crypto/ansi_cprng.c - kernel/common - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * PRNG: Pseudo Random Number Generator
  *       Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
  *       AES 128 cipher
  *
  *  (C) Neil Horman <nhorman@tuxdriver.com>
  */

 #include <crypto/internal/cipher.h>
 #include <crypto/internal/rng.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/string.h>

 #define DEFAULT_PRNG_KEY "0123456789abcdef"
 #define DEFAULT_PRNG_KSZ 16
 #define DEFAULT_BLK_SZ 16
 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"

 /*
  * Flags for the prng_context flags field
  */

 #define PRNG_FIXED_SIZE 0x1
 #define PRNG_NEED_RESET 0x2

 /*
  * Note: DT is our counter value
  *	 I is our intermediate value
  *	 V is our seed vector
  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
  * for implementation details
  */


 struct prng_context {
 	spinlock_t prng_lock;
 	unsigned char rand_data[DEFAULT_BLK_SZ];
 	unsigned char last_rand_data[DEFAULT_BLK_SZ];
 	unsigned char DT[DEFAULT_BLK_SZ];
 	unsigned char I[DEFAULT_BLK_SZ];
 	unsigned char V[DEFAULT_BLK_SZ];
 	u32 rand_data_valid;
 	struct crypto_cipher *tfm;
 	u32 flags;
 };

 static int dbg;

 static void hexdump(char *note, unsigned char *buf, unsigned int len)
 {
 	if (dbg) {
 		printk(KERN_CRIT "%s", note);
 		print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
 				16, 1,
 				buf, len, false);
 	}
 }

 #define dbgprint(format, args...) do {\
 if (dbg)\
 	printk(format, ##args);\
 } while (0)

 static void xor_vectors(unsigned char *in1, unsigned char *in2,
 			unsigned char *out, unsigned int size)
 {
 	int i;

 	for (i = 0; i < size; i++)
 		out[i] = in1[i] ^ in2[i];

 }
 /*
  * Returns DEFAULT_BLK_SZ bytes of random data per call
  * returns 0 if generation succeeded, <0 if something went wrong
  */
 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
 {
 	int i;
 	unsigned char tmp[DEFAULT_BLK_SZ];
 	unsigned char *output = NULL;


 	dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
 		ctx);

 	hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
 	hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
 	hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);

 	/*
 	 * This algorithm is a 3 stage state machine
 	 */
 	for (i = 0; i < 3; i++) {

 		switch (i) {
 		case 0:
 			/*
 			 * Start by encrypting the counter value
 			 * This gives us an intermediate value I
 			 */
 			memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
 			output = ctx->I;
 			hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
 			break;
 		case 1:

 			/*
 			 * Next xor I with our secret vector V
 			 * encrypt that result to obtain our
 			 * pseudo random data which we output
 			 */
 			xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
 			hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
 			output = ctx->rand_data;
 			break;
 		case 2:
 			/*
 			 * First check that we didn't produce the same
 			 * random data that we did last time around through this
 			 */
 			if (!memcmp(ctx->rand_data, ctx->last_rand_data,
 					DEFAULT_BLK_SZ)) {
 				if (cont_test) {
 					panic("cprng %p Failed repetition check!\n",
 						ctx);
 				}

 				printk(KERN_ERR
 					"ctx %p Failed repetition check!\n",
 					ctx);

 				ctx->flags |= PRNG_NEED_RESET;
 				return -EINVAL;
 			}
 			memcpy(ctx->last_rand_data, ctx->rand_data,
 				DEFAULT_BLK_SZ);

 			/*
 			 * Lastly xor the random data with I
 			 * and encrypt that to obtain a new secret vector V
 			 */
 			xor_vectors(ctx->rand_data, ctx->I, tmp,
 				DEFAULT_BLK_SZ);
 			output = ctx->V;
 			hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
 			break;
 		}


 		/* do the encryption */
 		crypto_cipher_encrypt_one(ctx->tfm, output, tmp);

