# Examples for decrypting message

{% tabs %}
{% tab title="C#" %}

```
using System;
using System.Linq;
using System.Text;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Parameters;
 
namespace DecryptionExample
{
    // You need to install bccrypto-csharp from BouncyCastle. Please see BouncyCastle page.
    class Program
    {
        static void Main(string[] args)
        {
            string keyFromConfiguration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f";
 
            // Data from server
            string ivFromHttpHeader = "000000000000000000000000";
            string authTagFromHttpHeader = "CE573FB7A41AB78E743180DC83FF09BD";
            string httpBody = "0A3471C72D9BE49A8520F79C66BBD9A12FF9";
 
            // Convert data to process
            byte[] key = ToByteArray(keyFromConfiguration);
            byte[] iv = ToByteArray(ivFromHttpHeader);
            byte[] authTag = ToByteArray(authTagFromHttpHeader);
            byte[] encryptedText = ToByteArray(httpBody);
            byte[] cipherText = encryptedText.Concat(authTag).ToArray();
 
            // Prepare decryption
            GcmBlockCipher cipher = new GcmBlockCipher(new AesFastEngine());
            AeadParameters parameters = new AeadParameters(new KeyParameter(key), 128, iv);
            cipher.Init(false, parameters);
 
            // Decrypt
            var plainText = new byte[cipher.GetOutputSize(cipherText.Length)];
            var len = cipher.ProcessBytes(cipherText, 0, cipherText.Length, plainText, 0);
            cipher.DoFinal(plainText, len);
            Console.WriteLine(Encoding.ASCII.GetString(plainText));
        }
 
        static byte[] ToByteArray(string HexString)
        {
            int NumberChars = HexString.Length;
            byte[] bytes = new byte[NumberChars / 2];
            for (int i = 0; i < NumberChars; i += 2)
            {
                bytes[i / 2] = Convert.ToByte(HexString.Substring(i, 2), 16);
            }
            return bytes;
        }
    }
}
```

{% endtab %}

{% tab title="Groovy" %}

```
import org.bouncycastle.jce.provider.BouncyCastleProvider
 
import javax.crypto.spec.IvParameterSpec
import javax.crypto.spec.SecretKeySpec
import java.security.Security
 
// For Java and JVM-based languages, you might need to install unrestricted policy file for JVM, 
// which is provided by Sun. Please refer BouncyCastle FAQ if you get 
// java.lang.SecurityException: Unsupported keysize or algorithm parameters or
// java.security.InvalidKeyException: Illegal key size.

// If you cannot install unrestricted policy file for JVM because of some reason, you can try with reflection: See here.
 
class Cipher {
    static void main(String[] args) {
        Security.addProvider(new BouncyCastleProvider())
 
        // Data from configuration
        def keyFromConfiguration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f"
 
        // Data from server
        def ivFromHttpHeader = "000000000000000000000000"
        def authTagFromHttpHeader = "CE573FB7A41AB78E743180DC83FF09BD"
        def httpBody = "0A3471C72D9BE49A8520F79C66BBD9A12FF9"
 
        // Convert data to process
        def key = keyFromConfiguration.decodeHex()
        def iv = ivFromHttpHeader.decodeHex()
        def authTag = authTagFromHttpHeader.decodeHex() as Byte[]
        def encryptedText = httpBody.decodeHex() as Byte[]
 
        // Unlike other programming language, We have to append auth tag at the end of encrypted text
        def cipherText = encryptedText + authTag as Byte[]
 
        // Prepare decryption
        def keySpec = new SecretKeySpec(key, 0, 32, "AES")
        def cipher = javax.crypto.Cipher.getInstance("AES/GCM/NoPadding")
        cipher.init(javax.crypto.Cipher.DECRYPT_MODE, keySpec, new IvParameterSpec(iv))
 
        // Decrypt
        def result = cipher.doFinal(cipherText)
        println(new String(result, "UTF-8"))
    }
}
```

