/*
   * 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>
   *
   *  This program is free software; you can redistribute it and/or modify it
   *  under the terms of the GNU General Public License as published by the
   *  Free Software Foundation; either version 2 of the License, or (at your
   *  any later version.
   *
   *
   */
  
  #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>
  
  #include "internal.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 succeded, <0 if something went wrong
   */
  static int _get_more_prng_bytes(struct prng_context *ctx)
  {
  	int i;
  	unsigned char tmp[DEFAULT_BLK_SZ];
  	unsigned char *output = NULL;
  
  
  	dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p
  ",
  		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 (fips_enabled) {
  					panic("cprng %p Failed repetition check!
  ",
  						ctx);
  				}

  				printk(KERN_ERR
  					"ctx %p Failed repetition check!
  ",
  					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
  ", 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)
  {

  	unsigned char *ptr = buf;
  	unsigned int byte_count = (unsigned int)nbytes;
  	int err;
  
  
  	if (nbytes < 0)
  		return -EINVAL;

  	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;
  	}
  
  	err = byte_count;
  
  	dbgprint(KERN_CRIT "getting %d random bytes for context %p
  ",
  		byte_count, ctx);
  
  
  remainder:
  	if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
  		if (_get_more_prng_bytes(ctx) < 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:

  		for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
  			ctx->rand_data_valid++) {
  			*ptr = ctx->rand_data[ctx->rand_data_valid];
  			ptr++;
  			byte_count--;
  			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) < 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
  ",
  		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,
  			      unsigned char *key, size_t klen,
  			      unsigned char *V, unsigned char *DT)
  {
  	int ret;

  	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
  ",
  			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
  ",
  				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, u8 *rdata,
  			    unsigned int dlen)
  {
  	struct prng_context *prng = crypto_rng_ctx(tfm);
  
  	return get_prng_bytes(rdata, dlen, prng);
  }

  /*
   *  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, u8 *seed, unsigned int slen)
  {
  	struct prng_context *prng = crypto_rng_ctx(tfm);

  	u8 *key = seed + DEFAULT_BLK_SZ;
  	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;
  }
  
  static struct crypto_alg rng_alg = {
  	.cra_name		= "stdrng",
  	.cra_driver_name	= "ansi_cprng",
  	.cra_priority		= 100,
  	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
  	.cra_ctxsize		= sizeof(struct prng_context),
  	.cra_type		= &crypto_rng_type,
  	.cra_module		= THIS_MODULE,
  	.cra_list		= LIST_HEAD_INIT(rng_alg.cra_list),
  	.cra_init		= cprng_init,
  	.cra_exit		= cprng_exit,
  	.cra_u			= {
  		.rng = {
  			.rng_make_random	= cprng_get_random,
  			.rng_reset		= cprng_reset,

  			.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,

  		}
  	}
  };
  
  
  /* Module initalization */
  static int __init prng_mod_init(void)
  {

  	if (fips_enabled)
  		rng_alg.cra_priority += 200;

  	return crypto_register_alg(&rng_alg);

  }
  
  static void __exit prng_mod_fini(void)
  {
  	crypto_unregister_alg(&rng_alg);
  	return;
  }
  
  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)");
  module_init(prng_mod_init);
  module_exit(prng_mod_fini);
  MODULE_ALIAS("stdrng");