RC6

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.

// Encryption/Decryption with RC6-w/r/b

//

// Input: Plaintext stored in four w-bit input registers A, B, C & D

// r is the number of rounds

// w-bit round keys S[0, ... , 2r + 3]

//

// Output: Ciphertext stored in A, B, C, D

//

// Encryption Procedure:

B = B + S[0]

D = D + S[1]

for i = 1 to r do

{

t = (B * (2B + 1)) <<< lg w

u = (D * (2D + 1)) <<< lg w

A = ((A ^ t) <<< u) + S[2i]

C = ((C ^ u) <<< t) + S[2i + 1]

(A, B, C, D) = (B, C, D, A)

}

A = A + S[2r + 2]

C = C + S[2r + 3]

// Decryption Procedure:

C = C - S[2r + 3]

A = A - S[2r + 2]

for i = r downto 1 do

{

(A, B, C, D) = (D, A, B, C)

u = (D * (2D + 1)) <<< lg w

t = (B * (2B + 1)) <<< lg w

C = ((C - S[2i + 1]) >>> t) ^ u

A = ((A - S[2i]) >>> u) ^ t

}

D = D - S[1]

B = B - S[0]

In August 2016, code reputed to be Equation Group or NSA "implants" for various network security devices was disclosed.{{cite news |title=Confirmed: hacking tool leak came from "omnipotent" NSA-tied group |work=Ars Technica |date=August 16, 2016 |url=https://arstechnica.com/security/2016/08/code-dumped-online-came-from-omnipotent-nsa-tied-hacking-group/ }} The accompanying instructions revealed that some of these programs use RC6 for confidentiality of network communications.{{cite web

| url=https://github.com/nneonneo/eqgrp-free-file/blob/master/Firewall/BLATSTING/BLATSTING_20322/opinstructions/install.txt

| title=These instructions guide the INSTALLATION of BLATSTING using ELIGIBLEBACHELOR via NOPEN tunnel.

| website=GitHub

| access-date=2016-08-16}}

As RC6 was not selected for the AES, it was not guaranteed that RC6 is royalty-free. {{As of|2017|1}}, a web page on the official web site of the designers of RC6, RSA Laboratories, states the following:{{cite web

| url=https://www.emc.com/emc-plus/rsa-labs/standards-initiatives/rc5-and-rc6.htm

| title=3.6.4 What are RC5 and RC6?

| publisher=RSA Laboratories

| archive-url=https://web.archive.org/web/20170706114310/https://www.emc.com/emc-plus/rsa-labs/standards-initiatives/rc5-and-rc6.htm

| archive-date=2017-07-06

| access-date=2015-08-02}}

:"We emphasize that if RC6 is selected for the AES, RSA Security will not require any licensing or royalty payments for products using the algorithm".

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 ({{US patent|5724428}} and {{US patent|5835600}}); however, the patents expired between 2015 and 2017.

{{reflist}}

{{refbegin}}

• {{cite web

| url=http://people.csail.mit.edu/rivest/pubs/RRSY98.pdf

| archive-url=https://web.archive.org/web/20181223080309/http://people.csail.mit.edu/rivest/rc6.pdf

| archive-date=2018-12-23

| title=The RC6 Block Cipher

| first1=R.L.

| last1=Pavan

| first2=M.J.B.

| last2=Robshaw

| first3=R.

| last3=Sidney

| first4=Y.L.

| last4=Yin.

| date=1998-08-20

| version=v1.1

| access-date=2015-08-02}}

• {{cite web

| url=http://perso.ens-lyon.fr/jean-luc.beuchat/Publications/fpl2003.pdf

| title=FPGA Implementations of the RC6 Block Cipher

| first=Jean-Luc

| last=Beuchat

| archive-url=https://web.archive.org/web/20060505225326/http://perso.ens-lyon.fr/jean-luc.beuchat/Publications/fpl2003.pdf

| archive-date=2006-05-05

| url-status=dead}}

• {{cite web

| url=https://www.theregister.co.uk/2013/12/31/nsa_weapons_catalogue_promises_pwnage_at_the_speed_of_light/

| title=How the NSA hacks PCs, phones, routers, hard disks 'at speed of light': Spy tech catalog leaks

| first=Iain

| last=Thompson

| date=2013-12-31

| website=The Register

| access-date=2015-08-02}}

{{refend}}

• {{cite web

| url=http://embeddedsw.net/Cipher_Reference_Home.html#RC6

| title=Cryptography - 256 bit Ciphers: Reference source code and submissions to international cryptographic designs contests}}

• {{cite web

| url=http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html#RC6

| title=Symmetric Ciphers: RC6

| publisher=Standard Cryptographic Algorithm Naming (SCAN)

| date=2009-04-15}}

• {{cite web

| url=https://www.emc.com/emc-plus/rsa-labs/historical/rc6-block-cipher.htm

| title=RC6® Block Cipher

| archive-url=https://web.archive.org/web/20160304055032/https://www.emc.com/emc-plus/rsa-labs/historical/rc6-block-cipher.htm

| archive-date=2016-03-04

| publisher=RSA Laboratories}}

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