ChaCha20 and Poly1305 and their use in IPsec
draft-nir-ipsecme-chacha20-poly1305-00

Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Intended status: Experimental                           January 21, 2014
Expires: July 25, 2014

              ChaCha20 and Poly1305 and their use in IPsec
                 draft-nir-ipsecme-chacha20-poly1305-00

Abstract

   This document describes the use of the ChaCha20 stream cipher in
   IPsec, as well as the use of the Poly1305 authenticator, both as
   stand-alone algorithms, and as a combined mode AEAD algorithm.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used in This Document  . . . . . . . . . . . .  3
   2.  The Algorithms . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  The ChaCha20 block function  . . . . . . . . . . . . . . .  3
     2.2.  The ChaCha20 encryption algorithm  . . . . . . . . . . . .  4
     2.3.  The Poly1305 algorithm . . . . . . . . . . . . . . . . . .  5
     2.4.  AEAD Construction  . . . . . . . . . . . . . . . . . . . .  5
   3.  Algorithms for ESP & AH  . . . . . . . . . . . . . . . . . . .  6
     3.1.  ENCR_ChaCha20 for ESP  . . . . . . . . . . . . . . . . . .  6
     3.2.  AUTH_Poly1305 for ESP and AH . . . . . . . . . . . . . . .  7
     3.3.  ESP_ChaCha20-Poly1305 for ESP  . . . . . . . . . . . . . .  7
       3.3.1.  AAD Construction . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Examples of the algorithms  . . . . . . . . . . . . . 10
     A.1.  Example of the block function  . . . . . . . . . . . . . . 10
     A.2.  Example of ChaCha20 Encryption in IPsec  . . . . . . . . . 11
     A.3.  Example of the AUTH_Poly1305 . . . . . . . . . . . . . . . 12
     A.4.  Example of ESP_ChaCha20-Poly1305 in IPsec  . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   The Advanced Encryption Standard (AES - [FIPS-197]) has become the
   gold standard in encryption.  Its efficient design, wide
   implementation, and hardware support allow for high performance in
   many areas, including IPsec VPNs.  On most modern platforms, AES is
   anywhere from 4x to 10x as fast as the previous most-used cipher,
   3-key Data Encryption Standard (3DES - [FIPS-46]), which makes it not
   only the best choice, but the only choice.

   The problem is that if future advances in cryptanalysis reveal a
   weakness in AES, VPN users will be in an unenviable position.  With
   the only other widely supported cipher being the much slower 3DES, it
   is not feasible to re-configure IPsec implementations to use 3DES.
   [standby-cipher] describes this issue and the need for a standby
   cipher in greater detail.

   This document proposes such a standby cipher for IPsec.  We use
   ChaCha20 ([chacha]) with or without the Poly1305 ([poly1305])
   authenticator.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  The Algorithms

   The subsections below describe the algorithms used and the AEAD
   construction.

2.1.  The ChaCha20 block function

   The ChaCha20 block function is part of the ChaCha20 stream cipher
   (Section 2.2).  It uses a 256-bit key.  There are some variations
   defined, such as 128-bit keys, and 8- and 12-round variants, but this
   document defines only a 256-bit key and a 20-round ChaCha.  ChaCha20
   works on 512-bit blocks (64 bytes, or 16 32-bit words).  In this
   section we will describe the ChaCha block function.

   ChaCha maps an array of sixteen 32-bit input words to sixteen 32-bit
   output words.  The input words are partitioned as follows:
   o  The first 4 words (0-3) are constants: 0x61707865, 0x3320646e,
      0x79622d32, 0x6b206574.

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   o  The next 8 words (4-11) are taken from the 256-bit key by reading
      the bytes in little-endian order, in 4-byte chunks.
   o  Word 12 is a block counter.  Since each block is 64-byte, a 32-bit
      word is enough for 256 Gigabytes of data.
   o  Word 13 is called Sender ID, or SID.  Note that in the original
      ChaCha20 word 13 is also part of the block count, in case the
      encrypted data exceeds 256 gigabytes.  That is not necessary for
      IPsec.
   o  Words 14-15 are a nonce, which should not be repeated for the same
      combination of key and sender ID.  The 14th word is the least
      significant 32 bits of the input nonce (nonce | 0xffffffff), while
      the 15th word is the most significant 32 bits (nonce >> 32).

