[dev.boringcrypto] crypto/tls/fipsonly: new package to force FIPS-allowed TLS settings

Change-Id: I3268cab2de8aed9e2424e9c3bc7667083bc5e1ce
Reviewed-on: https://go-review.googlesource.com/65250
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

boring.go

@@ -0,0 +1,121 @@
+// Copyright 2017 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 tls
+
+import (
+	"crypto/ecdsa"
+	"crypto/internal/boring/fipstls"
+	"crypto/rsa"
+	"crypto/x509"
+)
+
+// needFIPS returns fipstls.Required(); it avoids a new import in common.go.
+func needFIPS() bool {
+	return fipstls.Required()
+}
+
+// fipsMinVersion replaces c.minVersion in FIPS-only mode.
+func fipsMinVersion(c *Config) uint16 {
+	// FIPS requires TLS 1.2.
+	return VersionTLS12
+}
+
+// fipsMaxVersion replaces c.maxVersion in FIPS-only mode.
+func fipsMaxVersion(c *Config) uint16 {
+	// FIPS requires TLS 1.2.
+	return VersionTLS12
+}
+
+// default defaultFIPSCurvePreferences is the FIPS-allowed curves,
+// in preference order (most preferable first).
+var defaultFIPSCurvePreferences = []CurveID{CurveP256, CurveP384, CurveP521}
+
+// fipsCurvePreferences replaces c.curvePreferences in FIPS-only mode.
+func fipsCurvePreferences(c *Config) []CurveID {
+	if c == nil || len(c.CurvePreferences) == 0 {
+		return defaultFIPSCurvePreferences
+	}
+	var list []CurveID
+	for _, id := range c.CurvePreferences {
+		for _, allowed := range defaultFIPSCurvePreferences {
+			if id == allowed {
+				list = append(list, id)
+				break
+			}
+		}
+	}
+	return list
+}
+
+// default FIPSCipherSuites is the FIPS-allowed cipher suites,
+// in preference order (most preferable first).
+var defaultFIPSCipherSuites = []uint16{
+	TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+	TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+	TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+	TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+	TLS_RSA_WITH_AES_128_GCM_SHA256,
+	TLS_RSA_WITH_AES_256_GCM_SHA384,
+}
+
+// fipsCipherSuites replaces c.cipherSuites in FIPS-only mode.
+func fipsCipherSuites(c *Config) []uint16 {
+	if c == nil || c.CipherSuites == nil {
+		return defaultFIPSCipherSuites
+	}
+	var list []uint16
+	for _, id := range c.CipherSuites {
+		for _, allowed := range defaultFIPSCipherSuites {
+			if id == allowed {
+				list = append(list, id)
+				break
+			}
+		}
+	}
+	return list
+}
+
+// isBoringCertificate reports whether a certificate may be used
+// when constructing a verified chain.
+// It is called for each leaf, intermediate, and root certificate.
+func isBoringCertificate(c *x509.Certificate) bool {
+	if !needFIPS() {
+		// Everything is OK if we haven't forced FIPS-only mode.
+		return true
+	}
+
+	// Otherwise the key must be RSA 2048, RSA 3072, or ECDSA P-256.
+	switch k := c.PublicKey.(type) {
+	default:
+		return false
+	case *rsa.PublicKey:
+		if size := k.N.BitLen(); size != 2048 && size != 3072 {
+			return false
+		}
+	case *ecdsa.PublicKey:
+		if name := k.Curve.Params().Name; name != "P-256" && name != "P-384" {
+			return false
+		}
+	}
+
+	return true
+}
+
+// supportedSignatureAlgorithms returns the supported signature algorithms.
+// It knows that the FIPS-allowed ones are all at the beginning of
+// defaultSupportedSignatureAlgorithms.
+func supportedSignatureAlgorithms() []signatureAndHash {
+	all := defaultSupportedSignatureAlgorithms
+	if !needFIPS() {
+		return all
+	}
+	i := 0
+	for i < len(all) && all[i].hash != hashSHA1 {
+		i++
+	}
+	return all[:i]
+}
+
+var testingOnlyForceClientHelloSignatureAndHashes []signatureAndHash