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.\" ========================================================================
.\"
.IX Title "EVP_CHACHA20 3SSL"
.TH EVP_CHACHA20 3SSL "2023-10-23" "3.0.11" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_chacha20,
EVP_chacha20_poly1305
\&\- EVP ChaCha20 stream cipher
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& const EVP_CIPHER *EVP_chacha20(void);
\& const EVP_CIPHER *EVP_chacha20_poly1305(void);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The ChaCha20 stream cipher for \s-1EVP.\s0
.IP "\fBEVP_chacha20()\fR" 4
.IX Item "EVP_chacha20()"
The ChaCha20 stream cipher. The key length is 256 bits, the \s-1IV\s0 is 128 bits long.
The first 64 bits consists of a counter in little-endian order followed by a 64
bit nonce. For example a nonce of:
.Sp
0000000000000002
.Sp
With an initial counter of 42 (2a in hex) would be expressed as:
.Sp
2a000000000000000000000000000002
.IP "\fBEVP_chacha20_poly1305()\fR" 4
.IX Item "EVP_chacha20_poly1305()"
Authenticated encryption with ChaCha20\-Poly1305. Like \fBEVP_chacha20()\fR, the key
is 256 bits and the \s-1IV\s0 is 96 bits. This supports additional authenticated data
(\s-1AAD\s0) and produces a 128\-bit authentication tag. See the
\&\*(L"\s-1AEAD\s0 Interface\*(R" in \fBEVP_EncryptInit\fR\|(3) section for more information.
.SH "NOTES"
.IX Header "NOTES"
Developers should be aware of the negative performance implications of
calling these functions multiple times and should consider using
\&\fBEVP_CIPHER_fetch\fR\|(3) instead.
See \*(L"Performance\*(R" in \fBcrypto\fR\|(7) for further information.
.PP
\&\s-1RFC 7539\s0 <https://www.rfc-editor.org/rfc/rfc7539.html#section-2.4>
uses a 32 bit counter and a 96 bit nonce for the \s-1IV.\s0
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
These functions return an \fB\s-1EVP_CIPHER\s0\fR structure that contains the
implementation of the symmetric cipher. See \fBEVP_CIPHER_meth_new\fR\|(3) for
details of the \fB\s-1EVP_CIPHER\s0\fR structure.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBevp\fR\|(7),
\&\fBEVP_EncryptInit\fR\|(3),
\&\fBEVP_CIPHER_meth_new\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2017\-2023 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
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