Unsound implementation of Chacha20 in crypto2 (#1072)

crates/crypto2/RUSTSEC-0000-0000.md

@@ -0,0 +1,22 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "crypto2"
+date = "2021-10-08"
+url = "https://github.com/shadowsocks/crypto2/issues/27"
+informational = "unsound"
+keywords = ["crypto", "alignment", "unsound"]
+
+[affected.functions]
+"crypto2::streamcipher::Chacha20::encrypt_slice" = ["*"]
+"crypto2::streamcipher::Chacha20::decrypt_slice" = ["*"]
+"crypto2::streamcipher::xor_si512_inplace" = ["*"]
+
+[versions]
+patched = []
+```
+
+# Non-aligned u32 read in Chacha20 encryption and decryption
+The implementation does not enforce alignment requirements on input slices while incorrectly assuming 4-byte alignment through an unsafe call to `std::slice::from_raw_parts_mut`, which breaks the contract and introduces undefined behavior.
+
+This affects Chacha20 encryption and decryption in crypto2.