 	}

 	/*
 	 * Now update our DT value
 	 */
 	for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
 		ctx->DT[i] += 1;
 		if (ctx->DT[i] != 0)
 			break;
 	}

 	dbgprint("Returning new block for context %p\n", ctx);
 	ctx->rand_data_valid = 0;

 	hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
 	hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
 	hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
 	hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);

 	return 0;
 }

 /* Our exported functions */
 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
 				int do_cont_test)
 {
 	unsigned char *ptr = buf;
 	unsigned int byte_count = (unsigned int)nbytes;
 	int err;


 	spin_lock_bh(&ctx->prng_lock);

 	err = -EINVAL;
 	if (ctx->flags & PRNG_NEED_RESET)
 		goto done;

 	/*
 	 * If the FIXED_SIZE flag is on, only return whole blocks of
 	 * pseudo random data
 	 */
 	err = -EINVAL;
 	if (ctx->flags & PRNG_FIXED_SIZE) {
 		if (nbytes < DEFAULT_BLK_SZ)
 			goto done;
 		byte_count = DEFAULT_BLK_SZ;
 	}

 	/*
 	 * Return 0 in case of success as mandated by the kernel
 	 * crypto API interface definition.
 	 */
 	err = 0;

 	dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
 		byte_count, ctx);


 remainder:
 	if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 		if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
 			memset(buf, 0, nbytes);
 			err = -EINVAL;
 			goto done;
 		}
 	}

 	/*
 	 * Copy any data less than an entire block
 	 */
 	if (byte_count < DEFAULT_BLK_SZ) {
 empty_rbuf:
 		while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
 			*ptr = ctx->rand_data[ctx->rand_data_valid];
 			ptr++;
 			byte_count--;
 			ctx->rand_data_valid++;
 			if (byte_count == 0)
 				goto done;
 		}
 	}

 	/*
 	 * Now copy whole blocks
 	 */
 	for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
 		if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 			if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
 				memset(buf, 0, nbytes);
 				err = -EINVAL;
 				goto done;
 			}
 		}
 		if (ctx->rand_data_valid > 0)
 			goto empty_rbuf;
 		memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
 		ctx->rand_data_valid += DEFAULT_BLK_SZ;
 		ptr += DEFAULT_BLK_SZ;
 	}

 	/*
 	 * Now go back and get any remaining partial block
 	 */
 	if (byte_count)
 		goto remainder;

 done:
 	spin_unlock_bh(&ctx->prng_lock);
 	dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
 		err, ctx);
 	return err;
 }

 static void free_prng_context(struct prng_context *ctx)
 {
 	crypto_free_cipher(ctx->tfm);
 }

 static int reset_prng_context(struct prng_context *ctx,
 			      const unsigned char *key, size_t klen,
 			      const unsigned char *V, const unsigned char *DT)
 {
 	int ret;
 	const unsigned char *prng_key;

 	spin_lock_bh(&ctx->prng_lock);
 	ctx->flags |= PRNG_NEED_RESET;

 	prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;

 	if (!key)
 		klen = DEFAULT_PRNG_KSZ;

 	if (V)
 		memcpy(ctx->V, V, DEFAULT_BLK_SZ);
 	else
 		memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);

 	if (DT)
 		memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
 	else
 		memset(ctx->DT, 0, DEFAULT_BLK_SZ);

 	memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
 	memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);

 	ctx->rand_data_valid = DEFAULT_BLK_SZ;

 	ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
 	if (ret) {
 		dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
 			crypto_cipher_get_flags(ctx->tfm));
 		goto out;
 	}

 	ret = 0;
 	ctx->flags &= ~PRNG_NEED_RESET;
 out:
 	spin_unlock_bh(&ctx->prng_lock);
 	return ret;
 }

 static int cprng_init(struct crypto_tfm *tfm)
 {
 	struct prng_context *ctx = crypto_tfm_ctx(tfm);

 	spin_lock_init(&ctx->prng_lock);
 	ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
 	if (IS_ERR(ctx->tfm)) {
 		dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
 				ctx);
 		return PTR_ERR(ctx->tfm);
 	}

 	if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
 		return -EINVAL;

