crypto/fips140: new package

This package holds only the Enabled() function.

Updates #70123

Change-Id: If0e731724d9997001fa52002fa6ae72df4eb16ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/631017
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>

api/next/70123.txt

@@ -0,0 +1 @@
+pkg crypto/fips140, func Enabled() bool #70123

doc/next/6-stdlib/99-minor/crypto/fips140/70123.md

@@ -0,0 +1 @@
+<!-- FIPS 140 will be covered in its own section. -->

src/crypto/fips140/fips140.go

@@ -0,0 +1,33 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fips140
+
+import (
+	"crypto/internal/fips140"
+	"crypto/internal/fips140/check"
+	"internal/godebug"
+)
+
+var fips140GODEBUG = godebug.New("#fips140")
+
+// Enabled reports whether the cryptography libraries are operating in FIPS
+// 140-3 mode.
+//
+// It can be controlled at runtime using the GODEBUG setting "fips140". If set
+// to "on", FIPS 140-3 mode is enabled. If set to "only", non-approved
+// cryptography functions will additionally return errors or panic.
+//
+// This can't be changed after the program has started.
+func Enabled() bool {
+	godebug := fips140GODEBUG.Value()
+	currentlyEnabled := godebug == "on" || godebug == "only" || godebug == "debug"
+	if currentlyEnabled != fips140.Enabled {
+		panic("crypto/fips140: GODEBUG setting changed after program start")
+	}
+	if fips140.Enabled && !check.Enabled() {
+		panic("crypto/fips140: FIPS 140-3 mode enabled, but integrity check didn't pass")
+	}
+	return fips140.Enabled
+}

src/go/build/deps_test.go

@@ -491,6 +491,8 @@ var depsRules = `
 
 	FIPS, sync/atomic < crypto/tls/internal/fips140tls;
 
+	FIPS, internal/godebug < crypto/fips140;
+
 	NONE < crypto/internal/boring/sig, crypto/internal/boring/syso;
 	sync/atomic < crypto/internal/boring/bcache, crypto/internal/boring/fips140tls;
 	crypto/internal/boring/sig, crypto/tls/internal/fips140tls < crypto/tls/fipsonly;