openssl/doc/man3/EVP_chacha20.pod

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=pod
=head1 NAME
EVP_chacha20,
EVP_chacha20_poly1305
- EVP ChaCha20 stream cipher
=head1 SYNOPSIS
#include <openssl/evp.h>
const EVP_CIPHER *EVP_chacha20(void)
const EVP_CIPHER *EVP_chacha20_poly1305(void)
=head1 DESCRIPTION
The ChaCha20 stream cipher for EVP.
=over 4
=item EVP_chacha20()
The ChaCha20 stream cipher. The key length is 256 bits, the IV is 128 bits long.
The first 32 bits consists of a counter in little-endian order followed by a 96
bit nonce. For example a nonce of:
000000000000000000000002
With an initial counter of 42 (2a in hex) would be expressed as:
2a000000000000000000000000000002
=item EVP_chacha20_poly1305()
Authenticated encryption with ChaCha20-Poly1305. Like EVP_chacha20(), the key
is 256 bits and the IV is 96 bits. This supports additional authenticated data
(AAD) and produces a 128-bit authentication tag. See the
L<EVP_EncryptInit(3)/AEAD Interface> section for more information.
=back
=head1 RETURN VALUES
These functions return an B<EVP_CIPHER> structure that contains the
implementation of the symmetric cipher. See L<EVP_CIPHER_meth_new(3)> for
details of the B<EVP_CIPHER> structure.
=head1 SEE ALSO
L<evp(7)>,
L<EVP_EncryptInit(3)>,
L<EVP_CIPHER_meth_new(3)>
=head1 COPYRIGHT
Copyright 2017-2019 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.
=cut