4.2 step 2 -- calculate the entire length of all input data */
+	list_for_each_entry(seed, seedlist, list)
+		inputlen += seed->len;
+	drbg_cpu_to_be32(inputlen, &L_N[0]);
+
+	/* 10.4.2 step 3 */
+	drbg_cpu_to_be32(bytes_to_return, &L_N[4]);
+
+	/* 10.4.2 step 5: length is L_N, input_string, one byte, padding */
+	padlen = (inputlen + sizeof(L_N) + 1) % (blocklen_bytes);
+	/* wrap the padlen appropriately */
+	if (padlen)
+		padlen = blocklen_bytes - padlen;
+	/*
+	 * pad / padlen contains the 0x80 byte and the following zero bytes.
+	 * As the calculated padlen value only covers the number of zero
+	 * bytes, this value has to be incremented by one for the 0x80 byte.
+	 */
+	padlen++;
+	pad[0] = 0x80;
+
+	/* 10.4.2 step 4 -- first fill the linked list and then order it */
+	drbg_string_fill(&S1, iv, blocklen_bytes);
+	list_add_tail(&S1.list, &bcc_list);
+	drbg_string_fill(&S2, L_N, sizeof(L_N));
+	list_add_tail(&S2.list, &bcc_list);
+	list_splice_tail(seedlist, &bcc_list);
+	drbg_string_fill(&S4, pad, padlen);
+	list_add_tail(&S4.list, &bcc_list);
+
+	/* 10.4.2 step 9 */
+	while (templen < (keylen + (blocklen_bytes))) {
+		/*
+		 * 10.4.2 step 9.1 - the padding is implicit as the buffer
+		 * holds zeros after allocation -- even the increment of i
+		 * is irrelevant as the increment remains within length of i
+		 */
+		drbg_cpu_to_be32(i, iv);
+		/* 10.4.2 step 9.2 -- BCC and concatenation with temp */
+		ret = drbg_ctr_bcc(tfm, temp + templen, K, &bcc_list,
+				   blocklen_bytes, keylen);
+		if (ret)
+			goto out;
+		/* 10.4.2 step 9.3 */
+		i++;
+		templen += blocklen_bytes;
+	}
+
+	/* 10.4.2 step 11 */
+	X = temp + (keylen);
+	drbg_string_fill(&cipherin, X, blocklen_bytes);
+
+	/* 10.4.2 step 12: overwriting of outval is implemented in next step */
+
+	/* 10.4.2 step 13 */
+	drbg_kcapi_symsetkey(tfm, temp, keylen);
+	while (generated_len < bytes_to_return) {
+		short blocklen = 0;
+		/*
+		 * 10.4.2 step 13.1: the truncation of the key length is
+		 * implicit as the key is only drbg_blocklen in size based on
+		 * the implementation of the cipher function callback
+		 */
+		ret = drbg_kcapi_sym(tfm, X, &cipherin, blocklen_bytes);
+		if (ret)
+			goto out;
+		blocklen = (blocklen_bytes <
+				(bytes_to_return - generated_len)) ?
+			    blocklen_bytes :
+				(bytes_to_return - generated_len);
+		/* 10.4.2 step 13.2 and 14 */
+		memcpy(df_data + generated_len, X, blocklen);
+		generated_len += blocklen;
+	}
+
+	ret = 0;
+
+out:
+	memset(iv, 0, blocklen_bytes);
+	memset(temp, 0, statelen + blocklen_bytes);
+	memset(pad, 0, blocklen_bytes);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(crypto_drbg_ctr_df);
+
+MODULE_IMPORT_NS("CRYPTO_INTERNAL");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Stephan Mueller <[e-mail]>");
+MODULE_DESCRIPTION("Derivation Function conformant to SP800-90A");

crypto/drbg.c

···
  */
 
 #include <crypto/drbg.h>
+#include <crypto/df_sp80090a.h>
 #include <crypto/internal/cipher.h>
 #include <linux/kernel.h>
 #include <linux/jiffies.h>
···
 	return 0;
 }
 
