Remove the global noiseEndianness var (#1707)

noiseutil/chachapoly.go

@@ -0,0 +1,52 @@
+package noiseutil
+
+import (
+	"crypto/cipher"
+	"encoding/binary"
+	"errors"
+
+	"github.com/flynn/noise"
+)
+
+// CipherStateChaChaPoly is the data-plane wrapper for the ChaCha20-Poly1305 AEAD cipher.
+// ChaCha20-Poly1305 uses little-endian nonce encoding per the Noise spec.
+type CipherStateChaChaPoly struct {
+	c cipher.AEAD
+}
+
+// NewCipherStateChaChaPoly extracts the underlying AEAD from the post-handshake noise.CipherState.
+// The caller is responsible for ensuring the noise cipher is actually ChaCha20-Poly1305.
+func NewCipherStateChaChaPoly(s *noise.CipherState) *CipherStateChaChaPoly {
+	return &CipherStateChaChaPoly{c: s.Cipher().(cipher.AEAD)}
+}
+
+func (s *CipherStateChaChaPoly) EncryptDanger(out, ad, plaintext []byte, n uint64, nb []byte) ([]byte, error) {
+	if s == nil {
+		return nil, errors.New("no cipher state available to encrypt")
+	}
+	nb[0] = 0
+	nb[1] = 0
+	nb[2] = 0
+	nb[3] = 0
+	binary.LittleEndian.PutUint64(nb[4:], n)
+	return s.c.Seal(out, nb, plaintext, ad), nil
+}
+
+func (s *CipherStateChaChaPoly) DecryptDanger(out, ad, ciphertext []byte, n uint64, nb []byte) ([]byte, error) {
+	if s == nil {
+		return []byte{}, nil
+	}
+	nb[0] = 0
+	nb[1] = 0
+	nb[2] = 0
+	nb[3] = 0
+	binary.LittleEndian.PutUint64(nb[4:], n)
+	return s.c.Open(out, nb, ciphertext, ad)
+}
+
+func (s *CipherStateChaChaPoly) Overhead() int {
+	if s == nil {
+		return 0
+	}
+	return s.c.Overhead()
+}