openpgp: replace "currentTime" with "creationTime" as appropriate

RFC 4880 uses the term "creation time" to refer to when keys and
signatures are created, and this is partially followed already. This
CL applies it to the rest of places that were using "currentTime"
instead.

Change-Id: I8a83604b53a240689327defd89e22ddbebe3b679
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/175446
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

openpgp/keys.go

@@ -504,7 +504,7 @@ const defaultRSAKeyBits = 2048
 // which may be empty but must not contain any of "()<>\x00".
 // If config is nil, sensible defaults will be used.
 func NewEntity(name, comment, email string, config *packet.Config) (*Entity, error) {
-	currentTime := config.Now()
+	creationTime := config.Now()
 
 	bits := defaultRSAKeyBits
 	if config != nil && config.RSABits != 0 {
@@ -525,8 +525,8 @@ func NewEntity(name, comment, email string, config *packet.Config) (*Entity, err
 	}
 
 	e := &Entity{
-		PrimaryKey: packet.NewRSAPublicKey(currentTime, &signingPriv.PublicKey),
-		PrivateKey: packet.NewRSAPrivateKey(currentTime, signingPriv),
+		PrimaryKey: packet.NewRSAPublicKey(creationTime, &signingPriv.PublicKey),
+		PrivateKey: packet.NewRSAPrivateKey(creationTime, signingPriv),
 		Identities: make(map[string]*Identity),
 	}
 	isPrimaryId := true
@@ -534,7 +534,7 @@ func NewEntity(name, comment, email string, config *packet.Config) (*Entity, err
 		Name:   uid.Id,
 		UserId: uid,
 		SelfSignature: &packet.Signature{
-			CreationTime: currentTime,
+			CreationTime: creationTime,
 			SigType:      packet.SigTypePositiveCert,
 			PubKeyAlgo:   packet.PubKeyAlgoRSA,
 			Hash:         config.Hash(),
@@ -563,10 +563,10 @@ func NewEntity(name, comment, email string, config *packet.Config) (*Entity, err
 
 	e.Subkeys = make([]Subkey, 1)
 	e.Subkeys[0] = Subkey{
-		PublicKey:  packet.NewRSAPublicKey(currentTime, &encryptingPriv.PublicKey),
-		PrivateKey: packet.NewRSAPrivateKey(currentTime, encryptingPriv),
+		PublicKey:  packet.NewRSAPublicKey(creationTime, &encryptingPriv.PublicKey),
+		PrivateKey: packet.NewRSAPrivateKey(creationTime, encryptingPriv),
 		Sig: &packet.Signature{
-			CreationTime:              currentTime,
+			CreationTime:              creationTime,
 			SigType:                   packet.SigTypeSubkeyBinding,
 			PubKeyAlgo:                packet.PubKeyAlgoRSA,
 			Hash:                      config.Hash(),