-/*
- * Convert an integer into a byte representation of this integer.
- * The byte representation is big-endian
- *
- * @val value to be converted
- * @buf buffer holding the converted integer -- caller must ensure that
- *      buffer size is at least 32 bit
- */
-#if (defined(CONFIG_CRYPTO_DRBG_HASH) || defined(CONFIG_CRYPTO_DRBG_CTR))
-static inline void drbg_cpu_to_be32(__u32 val, unsigned char *buf)
-{
-	struct s {
-		__be32 conv;
-	};
-	struct s *conversion = (struct s *) buf;
-
-	conversion->conv = cpu_to_be32(val);
-}
-#endif /* defined(CONFIG_CRYPTO_DRBG_HASH) || defined(CONFIG_CRYPTO_DRBG_CTR) */
-
 /******************************************************************
  * CTR DRBG callback functions
  ******************************************************************/
···
 MODULE_ALIAS_CRYPTO("drbg_pr_ctr_aes128");
 MODULE_ALIAS_CRYPTO("drbg_nopr_ctr_aes128");
 
-static void drbg_kcapi_symsetkey(struct drbg_state *drbg,
-				 const unsigned char *key);
-static int drbg_kcapi_sym(struct drbg_state *drbg, unsigned char *outval,
-			  const struct drbg_string *in);
 static int drbg_init_sym_kernel(struct drbg_state *drbg);
 static int drbg_fini_sym_kernel(struct drbg_state *drbg);
 static int drbg_kcapi_sym_ctr(struct drbg_state *drbg,
···
 			      u8 *outbuf, u32 outlen);
 #define DRBG_OUTSCRATCHLEN 256
 