   ChaCha20 runs 20 rounds, alternating between "column" and "diagonal"
   rounds.  At the end of 20 rounds, the original input words are added
   to the output words, and the result is serialized by serializing the
   numbers in order, with the most significant octet of every 32-bit
   integer preceding the others.  See Appendix A.1 for an example of
   this serialization.

   The inputs to ChaCha20 are:
   o  A 256-bit key
   o  A 32-bit sender ID
   o  A 64-bit nonce, treated as a number
   o  A 32-bit block count parameter

   The output is 64 random-looking bytes.

2.2.  The ChaCha20 encryption algorithm

   ChaCha20 is a stream cipher designed by D. J. Bernstein.  It is a
   refinement of the Salsa20 algorithm, and uses a 256-bit key.  There
   are some variations defined, such as 128-bit keys, and 8- and 12-
   round variants, but this document defines only a 256-bit key and a
   20-round ChaCha.

   ChaCha20 successively calls the ChaCha20 block function, with the
   same key, sender ID and nonce, and with successively increasing block
   counter parameters.  Concatenating the results forms a key stream,
   which is then XOR-ed with the plaintext.  There is no requirement for
   the plaintext to be an integral multiple of 512-bits.  If there is
   extra keystream from the last block, it is discarded.

   The inputs to ChaCha20 are:
   o  A 256-bit key
   o  A 32-bit sender ID

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   o  A 32-bit initial counter
   o  A 64-bit nonce
   o  an arbitrary-length plaintext

   The output is an encrypted message of the same length.

2.3.  The Poly1305 algorithm

   Poly1305 is a one-time authenticator designed by D. J. Bernstein.
   Poly1305 takes a 32-byte one-time key and a message and produces a
   16-byte tag.

   The key MUST NOT be re-used.

   The inputs to Poly1305 are:
   o  A 256-bit one-time key
   o  An arbitrary length message

   The output is a 128-bit tag.

2.4.  AEAD Construction

   Note: Much of the content of this document, including this AEAD
   construction is taken from Adam Langley's draft ([agl-draft]) for the
   use of these algorithms in TLS.  The AEAD construction described here
   is called CHACHA20-POLY1305-ESP.

   The inputs to CHACHA20-POLY1305-ESP are:
   o  A 256-bit key
   o  A 32-bit sender ID
   o  A 64-bit nonce
   o  An arbitrary length plaintext
   o  Arbitrary length additional data

   The ChaCha20 and Poly1305 primitives are combined into an AEAD that
   takes a 256-bit key and 64-bit IV as follows:
   o  First the ChaCha20 block function with the key, sender ID, nonce,
      and zero for the block counter.  From the 64-byte output, the
      first 32 bytes are kept as the Poly1305 256-bit key.
   o  The ChaCha20 encryption function is called to encrypt the
      plaintext, using the same key, sender ID, nonce and plaintext, and
      with the initial counter set to 1.
   o  The Poly1305 function is called with the Poly1305 key calculated
      above, and a message constructed as a concatenation of the
      following:
      *  The additional data

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      *  The length of the additional data in octets (as a 32-bit
         network order integer)
      *  The ciphertext
      *  The length of the ciphertext in octets (as a 32-bit network
         order integer)

   Decryption is pretty much the same, but will be expanded later on.

   The output from the AEAD is twofold:
   o  A ciphertext of the same length as the plaintext.
   o  A 128-bit tag (the result of the Poly1305 function.

3.  Algorithms for ESP & AH

   This document defines three algorithms for use with the Encapsulated
   Security Protocol (ESP - [RFC4303]) and Authentication Header (AH -
   [RFC4302]):
   o  ChaCha20 for use as an encryption algorithms for ESP.
   o  Poly1305-MAC for use as a message authentication algorithm for ESP
      and AH.
   o  ChaCha20-Poly1305-ESP as an AEAD algorithm for ESP.

