EVP_CHACHA20(3ossl)

💜 EVP_CHACHA20 — like, the ChaCha20 stream cipher era 💜

okay so bestie, welcome to the 3ossl girlies' corner of the OpenSSL manual 💅 this one's all about EVP_chacha20 and EVP_chacha20_poly1305, which are literally the EVP ChaCha20 stream cipher functions. no cap, it's a short page but it ate ✨

---

🦋 SYNOPSIS 🦋

#include <openssl/evp.h>

const EVP_CIPHER *EVP_chacha20(void);
const EVP_CIPHER *EVP_chacha20_poly1305(void);

---

🎀 DESCRIPTION 🎀

so, it's the ChaCha20 stream cipher, but for EVP. main character energy fr fr 🔥

🌸 EVP_chacha20()

the ChaCha20 stream cipher, bestie. the key length is 256 bits and the IV is 128 bits long 👑

here's the cute part: the first 64 bits is a counter in little-endian order, followed by a 64 bit nonce. so like, for example, a nonce of:

0000000000000002

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

2a000000000000000000000000000002

the way that math works out… iconic 🧚

💖 EVP_chacha20_poly1305()

authenticated encryption with ChaCha20-Poly1305 🌈 just like EVP_chacha20(), the key is 256 bits and the IV is 96 bits. this one supports additional authenticated data (AAD) and produces a 128-bit authentication tag. if you want the deets, go check the "AEAD INTERFACE" in EVP_EncryptInit(3) section 🫶

---

⭐ NOTES ⭐

okay, real talk time 🙈 developers should be aware of the negative performance implications of calling these functions multiple times — like, don't just spam them, babe — and should consider using EVP_CIPHER_fetch(3) with EVP_CIPHER-CHACHA(7) instead. there's more about that in "Performance" in crypto(7) if you wanna go deeper 💀

also heads up: 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. just so you know 👀

---

👑 RETURN VALUES 👑

these functions return an EVP_CIPHER structure that contains the implementation of the symmetric cipher 💅 and if you wanna know what's inside that structure, see EVP_CIPHER_meth_new(3) for details 🎀

---

🌈 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> 🫶

---

and that's the whole vibe check bestie ✨ this page is from version 3.5.6, dated 2026-04-07 — mwah, slay, periodt 💋🎀