1 files changed, 60 insertions, 0 deletions
diff --git a/internal/nametransform/pad16.go b/internal/nametransform/pad16.go
new file mode 100644
index 0000000..c15160e
--- /dev/null
+++ b/internal/nametransform/pad16.go
@@ -0,0 +1,60 @@
+package nametransform
+
+import (
+	"fmt"
+	"crypto/aes"
+	"errors"
+)
+
+// pad16 - pad data to AES block size (=16 byte) using standard PKCS#7 padding
+// https://tools.ietf.org/html/rfc5652#section-6.3
+func pad16(orig []byte) (padded []byte) {
+	oldLen := len(orig)
+	if oldLen == 0 {
+		panic("Padding zero-length string makes no sense")
+	}
+	padLen := aes.BlockSize - oldLen%aes.BlockSize
+	if padLen == 0 {
+		padLen = aes.BlockSize
+	}
+	newLen := oldLen + padLen
+	padded = make([]byte, newLen)
+	copy(padded, orig)
+	padByte := byte(padLen)
+	for i := oldLen; i < newLen; i++ {
+		padded[i] = padByte
+	}
+	return padded
+}
+
+// unPad16 - remove padding
+func unPad16(padded []byte) ([]byte, error) {
+	oldLen := len(padded)
+	if oldLen%aes.BlockSize != 0 {
+		return nil, errors.New("Unaligned size")
+	}
+	// The last byte is always a padding byte
+	padByte := padded[oldLen-1]
+	// The padding byte's value is the padding length
+	padLen := int(padByte)
+	// Padding must be at least 1 byte
+	if padLen <= 0 {
+		return nil, errors.New("Padding cannot be zero-length")
+	}
+	// Larger paddings make no sense
+	if padLen > aes.BlockSize {
+		return nil, fmt.Errorf("Padding too long, padLen = %d > 16", padLen)
+	}
+	// All padding bytes must be identical
+	for i := oldLen - padLen; i < oldLen; i++ {
+		if padded[i] != padByte {
+			return nil, fmt.Errorf("Padding byte at i=%d is invalid", i)
+		}
+	}
+	newLen := oldLen - padLen
+	// Padding an empty string makes no sense
+	if newLen == 0 {
+		return nil, errors.New("Unpadded length is zero")
+	}
+	return padded[0:newLen], nil
+}