🔐 RSA Padding Oracle Attack | Cyber Fortress CTF

Stage 1/3

Identify the vulnerability type in this RSA implementation:

                            // Server-side validation function
                            function validate_padding($ciphertext) {
                            $decrypted = rsa_decrypt($ciphertext);
                            $padding = check_pkcs_padding($decrypted);

                            if ($padding == "INVALID") {
                            return "PADDING_ERROR";
                            } else if ($padding == "VALID") {
                            return "DECRYPTION_OK";
                            } else {
                            return "UNKNOWN_ERROR";
                            }
                            }
                        

Question: What type of oracle does this create?

Hint: The server reveals whether padding is valid or not

Learning Objectives

Understand RSA padding oracle attacks
Learn PKCS#1 v1.5 padding structure
Practice adaptive chosen ciphertext attacks
Implement padding validation exploitation