ISO/IEC 18033-2:2005 specifies encryption systems (ciphers) for the purpose of data confidentiality. The primary purpose of encryption (or encipherment ) techniques is to protect the confidentiality of stored or transmitted data. An encryption algorithm is applied to data (often called plaintext or cleartext ) to yield encrypted data (or ciphertext ); this process is known as encryption . The encryption algorithm should be designed so that the ciphertext yields no information about the plaintext except, perhaps, its length. Associated with every encryption algorithm is a corresponding decryption algorithm , which transforms ciphertext back into its original