lib: update Pkcs7PaddingUndo, AESDecryptCBC

Add error as the second return value to Pkcs7PaddingUndo and
AESDecryptCBC.

1 files changed, 19 insertions, 9 deletions

diff --git a/challenge/c15.go b/challenge/c15.go
index 40892ec..e974d64 100644
--- a/challenge/c15.go
+++ b/challenge/c15.go
@@ -15,7 +15,7 @@ func C15() {
 	padded_ice := lib.Pkcs7Padding(ice, 16)
 	fmt.Printf("ice padded: %v\n", padded_ice)
 
-	unpadded_ice := lib.Pkcs7PaddingUndo(padded_ice)
+	unpadded_ice, _ := lib.Pkcs7PaddingUndo(padded_ice)
 	for i := 0; i < len(ice); i++ {
 		if ice[i] != unpadded_ice[i] {
 			panic("padding undo failed!")
@@ -23,18 +23,28 @@ func C15() {
 	}
 	fmt.Printf("unpadded ice: %v\n", unpadded_ice)
 
-	// Will fail and panic
-	// bad_ice := append(ice, []byte{5, 5, 5, 5}...)
-	// fmt.Printf("bad ice: %v\n", bad_ice)
-	// lib.Pkcs7PaddingUndo(bad_ice)
+	// Will fail.
+	bad_ice := append(ice, []byte{5, 5, 5, 5}...)
+	fmt.Printf("bad ice: %v\n", bad_ice)
+	_, err := lib.Pkcs7PaddingUndo(bad_ice)
+	if err != nil {
+		fmt.Printf("bad ice upadding failed: %s\n", err.Error())
+	}
 
-	// Will fail and panic
-	// evil_ice := append(ice, []byte{1, 2, 3, 4}...)
-	// fmt.Printf("evil ice: %v\n", evil_ice)
-	// lib.Pkcs7PaddingUndo(evil_ice)
+	// Will fail.
+	evil_ice := append(ice, []byte{1, 2, 3, 4}...)
+	fmt.Printf("evil ice: %v\n", evil_ice)
+	_, err = lib.Pkcs7PaddingUndo(evil_ice)
+	if err != nil {
+		fmt.Printf("evil ice upadding failed: %s\n", err.Error())
+	}
 }
 
 // Output:
 // ice: [73 67 69 32 73 67 69 32 66 65 66 89]
 // ice padded: [73 67 69 32 73 67 69 32 66 65 66 89 4 4 4 4]
 // unpadded ice: [73 67 69 32 73 67 69 32 66 65 66 89]
+// bad ice: [73 67 69 32 73 67 69 32 66 65 66 89 5 5 5 5]
+// bad ice upadding failed: input is not pkcs#7 padded
+// evil ice: [73 67 69 32 73 67 69 32 66 65 66 89 1 2 3 4]
+// evil ice upadding failed: input is not pkcs#7 padded