In cryptography , RC6 ( Rivest cipher 6 ) is a symmetric key block cipher derived from RC5 . It was designed by Ron Rivest , Matt Robshaw , Ray Sidney, and Yiqun Lisa Yin to meet the requirements of the Advanced Encryption Standard (AES) competition . The algorithm was one of the five finalists, and also was submitted to the NESSIE and CRYPTREC projects. It was a proprietary algorithm, patented by RSA Security .
11-562: RC6 proper has a block size of 128 bits and supports key sizes of 128, 192, and 256 bits up to 2040-bits, but, like RC5, it may be parameterised to support a wide variety of word-lengths, key sizes, and number of rounds. RC6 is very similar to RC5 in structure, using data-dependent rotations, modular addition, and XOR operations; in fact, RC6 could be viewed as interweaving two parallel RC5 encryption processes, although RC6 does use an extra multiplication operation not present in RC5 in order to make
22-650: Is a Belgian cryptographer who is currently professor of digital security (symmetric encryption) at Radboud University . He co-designed with Vincent Rijmen the Rijndael cipher, which was selected as the Advanced Encryption Standard (AES) in 2001. More recently, he co-designed the Keccak cryptographic hash, which was selected as the new SHA-3 hash by NIST in October 2012. He has also designed or co-designed
33-541: The COSIC research group, and has worked on the design and cryptanalysis of block ciphers , stream ciphers and cryptographic hash functions . Daemen completed his PhD in 1995, at which point he worked for a year at Janssen Pharmaceutica in Beerse , Belgium . He subsequently worked at the BACOB bank, Banksys , Proton World and then STMicroelectronics . This article about
44-620: The MMB , Square , SHARK , NOEKEON , 3-Way , and BaseKing block ciphers . In 2017 he won the Levchin Prize for Real World Cryptography "for the development of AES and SHA3". He describes his development of encryption algorithms as creating the bricks which are needed to build the secure foundations online. In 1988, Daemen graduated in electro-mechanical engineering at the Katholieke Universiteit Leuven . He subsequently joined
55-413: The square root of the total number possible, there will be an approximately 50% chance of two or more being the same, which would start to leak information about the message contents. Thus even when used with a proper encryption mode (e.g. CBC or OFB), only 2 × 8 B = 32 GB of data can be safely sent under one key. In practice a greater margin of security is desired, restricting a single key to
66-735: The AES contest, Rijndael , supports block and key sizes of 128, 192, and 256 bits, but in AES the block size is always 128 bits. The extra block sizes were not adopted by the AES standard. Many block ciphers, such as RC5 , support a variable block size. The Luby-Rackoff construction and the Outerbridge construction can both increase the effective block size of a cipher. Joan Daemen 's 3-Way and BaseKing have unusual block sizes of 96 and 192 bits, respectively. Joan Daemen Joan Daemen ( Dutch pronunciation: [joːˈɑn ˈdaːmə(n)] ; born 1965)
77-479: The encryption of much less data — say a few hundred megabytes. At one point that seemed like a fair amount of data, but today it is easily exceeded. If the cipher mode does not properly randomise the input, the limit is even lower. Consequently, AES candidates were required to support a block length of 128 bits (16 bytes). This should be acceptable for up to 2 × 16 B = 256 exabytes of data, and would suffice for many years after introduction. The winner of
88-510: The input – this follows logically from the pigeonhole principle and the fact that the cipher must be reversible – and it is undesirable for the output to be longer than the input. Until the announcement of NIST 's AES contest , the majority of block ciphers followed the example of the DES in using a block size of 64 bits (8 bytes ). However, the birthday paradox indicates that after accumulating several blocks equal to
99-419: The patents expired between 2015 and 2017. Block size (cryptography) In modern cryptography , symmetric key ciphers are generally divided into stream ciphers and block ciphers . Block ciphers operate on a fixed length string of bits . The length of this bit string is the block size . Both the input ( plaintext ) and output ( ciphertext ) are the same length; the output cannot be shorter than
110-518: The rotation dependent on every bit in a word, and not just the least significant few bits. Note that the key expansion algorithm is practically identical to that of RC5. The only difference is that for RC6, more words are derived from the user-supplied key. In August 2016, code reputed to be Equation Group or NSA "implants" for various network security devices was disclosed. The accompanying instructions revealed that some of these programs use RC6 for confidentiality of network communications. As RC6
121-518: Was not selected for the AES , it was not guaranteed that RC6 is royalty-free. As of January 2017, a web page on the official web site of the designers of RC6, RSA Laboratories, states the following: The emphasis on the word "if" suggests that RSA Security Inc. may have required licensing and royalty payments for any products using the RC6 algorithm. RC6 was a patented encryption algorithm ( U.S. patent 5,724,428 and U.S. patent 5,835,600 ); however,
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