V2 certificate format (#1216)

Co-authored-by: Nate Brown <nbrown.us@gmail.com>
Co-authored-by: Jack Doan <jackdoan@rivian.com>
Co-authored-by: brad-defined <77982333+brad-defined@users.noreply.github.com>
Co-authored-by: Jack Doan <me@jackdoan.com>

cert/sign.go

@@ -1,11 +1,15 @@
 package cert
 
 import (
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha256"
 	"fmt"
+	"math/big"
 	"net/netip"
 	"time"
-
-	"github.com/slackhq/nebula/pkclient"
 )
 
 // TBSCertificate represents a certificate intended to be signed.
@@ -24,28 +28,61 @@ type TBSCertificate struct {
 	issuer         string
 }
 
+type beingSignedCertificate interface {
+	// fromTBSCertificate copies the values from the TBSCertificate to this versions internal representation
+	// Implementations must validate the resulting certificate contains valid information
+	fromTBSCertificate(*TBSCertificate) error
+
+	// marshalForSigning returns the bytes that should be signed
+	marshalForSigning() ([]byte, error)
+
+	// setSignature sets the signature for the certificate that has just been signed. The signature must not be blank.
+	setSignature([]byte) error
+}
+
+type SignerLambda func(certBytes []byte) ([]byte, error)
+
 // Sign will create a sealed certificate using details provided by the TBSCertificate as long as those
 // details do not violate constraints of the signing certificate.
 // If the TBSCertificate is a CA then signer must be nil.
 func (t *TBSCertificate) Sign(signer Certificate, curve Curve, key []byte) (Certificate, error) {
-	return t.sign(signer, curve, key, nil)
-}
-
-func (t *TBSCertificate) SignPkcs11(signer Certificate, curve Curve, client *pkclient.PKClient) (Certificate, error) {
-	if curve != Curve_P256 {
-		return nil, fmt.Errorf("only P256 is supported by PKCS#11")
+	switch t.Curve {
+	case Curve_CURVE25519:
+		pk := ed25519.PrivateKey(key)
+		sp := func(certBytes []byte) ([]byte, error) {
+			sig := ed25519.Sign(pk, certBytes)
+			return sig, nil
+		}
+		return t.SignWith(signer, curve, sp)
+	case Curve_P256:
+		pk := &ecdsa.PrivateKey{
+			PublicKey: ecdsa.PublicKey{
+				Curve: elliptic.P256(),
+			},
+			// ref: https://github.com/golang/go/blob/go1.19/src/crypto/x509/sec1.go#L95
+			D: new(big.Int).SetBytes(key),
+		}
+		// ref: https://github.com/golang/go/blob/go1.19/src/crypto/x509/sec1.go#L119
+		pk.X, pk.Y = pk.Curve.ScalarBaseMult(key)
+		sp := func(certBytes []byte) ([]byte, error) {
+			// We need to hash first for ECDSA
+			// - https://pkg.go.dev/crypto/ecdsa#SignASN1
+			hashed := sha256.Sum256(certBytes)
+			return ecdsa.SignASN1(rand.Reader, pk, hashed[:])
+		}
+		return t.SignWith(signer, curve, sp)
+	default:
+		return nil, fmt.Errorf("invalid curve: %s", t.Curve)
 	}
-
-	return t.sign(signer, curve, nil, client)
 }
 
-func (t *TBSCertificate) sign(signer Certificate, curve Curve, key []byte, client *pkclient.PKClient) (Certificate, error) {
+// SignWith does the same thing as sign, but uses the function in `sp` to calculate the signature.
+// You should only use SignWith if you do not have direct access to your private key.
+func (t *TBSCertificate) SignWith(signer Certificate, curve Curve, sp SignerLambda) (Certificate, error) {
 	if curve != t.Curve {
 		return nil, fmt.Errorf("curve in cert and private key supplied don't match")
 	}
 
-	//TODO: make sure we have all minimum properties to sign, like a public key
-
 	if signer != nil {
 		if t.IsCA {
 			return nil, fmt.Errorf("can not sign a CA certificate with another")
@@ -67,10 +104,64 @@ func (t *TBSCertificate) sign(signer Certificate, curve Curve, key []byte, clien
 		}
 	}
 
+	var c beingSignedCertificate
 	switch t.Version {
 	case Version1:
-		return signV1(t, curve, key, client)
+		c = &certificateV1{}
+		err := c.fromTBSCertificate(t)
+		if err != nil {
+			return nil, err
+		}
+	case Version2:
+		c = &certificateV2{}
+		err := c.fromTBSCertificate(t)
+		if err != nil {
+			return nil, err
+		}
 	default:
 		return nil, fmt.Errorf("unknown cert version %d", t.Version)
 	}
+
+	certBytes, err := c.marshalForSigning()
+	if err != nil {
+		return nil, err
+	}
+
+	sig, err := sp(certBytes)
+	if err != nil {
+		return nil, err
+	}
+
+	err = c.setSignature(sig)
+	if err != nil {
+		return nil, err
+	}
+
+	sc, ok := c.(Certificate)
+	if !ok {
+		return nil, fmt.Errorf("invalid certificate")
+	}
+
+	return sc, nil
+}
+
+func comparePrefix(a, b netip.Prefix) int {
+	addr := a.Addr().Compare(b.Addr())
+	if addr == 0 {
+		return a.Bits() - b.Bits()
+	}
+	return addr
+}
+
+// findDuplicatePrefix returns an error if there is a duplicate prefix in the pre-sorted input slice sortedPrefixes
+func findDuplicatePrefix(sortedPrefixes []netip.Prefix) error {
+	if len(sortedPrefixes) < 2 {
+		return nil
+	}
+	for i := 1; i < len(sortedPrefixes); i++ {
+		if comparePrefix(sortedPrefixes[i], sortedPrefixes[i-1]) == 0 {
+			return NewErrInvalidCertificateProperties("duplicate network detected: %v", sortedPrefixes[i])
+		}
+	}
+	return nil
 }