3.1.  ENCR_ChaCha20 for ESP

   For ChaCha20 used in ESP, the following parameters are used:
   o  The IV is 64-bit.  Since this is used as the nonce for the
      ChaCha20 function, this IV MUST NOT repeat.  The most natural way
      to implement this is with a counter, but anything that guarantees
      uniqueness can be used, such as a linear feedback shift register
      (LFSR).  Note that the encrypter can use any IV generation method
      that meets the uniqueness requirement, without coordinating with
      the decrypter.
   o  The Internet Key Exchange protocol (IKE - [RFC5996]) generates a
      bitstring called KEYMAT that is generated from a PRF.  That KEYMAT
      is divided into keys for encryption, message authentication and
      whatever else is needed.  For the ChaCha20 algorithm, 256 bits are
      used for the key.
   o  The ChaCha20 encryption algorithm is called with the 256-bit key,
      one (1) for the initial counter, the packet IV as a nonce, and the
      plaintext.  For regular IPsec, the Sender ID is set to zero.  For
      multi-sender SAs, such as described in [RFC6054], there sender ID
      can be set to a different value for each sender.  The 64-bit IV is
      treated as a 64-bit network order integer, and passed to the
      ChaCha20 function as a number.  The reason that one (1) is used
      for the initial counter rather than zero is that one is used for
      encryption in the AEAD algorithm (because zero is reserved for
      generating the one-time Poly1305 key), so one was used here for

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      consistency.
   o  As ChaCha20 is not a block cipher, no padding should be necessary.
      However, in keeping with the specification in RFC 4303, the ESP
      does have padding, so as to align the buffer to an integral
      multiple of 4 octets.

   The encryption algorithm transform ID for negotiating this algorithm
   in IKE is TBA by IANA.

3.2.  AUTH_Poly1305 for ESP and AH

   You cannot use a part of the keying material directly, because
   Poly1305 requires a different key for each authenticated message.  So
   the Poly1305 key for each message is generated as follows:
   o  The key for AUTH_Poly1305 is 256-bits.
   o  To determine the per-packet Poly1305 key, the ChaCha20 block
      function is called with the following parameters:
      *  The AUTH_Poly1305 256-bit key is used as the key.
      *  The sender ID is set to zero.
      *  The packet replay counter is used as the nonce.  If Extended
         Sequence Numbers (ESN) are employed, then the full 64-bit is
         used for the nonce.
      *  Zero is used for the block counter.
   o  The 512-bit result is then truncated.  The top 256 bits are used
      as the one-time key for Poly1305 to calculate the message
      authentication code (MAC).
   o  The 128-bit output serves as the MAC for the packet.  All 16 bytes
      are included in the packet.

   The integrity algorithm transform ID for negotiating this algorithm
   in IKE is TBA by IANA.

3.3.  ESP_ChaCha20-Poly1305 for ESP

   ESP_ChaCha20-Poly1305 is a combined mode algorithm, or AEAD.  The
   construction follows the AEAD construction in Section 2.4:
   o  As in Section 3.1, the IV is 64-bit, and is used as a nonce.
   o  Also as in Section 3.1, the encryption key is 256-bit.
   o  As in Section 3.2, the nonce, along with a block counter of zero
      is passed to the ChaCha20 block function, and the top part of the
      result used as the Poly1305 key.
   o  The ChaCha20 encryption function is then called with the nonce,
      the key, and an initial counter of zero.
   o  Finally, the Poly1305 function is run on the data to be
      authenticated, which is, as specified in Section 2.4 a
      concatenation of the following:

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      *  The Authenticated Additional Data (AAD) - see Section 3.3.1.
      *  The AAD length in bytes as a 32-bit network order quantity.
      *  The ciphertext
      *  The length of the ciphertext as a 32-bit network order
         quantity.
   o  The 128-bit output of Poly1305 is used as the tag.  All 16 bytes
      are included in the packet.

