chacha.h File Reference

ChaCha stream cipher. More...

Detailed Description

ChaCha stream cipher.

Author

René Kijewski rene..nosp@m.kije.nosp@m.wski@.nosp@m.fu-b.nosp@m.erlin.nosp@m..de

Definition in file chacha.h.

#include <stdint.h>
#include <stddef.h>

Include dependency graph for chacha.h:

Go to the source code of this file.

Data Structures
struct	chacha_ctx
	A ChaCha cipher stream context. More...
int	chacha_init (chacha_ctx *ctx, unsigned rounds, const uint8_t *key, uint32_t keylen, const uint8_t nonce[8])
	Initialize a ChaCha context.
void	chacha_keystream_bytes (chacha_ctx *ctx, void *x)
	Generate next block in the keystream.
void	chacha_encrypt_bytes (chacha_ctx *ctx, const uint8_t *m, uint8_t *c)
	Encode or decode a block of data.
static void	chacha_decrypt_bytes (chacha_ctx *ctx, const uint8_t *m, uint8_t *c)
	Encode or decode a block of data.
void	chacha_prng_seed (const void *data, size_t bytes)
	Seed the pseudo-random number generator.
uint32_t	chacha_prng_next (void)
	Extract a number from the pseudo-random number generator.

Function Documentation

chacha_decrypt_bytes()

static void chacha_decrypt_bytes ( chacha_ctx *  ctx, const uint8_t *  m, uint8_t *  c  )

inlinestatic

Encode or decode a block of data.

m is always the input regardless if it is the plaintext or ciphertext, and c vice verse.

Warning

You need to re-initialize the context with a new nonce after 2^64 encrypted blocks, or the keystream will repeat!

Parameters

[in,out]	ctx	The ChaCha context.
[in]	m	The input.
[out]	c	The output.

Definition at line 102 of file chacha.h.

chacha_encrypt_bytes()

void chacha_encrypt_bytes	(	chacha_ctx *	ctx,
		const uint8_t *	m,
		uint8_t *	c
	)

Encode or decode a block of data.

m is always the input regardless if it is the plaintext or ciphertext, and c vice verse.

Warning

You need to re-initialize the context with a new nonce after 2^64 encrypted blocks, or the keystream will repeat!

Parameters

[in,out]	ctx	The ChaCha context.
[in]	m	The input.
[out]	c	The output.

chacha_init()

int chacha_init	(	chacha_ctx *	ctx,
		unsigned	rounds,
		const uint8_t *	key,
		uint32_t	keylen,
		const uint8_t	nonce[8]
	)

Initialize a ChaCha context.

Parameters

[out]	ctx	The context to initialize
[in]	rounds	Number of rounds. Recommended: 20. Also in use: 8 and 12.
[in]	key	The key to use.
[in]	keylen	Length (in bytes) of key. Must be 16 or 32.
[in]	nonce	IV / nonce to use.

Returns

== 0 on success.

< 0 if an illegal value for rounds or keylen was supplied.

chacha_keystream_bytes()

void chacha_keystream_bytes	(	chacha_ctx *	ctx,
		void *	x
	)

Generate next block in the keystream.

If you want to seek inside the cipher steam, then you have to update the clock in ctx->state[13]:ctx->state[12] manually.

Warning

You need to re-initialize the context with a new nonce after 2^64 encrypted blocks, or the keystream will repeat!

Parameters

[in,out]	ctx	The ChaCha context
[out]	x	The block of the keystream (sizeof(x) == 64).

chacha_prng_next()

uint32_t chacha_prng_next

(

void

)

Extract a number from the pseudo-random number generator.

Warning

After you have read 2^68 numbers you have to re-seed the PRNG. Otherwise the sequence will repeat.

Returns

The random value

chacha_prng_seed()

void chacha_prng_seed	(	const void *	data,
		size_t	bytes
	)

Seed the pseudo-random number generator.

You can seed the random number generator with up to 64 bytes of data. If you feed less than 64 bytes of data, then the privous state gets only partially overwritten.

If you want to supply multiple information, then you have to concatenate them manually before invoking the function.

The PRNG gets a random seed in the build process. You can set a deterministic value by supplying a comma separated argument to make like RIOT_CHACHA_PRNG_DEFAULT="0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15".

Parameters

[in]	data	Some random data.
[in]	bytes	Length of data in bytes where 0 < bytes <= 64.