---
name: "EVP_chacha20"
section: "3ssl"
platform: "linux"
package: "openssl"
version: "3.6.5-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/EVP_chacha20"
---

# EVP\_chacha20(3ssl)

EVP ChaCha20 stream cipher

## NAME

EVP\_chacha20, EVP\_chacha20\_poly1305 - EVP ChaCha20 stream cipher

## SYNOPSIS

```
 #include <openssl/evp.h>
 const EVP_CIPHER *EVP_chacha20(void);
 const EVP_CIPHER *EVP_chacha20_poly1305(void);
```

## DESCRIPTION

The ChaCha20 stream cipher for EVP.

- **EVP\_chacha20()**

  The ChaCha20 stream cipher. The key length is 256 bits, the IV 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:

  0000000000000002

  With an initial counter of 42 (2a in hex) would be expressed as:

  2a000000000000000000000000000002

- **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 "AEAD INTERFACE" in **EVP\_EncryptInit**(3) section for more information.

## NOTES

Developers should be aware of the negative performance implications of calling these functions multiple times and should consider using **EVP\_CIPHER\_fetch**(3) with **EVP\_CIPHER-CHACHA**(7) instead. See "Performance" in [**crypto**(7)](/crypto/7.md) for further information.

RFC 7539 \<https://www.rfc-editor.org/rfc/rfc7539.html#section-2.4\> uses a 32 bit counter and a 96 bit nonce for the IV.

## RETURN VALUES

These functions return an **EVP\_CIPHER** structure that contains the implementation of the symmetric cipher. See **EVP\_CIPHER\_meth\_new**(3) for details of the **EVP\_CIPHER** structure.

## SEE ALSO

**evp**(7), **EVP\_EncryptInit**(3), **EVP\_CIPHER\_meth\_new**(3)

## COPYRIGHT

Copyright 2017-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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 \<https://www.openssl.org/source/license.html\>.