Input length must be multiple of 16 when decrypting with padded cipher

 In the context of Salesforce, here are the best approaches given:-

Technical explanation

When you are trying to decrypt a message encrypted with AES and PKC7 padding, the ciphertext’s length should be a multiple of 16 bytes. If the decrypted plaintext doesn’t have valid padding, it would indicate potential tampering or a decryption error.

Coding approach

Here is a basic example given below by using python’s “cryptography” library to handle description with PKCS7 padding:-

From cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes

From cryptography.hazmat.primitives.ciphers.aead import AESGCM

From cryptography.hazmat.primitives import padding

From cryptography.hazmat.backends import default_backend

Import base64

Def decrypt_message(key, iv, ciphertext):

    Backend = default_backend()

    Cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)

    Decryptor = cipher.decryptor()

    Decrypted_data = decryptor.update(ciphertext) + decryptor.finalize()

    # PKCS7 unpadding

    Unpadder = padding.PKCS7(128).unpadder()

    Unpadded_data = unpadder.update(decrypted_data) + unpadder.finalize()

    Return unpadded_data

# Example usage

Key = b’Sixteen byte key’

Iv = b’InitializationVe’  # 16 bytes for AES

Encrypted_data = base64.b64decode(‘BASE64_ENCODED_CIPHERTEXT_HERE’)

Decrypted_message = decrypt_message(key, iv, encrypted_data)

Print(decrypted_message.decode(‘utf-8’))

Here is the example given in java programming language:-

Import javax.crypto.Cipher;

Import javax.crypto.spec.IvParameterSpec;

Import javax.crypto.spec.SecretKeySpec;

Import java.util.Base64;

Public class AESDecryptor {

    Public static void main(String[] args) throws Exception {

        String key = “Sixteen byte key”; // 16 bytes key

        String iv = “InitializationVe”; // 16 bytes IV

        // Base64 encoded ciphertext

        String base64Ciphertext = “BASE64_ENCODED_CIPHERTEXT_HERE”;

        Byte[] ciphertext = Base64.getDecoder().decode(base64Ciphertext);

        // Decrypt the ciphertext

        String decryptedMessage = decrypt(key, iv, ciphertext);

        System.out.println(“Decrypted Message: “ + decryptedMessage);

    }

    Public static String decrypt(String key, String iv, byte[] ciphertext) throws Exception {

        SecretKeySpec secretKeySpec = new SecretKeySpec(key.getBytes(), “AES”);

        IvParameterSpec ivParameterSpec = new IvParameterSpec(iv.getBytes());

        Cipher cipher = Cipher.getInstance(“AES/CBC/PKCS5Padding”);

        Cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);

        Byte[] decryptedBytes = cipher.doFinal(ciphertext);

        // Remove PKCS7 padding

        Int paddingLength = decryptedBytes[decryptedBytes.length – 1];

        Byte[] unpaddedBytes = new byte[decryptedBytes.length – paddingLength];

        System.arraycopy(decryptedBytes, 0, unpaddedBytes, 0, unpaddedBytes.length);

        Return new String(unpaddedBytes);

    }

}

Here is the example given in HTML:-

   

    [removed]

          Function decryptMessage() {

            Var key = “Sixteen byte key”; // 16 bytes key

            Var iv = “InitializationVe”; // 16 bytes IV

            Var base64Ciphertext = document.getElementById(“cipherInput”).value;

            Var ciphertext = atob(base64Ciphertext); // Decode Base64

            Var decryptedMessage = decrypt(key, iv, ciphertext);

            Document.getElementById(“decryptedMessage”).innerText = decryptedMessage;

        }        Function decrypt(key, iv, ciphertext) {

            Var secretKey = crypto.subtle.importKey(

                “raw”, 

                New TextEncoder().encode(key),

                { name: “AES-CBC” },

                False,

                [“decrypt”]

            );

            Var ivBuffer = new Uint8Array(new TextEncoder().encode(iv));

            Return crypto.subtle.decrypt(

                { name: “AES-CBC”, iv: ivBuffer },

                secretKey,

                ciphertext

            ).then(function(decrypted) {

                // Convert decrypted ArrayBuffer to string

                Return new TextDecoder().decode(decrypted);

            });

        }

    [removed]

    AES Decryption

    Enter Base64 Encoded Ciphertext:

    Decrypt