did: simplify public API, add missing required algorithm

did/crypto.go

@@ -1,6 +1,7 @@
 package did
 
 import (
+	"crypto/rand"
 	"errors"
 
 	crypto "github.com/libp2p/go-libp2p/core/crypto"
@@ -9,6 +10,42 @@ import (
 	"github.com/multiformats/go-varint"
 )
 
+// GenerateEd25519 generates an Ed25519 private key and the matching DID.
+// This is the RECOMMENDED algorithm.
+func GenerateEd25519() (crypto.PrivKey, DID, error) {
+	priv, pub, err := crypto.GenerateEd25519Key(rand.Reader)
+	if err != nil {
+		return nil, Undef, nil
+	}
+	did, err := FromPubKey(pub)
+	return priv, did, err
+}
+
+// GenerateRSA generates a RSA private key and the matching DID.
+func GenerateSecp256k1() (crypto.PrivKey, DID, error) {
+	// NIST Special Publication 800-57 Part 1 Revision 5
+	// Section 5.6.1.1 (Table 2)
+	// Paraphrased: 2048-bit RSA keys are secure until 2030 and 3072-bit keys are recommended for longer-term security.
+	const keyLength = 3072
+
+	priv, pub, err := crypto.GenerateRSAKeyPair(keyLength, rand.Reader)
+	if err != nil {
+		return nil, Undef, nil
+	}
+	did, err := FromPubKey(pub)
+	return priv, did, err
+}
+
+// GenerateEd25519 generates a Secp256k1 private key and the matching DID.
+func GenerateRSA() (crypto.PrivKey, DID, error) {
+	priv, pub, err := crypto.GenerateSecp256k1Key(rand.Reader)
+	if err != nil {
+		return nil, Undef, nil
+	}
+	did, err := FromPubKey(pub)
+	return priv, did, err
+}
+
 func FromPrivKey(privKey crypto.PrivKey) (DID, error) {
 	return FromPubKey(privKey.GetPublic())
 }
@@ -21,20 +58,17 @@ func FromPubKey(pubKey crypto.PubKey) (DID, error) {
 		pb.KeyType_ECDSA:     multicodec.Es256,
 	}[pubKey.Type()]
 	if !ok {
-		return Undef, errors.New("Blah")
+		return Undef, errors.New("unsupported key type")
 	}
 
-	buf := varint.ToUvarint(uint64(code))
-
 	pubBytes, err := pubKey.Raw()
 	if err != nil {
 		return Undef, err
 	}
 
 	return DID{
-		str:  string(append(buf, pubBytes...)),
-		code: uint64(code),
-		key:  true,
+		code:  code,
+		bytes: string(append(varint.ToUvarint(uint64(code)), pubBytes...)),
 	}, nil
 }