AES256EncryptionUtil

// Generate an AES key for the purpose of this sample. 
// Normally this key should be stored in a protected custom setting 
// or an encrypted field on a custom object
Blob cryptoKey = Crypto.generateAesKey(256);

// Generate the data to be encrypted.
Blob data = Blob.valueOf('Test data to encrypted');
// Encrypt the data and have Salesforce.com generate the initialization vector
Blob encryptedData = Crypto.encryptWithManagedIV('AES256', cryptoKey, data);
// Decrypt the data - the first 16 bytes contain the initialization vector
Blob decryptedData = Crypto.decryptWithManagedIV('AES256', cryptoKey, encryptedData);

// Decode the decrypted data for subsequent use
String decryptedDataString = decryptedData.toString();