 	/*
 	 * after allocation, we should always force the user to reset
 	 * so they don't inadvertently use the insecure default values
 	 * without specifying them intentially
 	 */
 	ctx->flags |= PRNG_NEED_RESET;
 	return 0;
 }

 static void cprng_exit(struct crypto_tfm *tfm)
 {
 	free_prng_context(crypto_tfm_ctx(tfm));
 }

 static int cprng_get_random(struct crypto_rng *tfm,
 			    const u8 *src, unsigned int slen,
 			    u8 *rdata, unsigned int dlen)
 {
 	struct prng_context *prng = crypto_rng_ctx(tfm);

 	return get_prng_bytes(rdata, dlen, prng, 0);
 }

 /*
  *  This is the cprng_registered reset method the seed value is
  *  interpreted as the tuple { V KEY DT}
  *  V and KEY are required during reset, and DT is optional, detected
  *  as being present by testing the length of the seed
  */
 static int cprng_reset(struct crypto_rng *tfm,
 		       const u8 *seed, unsigned int slen)
 {
 	struct prng_context *prng = crypto_rng_ctx(tfm);
 	const u8 *key = seed + DEFAULT_BLK_SZ;
 	const u8 *dt = NULL;

 	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 		return -EINVAL;

 	if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
 		dt = key + DEFAULT_PRNG_KSZ;

 	reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);

 	if (prng->flags & PRNG_NEED_RESET)
 		return -EINVAL;
 	return 0;
 }

 #ifdef CONFIG_CRYPTO_FIPS
 static int fips_cprng_get_random(struct crypto_rng *tfm,
 				 const u8 *src, unsigned int slen,
 				 u8 *rdata, unsigned int dlen)
 {
 	struct prng_context *prng = crypto_rng_ctx(tfm);

 	return get_prng_bytes(rdata, dlen, prng, 1);
 }

 static int fips_cprng_reset(struct crypto_rng *tfm,
 			    const u8 *seed, unsigned int slen)
 {
 	u8 rdata[DEFAULT_BLK_SZ];
 	const u8 *key = seed + DEFAULT_BLK_SZ;
 	int rc;

 	struct prng_context *prng = crypto_rng_ctx(tfm);

 	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 		return -EINVAL;

 	/* fips strictly requires seed != key */
 	if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
 		return -EINVAL;

 	rc = cprng_reset(tfm, seed, slen);

 	if (!rc)
 		goto out;

 	/* this primes our continuity test */
 	rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
 	prng->rand_data_valid = DEFAULT_BLK_SZ;

 out:
 	return rc;
 }
 #endif

 static struct rng_alg rng_algs[] = { {
 	.generate		= cprng_get_random,
 	.seed			= cprng_reset,
 	.seedsize		= DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
 	.base			=	{
 		.cra_name		= "stdrng",
 		.cra_driver_name	= "ansi_cprng",
 		.cra_priority		= 100,
 		.cra_ctxsize		= sizeof(struct prng_context),
 		.cra_module		= THIS_MODULE,
 		.cra_init		= cprng_init,
 		.cra_exit		= cprng_exit,
 	}
 #ifdef CONFIG_CRYPTO_FIPS
 }, {
 	.generate		= fips_cprng_get_random,
 	.seed			= fips_cprng_reset,
 	.seedsize		= DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
 	.base			=	{
 		.cra_name		= "fips(ansi_cprng)",
 		.cra_driver_name	= "fips_ansi_cprng",
 		.cra_priority		= 300,
 		.cra_ctxsize		= sizeof(struct prng_context),
 		.cra_module		= THIS_MODULE,
 		.cra_init		= cprng_init,
 		.cra_exit		= cprng_exit,
 	}
 #endif
 } };

 /* Module initalization */
 static int __init prng_mod_init(void)
 {
 	return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
 }

 static void __exit prng_mod_fini(void)
 {
 	crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
 }

