A Description of the ARIA Encryption Algorithm
RFC 5794

Document Type RFC - Informational (March 2010; Errata)
Last updated 2015-10-14
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Independent Submission                                            J. Lee
Request for Comments: 5794                                        J. Lee
Category: Informational                                           J. Kim
ISSN: 2070-1721                                                  D. Kwon
                                                                  C. Kim
                                                                    NSRI
                                                              March 2010

             A Description of the ARIA Encryption Algorithm

Abstract

   This document describes the ARIA encryption algorithm.  ARIA is a
   128-bit block cipher with 128-, 192-, and 256-bit keys.  The
   algorithm consists of a key scheduling part and data randomizing
   part.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5794.

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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   to this document.

Lee, et al.                   Informational                     [Page 1]
RFC 5794              The ARIA Encryption Algorithm           March 2010

1.  Introduction

1.1.  ARIA Overview

   ARIA is a general-purpose block cipher algorithm developed by Korean
   cryptographers in 2003.  It is an iterated block cipher with 128-,
   192-, and 256-bit keys and encrypts 128-bit blocks in 12, 14, and 16
   rounds, depending on the key size.  It is secure and suitable for
   most software and hardware implementations on 32-bit and 8-bit
   processors.  It was established as a Korean standard block cipher
   algorithm in 2004 [ARIAKS] and has been widely used in Korea,
   especially for government-to-public services.  It was included in
   PKCS #11 in 2007 [ARIAPKCS].

2.  Algorithm Description

   The algorithm consists of a key scheduling part and data randomizing
   part.

2.1.  Notations

   The following notations are used in this document to describe the
   algorithm.

      ^   bitwise XOR operation
      <<< left circular rotation
      >>> right circular rotation
      ||  concatenation of bit strings
      0x  hexadecimal representation

2.2.  Key Scheduling Part

   Let K denote a master key of 128, 192, or 256 bits.  Given the master
   key K, we first define 128-bit values KL and KR as follows.

   KL || KR = K || 0 ... 0,

   where the number of zeros is 128, 64, or 0, depending on the size of
   K.  That is, KL is set to the leftmost 128 bits of K and KR is set to
   the remaining bits of K (if any), right-padded with zeros to a
   128-bit value.  Then, we define four 128-bit values (W0, W1, W2, and
   W3) as the intermediate round values appearing in the encryption of
   KL || KR by a 3-round, 256-bit Feistel cipher.

   W0 = KL,
   W1 = FO(W0, CK1) ^ KR,
   W2 = FE(W1, CK2) ^ W0,
   W3 = FO(W2, CK3) ^ W1.

Lee, et al.                   Informational                     [Page 2]
RFC 5794              The ARIA Encryption Algorithm           March 2010

   Here, FO and FE, respectively called odd and even round functions,
   are defined in Section 2.4.1.  CK1, CK2, and CK3 are 128-bit
   constants, taking one of the following values.

   C1 =  0x517cc1b727220a94fe13abe8fa9a6ee0
   C2 =  0x6db14acc9e21c820ff28b1d5ef5de2b0
   C3 =  0xdb92371d2126e9700324977504e8c90e

   These values are obtained from the first 128*3 bits of the fractional
   part of 1/PI, where PI is the circle ratio.  Now the constants CK1,
   CK2, and CK3 are defined by the following table.

       Key size  CK1  CK2  CK3
         128     C1   C2   C3
         192     C2   C3   C1
         256     C3   C1   C2

   For example, if the key size is 192 bits, CK1 = C2, CK2 = C3, and
   CK3 = C1.

   Once W0, W1, W2, and W3 are determined, we compute encryption round
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