-/* BCC function for CTR DRBG as defined in 10.4.3 */
-static int drbg_ctr_bcc(struct drbg_state *drbg,
-			unsigned char *out, const unsigned char *key,
-			struct list_head *in)
-{
-	int ret = 0;
-	struct drbg_string *curr = NULL;
-	struct drbg_string data;
-	short cnt = 0;
-
-	drbg_string_fill(&data, out, drbg_blocklen(drbg));
-
-	/* 10.4.3 step 2 / 4 */
-	drbg_kcapi_symsetkey(drbg, key);
-	list_for_each_entry(curr, in, list) {
-		const unsigned char *pos = curr->buf;
-		size_t len = curr->len;
-		/* 10.4.3 step 4.1 */
-		while (len) {
-			/* 10.4.3 step 4.2 */
-			if (drbg_blocklen(drbg) == cnt) {
-				cnt = 0;
-				ret = drbg_kcapi_sym(drbg, out, &data);
-				if (ret)
-					return ret;
-			}
-			out[cnt] ^= *pos;
-			pos++;
-			cnt++;
-			len--;
-		}
-	}
-	/* 10.4.3 step 4.2 for last block */
-	if (cnt)
-		ret = drbg_kcapi_sym(drbg, out, &data);
-
-	return ret;
-}
-
-/*
- * scratchpad usage: drbg_ctr_update is interlinked with drbg_ctr_df
- * (and drbg_ctr_bcc, but this function does not need any temporary buffers),
- * the scratchpad is used as follows:
- * drbg_ctr_update:
- *	temp
- *		start: drbg->scratchpad
- *		length: drbg_statelen(drbg) + drbg_blocklen(drbg)
- *			note: the cipher writing into this variable works
- *			blocklen-wise. Now, when the statelen is not a multiple
- *			of blocklen, the generateion loop below "spills over"
- *			by at most blocklen. Thus, we need to give sufficient
- *			memory.
- *	df_data
- *		start: drbg->scratchpad +
- *				drbg_statelen(drbg) + drbg_blocklen(drbg)
- *		length: drbg_statelen(drbg)
- *
- * drbg_ctr_df:
- *	pad
- *		start: df_data + drbg_statelen(drbg)
- *		length: drbg_blocklen(drbg)
- *	iv
- *		start: pad + drbg_blocklen(drbg)
- *		length: drbg_blocklen(drbg)
- *	temp
- *		start: iv + drbg_blocklen(drbg)
- *		length: drbg_satelen(drbg) + drbg_blocklen(drbg)
- *			note: temp is the buffer that the BCC function operates
- *			on. BCC operates blockwise. drbg_statelen(drbg)
- *			is sufficient when the DRBG state length is a multiple
- *			of the block size. For AES192 (and maybe other ciphers)
- *			this is not correct and the length for temp is
- *			insufficient (yes, that also means for such ciphers,
- *			the final output of all BCC rounds are truncated).
- *			Therefore, add drbg_blocklen(drbg) to cover all
- *			possibilities.
- */
-
-/* Derivation Function for CTR DRBG as defined in 10.4.2 */
 static int drbg_ctr_df(struct drbg_state *drbg,
 		       unsigned char *df_data, size_t bytes_to_return,
 		       struct list_head *seedlist)
 {
-	int ret = -EFAULT;
-	unsigned char L_N[8];
-	/* S3 is input */
-	struct drbg_string S1, S2, S4, cipherin;
-	LIST_HEAD(bcc_list);
-	unsigned char *pad = df_data + drbg_statelen(drbg);
-	unsigned char *iv = pad + drbg_blocklen(drbg);
-	unsigned char *temp = iv + drbg_blocklen(drbg);
-	size_t padlen = 0;
-	unsigned int templen = 0;
-	/* 10.4.2 step 7 */
-	unsigned int i = 0;
-	/* 10.4.2 step 8 */
-	const unsigned char *K = (unsigned char *)
-			   "\x00\x01\x02\x03\x04\x05\x06\x07"
-			   "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f"
-			   "\x10\x11\x12\x13\x14\x15\x16\x17"
-			   "\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f";
-	unsigned char *X;
-	size_t generated_len = 0;
-	size_t inputlen = 0;
-	struct drbg_string *seed = NULL;
-
-	memset(pad, 0, drbg_blocklen(drbg));
-	memset(iv, 0, drbg_blocklen(drbg));
-
-	/* 10.4.2 step 1 is implicit as we work byte-wise */
-
-	/* 10.4.2 step 2 */
-	if ((512/8) < bytes_to_return)
-		return -EINVAL;
-
-	/* 10.4.2 step 2 -- calculate the entire length of all input data */
-	list_for_each_entry(seed, seedlist, list)
-		inputlen += seed->len;
-	drbg_cpu_to_be32(inputlen, &L_N[0]);
-
-	/* 10.4.2 step 3 */
-	drbg_cpu_to_be32(bytes_to_return, &L_N[4]);
-
-	/* 10.4.2 step 5: length is L_N, input_string, one byte, padding */
-	padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg));
-	/* wrap the padlen appropriately */
-	if (padlen)
-		padlen = drbg_blocklen(drbg) - padlen;
-	/*
-	 * pad / padlen contains the 0x80 byte and the following zero bytes.
-	 * As the calculated padlen value only covers the number of zero
-	 * bytes, this value has to be incremented by one for the 0x80 byte.
-	 */
-	padlen++;
-	pad[0] = 0x80;
-
-	/* 10.4.2 step 4 -- first fill the linked list and then order it */
-	drbg_string_fill(&S1, iv, drbg_blocklen(drbg));
-	list_add_tail(&S1.list, &bcc_list);
-	drbg_string_fill(&S2, L_N, sizeof(L_N));
-	list_add_tail(&S2.list, &bcc_list);
-	list_splice_tail(seedlist, &bcc_list);
-	drbg_string_fill(&S4, pad, padlen);
-	list_add_tail(&S4.list, &bcc_list);
-
-	/* 10.4.2 step 9 */
-	while (templen < (drbg_keylen(drbg) + (drbg_blocklen(drbg)))) {
-		/*
-		 * 10.4.2 step 9.1 - the padding is implicit as the buffer
-		 * holds zeros after allocation -- even the increment of i
-		 * is irrelevant as the increment remains within length of i
-		 */
-		drbg_cpu_to_be32(i, iv);
-		/* 10.4.2 step 9.2 -- BCC and concatenation with temp */
-		ret = drbg_ctr_bcc(drbg, temp + templen, K, &bcc_list);
-		if (ret)
-			goto out;
-		/* 10.4.2 step 9.3 */
-		i++;
-		templen += drbg_blocklen(drbg);
-	}
-
-	/* 10.4.2 step 11 */
-	X = temp + (drbg_keylen(drbg));
-	drbg_string_fill(&cipherin, X, drbg_blocklen(drbg));
-
-	/* 10.4.2 step 12: overwriting of outval is implemented in next step */
-
-	/* 10.4.2 step 13 */
-	drbg_kcapi_symsetkey(drbg, temp);
-	while (generated_len < bytes_to_return) {
-		short blocklen = 0;
-		/*
-		 * 10.4.2 step 13.1: the truncation of the key length is
-		 * implicit as the key is only drbg_blocklen in size based on
-		 * the implementation of the cipher function callback
-		 */
-		ret = drbg_kcapi_sym(drbg, X, &cipherin);
-		if (ret)
-			goto out;
-		blocklen = (drbg_blocklen(drbg) <
-				(bytes_to_return - generated_len)) ?
-			    drbg_blocklen(drbg) :
-				(bytes_to_return - generated_len);
-		/* 10.4.2 step 13.2 and 14 */
-		memcpy(df_data + generated_len, X, blocklen);
-		generated_len += blocklen;
-	}
-
-	ret = 0;
-
-out:
-	memset(iv, 0, drbg_blocklen(drbg));
-	memset(temp, 0, drbg_statelen(drbg) + drbg_blocklen(drbg));
-	memset(pad, 0, drbg_blocklen(drbg));
-	return ret;
+	return crypto_drbg_ctr_df(drbg->priv_data, df_data, drbg_statelen(drbg),
+				  seedlist, drbg_blocklen(drbg), drbg_statelen(drbg));
 }
 
