Usando mcrypt com Zend Framework via helpers

application.ini

[production]
; Configuração normal do ZF

my.crypto.IV = "nononononononononononono"
my.crypto.Key = "nononononononononononononononono"

; A cifra e o modo devem ser CONSTANTES e não strings.
my.crypto.Cipher = MCRYPT_RIJNDAEL_192
my.crypto.Mode = MCRYPT_MODE_CFB

Decrypt.php

<?php
class Helper_Decrypt extends Zend_Controller_Action_Helper_Abstract
{
    private $applicationConfig, $cryptoConfig, $result;
    
    public function direct($cryptedData, $base64Decode = TRUE)
    {
        $this->applicationConfig = new Zend_Config_Ini(APPLICATION_PATH . '/configs/application.ini', APPLICATION_ENV);
        $this->cryptoConfig = $this->applicationConfig->my->crypto;

        if ($base64Decode) {
            $cryptedData = base64_decode($cryptedData);
        }

        $this->result = mcrypt_decrypt($this->cryptoConfig->Cipher, $this->cryptoConfig->Key, $cryptedData, $this->cryptoConfig->Mode, $this->cryptoConfig->IV);

        return $this->result;
    }
}
?>

Encrypt.php

<?php
class Helper_Encrypt extends Zend_Controller_Action_Helper_Abstract
{
    private $applicationConfig, $cryptoConfig, $result;
    
    public function direct($rawData, $base64Encode = TRUE)
    {
        $this->applicationConfig = new Zend_Config_Ini(APPLICATION_PATH . '/configs/application.ini', APPLICATION_ENV);
        $this->cryptoConfig = $this->applicationConfig->my->crypto;

        $this->result = mcrypt_encrypt($this->cryptoConfig->Cipher, $this->cryptoConfig->Key, $rawData, $this->cryptoConfig->Mode, $this->cryptoConfig->IV);

        if ($base64Encode) {
            return base64_encode($this->result);
        } else {
            return $this->result;
        }
    }
}
?>