AESDecrypt.java

/*
Apex encryption

String clearText = 'A sample message';
String key = 'b7zfYEKhkmVrl9P3yGN/p+3AOkjWK5D6s2JOJzW6lpo=';
Blob cipherText = Crypto.encryptWithManagedIV('AES256', EncodingUtil.base64Decode(key), Blob.valueOf(clearText));
String encodedCipherText = EncodingUtil.base64Encode(cipherText); 
System.debug(key);
System.debug(encodedCipherText);
*/
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;
import java.util.Arrays;

public class AESDecrypt {

  private static final String characterEncoding = "UTF-8";
  private static final String cipherTransformation = "AES/CBC/PKCS5Padding";
  private static final String aesEncryptionAlgorithm = "AES";

  public static byte[] decryptBase64EncodedWithManagedIV(String encryptedText, String key) throws Exception {
    byte[] cipherText = Base64.decodeBase64(encryptedText.getBytes());
    byte[] keyBytes = Base64.decodeBase64(key.getBytes());
    return decryptWithManagedIV(cipherText, keyBytes);
  }

  public static byte[] decryptWithManagedIV(byte[] cipherText, byte[] key) throws Exception {
    byte[] initialVector = Arrays.copyOfRange(cipherText, 0, 16);
    byte[] trimmedCipherText = Arrays.copyOfRange(cipherText, 16, cipherText.length);
    return decrypt(trimmedCipherText, key, initialVector);
  }

  public static byte[] decrypt(byte[] cipherText, byte[] key, byte[] initialVector) throws Exception {
    Cipher cipher = Cipher.getInstance(cipherTransformation);
    SecretKeySpec secretKeySpecy = new SecretKeySpec(key, aesEncryptionAlgorithm);
    IvParameterSpec ivParameterSpec = new IvParameterSpec(initialVector);
    cipher.init(Cipher.DECRYPT_MODE, secretKeySpecy, ivParameterSpec);
    cipherText = cipher.doFinal(cipherText);
    return cipherText;
  }

  public static void main(String args[]) throws Exception {
    byte[] clearText = decryptBase64EncodedWithManagedIV(
        "shZiijRRaNy8HSDcZeAwYELhBltiBrInSz0MH/F7Ol23VHmJmm3QD1xOMQqaN4FP",
        "b7zfYEKhkmVrl9P3yGN/p+3AOkjWK5D6s2JOJzW6lpo=");
    System.out.println("ClearText:" + new String(clearText, characterEncoding));
  }

}