overdue

.rclone_repo/backend/crypt/pkcs7/pkcs7.go

@@ -0,0 +1,63 @@
+// Package pkcs7 implements PKCS#7 padding
+//
+// This is a standard way of encoding variable length buffers into
+// buffers which are a multiple of an underlying crypto block size.
+package pkcs7
+
+import "github.com/pkg/errors"
+
+// Errors Unpad can return
+var (
+	ErrorPaddingNotFound      = errors.New("Bad PKCS#7 padding - not padded")
+	ErrorPaddingNotAMultiple  = errors.New("Bad PKCS#7 padding - not a multiple of blocksize")
+	ErrorPaddingTooLong       = errors.New("Bad PKCS#7 padding - too long")
+	ErrorPaddingTooShort      = errors.New("Bad PKCS#7 padding - too short")
+	ErrorPaddingNotAllTheSame = errors.New("Bad PKCS#7 padding - not all the same")
+)
+
+// Pad buf using PKCS#7 to a multiple of n.
+//
+// Appends the padding to buf - make a copy of it first if you don't
+// want it modified.
+func Pad(n int, buf []byte) []byte {
+	if n <= 1 || n >= 256 {
+		panic("bad multiple")
+	}
+	length := len(buf)
+	padding := n - (length % n)
+	for i := 0; i < padding; i++ {
+		buf = append(buf, byte(padding))
+	}
+	if (len(buf) % n) != 0 {
+		panic("padding failed")
+	}
+	return buf
+}
+
+// Unpad buf using PKCS#7 from a multiple of n returning a slice of
+// buf or an error if malformed.
+func Unpad(n int, buf []byte) ([]byte, error) {
+	if n <= 1 || n >= 256 {
+		panic("bad multiple")
+	}
+	length := len(buf)
+	if length == 0 {
+		return nil, ErrorPaddingNotFound
+	}
+	if (length % n) != 0 {
+		return nil, ErrorPaddingNotAMultiple
+	}
+	padding := int(buf[length-1])
+	if padding > n {
+		return nil, ErrorPaddingTooLong
+	}
+	if padding == 0 {
+		return nil, ErrorPaddingTooShort
+	}
+	for i := 0; i < padding; i++ {
+		if buf[length-1-i] != byte(padding) {
+			return nil, ErrorPaddingNotAllTheSame
+		}
+	}
+	return buf[:length-padding], nil
+}