# Random Number Algorithm Definitions¶

struct rng_alg

random number generator definition

Definition:

```struct rng_alg {
int (*generate)(struct crypto_rng *tfm,const u8 *src, unsigned int slen, u8 *dst, unsigned int dlen);
int (*seed)(struct crypto_rng *tfm, const u8 *seed, unsigned int slen);
void (*set_ent)(struct crypto_rng *tfm, const u8 *data, unsigned int len);
unsigned int seedsize;
struct crypto_alg base;
};
```

Members

`generate`

The function defined by this variable obtains a random number. The random number generator transform must generate the random number out of the context provided with this call, plus any additional data if provided to the call.

`seed`

Seed or reseed the random number generator. With the invocation of this function call, the random number generator shall become ready for generation. If the random number generator requires a seed for setting up a new state, the seed must be provided by the consumer while invoking this function. The required size of the seed is defined with seedsize .

`set_ent`

Set entropy that would otherwise be obtained from entropy source. Internal use only.

`seedsize`

The seed size required for a random number generator initialization defined with this variable. Some random number generators does not require a seed as the seeding is implemented internally without the need of support by the consumer. In this case, the seed size is set to zero.

`base`

Common crypto API algorithm data structure.

# Crypto API Random Number API¶

The random number generator API is used with the ciphers of type CRYPTO_ALG_TYPE_RNG (listed as type “rng” in /proc/crypto)

struct crypto_rng *crypto_alloc_rng(const char *alg_name, u32 type, u32 mask)
• allocate RNG handle

Parameters

`const char *alg_name`

is the cra_name / name or cra_driver_name / driver name of the message digest cipher

`u32 type`

specifies the type of the cipher

`u32 mask`

specifies the mask for the cipher

Description

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.

struct rng_alg *crypto_rng_alg(struct crypto_rng *tfm)

obtain name of RNG

Parameters

`struct crypto_rng *tfm`

cipher handle

Description

Return the generic name (cra_name) of the initialized random number generator

Return

generic name string

void crypto_free_rng(struct crypto_rng *tfm)

zeroize and free RNG handle

Parameters

`struct crypto_rng *tfm`

cipher handle to be freed

Description

If tfm is a NULL or error pointer, this function does nothing.

int crypto_rng_generate(struct crypto_rng *tfm, const u8 *src, unsigned int slen, u8 *dst, unsigned int dlen)

get random number

Parameters

`struct crypto_rng *tfm`

cipher handle

`const u8 *src`

Input buffer holding additional data, may be NULL

`unsigned int slen`

`u8 *dst`

output buffer holding the random numbers

`unsigned int dlen`

length of the output buffer

Description

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; < 0 if an error occurred

int crypto_rng_get_bytes(struct crypto_rng *tfm, u8 *rdata, unsigned int dlen)

get random number

Parameters

`struct crypto_rng *tfm`

cipher handle

`u8 *rdata`

output buffer holding the random numbers

`unsigned int dlen`

length of the output buffer

Description

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; < 0 if an error occurred

int crypto_rng_reset(struct crypto_rng *tfm, const u8 *seed, unsigned int slen)

re-initialize the RNG

Parameters

`struct crypto_rng *tfm`

cipher handle

`const u8 *seed`

seed input data

`unsigned int slen`

length of the seed input data

Description

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

int crypto_rng_seedsize(struct crypto_rng *tfm)

obtain seed size of RNG

Parameters

`struct crypto_rng *tfm`

cipher handle

Description

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