These filters allow to encrypt and decrypt any given string. Therefor they make use of Adapters. Actually there are adapters for the Mcrypt and OpenSSL extensions from PHP. The following options are supported for Zend_Filter_Encrypt and Zend_Filter_Decrypt: adapter: This sets the encryption adapter which should be used algorithm: Only MCrypt. The algorithm which has to be used. It should be one of the algorithm ciphers which can be found under PHP's mcrypt ciphers. If not set it defaults to blowfish. algorithm_directory: Only MCrypt. The directory where the algorithm can be found. If not set it defaults to the path set within the mcrypt extension. compression: If the encrypted value should be compressed. Default is no compression. envelope: Only OpenSSL. The encrypted envelope key from the user who encrypted the content. You can either provide the path and filename of the key file, or just the content of the key file itself. When the package option has been set, then you can omit this parameter. key: Only MCrypt. The encryption key with which the input will be encrypted. You need the same key for decryption. mode: Only MCrypt. The encryption mode which has to be used. It should be one of the modes which can be found under PHP's mcrypt modes. If not set it defaults to 'cbc'. mode_directory: Only MCrypt. The directory where the mode can be found. If not set it defaults to the path set within the Mcrypt extension. package: Only OpenSSL. If the envelope key should be packed with the encrypted value. Default is FALSE. private: Only OpenSSL. Your private key which will be used for encrypting the content. Also the private key can be either a filename with path of the key file, or just the content of the key file itself. public: Only OpenSSL. The public key of the user whom you want to provide the encrpted content. You can give multiple public keys by using an array. You can eigther provide the path and filename of the key file, or just the content of the key file itself. salt: Only MCrypt. If the key should be used as salt value. The key used for encryption will then itself also be encrypted. Default is FALSE. vector: Only MCrypt. The initialization vector which shall be used. If not set it will be a random vector. As these two encryption methodologies work completely different, also the usage of the adapters differ. You have to select the adapter you want to use when initiating the filter. 'mcrypt')); // Use the OpenSSL adapter $filter2 = new Zend_Filter_Encrypt(array('adapter' => 'openssl')); ]]> To set another adapter you can also use setAdapter(), and the getAdapter() method to receive the actual set adapter. setAdapter('openssl'); ]]> When you do not supply the adapter option or do not use setAdapter(), then the Mcrypt adapter will be used per default. When you have installed the Mcrypt extension you can use the Mcrypt adapter. If you provide a string instead of an array of options, this string will be used as key. You can get and set the encryption values also afterwards with the getEncryption() and setEncryption() methods. Note that you will get an exception if the mcrypt extension is not available in your environment. You should also note that all settings which be checked when you create the instance or when you call setEncryption(). If mcrypt detects problem with your settings an exception will be thrown. You can get or set the encryption vector by calling getVector() and setVector(). A given string will be truncated or padded to the needed vector size of the used algorithm. Note that when you are not using an own vector, you must get the vector and store it. Otherwise you will not be able to decode the encoded string. setVector('myvector'); // $filter->getVector(); $encrypted = $filter->filter('text_to_be_encoded'); print $encrypted; // For decryption look at the Decrypt filter ]]> For decrypting content which was previously encrypted with Mcrypt you need to have the options with which the encryption has been called. There is one eminent difference for you. When you did not provide a vector at encryption you need to get it after you encrypted the content by using the getVector() method on the encryption filter. Without the correct vector you will not be able to decrypt the content. As soon as you have provided all options decryption is as simple as encryption. setVector('myvector'); $decrypted = $filter->filter('encoded_text_normally_unreadable'); print $decrypted; ]]> Note that you will get an exception if the mcrypt extension is not available in your environment. You should also note that all settings which be checked when you create the instance or when you call setEncryption(). If mcrypt detects problem with your settings an exception will be thrown. When you have installed the OpenSSL extension you can use the OpenSSL adapter. You can get or set the public keys also afterwards with the getPublicKey() and setPublicKey() methods. The private key can also be get and set with the related getPrivateKey() and setPrivateKey() methods. 