fileca: add support for intermedate CA

Signed-off-by: Nathan Smith <nathan@nfsmith.ca>

pkg/ca/fileca/fileca.go

@@ -16,6 +16,7 @@
 package fileca
 
 import (
+	"bytes"
 	"context"
 	"crypto"
 	"crypto/rand"
@@ -32,8 +33,8 @@ import (
 type fileCA struct {
 	sync.RWMutex
 
-	cert *x509.Certificate
-	key  crypto.Signer
+	certs []*x509.Certificate
+	key   crypto.Signer
 }
 
 // NewFileCA returns a file backed certificate authority. Expects paths to a
@@ -43,7 +44,7 @@ func NewFileCA(certPath, keyPath, keyPass string, watch bool) (ca.CertificateAut
 	var fca fileCA
 
 	var err error
-	fca.cert, fca.key, err = loadKeyPair(certPath, keyPath, keyPass)
+	fca.certs, fca.key, err = loadKeyPair(certPath, keyPath, keyPass)
 	if err != nil {
 		return nil, err
 	}
@@ -68,21 +69,21 @@ func NewFileCA(certPath, keyPath, keyPass string, watch bool) (ca.CertificateAut
 	return &fca, err
 }
 
-func (fca *fileCA) updateX509KeyPair(cert *x509.Certificate, key crypto.Signer) {
+func (fca *fileCA) updateX509KeyPair(certs []*x509.Certificate, key crypto.Signer) {
 	fca.Lock()
 	defer fca.Unlock()
 
 	// NB: We use the RWLock to unsure a reading thread can't get a mismatching
 	// cert / key pair by reading the attributes halfway through the update
 	// below.
-	fca.cert = cert
+	fca.certs = certs
 	fca.key = key
 }
 
 func (fca *fileCA) getX509KeyPair() (*x509.Certificate, crypto.Signer) {
 	fca.RLock()
 	defer fca.RUnlock()
-	return fca.cert, fca.key
+	return fca.certs[0], fca.key
 }
 
 // CreateCertificate issues code signing certificates
@@ -103,8 +104,19 @@ func (fca *fileCA) CreateCertificate(_ context.Context, subject *challenges.Chal
 }
 
 func (fca *fileCA) Root(ctx context.Context) ([]byte, error) {
-	return pem.EncodeToMemory(&pem.Block{
-		Type:  "CERTIFICATE",
-		Bytes: fca.cert.Raw,
-	}), nil
+	fca.RLock()
+	defer fca.RUnlock()
+
+	buf := new(bytes.Buffer)
+	for _, cert := range fca.certs {
+		err := pem.Encode(buf, &pem.Block{
+			Type:  "CERTIFICATE",
+			Bytes: cert.Raw,
+		})
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
 }

pkg/ca/fileca/load.go

@@ -27,21 +27,64 @@ import (
 	"go.step.sm/crypto/pemutil"
 )
 
-func loadKeyPair(certPath, keyPath, keyPass string) (*x509.Certificate, crypto.Signer, error) {
+func loadKeyPair(certPath, keyPath, keyPass string) ([]*x509.Certificate, crypto.Signer, error) {
 
 	var (
-		cert *x509.Certificate
-		err  error
-		key  crypto.Signer
+		certs []*x509.Certificate
+		err   error
+		key   crypto.Signer
 	)
 
-	// TODO: Load chain of certs (intermediates and root) instead of just one
-	// certificate.
-	cert, err = pemutil.ReadCertificate(certPath)
+	// NB: certs are ordered from leaf at certs[0] to root at
+	// certs[len(certs)-1]
+	certs, err = pemutil.ReadCertificateBundle(certPath)
 	if err != nil {
 		return nil, nil, err
 	}
 
+	// Verify certificate chain
+	{
+		roots := x509.NewCertPool()
+		roots.AddCert(certs[len(certs)-1])
+
+		intermediates := x509.NewCertPool()
+		if len(certs) > 2 {
+			for _, intermediate := range certs[1 : len(certs)-1] {
+				intermediates.AddCert(intermediate)
+			}
+		}
+
+		opts := x509.VerifyOptions{
+			Roots:         roots,
+			Intermediates: intermediates,
+			KeyUsages: []x509.ExtKeyUsage{
+				x509.ExtKeyUsageCodeSigning,
+			},
+		}
+		if _, err := certs[0].Verify(opts); err != nil {
+			return nil, nil, err
+		}
+
+		if !certs[0].IsCA {
+			return nil, nil, errors.New(`fileca: certificate is not a CA`)
+		}
+
+		// If using an intermediate, verify that code signing extended key
+		// usage is set to satify extended key usage chainging
+		if len(certs) > 1 {
+			var hasExtKeyUsageCodeSigning bool
+			for _, extKeyUsage := range certs[0].ExtKeyUsage {
+				if extKeyUsage == x509.ExtKeyUsageCodeSigning {
+					hasExtKeyUsageCodeSigning = true
+					break
+				}
+			}
+			if !hasExtKeyUsageCodeSigning {
+				return nil, nil, errors.New(`fileca: certificate must have extended key usage code signing set to sign code signing certificates`)
+			}
+		}
+	}
+
 	{
 		opaqueKey, err := pemutil.Read(keyPath, pemutil.WithPassword([]byte(keyPass)))
 		if err != nil {
@@ -55,15 +98,11 @@ func loadKeyPair(certPath, keyPath, keyPass string) (*x509.Certificate, crypto.S
 		}
 	}
 