 /*
···
 		sb_size = 0;
 	else if (drbg->core->flags & DRBG_CTR)
 		sb_size = drbg_statelen(drbg) + drbg_blocklen(drbg) + /* temp */
-			  drbg_statelen(drbg) +	/* df_data */
-			  drbg_blocklen(drbg) +	/* pad */
-			  drbg_blocklen(drbg) +	/* iv */
-			  drbg_statelen(drbg) + drbg_blocklen(drbg); /* temp */
+			  crypto_drbg_ctr_df_datalen(drbg_statelen(drbg),
+						     drbg_blocklen(drbg));
 	else
 		sb_size = drbg_statelen(drbg) + drbg_blocklen(drbg);
 
···
 	sg_init_one(&drbg->sg_out, drbg->outscratchpad, DRBG_OUTSCRATCHLEN);
 
 	return alignmask;
-}
-
-static void drbg_kcapi_symsetkey(struct drbg_state *drbg,
-				 const unsigned char *key)
-{
-	struct crypto_cipher *tfm = drbg->priv_data;
-
-	crypto_cipher_setkey(tfm, key, (drbg_keylen(drbg)));
-}
-
-static int drbg_kcapi_sym(struct drbg_state *drbg, unsigned char *outval,
-			  const struct drbg_string *in)
-{
-	struct crypto_cipher *tfm = drbg->priv_data;
-
-	/* there is only component in *in */
-	BUG_ON(in->len < drbg_blocklen(drbg));
-	crypto_cipher_encrypt_one(tfm, outval, in->buf);
-	return 0;
 }
 