'openssl', 'private' => '/path/to/mykey/private.pem' )); // of course you can also give the public keys at initiation $filter->setPublicKey(array( '/public/key/path/first.pem', '/public/key/path/second.pem' )); ]]> Note that the OpenSSL adapter will not work when you do not provide valid keys. When you want to encode also the keys, then you have to provide a passphrase with the setPassphrase() method. When you want to decode content which was encoded with a passphrase you will not only need the public key, but also the passphrase to decode the encrypted key. 'openssl', 'private' => '/path/to/mykey/private.pem' )); // of course you can also give the public keys at initiation $filter->setPublicKey(array( '/public/key/path/first.pem', '/public/key/path/second.pem' )); $filter->setPassphrase('mypassphrase'); ]]> At last, when you use OpenSSL you need to give the receiver the encrypted content, the passphrase when have provided one, and the envelope keys for decryption. This means for you, that you have to get the envelope keys after the encryption with the getEnvelopeKey() method. So our complete example for encrypting content with OpenSSL look like this. 'openssl', 'private' => '/path/to/mykey/private.pem' )); // of course you can also give the public keys at initiation $filter->setPublicKey(array( '/public/key/path/first.pem', '/public/key/path/second.pem' )); $filter->setPassphrase('mypassphrase'); $encrypted = $filter->filter('text_to_be_encoded'); $envelope = $filter->getEnvelopeKey(); print $encrypted; // For decryption look at the Decrypt filter ]]> As seen before, you need to get the envelope key to be able to decrypt the previous encrypted value. This can be very annoying when you work with multiple values. To have a simplified usage you can set the package option to TRUE. The default value is FALSE. 'openssl', 'private' => '/path/to/mykey/private.pem', 'public' => '/public/key/path/public.pem', 'package' => true )); $encrypted = $filter->filter('text_to_be_encoded'); print $encrypted; // For decryption look at the Decrypt filter ]]> Now the returned value contains the encrypted value and the envelope. You don't need to get them after the compression. But, and this is the negative aspect of this feature, the encrypted value can now only be decrypted by using Zend_Filter_Encrypt. Based on the original value, the encrypted value can be a very large string. To reduce the value Zend_Filter_Encrypt allows the usage of compression. The compression option can eighter be set to the name of a compression adapter, or to an array which sets all wished options for the compression adapter. 'openssl', 'private' => '/path/to/mykey/private.pem', 'public' => '/public/key/path/public.pem', 'package' => true, 'compression' => 'bz2' )); // Use basic compression adapter $filter2 = new Zend_Filter_Encrypt(array( 'adapter' => 'openssl', 'private' => '/path/to/mykey/private.pem', 'public' => '/public/key/path/public.pem', 'package' => true, 'compression' => array('adapter' => 'zip', 'target' => '\usr\tmp\tmp.zip') )); ]]> When you want to decrypt a value which is additionally compressed, then you need to set the same compression settings for decryption as for encryption. Otherwise the decryption will fail. Decryption with OpenSSL is as simple as encryption. But you need to have all data from the person who encrypted the content. See the following example: 'openssl', 'private' => '/path/to/mykey/private.pem' )); // of course you can also give the envelope keys at initiation $filter->setEnvelopeKey(array( '/key/from/encoder/first.pem', '/key/from/encoder/second.pem' )); ]]> Note that the OpenSSL adapter will not work when you do not provide valid keys. Optionally it could be necessary to provide the passphrase for decrypting the keys themself by using the setPassphrase() method. 'openssl', 'private' => '/path/to/mykey/private.pem' )); // of course you can also give the envelope keys at initiation $filter->setEnvelopeKey(array( '/key/from/encoder/first.pem', '/key/from/encoder/second.pem' )); $filter->setPassphrase('mypassphrase'); ]]> At last, decode the content. Our complete example for decrypting the previously encrypted content looks like this. 'openssl', 'private' => '/path/to/mykey/private.pem' )); // of course you can also give the envelope keys at initiation $filter->setEnvelopeKey(array( '/key/from/encoder/first.pem', '/key/from/encoder/second.pem' )); $filter->setPassphrase('mypassphrase'); $decrypted = $filter->filter('encoded_text_normally_unreadable'); print $decrypted; ]]>