NAME
ChaCha_set_key,
ChaCha_set_iv, ChaCha,
CRYPTO_chacha_20,
CRYPTO_hchacha_20,
CRYPTO_xchacha_20 —
ChaCha20 stream cipher
SYNOPSIS
#include
<openssl/chacha.h>
void
ChaCha_set_key(ChaCha_ctx *ctx,
const unsigned char *key, unsigned int
keybits);
void
ChaCha_set_iv(ChaCha_ctx *ctx,
const unsigned char *iv, const
unsigned char *counter);
void
ChaCha(ChaCha_ctx *ctx,
unsigned char *out, const unsigned
char *in, size_t len);
void
CRYPTO_chacha_20(unsigned char
*out, const unsigned char *in,
size_t len, const unsigned char
key[32], const unsigned char iv[8],
uint64_t counter);
void
CRYPTO_hchacha_20(unsigned char
out[32], const unsigned char key[32],
const unsigned char iv[16]);
void
CRYPTO_xchacha_20(unsigned char
*out, const unsigned char *in,
size_t len, const unsigned char
key[32], const unsigned char iv[24]);
DESCRIPTION
These functions provide a low-level implementation of the ChaCha stream cipher with 256 and 128-bit keys. The number of rounds is hardcoded to 20; variants with 8 or 12 rounds are not supported.
Instead of using these functions directly, application programs normally use the more portable EVP_chacha20(3) high-level interface.
The ChaCha state is contained in the ChaCha_ctx structure and consists of sixteen 32-bit unsigned integers.
For the recommended value of 256
keybits,
ChaCha_set_key()
copies 32 bytes (256 bits) from key to the middle
eight integers of the ChaCha state, using little endian order for each
integer. For the alternative value of 128 keybits,
only 16 bytes (128 bits) are copied from key to the
ChaCha state, but they are copied twice, once to the second quarter and once
to the third quarter. The first quarter of the ChaCha state is set to four
constant integers; these constants differ depending on whether
keybits is 128 or 256. The last quarter of the ChaCha
state remains unchanged.
ChaCha_set_iv()
copies eight bytes (64 bits) from counter and eight
bytes (64 bits) from iv to the last quarter of the
ChaCha state, the counter to the first two integers and the initialization
vector to the last two integers, again in little endian order. If
counter is NULL, the two
respective integers are set to 0 instead. The first three quarters of the
ChaCha state remain unchanged.
ChaCha()
encrypts len bytes of data from
in to out using the
ctx that was previously set up with
ChaCha_set_key() and
ChaCha_set_iv(). Providing an
out buffer of at least len bytes
is the responsibility of the caller. This function can be called multiple
times in a row with varying len arguments. The
len does not need to be a multiple of 64.
CRYPTO_chacha_20()
encrypts len bytes of data from
in to out in a one-shot
operation, using the given key and
iv as described for
ChaCha_set_key() and
ChaCha_set_iv() and copying the less significant
half of counter to the first counter integer in the
initial ChaCha state and the more significant half to the second integer.
Providing an out buffer of at least
len bytes is again the responsibility of the caller.
The maximum supported value for len is 2^32 - 1.
XChaCha is a variant of ChaCha designed to support longer nonces, just like XSalsa20 is a variant of Salsa20 supporting longer nonces.
CRYPTO_xchacha_20()
encrypts len bytes of data from
in to out in a one-shot
operation with the XChaCha algorithm, using the given
key and iv. It is equivalent to
CRYPTO_chacha_20() with the last third of
iv, a counter of 0, and a key
generated with
CRYPTO_hchacha_20()
from the first two thirds of iv.
SEE ALSO
Daniel J. Bernstein, ChaCha, a variant of Salsa20, https://cr.yp.to/chacha/chacha-20080128.pdf, Chicago, January 28, 2008.
Daniel J. Bernstein, Extending the Salsa20 nonce, https://cr.yp.to/snuffle/xsalsa-20110204.pdf, Chicago, August 22, 2017.
STANDARDS
RFC 8439: ChaCha20 and Poly1305 for IETF Protocols
Note that the standard specifies a 32-bit counter and a 96-bit initialization vector whereas this implementation follows Bernstein's original specification and uses a 64-bit counter and a 64-bit initialization vector.
These functions are specific to LibreSSL and not provided by
OpenSSL. BoringSSL does provide CRYPTO_chacha_20(),
but with an incompatible interface, taking a 96-bit iv
and a 32-bit counter.
HISTORY
ChaCha_set_key(),
ChaCha_set_iv(), ChaCha(),
and CRYPTO_chacha_20() first appeared in
OpenBSD 5.6.
CRYPTO_hchacha_20() and
CRYPTO_xchacha_20() first appeared in
OpenBSD 6.5.
AUTHORS
This implementation was written by Daniel J. Bernstein <[email protected]>. The API layer was added by Joel Sing <[email protected]> for ChaCha, and for XChaCha by David Gwynne <[email protected]>.