Re: [PATCH v2 03/11] crypto: Documentation - RNG API documentation

["Joy M. Latten" <jmlatten@linux.vnet.ibm.com>]

Hi Stephan,

Just one quick comment below...

regards,
Joy

On Sun, 2014-11-02 at 21:36 +0100, Stephan Mueller wrote:
> The API function calls exported by the kernel crypto API for RNGs to
> be used by consumers are documented.
> 
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> CC: Marek Vasut <marex@denx.de>
> ---
>  include/crypto/rng.h | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 113 insertions(+)
> 
> diff --git a/include/crypto/rng.h b/include/crypto/rng.h
> index c93f9b9..83c4238 100644
> --- a/include/crypto/rng.h
> +++ b/include/crypto/rng.h
> @@ -20,11 +20,68 @@ extern struct crypto_rng *crypto_default_rng;
>  int crypto_get_default_rng(void);
>  void crypto_put_default_rng(void);
> 
> +/**
> + * Random number generator API to use the ciphers of type
> + * CRYPTO_ALG_TYPE_RNG (listed as type "rng" in /proc/crypto)
> + *
> + * Example code:
> + *
> + *static int get_random_numbers(u8 *buf, unsigned int len)
> + *{
> + *	struct crypto_rng *rng = NULL;
> + *	char *drbg = "drbg_nopr_sha256"; // Hash DRBG with SHA-256, no PR
> + *	int ret;
> + *
> + *	if (!buf || !len) {
> + *		pr_debug("No output buffer provided\n");
> + *		return -EINVAL;
> + *	}
> + *
> + *	rng = crypto_alloc_rng(drbg, 0, 0);
> + *	if (IS_ERR(rng)) {
> + *		pr_debug("could not allocate RNG handle for %s\n", drbg);
> + *		return -PTR_ERR(rng);
> + *	}
> + *
> + *	ret = crypto_rng_get_bytes(rng, buf, len);
> + *	if (ret < 0)
> + *		pr_debug("generation of random numbers failed\n");
> + *	else if (ret == 0)
> + *		pr_debug("RNG returned no data");
> + *	else
> + *		pr_debug("RNG returned %d bytes of data\n", ret);
> + *
> + *out:
> + *	crypto_free_rng(rng);
> + *	return ret;
> + *}
> + */
> +
>  static inline struct crypto_rng *__crypto_rng_cast(struct crypto_tfm *tfm)
>  {
>  	return (struct crypto_rng *)tfm;
>  }
> 
> +/**
> + * Allocate a cipher handle for a random number generator. The returned struct
> + * crypto_rng is the cipher handle that is required for any subsequent
> + * API invocation for that random number generator.
> + *
> + * For all random number generators, this call creates a new private copy of
> + * the random number generator that does not share a state with other
> + * instances. The only exception is the "krng" random number generator which
> + * is a kernel crypto API use case for the get_random_bytes() function of the
> + * /dev/random driver.
> + *
> + * @alg_name is the cra_name / name or cra_driver_name / driver name of the
> + *	     message digest cipher
> + * @type specifies the type of the cipher (see Documentation/crypto/)
> + * @mask specifies the mask for the cipher (see Documentation/crypto/)
> + *
> + * return value:
> + *	allocated cipher handle in case of success
> + *	IS_ERR() is true in case of an error, PTR_ERR() returns the error code.
> + */
>  static inline struct crypto_rng *crypto_alloc_rng(const char *alg_name,
>  						  u32 type, u32 mask)
>  {
> @@ -40,6 +97,14 @@ static inline struct crypto_tfm *crypto_rng_tfm(struct crypto_rng *tfm)
>  	return &tfm->base;
>  }
> 
> +/**
> + * Return the generic name (cra_name) of the initialized random number generator
> + *
> + * @tfm cipher handle
> + *
> + * return value:
> + *	generic name string
> + */
>  static inline struct rng_alg *crypto_rng_alg(struct crypto_rng *tfm)
>  {
>  	return &crypto_rng_tfm(tfm)->__crt_alg->cra_rng;
> @@ -50,23 +115,71 @@ static inline struct rng_tfm *crypto_rng_crt(struct crypto_rng *tfm)
>  	return &crypto_rng_tfm(tfm)->crt_rng;
>  }
> 
> +/**
> + * The referenced random number generator handle is zeroized and subsequently
> + * freed.
> + *
> + * @tfm cipher handle to be freed
> + */
>  static inline void crypto_free_rng(struct crypto_rng *tfm)
>  {
>  	crypto_free_tfm(crypto_rng_tfm(tfm));
>  }
> 
> +/**
> + * This function fills the caller-allocated buffer with random numbers using the
> + * random number generator referenced by the cipher handle.
> + *
> + * @tfm cipher handle
> + * @rdata output buffer holding the random numbers
> + * @dlen length of the output buffer
> + *
> + * return value:
> + *	> 0 function was successful and returns the number of generated bytes
> + *	< 0 if an error occurred
> + */
>  static inline int crypto_rng_get_bytes(struct crypto_rng *tfm,
>  				       u8 *rdata, unsigned int dlen)
>  {
>  	return crypto_rng_crt(tfm)->rng_gen_random(tfm, rdata, dlen);
>  }
> 
> +/**
> + * The reset function completely re-initializes the random number generator
> + * referenced by the cipher handle by clearing the current state. The new state
> + * is initialized with the caller provided seed or automatically, depending
> + * on the random number generator type (the ANSI X9.31 RNG requires
> + * caller-provided seed, the SP800-90A DRBGs perform an automatic seeding).
> + * The seed is provided with the. The provided seed should have the length of
dangling sentence... 

> + * the seed size defined for the random number generator as defined by
> + * crypto_rng_seedsize.
> + *
> + * @tfm cipher handle
> + * @seed seed input data
> + * @slen length of the seed input data
> + *
> + * return value:
> + *	0 if the setting of the key was successful
> + *	< 0 if an error occurred
> + */
>  static inline int crypto_rng_reset(struct crypto_rng *tfm,
>  				   u8 *seed, unsigned int slen)
>  {
>  	return crypto_rng_crt(tfm)->rng_reset(tfm, seed, slen);
>  }
> 
> +/**
> + * The function returns the seed size for the random number generator
> + * referenced by the cipher handle. This value may be zero if the random
> + * number generator does not implement or require a reseeding. For example,
> + * the SP800-90A DRBGs implement an automated reseeding after reaching a
> + * pre-defined threshold.
> + *
> + * @tfm cipher handle
> + *
> + * return value:
> + *	seed size for the random number generator
> + */
>  static inline int crypto_rng_seedsize(struct crypto_rng *tfm)
>  {
>  	return crypto_rng_alg(tfm)->seedsize;