crypto: add pkcs7v0.8.1

1 files changed, 41 insertions, 0 deletions

diff --git a/crypto/pkcs7/padding.go b/crypto/pkcs7/padding.go
new file mode 100644
index 0000000..1f90643
--- /dev/null
+++ b/crypto/pkcs7/padding.go
@@ -0,0 +1,41 @@
+package pkcs7
+
+// Shamelessly stolen from: https://wgallagher86.medium.com/pkcs-7-padding-in-go-6da5d1d14590
+
+import "errors"
+
+func Unpad(input []byte) ([]byte, error) {
+        if input == nil || len(input) == 0 {
+                return nil, nil
+        }
+
+        pc := input[len(input)-1]
+        pl := int(pc)
+        err := checkPaddingIsValid(input, pl)
+        if err != nil {
+                return nil, err
+        }
+        return input[:len(input)-pl], nil
+}
+
+func checkPaddingIsValid(input []byte, paddingLength int) error {
+        if len(input) < paddingLength {
+                return errors.New("invalid padding")
+        }
+        p := input[len(input)-(paddingLength):]
+        for _, pc := range p {
+                if uint(pc) != uint(len(p)) {
+                        return errors.New("invalid padding")
+                }
+        }
+        return nil
+}
+
+func Pad(input []byte, blockSize int) []byte {
+        r := len(input) % blockSize
+        pl := blockSize - r
+        for i := 0; i < pl; i++ {
+                input = append(input, byte(pl))
+        }
+        return input
+}