1 files changed, 63 insertions, 0 deletions
diff --git a/internal/nametransform/names_core.go b/internal/nametransform/names_core.go
new file mode 100644
index 0000000..452ab45
--- /dev/null
+++ b/internal/nametransform/names_core.go
@@ -0,0 +1,63 @@
+package nametransform
+
+// Filename encryption / decryption functions
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/base64"
+	"fmt"
+
+	"github.com/rfjakob/eme"
+)
+
+// DecryptName - decrypt base64-encoded encrypted filename "cipherName"
+// The used encryption is either CBC or EME, depending on "useEME".
+//
+// This function is exported because it allows for a very efficient readdir
+// implementation (read IV once, decrypt all names using this function).
+func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
+
+	bin, err := base64.URLEncoding.DecodeString(cipherName)
+	if err != nil {
+		return "", err
+	}
+
+	if len(bin)%aes.BlockSize != 0 {
+		return "", fmt.Errorf("Decoded length %d is not a multiple of the AES block size", len(bin))
+	}
+
+	if n.useEME {
+		bin = eme.Transform(n.cryptoCore.BlockCipher, iv, bin, eme.DirectionDecrypt)
+	} else {
+		cbc := cipher.NewCBCDecrypter(n.cryptoCore.BlockCipher, iv)
+		cbc.CryptBlocks(bin, bin)
+	}
+
+	bin, err = unPad16(bin)
+	if err != nil {
+		return "", err
+	}
+
+	plain := string(bin)
+	return plain, err
+}
+
+// encryptName - encrypt "plainName", return base64-encoded "cipherName64"
+// The used encryption is either CBC or EME, depending on "useEME".
+func (n *NameTransform) encryptName(plainName string, iv []byte) (cipherName64 string) {
+
+	bin := []byte(plainName)
+	bin = pad16(bin)
+
+	if n.useEME {
+		bin = eme.Transform(n.cryptoCore.BlockCipher, iv, bin, eme.DirectionEncrypt)
+	} else {
+		cbc := cipher.NewCBCEncrypter(n.cryptoCore.BlockCipher, iv)
+		cbc.CryptBlocks(bin, bin)
+	}
+
+	cipherName64 = base64.URLEncoding.EncodeToString(bin)
+	return cipherName64
+}
+