Merge pull request #4187 from Artoria2e5/patch-1

Create chacha-cipher

topics/chacha-cipher/index.md

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+---
+aliases: chacha20, xchacha20, chacha12, xchacha12, chacha8, xchacha8, chacha20-poly1305, xchacha-poly1305
+display_name: ChaCha
+short_description: ChaCha is a family of stream ciphers developed by Daniel J. Bernstein.
+topic: chacha-cipher
+wikipedia_url: https://en.wikipedia.org/wiki/Salsa20#ChaCha_variant
+---
+ChaCha is a family of stream ciphers developed by Daniel J. Bernstein. It is part of the popular authenticated encryption algorithm ChaCha20-Poly1305.
+
+The canonical 20-round version is ChaCha20, though the faster, reduced-round variants ChaCha8 and ChaCha12 also see some use.
+The XChaCha family features an extended nonce.