 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 module_param(dbg, int, 0);
 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 subsys_initcall(prng_mod_init);
 module_exit(prng_mod_fini);
 MODULE_ALIAS_CRYPTO("stdrng");
 MODULE_ALIAS_CRYPTO("ansi_cprng");
 MODULE_IMPORT_NS(CRYPTO_INTERNAL);
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* PRNG: Pseudo Random Number Generator
	* Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
	* AES 128 cipher
	*
	* (C) Neil Horman <nhorman@tuxdriver.com>
	*/

	#include <crypto/internal/cipher.h>
	#include <crypto/internal/rng.h>
	#include <linux/err.h>
	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/moduleparam.h>
	#include <linux/string.h>

	#define DEFAULT_PRNG_KEY "0123456789abcdef"
	#define DEFAULT_PRNG_KSZ 16
	#define DEFAULT_BLK_SZ 16
	#define DEFAULT_V_SEED "zaybxcwdveuftgsh"

	/*
	* Flags for the prng_context flags field
	*/

	#define PRNG_FIXED_SIZE 0x1
	#define PRNG_NEED_RESET 0x2

	/*
	* Note: DT is our counter value
	* I is our intermediate value
	* V is our seed vector
	* See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
	* for implementation details
	*/


	struct prng_context {
	spinlock_t prng_lock;
	unsigned char rand_data[DEFAULT_BLK_SZ];
	unsigned char last_rand_data[DEFAULT_BLK_SZ];
	unsigned char DT[DEFAULT_BLK_SZ];
	unsigned char I[DEFAULT_BLK_SZ];
	unsigned char V[DEFAULT_BLK_SZ];
	u32 rand_data_valid;
	struct crypto_cipher *tfm;
	u32 flags;
	};

	static int dbg;

	static void hexdump(char note, unsigned char buf, unsigned int len)
	{
	if (dbg) {
	printk(KERN_CRIT "%s", note);
	print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
	16, 1,
	buf, len, false);
	}
	}

	#define dbgprint(format, args...) do {\
	if (dbg)\
	printk(format, ##args);\
	} while (0)

	static void xor_vectors(unsigned char in1, unsigned char in2,
	unsigned char *out, unsigned int size)
	{
	int i;

	for (i = 0; i < size; i++)
	out[i] = in1[i] ^ in2[i];

	}
	/*
	* Returns DEFAULT_BLK_SZ bytes of random data per call
	* returns 0 if generation succeeded, <0 if something went wrong
	*/
	static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
	{
	int i;
	unsigned char tmp[DEFAULT_BLK_SZ];
	unsigned char *output = NULL;


	dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
	ctx);

	hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
	hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
	hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);

	/*
	* This algorithm is a 3 stage state machine
	*/
	for (i = 0; i < 3; i++) {

	switch (i) {
	case 0:
	/*
	* Start by encrypting the counter value
	* This gives us an intermediate value I
	*/
	memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
	output = ctx->I;
	hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
	break;
	case 1:

	/*
	* Next xor I with our secret vector V
	* encrypt that result to obtain our
	* pseudo random data which we output
	*/
	xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
	hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
	output = ctx->rand_data;
	break;
	case 2:
	/*
	* First check that we didn't produce the same
	* random data that we did last time around through this
	*/
	if (!memcmp(ctx->rand_data, ctx->last_rand_data,
	DEFAULT_BLK_SZ)) {
	if (cont_test) {
	panic("cprng %p Failed repetition check!\n",
	ctx);
	}

	printk(KERN_ERR
	"ctx %p Failed repetition check!\n",
	ctx);

	ctx->flags \|= PRNG_NEED_RESET;
	return -EINVAL;
	}
	memcpy(ctx->last_rand_data, ctx->rand_data,
	DEFAULT_BLK_SZ);

	/*
	* Lastly xor the random data with I
	* and encrypt that to obtain a new secret vector V
	*/
	xor_vectors(ctx->rand_data, ctx->I, tmp,
	DEFAULT_BLK_SZ);
	output = ctx->V;
	hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
	break;
	}