{% endtab %}

{% tab title="Java" %}

```
import com.google.common.base.Charsets;
import org.apache.commons.lang3.ArrayUtils;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import javax.xml.bind.DatatypeConverter;
import java.security.Security;
 
// For Java and JVM-based languages, you might need to install unrestricted policy file for JVM, 
// which is provided by Sun. Please refer BouncyCastle FAQ if you get 
// java.lang.SecurityException: Unsupported keysize or algorithm parameters or
// java.security.InvalidKeyException: Illegal key size.

// If you cannot install unrestricted policy file for JVM because of some reason, you can try with reflection: See here.
 
public class Decryption
{
    public static void main(String[] args) throws Exception
    {
        Security.addProvider(new BouncyCastleProvider());
 
        // Data from configuration
        String keyFromConfiguration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f";
 
        // Data from server
        String ivFromHttpHeader = "000000000000000000000000";
        String authTagFromHttpHeader = "CE573FB7A41AB78E743180DC83FF09BD";
        String httpBody = "0A3471C72D9BE49A8520F79C66BBD9A12FF9";
 
        // Convert data to process
        byte[] key = DatatypeConverter.parseHexBinary(keyFromConfiguration);
        byte[] iv = DatatypeConverter.parseHexBinary(ivFromHttpHeader);
        byte[] authTag = DatatypeConverter.parseHexBinary(authTagFromHttpHeader);
        byte[] encryptedText = DatatypeConverter.parseHexBinary(httpBody);
 
        // Unlike other programming language, We have to append auth tag at the end of encrypted text in Java
        byte[] cipherText = ArrayUtils.addAll(encryptedText, authTag);
 
        // Prepare decryption
        SecretKeySpec keySpec = new SecretKeySpec(key, 0, 32, "AES");
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        cipher.init(Cipher.DECRYPT_MODE, keySpec, new IvParameterSpec(iv));
 
        // Decrypt
        byte[] bytes = cipher.doFinal(cipherText);
        System.out.println(new String(bytes, Charsets.UTF_8));
    }
}
```

{% endtab %}

{% tab title="Node.js" %}

```
var crypto = require("crypto");
 
// Data from configuration
var secretFromConfiguration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f";
 
// Data from server
var ivfromHttpHeader = "000000000000000000000000";
var authTagFromHttpHeader = "CE573FB7A41AB78E743180DC83FF09BD";
var httpBody = "0A3471C72D9BE49A8520F79C66BBD9A12FF9";
 
// Convert data to process
var key = new Buffer(secretFromConfiguration, "hex");
var iv = new Buffer(ivfromHttpHeader, "hex");
var authTag = new Buffer(authTagFromHttpHeader, "hex");
var cipherText = new Buffer(httpBody, "hex");
 
// Prepare descryption
var decipher = crypto.createDecipheriv("aes-256-gcm", key, iv);
decipher.setAuthTag(authTag);
 
// Decrypt
var result = decipher.update(cipherText) + decipher.final();
console.log(result);
```

{% endtab %}

{% tab title="Php" %}

```
<?php
/* Php 7.1 or later */
    $key_from_configuration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f";
    $iv_from_http_header = "000000000000000000000000";
    $auth_tag_from_http_header = "CE573FB7A41AB78E743180DC83FF09BD";
    $http_body = "0A3471C72D9BE49A8520F79C66BBD9A12FF9";
    
    $key = hex2bin($key_from_configuration);
    $iv = hex2bin($iv_from_http_header);
    $auth_tag = hex2bin($auth_tag_from_http_header);
    $cipher_text = hex2bin($http_body);
    
    $result = openssl_decrypt($cipher_text, "aes-256-gcm", $key, OPENSSL_RAW_DATA, $iv, $auth_tag);
    print($result);
    
/* Php prior to 7.1 */
    /* Please refer Using Libsodium in PHP Projects */
    $key_from_configuration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f";
    $iv_from_http_header = "000000000000000000000000";
    $auth_tag_from_http_header = "CE573FB7A41AB78E743180DC83FF09BD";
    $http_body = "0A3471C72D9BE49A8520F79C66BBD9A12FF9";
    
    $key = hex2bin($key_from_configuration);
    $iv = hex2bin($iv_from_http_header);
    $cipher_text = hex2bin($http_body . $auth_tag_from_http_header);
    
    $result = \Sodium\crypto_aead_aes256gcm_decrypt($cipher_text, NULL, $iv, $key);
    print($result);
?>
```

