incorporates code review from @Stebalien

crypto/key.go

-// Package crypto implements various cryptographic utilities used by libp2p.
+// Cackage crypto implements various cryptographic utilities used by libp2p.
 // This includes a Public and Private key interface and key implementations
 // for supported key algorithms.
 package crypto
 
 import (
-	"crypto"
-	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/hmac"
 	"crypto/rand"
-	"crypto/rsa"
 	"crypto/sha1"
 	"crypto/sha512"
 	"crypto/subtle"
@@ -18,14 +15,11 @@ import (
 	"fmt"
 	"hash"
 	"io"
-	"log"
 
 	pb "github.com/libp2p/go-libp2p-core/crypto/pb"
 
-	btcec "github.com/btcsuite/btcd/btcec"
 	"github.com/gogo/protobuf/proto"
 	sha256 "github.com/minio/sha256-simd"
-	"golang.org/x/crypto/ed25519"
 )
 
 const (
@@ -180,42 +174,6 @@ func GenerateEKeyPair(curveName string) ([]byte, GenSharedKey, error) {
 	return pubKey, done, nil
 }
 
-// KeyPairFromKey generates a new private and public key from an input private key
-func KeyPairFromKey(priv crypto.PrivateKey) (PrivKey, PubKey, error) {
-	if priv == nil {
-		return nil, nil, ErrNilPrivateKey
-	}
-
-	switch priv.(type) {
-	case *rsa.PrivateKey:
-		log.Println("1")
-		rPriv, _ := priv.(*rsa.PrivateKey)
-		return &RsaPrivateKey{*rPriv}, &RsaPublicKey{rPriv.PublicKey}, nil
-
-	case *ecdsa.PrivateKey:
-		log.Println("2")
-		ePriv, _ := priv.(*ecdsa.PrivateKey)
-		return &ECDSAPrivateKey{ePriv}, &ECDSAPublicKey{&ePriv.PublicKey}, nil
-
-	case *ed25519.PrivateKey:
-		log.Println("3")
-		ePriv, _ := priv.(*ed25519.PrivateKey)
-		pubIfc := ePriv.Public()
-		pub, _ := pubIfc.(ed25519.PublicKey)
-		return &Ed25519PrivateKey{*ePriv}, &Ed25519PublicKey{pub}, nil
-
-	case *btcec.PrivateKey:
-		log.Println("4")
-		bPriv, _ := priv.(*btcec.PrivateKey)
-		sPriv := Secp256k1PrivateKey(*bPriv)
-		sPub := Secp256k1PublicKey(*bPriv.PubKey())
-		return &sPriv, &sPub, nil
-
-	default:
-		return nil, nil, ErrBadKeyType
-	}
-}
-
 // StretchedKeys ...
 type StretchedKeys struct {
 	IV        []byte

crypto/key_not_openssl.go

+// +build !openssl
+
+package crypto
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/rsa"
+
+	btcec "github.com/btcsuite/btcd/btcec"
+	"golang.org/x/crypto/ed25519"
+)
+
+// KeyPairFromKey generates a new private and public key from an input private key
+func KeyPairFromKey(priv crypto.PrivateKey) (PrivKey, PubKey, error) {
+	if priv == nil {
+		return nil, nil, ErrNilPrivateKey
+	}
+
+	switch p := priv.(type) {
+	case *rsa.PrivateKey:
+		return &RsaPrivateKey{*p}, &RsaPublicKey{p.PublicKey}, nil
+
+	case *ecdsa.PrivateKey:
+		return &ECDSAPrivateKey{p}, &ECDSAPublicKey{&p.PublicKey}, nil
+
+	case *ed25519.PrivateKey:
+		pubIfc := p.Public()
+		pub, _ := pubIfc.(ed25519.PublicKey)
+		return &Ed25519PrivateKey{*p}, &Ed25519PublicKey{pub}, nil
+
+	case *btcec.PrivateKey:
+		sPriv := Secp256k1PrivateKey(*p)
+		sPub := Secp256k1PublicKey(*p.PubKey())
+		return &sPriv, &sPub, nil
+
+	default:
+		return nil, nil, ErrBadKeyType
+	}
+}

crypto/key_openssl.go

+// +build openssl
+
+package crypto
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/rsa"
+	"crypto/x509"
+
+	btcec "github.com/btcsuite/btcd/btcec"
+	openssl "github.com/libp2p/go-openssl"
+	"golang.org/x/crypto/ed25519"
+)
+
+// KeyPairFromKey generates a new private and public key from an input private key
+func KeyPairFromKey(priv crypto.PrivateKey) (PrivKey, PubKey, error) {
+	if priv == nil {
+		return nil, nil, ErrNilPrivateKey
+	}
+
+	switch p := priv.(type) {
+	case *rsa.PrivateKey:
+		pk, err := openssl.LoadPrivateKeyFromDER(x509.MarshalPKCS1PrivateKey(p))
+		if err != nil {
+			return nil, nil, err
+		}
+
+		return &opensslPrivateKey{pk}, &opensslPublicKey{pk}, nil
+
+	case *ecdsa.PrivateKey:
+		return &ECDSAPrivateKey{p}, &ECDSAPublicKey{&p.PublicKey}, nil
+
+	case *ed25519.PrivateKey:
+		pubIfc := p.Public()
+		pub, _ := pubIfc.(ed25519.PublicKey)
+		return &Ed25519PrivateKey{*p}, &Ed25519PublicKey{pub}, nil
+
+	case *btcec.PrivateKey:
+		sPriv := Secp256k1PrivateKey(*p)
+		sPub := Secp256k1PublicKey(*p.PubKey())
+		return &sPriv, &sPub, nil
+
+	default:
+		return nil, nil, ErrBadKeyType
+	}
+}