WIP support new Go fips140 module

This will replace boring crypto at some point.

We should modify our protocol a bit and instead change to
NewGCMWithRandomNonce.

noiseutil/fips140.go

@@ -0,0 +1,64 @@
+//go:build fips140
+// +build fips140
+
+package noiseutil
+
+import (
+	"crypto/cipher"
+	"encoding/binary"
+
+	// unsafe needed for go:linkname
+	_ "unsafe"
+
+	"github.com/flynn/noise"
+)
+
+// EncryptLockNeeded indicates if calls to Encrypt need a lock
+// This is true for boringcrypto because the Seal function verifies that the
+// nonce is strictly increasing.
+const EncryptLockNeeded = true
+
+//go:linkname aeadAESGCM crypto/tls.aeadAESGCM
+func aeadAESGCM(key, noncePrefix []byte) cipher.AEAD
+
+type cipherFn struct {
+	fn   func([32]byte) noise.Cipher
+	name string
+}
+
+func (c cipherFn) Cipher(k [32]byte) noise.Cipher { return c.fn(k) }
+func (c cipherFn) CipherName() string             { return c.name }
+
+// CipherAESGCM is the AES256-GCM AEAD cipher (using aeadAESGCM when fips140 is enabled)
+var CipherAESGCM noise.CipherFunc = cipherFn{cipherAESGCM, "AESGCM"}
+
+var emptyPrefix = []byte{0, 0, 0, 0}
+
+func cipherAESGCM(k [32]byte) noise.Cipher {
+	// c, err := aes.NewCipher(k[:])
+	// if err != nil {
+	// 	panic(err)
+	// }
+	gcm := aeadAESGCM(k[:], emptyPrefix)
+	return aeadCipher{
+		gcm,
+		func(n uint64) []byte {
+			var nonce [12]byte
+			binary.BigEndian.PutUint64(nonce[4:], n)
+			return nonce[:]
+		},
+	}
+}
+
+type aeadCipher struct {
+	cipher.AEAD
+	nonce func(uint64) []byte
+}
+
+func (c aeadCipher) Encrypt(out []byte, n uint64, ad, plaintext []byte) []byte {
+	return c.Seal(out, c.nonce(n), plaintext, ad)
+}
+
+func (c aeadCipher) Decrypt(out []byte, n uint64, ad, ciphertext []byte) ([]byte, error) {
+	return c.Open(out, c.nonce(n), ciphertext, ad)
+}