Start ChaCha20Poly1305 integration (BearSSL)

libp2p/crypto/chacha20poly1305.nim

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+## Nim-Libp2p
+## Copyright (c) 2020 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+## This module integrates BearSSL ChaCha20+Poly1305
+##
+## This module uses unmodified parts of code from
+## BearSSL library <https://bearssl.org/>
+## Copyright(C) 2018 Thomas Pornin <pornin@bolet.org>.
+
+# RFC @ https://tools.ietf.org/html/rfc7539
+
+import bearssl
+
+const
+  ChaChaPolyKeySize = 32
+  ChaChaPolyNonceSize = 12
+  ChaChaPolyTagSize = 16
+  
+type
+  ChaChaPoly = object
+  ChaChaPolyKey* = array[ChaChaPolyKeySize, byte]
+  ChaChaPolyNonce* = array[ChaChaPolyNonceSize, byte]
+  ChaChaPolyTag* = array[ChaChaPolyTagSize, byte]
+
+# bearssl allows us to use optimized versions
+# this is reconciled at runtime
+# we do this in the global scope / module init
+
+# try for the best first
+var
+  chachapoly_native_impl: Poly1305Run = poly1305CtmulqGet()
+  chacha_native_impl: Chacha20Run = chacha20Sse2Get()
+
+# fall back if not available
+if chachapoly_native_impl == nil:
+  echo "ChaChaPoly could not use the fastest implementation, falling back"
+  chachapoly_native_impl = poly1305CtmulRun
+
+if chacha_native_impl == nil:
+  echo "ChaCha could not use the fastest implementation, falling back"
+  chacha_native_impl = chacha20CtRun
+
+echo "ChaCha20Poly1305 global init done."
+
+proc encrypt*(_: type[ChaChaPoly],
+                 key: var ChaChaPolyKey,
+                 nonce: var ChaChaPolyNonce,
+                 tag: var ChaChaPolyTag,
+                 data: var openarray[byte],
+                 aad: var openarray[byte]) =
+  chachapoly_native_impl(
+    addr key[0],
+    addr nonce[0],
+    addr data[0],
+    data.len,
+    addr aad[0],
+    aad.len,
+    addr tag[0],
+    chacha_native_impl,
+    #[encrypt]# 1.cint)
+
+proc decrypt*(_: type[ChaChaPoly],
+                 key: var ChaChaPolyKey,
+                 nonce: var ChaChaPolyNonce,
+                 tag: var ChaChaPolyTag,
+                 data: var openarray[byte],
+                 aad: var openarray[byte]) =
+  chachapoly_native_impl(
+    addr key[0],
+    addr nonce[0],
+    addr data[0],
+    data.len,
+    addr aad[0],
+    aad.len,
+    addr tag[0],
+    chacha_native_impl,
+    #[decrypt]# 0.cint)
+
+when isMainModule:
+  var
+    key: ChaChaPolyKey
+    iv: ChaChaPolyNonce
+    tag: ChaChaPolyTag
+    data = [0.byte, 1, 2, 3, 4]
+    aad = [0.byte, 1, 2, 3, 4]
+
+  ChaChaPoly.encrypt(key, iv, tag, data, aad)
+  assert data != [0.byte, 1, 2, 3, 4]
+  ChaChaPoly.decrypt(key, iv, tag, data, aad)
+  assert data == [0.byte, 1, 2, 3, 4]