{% endtab %}

{% tab title="Phyton" %}

```
import os
import binascii
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
 
# Data from configuration
key_from_configuration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f"
 
# Data from server
iv_from_http_header = "000000000000000000000000"
auth_tag_from_http_header = "CE573FB7A41AB78E743180DC83FF09BD"
http_body = "0A3471C72D9BE49A8520F79C66BBD9A12FF9"
 
# Convert data to process
key = binascii.unhexlify(key_from_configuration)
iv = binascii.unhexlify(iv_from_http_header)
auth_tag = binascii.unhexlify(auth_tag_from_http_header)
cipher_text = binascii.unhexlify(http_body)
 
# Prepare decryption
decryptor = Cipher(algorithms.AES(key), modes.GCM(iv, auth_tag), backend = default_backend()).decryptor()
 
# Decrypt
result = decryptor.update(cipher_text) + decryptor.finalize()
print(result)
```

{% endtab %}

{% tab title="Ruby" %}

```
require("openssl")
 
# Convert hexadecimal string
def convert(hex)
    return [hex].pack("H*")
end
 
# Create new decipher
def new_decipher(key, iv)
    cipher = OpenSSL::Cipher.new("aes-256-gcm")
    cipher.decrypt
    cipher.key = key
    cipher.iv = iv
     
    return cipher
end
 
# Data from configuration
key_from_configuration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f"
 
# Data from server
iv_from_http_header = "000000000000000000000000"
auth_tag_from_http_header = "CE573FB7A41AB78E743180DC83FF09BD"
http_body = "0A3471C72D9BE49A8520F79C66BBD9A12FF9"
 
# Convert data to process
key = convert(key_from_configuration)
iv = convert(iv_from_http_header)
auth_tag = convert(auth_tag_from_http_header)
cipher_text = convert(http_body)
 
# Prepare decryption
decipher = new_decipher(key, iv)
decipher.auth_tag = auth_tag
 
# Decrypt
result = decipher.update(cipher_text) + decipher.final
puts result
```

{% endtab %}

{% tab title="Scala" %}

```
import java.nio.charset.Charset;
import java.security.Security
import java.security.SecureRandom;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import javax.xml.bind.DatatypeConverter;
import org.bouncycastle.jce.provider.BouncyCastleProvider
 
// For Java and JVM-based languages, you might need to install unrestricted policy file for JVM, 
// which is provided by Sun. Please refer BouncyCastle FAQ if you get 
// java.lang.SecurityException: Unsupported keysize or algorithm parameters or
// java.security.InvalidKeyException: Illegal key size.

// If you cannot install unrestricted policy file for JVM because of some reason, you can try with reflection: See here.
 
object Cipher {
  def main(args: Array[String]) = {
    Security.addProvider(new BouncyCastleProvider())
 
    // Data from configuration
    val keyFromConfiguration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f"
     
    // Data from server
    val ivFromHttpHeader = "000000000000000000000000"
    val authTagFromHttpHeader = "CE573FB7A41AB78E743180DC83FF09BD"
    val httpBody = "0A3471C72D9BE49A8520F79C66BBD9A12FF9"
     
    // Convert data to process
    val key = hexToBin(keyFromConfiguration)
    val iv = hexToBin(ivFromHttpHeader)
    val authTag = hexToBin(authTagFromHttpHeader)
    val encryptedText = hexToBin(httpBody)
     
    // Unlike other programming language, We have to append auth tag at the end of encrypted text
    val cipherText = encryptedText ++ authTag
     
    // Prepare decryption
    val keySpec = new SecretKeySpec(key, 0, 32, "AES")
    val cipher = javax.crypto.Cipher.getInstance("AES/GCM/NoPadding")
    cipher.init(javax.crypto.Cipher.DECRYPT_MODE, keySpec, new IvParameterSpec(iv))
 
    // Decrypt
    val result = cipher.doFinal(cipherText)
    println(new String(result, "UTF-8"))
  }
 
  def hexToBin(hex: String) : Array[Byte] = {
    return DatatypeConverter.parseHexBinary(hex)
  }
}
```

{% endtab %}
{% endtabs %}


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