[#1216] neofs-cli: Reuse key retrieving code between modules

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

cmd/neofs-cli/internal/key/nep2.go

@@ -0,0 +1,26 @@
+package key
+
+import (
+	"crypto/ecdsa"
+
+	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
+)
+
+const nep2Base58Length = 58
+
+// FromNEP2 extracts private key from NEP2-encrypted string.
+func FromNEP2(encryptedWif string) (*ecdsa.PrivateKey, error) {
+	pass, err := getPassword()
+	if err != nil {
+		printVerbose("Can't read password: %v", err)
+		return nil, ErrInvalidPassword
+	}
+
+	k, err := keys.NEP2Decrypt(encryptedWif, pass, keys.NEP2ScryptParams())
+	if err != nil {
+		printVerbose("Invalid key or password: %v", err)
+		return nil, ErrInvalidPassword
+	}
+
+	return &k.PrivateKey, nil
+}