	/* do the encryption */
	crypto_cipher_encrypt_one(ctx->tfm, output, tmp);

	}

	/*
	* Now update our DT value
	*/
	for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
	ctx->DT[i] += 1;
	if (ctx->DT[i] != 0)
	break;
	}

	dbgprint("Returning new block for context %p\n", ctx);
	ctx->rand_data_valid = 0;

	hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
	hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
	hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
	hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);

	return 0;
	}

	/* Our exported functions */
	static int get_prng_bytes(char buf, size_t nbytes, struct prng_context ctx,
	int do_cont_test)
	{
	unsigned char *ptr = buf;
	unsigned int byte_count = (unsigned int)nbytes;
	int err;


	spin_lock_bh(&ctx->prng_lock);

	err = -EINVAL;
	if (ctx->flags & PRNG_NEED_RESET)
	goto done;

	/*
	* If the FIXED_SIZE flag is on, only return whole blocks of
	* pseudo random data
	*/
	err = -EINVAL;
	if (ctx->flags & PRNG_FIXED_SIZE) {
	if (nbytes < DEFAULT_BLK_SZ)
	goto done;
	byte_count = DEFAULT_BLK_SZ;
	}

	/*
	* Return 0 in case of success as mandated by the kernel
	* crypto API interface definition.
	*/
	err = 0;

	dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
	byte_count, ctx);


	remainder:
	if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
	if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
	memset(buf, 0, nbytes);
	err = -EINVAL;
	goto done;
	}
	}

	/*
	* Copy any data less than an entire block
	*/
	if (byte_count < DEFAULT_BLK_SZ) {
	empty_rbuf:
	while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
	*ptr = ctx->rand_data[ctx->rand_data_valid];
	ptr++;
	byte_count--;
	ctx->rand_data_valid++;
	if (byte_count == 0)
	goto done;
	}
	}

	/*
	* Now copy whole blocks
	*/
	for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
	if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
	if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
	memset(buf, 0, nbytes);
	err = -EINVAL;
	goto done;
	}
	}
	if (ctx->rand_data_valid > 0)
	goto empty_rbuf;
	memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
	ctx->rand_data_valid += DEFAULT_BLK_SZ;
	ptr += DEFAULT_BLK_SZ;
	}

	/*
	* Now go back and get any remaining partial block
	*/
	if (byte_count)
	goto remainder;

	done:
	spin_unlock_bh(&ctx->prng_lock);
	dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
	err, ctx);
	return err;
	}

	static void free_prng_context(struct prng_context *ctx)
	{
	crypto_free_cipher(ctx->tfm);
	}

	static int reset_prng_context(struct prng_context *ctx,
	const unsigned char *key, size_t klen,
	const unsigned char V, const unsigned char DT)
	{
	int ret;
	const unsigned char *prng_key;

	spin_lock_bh(&ctx->prng_lock);
	ctx->flags \|= PRNG_NEED_RESET;

	prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;

	if (!key)
	klen = DEFAULT_PRNG_KSZ;

	if (V)
	memcpy(ctx->V, V, DEFAULT_BLK_SZ);
	else
	memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);

	if (DT)
	memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
	else
	memset(ctx->DT, 0, DEFAULT_BLK_SZ);

	memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
	memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);

	ctx->rand_data_valid = DEFAULT_BLK_SZ;

	ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
	if (ret) {
	dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
	crypto_cipher_get_flags(ctx->tfm));
	goto out;
	}

	ret = 0;
	ctx->flags &= ~PRNG_NEED_RESET;
	out:
	spin_unlock_bh(&ctx->prng_lock);
	return ret;
	}

	static int cprng_init(struct crypto_tfm *tfm)
	{
	struct prng_context *ctx = crypto_tfm_ctx(tfm);

	spin_lock_init(&ctx->prng_lock);
	ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
	if (IS_ERR(ctx->tfm)) {
	dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
	ctx);
	return PTR_ERR(ctx->tfm);
	}

	if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
	return -EINVAL;

