ctr_prng.h File Reference

Interface to a CTR-PRNG implementation. More...

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Functions
int	tc_ctr_prng_init (TCCtrPrng_t *const ctx, uint8_t const *const entropy, unsigned int entropyLen, uint8_t const *const personalization, unsigned int pLen)
	CTR-PRNG initialization procedure Initializes prng context with entropy and personalization string (if any)
int	tc_ctr_prng_reseed (TCCtrPrng_t *const ctx, uint8_t const *const entropy, unsigned int entropyLen, uint8_t const *const additional_input, unsigned int additionallen)
	CTR-PRNG reseed procedure Mixes entropy and additional_input into the prng context.
int	tc_ctr_prng_generate (TCCtrPrng_t *const ctx, uint8_t const *const additional_input, unsigned int additionallen, uint8_t *const out, unsigned int outlen)
	CTR-PRNG generate procedure Generates outlen pseudo-random bytes into out buffer, updates prng.
void	tc_ctr_prng_uninstantiate (TCCtrPrng_t *const ctx)
	CTR-PRNG uninstantiate procedure Zeroes the internal state of the supplied prng context.

Detailed Description

Interface to a CTR-PRNG implementation.

Overview: A pseudo-random number generator (PRNG) generates a sequence of numbers that have a distribution close to the one expected for a sequence of truly random numbers. The NIST Special Publication 800-90A specifies several mechanisms to generate sequences of pseudo random numbers, including the CTR-PRNG one which is based on AES. TinyCrypt implements CTR-PRNG with AES-128.

Security: A cryptographically secure PRNG depends on the existence of an entropy source to provide a truly random seed as well as the security of the primitives used as the building blocks (AES-128 in this instance).

Requires: - AES-128

Usage: 1) call tc_ctr_prng_init to seed the prng context

        2) call tc_ctr_prng_reseed to mix in additional entropy into
        the prng context

        3) call tc_ctr_prng_generate to output the pseudo-random data

        4) call tc_ctr_prng_uninstantiate to zero out the prng context

Function Documentation

tc_ctr_prng_generate()

int tc_ctr_prng_generate	(	TCCtrPrng_t *const	ctx,
		uint8_t const *const	additional_input,
		unsigned int	additionallen,
		uint8_t *const	out,
		unsigned int	outlen
	)

CTR-PRNG generate procedure Generates outlen pseudo-random bytes into out buffer, updates prng.

Returns

returns TC_CRYPTO_SUCCESS (1) returns TC_CTR_PRNG_RESEED_REQ (-1) if a reseed is needed returns TC_CRYPTO_FAIL (0) if: ctx == NULL, out == NULL, outlen >= 2^16

Note

Assumes tc_ctr_prng_init has been called for ctx

Parameters

ctx	IN/OUT – the PRNG context
additional_input	IN – additional input to the prng (may be null)
additionallen	IN – additional input length in bytes
out	IN/OUT – buffer to receive output
outlen	IN – size of out buffer in bytes

tc_ctr_prng_init()

int tc_ctr_prng_init	(	TCCtrPrng_t *const	ctx,
		uint8_t const *const	entropy,
		unsigned int	entropyLen,
		uint8_t const *const	personalization,
		unsigned int	pLen
	)

CTR-PRNG initialization procedure Initializes prng context with entropy and personalization string (if any)

Returns

returns TC_CRYPTO_SUCCESS (1) returns TC_CRYPTO_FAIL (0) if: ctx == NULL, entropy == NULL, entropyLen < (TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE)

Note

Only the first (TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE) bytes of both the entropy and personalization inputs are used - supplying additional bytes has no effect.

Parameters

ctx	IN/OUT – the PRNG context to initialize
entropy	IN – entropy used to seed the PRNG
entropyLen	IN – entropy length in bytes
personalization	IN – personalization string used to seed the PRNG (may be null)
plen	IN – personalization length in bytes

tc_ctr_prng_reseed()

int tc_ctr_prng_reseed	(	TCCtrPrng_t *const	ctx,
		uint8_t const *const	entropy,
		unsigned int	entropyLen,
		uint8_t const *const	additional_input,
		unsigned int	additionallen
	)

CTR-PRNG reseed procedure Mixes entropy and additional_input into the prng context.

Returns

returns TC_CRYPTO_SUCCESS (1) returns TC_CRYPTO_FAIL (0) if: ctx == NULL, entropy == NULL, entropylen < (TC_AES_KEY_SIZE + TC_AES_BLOCK_SIZE)

Note

It is better to reseed an existing prng context rather than re-initialise, so that any existing entropy in the context is presereved. This offers some protection against undetected failures of the entropy source.

Assumes tc_ctr_prng_init has been called for ctx

Parameters

ctx	IN/OUT – the PRNG state
entropy	IN – entropy to mix into the prng
entropylen	IN – length of entropy in bytes
additional_input	IN – additional input to the prng (may be null)
additionallen	IN – additional input length in bytes

tc_ctr_prng_uninstantiate()

void tc_ctr_prng_uninstantiate

(

TCCtrPrng_t *const

ctx

)

CTR-PRNG uninstantiate procedure Zeroes the internal state of the supplied prng context.

Returns

none

Parameters

ctx	IN/OUT – the PRNG context