-	if !valid(cert, key) {
+	if !valid(certs[0], key) {
 		return nil, nil, errors.New(`fileca: certificate public key and private key don't match`)
 	}
 
-	if !cert.IsCA {
-		return nil, nil, errors.New(`fileca: certificate is not a CA`)
-	}
-
-	return cert, key, nil
+	return certs, key, nil
 }
 
 func valid(cert *x509.Certificate, key crypto.Signer) bool {

pkg/ca/fileca/load_test.go

@@ -25,6 +25,8 @@ func TestValidLoadKeyPair(t *testing.T) {
 		"ecdsa",
 		"ed25519",
 		"rsa4096",
+		"openssl",
+		"intermediate",
 	}
 
 	for _, keypair := range keypairs {
@@ -42,6 +44,7 @@ func TestInvalidLoadKeyPair(t *testing.T) {
 	keypairs := []string{
 		"notca",
 		"mismatch",
+		"eku-chaining-violation",
 	}
 
 	for _, keypair := range keypairs {

pkg/ca/fileca/testdata/ecdsa-cert.pem

@@ -1,12 +1,11 @@
 -----BEGIN CERTIFICATE-----
-MIIBxzCCAU6gAwIBAgIUbQqE8rDPWDqJexmvpaeamgZe/HIwCgYIKoZIzj0EAwIw
-EDEOMAwGA1UEAwwFZWNkc2EwIBcNMjExMjIxMTkxMzI2WhgPMjEyMTExMjcxOTEz
-MjZaMBAxDjAMBgNVBAMMBWVjZHNhMHYwEAYHKoZIzj0CAQYFK4EEACIDYgAEMV9i
-0e3Ld1eQy9UXII5MOymw2IFBo288zuOMeH+7w0ejJlY0PFowY4rItKIhqRIWOqFA
-luSaVC59sKsqjsiLdQQW2CV19eYFhVvYQS1S2QaROpFA5Zt8ALOACyp5s+6+o2cw
-ZTAdBgNVHQ4EFgQU3QF9mKDrefmeiE3lqC46PSmhEOkwHwYDVR0jBBgwFoAU3QF9
-mKDrefmeiE3lqC46PSmhEOkwDwYDVR0TAQH/BAUwAwEB/zASBgNVHRMBAf8ECDAG
-AQH/AgEBMAoGCCqGSM49BAMCA2cAMGQCMAQ/g18eRvqITDZEKdzf4bI4qKF/ZbVL
-GTZ+2HHZYwDvsuHeznTl1Uq1stzmySi4owIwV1jCF8f4gikxT0XCF+u1CJlVYiZP
-tyRnLdZaKl/seNUmBO0RRR72tsRd/X1QR3NK
+MIIBojCCASigAwIBAgIQdN97RoNpSe/j6zMPBRiEjTAKBggqhkjOPQQDAzAQMQ4w
+DAYDVQQDEwVlY2RzYTAgFw0yMjAxMTUyMTM5NDZaGA8yMTIxMTIyMjIxMzk0Nlow
+EDEOMAwGA1UEAxMFZWNkc2EwdjAQBgcqhkjOPQIBBgUrgQQAIgNiAAQkL81PCeoj
+XHCTnkv5DtkFiTR14i9ud+xMTCURLDlxBXk1fBywg1o3P6vHzYZpyEVRligoxELH
+cPyY1xx4B0es6PJKlN95WoLYZXW10Y5R1aahTxVYSv+kEztt8Syp3zGjRTBDMA4G
+A1UdDwEB/wQEAwIBBjASBgNVHRMBAf8ECDAGAQH/AgEBMB0GA1UdDgQWBBS+Jr+X
+Ci1VSjK6/sMMTsQcX6K1MDAKBggqhkjOPQQDAwNoADBlAjEA8swYU8cQcmTLa7Y7
+/yyzpQ6Z+Xwts5d2U9jxvsUchietQfMAjTTZfqF/WZRMLRvwAjBciWw9cL9PUzG3
+1RD+fH+Z8RKcxs2A1NboUcfVEiYbQ3XSZlDX0GhjguI4xgdL6DY=
 -----END CERTIFICATE-----