	/*
	* after allocation, we should always force the user to reset
	* so they don't inadvertently use the insecure default values
	* without specifying them intentially
	*/
	ctx->flags \|= PRNG_NEED_RESET;
	return 0;
	}

	static void cprng_exit(struct crypto_tfm *tfm)
	{
	free_prng_context(crypto_tfm_ctx(tfm));
	}

	static int cprng_get_random(struct crypto_rng *tfm,
	const u8 *src, unsigned int slen,
	u8 *rdata, unsigned int dlen)
	{
	struct prng_context *prng = crypto_rng_ctx(tfm);

	return get_prng_bytes(rdata, dlen, prng, 0);
	}

	/*
	* This is the cprng_registered reset method the seed value is
	* interpreted as the tuple { V KEY DT}
	* V and KEY are required during reset, and DT is optional, detected
	* as being present by testing the length of the seed
	*/
	static int cprng_reset(struct crypto_rng *tfm,
	const u8 *seed, unsigned int slen)
	{
	struct prng_context *prng = crypto_rng_ctx(tfm);
	const u8 *key = seed + DEFAULT_BLK_SZ;
	const u8 *dt = NULL;

	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
	return -EINVAL;

	if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
	dt = key + DEFAULT_PRNG_KSZ;

	reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);

	if (prng->flags & PRNG_NEED_RESET)
	return -EINVAL;
	return 0;
	}

	#ifdef CONFIG_CRYPTO_FIPS
	static int fips_cprng_get_random(struct crypto_rng *tfm,
	const u8 *src, unsigned int slen,
	u8 *rdata, unsigned int dlen)
	{
	struct prng_context *prng = crypto_rng_ctx(tfm);

	return get_prng_bytes(rdata, dlen, prng, 1);
	}

	static int fips_cprng_reset(struct crypto_rng *tfm,
	const u8 *seed, unsigned int slen)
	{
	u8 rdata[DEFAULT_BLK_SZ];
	const u8 *key = seed + DEFAULT_BLK_SZ;
	int rc;

	struct prng_context *prng = crypto_rng_ctx(tfm);

	if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
	return -EINVAL;

	/* fips strictly requires seed != key */
	if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
	return -EINVAL;

	rc = cprng_reset(tfm, seed, slen);

	if (!rc)
	goto out;

	/* this primes our continuity test */
	rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
	prng->rand_data_valid = DEFAULT_BLK_SZ;

	out:
	return rc;
	}
	#endif

	static struct rng_alg rng_algs[] = { {
	.generate = cprng_get_random,
	.seed = cprng_reset,
	.seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
	.base = {
	.cra_name = "stdrng",
	.cra_driver_name = "ansi_cprng",
	.cra_priority = 100,
	.cra_ctxsize = sizeof(struct prng_context),
	.cra_module = THIS_MODULE,
	.cra_init = cprng_init,
	.cra_exit = cprng_exit,
	}
	#ifdef CONFIG_CRYPTO_FIPS
	}, {
	.generate = fips_cprng_get_random,
	.seed = fips_cprng_reset,
	.seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
	.base = {
	.cra_name = "fips(ansi_cprng)",
	.cra_driver_name = "fips_ansi_cprng",
	.cra_priority = 300,
	.cra_ctxsize = sizeof(struct prng_context),
	.cra_module = THIS_MODULE,
	.cra_init = cprng_init,
	.cra_exit = cprng_exit,
	}
	#endif
	} };

	/* Module initalization */
	static int __init prng_mod_init(void)
	{
	return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
	}

	static void __exit prng_mod_fini(void)
	{
	crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
	}

	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
	MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
	module_param(dbg, int, 0);
	MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
	subsys_initcall(prng_mod_init);
	module_exit(prng_mod_fini);
	MODULE_ALIAS_CRYPTO("stdrng");
	MODULE_ALIAS_CRYPTO("ansi_cprng");
	MODULE_IMPORT_NS(CRYPTO_INTERNAL);