crypto: doc - RNG API documentation

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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/rng.h

@@ -20,11 +20,38 @@ extern struct crypto_rng *crypto_default_rng;
 int crypto_get_default_rng(void);
 void crypto_put_default_rng(void);
 
+/**
+ * DOC: Random number generator API
+ *
+ * The random number generator API is used with the ciphers of type
+ * CRYPTO_ALG_TYPE_RNG (listed as type "rng" in /proc/crypto)
+ */
+
 static inline struct crypto_rng *__crypto_rng_cast(struct crypto_tfm *tfm)
 {
 	return (struct crypto_rng *)tfm;
 }
 
+/**
+ * crypto_alloc_rng() -- allocate RNG handle
+ * @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
+ * @mask: specifies the mask for the cipher
+ *
+ * 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.
+ *
+ * Return: 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 +67,14 @@ static inline struct crypto_tfm *crypto_rng_tfm(struct crypto_rng *tfm)
 	return &tfm->base;
 }
 
+/**
+ * crypto_rng_alg - obtain name of RNG
+ * @tfm: cipher handle
+ *
+ * Return the generic name (cra_name) of the initialized random number generator
+ *
+ * Return: 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 +85,68 @@ static inline struct rng_tfm *crypto_rng_crt(struct crypto_rng *tfm)
 	return &crypto_rng_tfm(tfm)->crt_rng;
 }
 
+/**
+ * crypto_free_rng() - zeroize and free RNG handle
+ * @tfm: cipher handle to be freed
+ */
 static inline void crypto_free_rng(struct crypto_rng *tfm)
 {
 	crypto_free_tfm(crypto_rng_tfm(tfm));
 }
 
+/**
+ * crypto_rng_get_bytes() - get random number
+ * @tfm: cipher handle
+ * @rdata: output buffer holding the random numbers
+ * @dlen: length of the output buffer
+ *
+ * This function fills the caller-allocated buffer with random numbers using the
+ * random number generator referenced by the cipher handle.
+ *
+ * Return: > 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);
 }
 
+/**
+ * crypto_rng_reset() - re-initialize the RNG
+ * @tfm: cipher handle
+ * @seed: seed input data
+ * @slen: length of the seed input data
+ *
+ * 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 as a parameter to this function call. The provided seed
+ * should have the length of the seed size defined for the random number
+ * generator as defined by crypto_rng_seedsize.
+ *
+ * Return: 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);
 }
 
+/**
+ * crypto_rng_seedsize() - obtain seed size of RNG
+ * @tfm: cipher handle
+ *
+ * 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.
+ *
+ * Return: seed size for the random number generator
+ */
 static inline int crypto_rng_seedsize(struct crypto_rng *tfm)
 {
 	return crypto_rng_alg(tfm)->seedsize;