pkg/ca/fileca/testdata/ecdsa-key.pem

@@ -1,8 +1,9 @@
------BEGIN ENCRYPTED PRIVATE KEY-----
-MIIBEzBOBgkqhkiG9w0BBQ0wQTApBgkqhkiG9w0BBQwwHAQIGCeFiJ2rs3wCAggA
-MAwGCCqGSIb3DQIJBQAwFAYIKoZIhvcNAwcECGZQSOBsvcjqBIHAGdU9wj136ikM
-QUqJqDt5oSDKJAU2Yrv+pCRLz6VENGUvxFrPsn9fbjSt69fSZMm09mITfEg1eLO4
-9LDl7PW1Bza803IXKQnZ0xnRUkkY1GQfDtQEGCYFaojRpYNLmmSiHpeFrqAPz83K
-+oXsRTwuRkDrABNpwTCEXYVmcHUmk9NqC6E2qjmYOyDx0ktA4HG62H3/cpGZleBs
-l58oyOg658erxF1rnASN15lw9/1g0lWACsXsMgbkjDnY51LU71pR
------END ENCRYPTED PRIVATE KEY-----
+-----BEGIN EC PRIVATE KEY-----
+Proc-Type: 4,ENCRYPTED
+DEK-Info: AES-256-CBC,4a2a1826bd853f1c2c0117902551c0a9
+
+Flk9LwvoP6yjUQQlr57AMLN2NN6VKV1hnPQ8art2O2aXidLqwgi2ZcpfIuCGuAJn
+zcOXJAiXmkvOzWnXkDRW5xmzsuwVp1RzwkF/DbmleO+Bw4SdylOB4OJj2Pu0huv2
+hH+xcym5XdsclLn8gOZZBH01i23oH+O/poHE9JjxnxWX0wALovghbvGMoPiz9unn
+JVH9OewvTL8JINsr6vmDMyOX0D+GIAvYmTF518U+ykA=
+-----END EC PRIVATE KEY-----

pkg/ca/fileca/testdata/ed25519-cert.pem

@@ -1,10 +1,9 @@
 -----BEGIN CERTIFICATE-----
-MIIBTzCCAQGgAwIBAgIUeObF4LopbObr0zVOX7BAZbvy4MswBQYDK2VwMBIxEDAO
-BgNVBAMMB2VkMjU1MTkwIBcNMjExMjIxMTkxMzI2WhgPMjEyMTExMjcxOTEzMjZa
-MBIxEDAOBgNVBAMMB2VkMjU1MTkwKjAFBgMrZXADIQBNNJP9Ys+Sx0Cx/c5pQNAF
-cuECdESA0vB2IqXVAG5OiaNnMGUwHQYDVR0OBBYEFJEGm0OzRNsdBVLdDBCcx21i
-nEySMB8GA1UdIwQYMBaAFJEGm0OzRNsdBVLdDBCcx21inEySMA8GA1UdEwEB/wQF
-MAMBAf8wEgYDVR0TAQH/BAgwBgEB/wIBATAFBgMrZXADQQD6quk/tnnZpFgabR2Q
-4WCweJfZ4NfrhMOVvAPdECW/P57NH0P2BUSOK+/DktOBFIjLUWG6ptRExHDcRsFm
-WTsA
+MIIBKTCB3KADAgECAhEAlbs/LTFVoOGgJ4IoVq5VbDAFBgMrZXAwEjEQMA4GA1UE
+AxMHZWQyNTUxOTAgFw0yMjAxMTUyMTM5NDRaGA8yMTIxMTIyMjIxMzk0NFowEjEQ
+MA4GA1UEAxMHZWQyNTUxOTAqMAUGAytlcAMhACrmjkFJH7p3ZV3xJhXAVZtUK4Wb
+8SQI3xxkYf+zjdEzo0UwQzAOBgNVHQ8BAf8EBAMCAQYwEgYDVR0TAQH/BAgwBgEB
+/wIBATAdBgNVHQ4EFgQUgjQqhKp/TfTOGOMJUUqd5j/SWRgwBQYDK2VwA0EAFJtY
+O7Xb2hUvJOtimrx1Ag3l+aDcgSA8DHT+ibqInGAVhUghkyEmbWv055FQSiIX46Zt
+lo9wHPvcSE7LMoa8AA==
 -----END CERTIFICATE-----

