Interestingly, the different modes result in different properties being achieved which add to the security of the underlying block cipher. These schemes are known as "block cipher modes of operation" and are applicable for most block ciphers like AES, RC6, Camellia, Serpent and many others. SP 800-38A (DOI) video streaming). If authenticated encryption scheme is used, at the moment of decryption it will be known if the decryption is successful (i.e. Examples: The main idea behind the block cipher modes (like CBC, CFB, OFB, CTR, EAX, CCM and GCM) is to repeatedly apply a cipher's single-block encryption / decryption to securely encrypt / decrypt amounts of data larger than a block. In cryptography block ciphers (like AES) are designed to encrypt a block of data of fixed size (e.g. For plaintext messages exceeding one block in length, various modes of operation for block ciphers are used (seex7.2.2). In other words, AEAD adds the ability to check the integrity and authenticity of some Associated Data (AD), also called "Additional Authenticated Data" (AAD), that is not encrypted. The following diagram explains visually how the GCM block mode (Galois/Counter Mode) works: The GCM mode uses a counter, which is increased for each block and calculated a message authentication tag (MAC code) after each processed block.

12/01/01: SP 800-38A (Final), Security and Privacy Like all counter modes, GCM works as a stream cipher, and so it is essential that a different IV is used at the start for each stream that is encrypted. Basically, encrypting a large input data works like this: the encryption algorithm state is initialized (using the encryption key + a random salt), then the first portion of data (e.g. Subscribe, Webmaster | When a symmetric cipher is combined with block mode of operation, the obtained cipher construction is denoted by the names of the cipher and the block mode and the key size. Books, TOPICS add a special padding character). The others might be helpful in certain situations, but some of them are less secure, so use them only if you know well what are you doing. SP 800-38A Addendum, Document History: H��WˎI�߯�% �:#�ŌF��ۈba����#M��$��q"������CKn��ff�'d{wy��M�w���6��%m]��͗�������궥k�e&Ň�4������^]d�bK�W�\��w����_������~�Ԛ�k�j�^�Y��m/ZK�2LJ�W0�����w��ww��v���6����v�J�r���]�V�ۻ7�����_�}eoo�ޔy�sk�_��C{��ы����֔����_m_���`\^(,��q����I�n�A�����{�k�~����������������o����n�^�����Gc�����"�_{�t@]s��\�,Wx�=�q���\�n:ӵ��-_G;�c؇�i?��(��x����/��5�-�v�~?ϫ*�B�=�"����B�. In this chapter, we will discuss the different modes of operation of a block cipher. 128 bits). Quantum-Safe Asymmetric Encryption - Example. Applications Use a random and unpredictable IV (nonce) for each encrypted message. The size of the input block is usually the same as the size of the encrypted output block, while the key length may be different. The size of the IV should be the same as the cipher block size, e.g. Activities & Products, ABOUT CSRC Cipher Block Chaining (CBC) 3. This recommendation defines five confidentiality modes of operation for use with an underlying symmetric key block cipher algorithm: Electronic Codebook (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), Output Feedback (OFB), and Counter (CTR). Healthcare.gov | Environmental Policy Statement | Used with an underlying block cipher algorithm... Security Testing, Validation, and Measurement, National Cybersecurity Center of Excellence (NCCoE), National Initiative for Cybersecurity Education (NICE). 128-bits for AES, Serpent and Camellia. Privacy Policy | 154 0 obj<> endobj 155 0 obj<> endobj 1 0 obj<> endobj 2 0 obj<>/Font<>/ProcSet[/PDF/Text]/ExtGState<>>> endobj 3 0 obj<>stream Local Download, Supplemental Material: modes of operation of the Advanced Encryption Standard (AES) algorithm: the AES Key Wrap (KW) mode and the AES Key Wrap With Padding (KWP) mode. Other block modes (like CTR, CFB, OFB, CCM, EAX and GCM) do not require padding at all, because they perform XOR between portions of the plaintext and the internal cipher's state at each step.