DANSK DS/ISO/IEC 18033-2 PDF

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 plaintext.
An asymmetric, i.e. public-key, encryption scheme allows a sender to use a recipient's public key to transmit an encryption of a message to the receiver, who can use his secret key to decrypt the given ciphertext, thereby obtaining the original message.
Such a scheme should be secure in the sense that no information about the message should be leaked to a (resource-bounded) attacker, even if that attacker mounts a so-called 'chosen ciphertext' attack, in which he may obtain decryptions of other ciphertexts. This is the strongest type of attack that has been proposed for a public-key encryption scheme.
ISO/IEC 18033-2:2005 specifies the functional interface of such a scheme, and in addition specifies a number of particular schemes that appear to be secure against chosen ciphertext attack. The different schemes offer different trade-offs between security properties and efficiency.