pkg/ca/fileca/testdata/ed25519-key.pem

@@ -1,5 +1,6 @@
 -----BEGIN ENCRYPTED PRIVATE KEY-----
-MIGKME4GCSqGSIb3DQEFDTBBMCkGCSqGSIb3DQEFDDAcBAggWEDSFylYswICCAAw
-DAYIKoZIhvcNAgkFADAUBggqhkiG9w0DBwQIaecFy/8IbAYEOHb3xUdAVad3ZcXk
-dkwJjtPNP2t2PA/6ngVgfsx2dgqKBhjg9JXG98Yw2eeYqJsbZ4jrHAJK0l8E
+MIGkMGAGCSqGSIb3DQEFDTBTMDIGCSqGSIb3DQEFDDAlBBC5ebV8jVzdeumTeg0K
+1YR4AgMBhqAwDAYIKoZIhvcNAgkAADAdBglghkgBZQMEASoEEIN6WmojJPzZuNxj
+mmET4yYEQGSmy/JMfleTGL9FHT/f6dvV2xcHAJ2aFaNy8/JPLbcV9QgHAc2ze2+e
+CPumY7wCCcdvRsMXgxFSsivigqhiPIE=
 -----END ENCRYPTED PRIVATE KEY-----

pkg/ca/fileca/testdata/eku-chaining-violation-cert.pem

@@ -0,0 +1,31 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBcjCCARegAwIBAgIQJFdlkkJeEz/Nx4qDHVBpOTAKBggqhkjOPQQDAjAPMQ0w
+CwYDVQQDEwRyb290MB4XDTIyMDExNTIxMzk1NVoXDTIyMDExNjIxMzk1NVowGDEW
+MBQGA1UEAxMNaW50ZXJtZWRpYXRlMTAqMAUGAytlcAMhAPKV6IWCMdQ/n1VcdgSh
+lC5MH/m7uilfelOMN9tDpYUZo3sweTAOBgNVHQ8BAf8EBAMCAQYwEwYDVR0lBAww
+CgYIKwYBBQUHAwMwEgYDVR0TAQH/BAgwBgEB/wIBATAdBgNVHQ4EFgQUBaizUbdN
+6AIQBe9r8kSqadH3OIswHwYDVR0jBBgwFoAUpzPc0nDf/4hdxMCkLvk6Y9KsJJQw
+CgYIKoZIzj0EAwIDSQAwRgIhAJM0z+Z8fTtHz0M4nDaCDJsKRLCpfoSZ/i8TtD/I
+J65qAiEA6UudGaQGnEPQjW4QSiFJkD/E2vHxAu0SkSxV1UjGv30=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBYTCCAQagAwIBAgIPSynyoAutDD5fyCjqMj5xMAoGCCqGSM49BAMCMA8xDTAL
+BgNVBAMTBHJvb3QwHhcNMjIwMTE1MjEzOTU1WhcNMjIwMTE2MjEzOTU1WjAPMQ0w
+CwYDVQQDEwRyb290MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEOAKo0hjeKCzW
+q3rW/g30/42ltirz39aKQElOe83sgJ8N63t3j7yvhSQ+5puIE83Q9Vb98fteVe+y
+Izy9RoKyI6NFMEMwDgYDVR0PAQH/BAQDAgEGMBIGA1UdEwEB/wQIMAYBAf8CAQIw
+HQYDVR0OBBYEFKcz3NJw3/+IXcTApC75OmPSrCSUMAoGCCqGSM49BAMCA0kAMEYC
+IQCifL/yAa+bBBc04p5/nrp0riyVQTWT4l9YzWYZCTHrjAIhALemgiIT1bV3hRgN
+iHHAj9HfVuFpQwTfwtlOyo5wvL5o
+-----END CERTIFICATE-----

pkg/ca/fileca/testdata/eku-chaining-violation-key.pem

@@ -0,0 +1,8 @@
+-----BEGIN EC PRIVATE KEY-----
+Proc-Type: 4,ENCRYPTED
+DEK-Info: AES-256-CBC,226887dd5435da96ca6b5563dc3a3a04
+
+9Rb2H57DxtFouMfwLSJw1upKHnD44xorC1fj2CttqT3kYv7MX+O+8WqzDZHeY4Vh
+DiWEhXt89FnH+JOkGY8t0WnrbIHxwzVlkA8Y8vaaC+hf2V8gYJJP4uVdeZAqQH6W
+/ywHRU6k0Ok2W+nQcT+X/nupMN6gBf/4+dptYlwNPsk=
+-----END EC PRIVATE KEY-----