Support native Golang "fips140" mode (#1696)

Add support for the "fips140" mode of Go:

- https://go.dev/doc/security/fips140
- https://csrc.nist.gov/projects/cryptographic-module-validation-program/certificate/5247

You can build with `make fips140`, see the README changes for more info.

Some differences from the boringcrypto builds:

- We switch to using `go:linkname crypto/tls.aeadAESGCMTLS13`, which gives us the fips implementation for both `boringcrypto` and `fips140` modes. This means we also no longer need `-checklinkname=0`
- Go native `fips140` doesn't need CGO_ENABLED=1
- We decide if we should use the fips140 GCM at runtime, if `fips140.Enabled()` is true. If you use the `make release-fips140`, we build with build tag `fips140enforce` which ensures the binary is running with fips140 enabled and that only P256 / AES-GCM is being used. If you don't want this enforce mode, you can build without the build tag.

noiseutil/boring.go

@@ -4,77 +4,16 @@
 package noiseutil
 
 import (
-	"crypto/aes"
-	"crypto/cipher"
-	"encoding/binary"
-
-	// unsafe needed for go:linkname
-	_ "unsafe"
+	"crypto/boring"
 
 	"github.com/flynn/noise"
 )
 
+var CipherAESGCM noise.CipherFunc = CipherAESGCMFIPS140
+
 // 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
 
-// NewGCMTLS is no longer exposed in go1.19+, so we need to link it in
-// See: https://github.com/golang/go/issues/56326
-//
-// NewGCMTLS is the internal method used with boringcrypto that provides a
-// validated mode of AES-GCM which enforces the nonce is strictly
-// monotonically increasing.  This is the TLS 1.2 specification for nonce
-// generation (which also matches the method used by the Noise Protocol)
-//
-// - https://github.com/golang/go/blob/go1.19/src/crypto/tls/cipher_suites.go#L520-L522
-// - https://github.com/golang/go/blob/go1.19/src/crypto/internal/boring/aes.go#L235-L237
-// - https://github.com/golang/go/blob/go1.19/src/crypto/internal/boring/aes.go#L250
-// - https://github.com/google/boringssl/blob/ae223d6138807a13006342edfeef32e813246b39/include/openssl/aead.h#L379-L381
-// - https://github.com/google/boringssl/blob/ae223d6138807a13006342edfeef32e813246b39/crypto/fipsmodule/cipher/e_aes.c#L1082-L1093
-//
-//go:linkname newGCMTLS crypto/internal/boring.NewGCMTLS
-func newGCMTLS(c cipher.Block) (cipher.AEAD, error)
-
-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 NewGCMTLS when GoBoring is present)
-var CipherAESGCM noise.CipherFunc = cipherFn{cipherAESGCMBoring, "AESGCM"}
-
-func cipherAESGCMBoring(k [32]byte) noise.Cipher {
-	c, err := aes.NewCipher(k[:])
-	if err != nil {
-		panic(err)
-	}
-	gcm, err := newGCMTLS(c)
-	if err != nil {
-		panic(err)
-	}
-	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)
-}
+var boringEnabled = boring.Enabled()