 static int drbg_kcapi_sym_ctr(struct drbg_state *drbg,

drivers/crypto/Kconfig

···
 config CRYPTO_DEV_XILINX_TRNG
 	tristate "Support for Xilinx True Random Generator"
 	depends on ZYNQMP_FIRMWARE || COMPILE_TEST
+	select CRYPTO_DF80090A
 	select CRYPTO_RNG
 	select HW_RANDOM
 	help

include/crypto/df_sp80090a.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright Stephan Mueller <[e-mail]>, 2014
+ */
+
+#ifndef _CRYPTO_DF80090A_H
+#define _CRYPTO_DF80090A_H
+
+#include <crypto/internal/cipher.h>
+
+static inline int crypto_drbg_ctr_df_datalen(u8 statelen, u8 blocklen)
+{
+	return statelen +       /* df_data */
+		blocklen +      /* pad */
+		blocklen +      /* iv */
+		statelen + blocklen;  /* temp */
+}
+
+int crypto_drbg_ctr_df(struct crypto_cipher *tfm,
+		       unsigned char *df_data,
+		       size_t bytes_to_return,
+		       struct list_head *seedlist,
+		       u8 blocklen_bytes,
+		       u8 statelen);
+
+#endif /* _CRYPTO_DF80090A_H */

include/crypto/drbg.h

···
 #include <linux/module.h>
 #include <linux/crypto.h>
 #include <linux/slab.h>
+#include <crypto/internal/drbg.h>
 #include <crypto/internal/rng.h>
 #include <crypto/rng.h>
 #include <linux/fips.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
 #include <linux/workqueue.h>
-
-/*
- * Concatenation Helper and string operation helper
- *
- * SP800-90A requires the concatenation of different data. To avoid copying
- * buffers around or allocate additional memory, the following data structure
- * is used to point to the original memory with its size. In addition, it
- * is used to build a linked list. The linked list defines the concatenation
- * of individual buffers. The order of memory block referenced in that
- * linked list determines the order of concatenation.
- */
-struct drbg_string {
-	const unsigned char *buf;
-	size_t len;
-	struct list_head list;
-};
-
-static inline void drbg_string_fill(struct drbg_string *string,
-				    const unsigned char *buf, size_t len)
-{
-	string->buf = buf;
-	string->len = len;
-	INIT_LIST_HEAD(&string->list);
-}
 
 struct drbg_state;
 typedef uint32_t drbg_flag_t;

include/crypto/internal/drbg.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * NIST SP800-90A DRBG derivation function
+ *
+ * Copyright (C) 2014, Stephan Mueller <[e-mail]>
+ */
+
+#ifndef _INTERNAL_DRBG_H
+#define _INTERNAL_DRBG_H
+
+/*
+ * Convert an integer into a byte representation of this integer.
+ * The byte representation is big-endian
+ *
+ * @val value to be converted
+ * @buf buffer holding the converted integer -- caller must ensure that
+ *      buffer size is at least 32 bit
+ */
+static inline void drbg_cpu_to_be32(__u32 val, unsigned char *buf)
+{
+	struct s {
+		__be32 conv;
+	};
+	struct s *conversion = (struct s *)buf;
+
+	conversion->conv = cpu_to_be32(val);
+}
+
+/*
+ * Concatenation Helper and string operation helper
+ *
+ * SP800-90A requires the concatenation of different data. To avoid copying
+ * buffers around or allocate additional memory, the following data structure
+ * is used to point to the original memory with its size. In addition, it
+ * is used to build a linked list. The linked list defines the concatenation
+ * of individual buffers. The order of memory block referenced in that
+ * linked list determines the order of concatenation.
+ */
+struct drbg_string {
+	const unsigned char *buf;
+	size_t len;
+	struct list_head list;
+};
+
+static inline void drbg_string_fill(struct drbg_string *string,
+				    const unsigned char *buf, size_t len)
+{
+	string->buf = buf;
+	string->len = len;
+	INIT_LIST_HEAD(&string->list);
+}
+
+#endif //_INTERNAL_DRBG_H