   The encryption algorithm transform ID for negotiating this algorithm
   in IKE is TBA by IANA.

3.3.1.  AAD Construction

   The construction of the Additional Authenticated Data (AAD) is
   similar to the one in [RFC4106].  For security associations (SAs)
   with 32-bit sequence numbers the AAD is 8 bytes: 4-byte SPI followed
   by 4-byte sequence number ordered exactly as it is in the packet.
   For SAs with ESN the AAD is 12 bytes: 4-byte SPI followed by an
   8-byte sequence number as a 64-bit network order integer.

4.  Security Considerations

   The ChaCha20 cipher is designed to provide 256-bit security.

   The Poly1305 authenticator is designed to ensure that forged messages
   are rejected with a probability of 1-(n/(2^102)) for a 16n-byte
   message, even after sending 2^64 legitimate messages, so it is SUF-
   CMA in the terminology of [AE].

   The most important security consideration in implementing this draft
   is the uniqueness of the nonce used in ChaCha20.  This is trivial in
   AUTH_Poly1305, because the packet sequence number is used as a nonce,
   but is required for ChaCha20 as well.  As said in Section 3.1, the
   nonce should be selected uniquely for a particular key. counters and
   LFSRs are both acceptable ways of generating unique nonces, as is
   encrypting a counter using a 64-bit cipher such as DES.  Note that it
   is not acceptable to use a truncation of a counter encrypted with a
   128-bit or 256-bit cipher, because such a truncation may repeat after
   a short time.

   The same kind of collision risk as in the above paragraph also exists
   in the selection of the Poly1305 key in both the AEAD construction
   (Section 2.4) and in the AUTH_Poly1305 algorithm (Section 3.2).
   ChaCha20 is used to generate a 512-bit value, which is unique to each
   packet, but this uniqueness is not guaranteed for its 256-bit
   truncation, which serves as the actual key for Poly1305.  While
   uniqueness is not guaranteed, it is still very likely.  Birthday

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   paradox calculations show that generating Poly1305 keys needs to
   happen over 2^101 times (way more than the 2^64 allowed by IPsec) to
   drive the chances of collision up to 0.00000000000001%.  This is why
   we may safely ignore the possibility of collision.

5.  IANA Considerations

   IANA is requested to assign two values from the IKEv2 "Transform Type
   1 - Encryption Algorithm Transform IDs" registry, as follows:
   o  ENCR_ChaCha20
   o  ESP_ChaCha20-Poly1305

   IANA is also requested to assign one value from the IKEv2 "Transform
   Type 3 - Integrity Algorithm Transform IDs" registry with name
   "AUTH_Poly1305".

6.  Acknowledgements

   Much of the text in this document was inspired by Adam Langley's
   draft for TLS, and by "inspired" I mean "shamelessly copied".  The
   author would also like to thank Adam, Watson Ladd and Dave McGrew for
   allaying his fears about writing a document describing crypto.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5996, September 2010.

   [RFC6054]  McGrew, D. and B. Weis, "Using Counter Modes with
              Encapsulating Security Payload (ESP) and Authentication
              Header (AH) to Protect Group Traffic", RFC 6054,
              November 2010.

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   [chacha]   Bernstein, D., "ChaCha, a variant of Salsa20", Jan 2008.

   [poly1305]
              Bernstein, D., "The Poly1305-AES message-authentication
              code", Mar 2005.

7.2.  Informative References

   [AE]       Bellare, M. and C. Namprempre, "Authenticated Encryption:
              Relations among notions and analysis of the generic
              composition paradigm",
              <http://cseweb.ucsd.edu/~mihir/papers/oem.html>.

   [FIPS-197]
              National Institute of Standards and Technology, "Advanced
              Encryption Standard (AES)", FIPS PUB 197, November 2001, <
              http://csrc.nist.gov/publications/fips/fips197/
              fips-197.pdf>.

   [FIPS-46]  National Institute of Standards and Technology, "Data
              Encryption Standard", FIPS PUB 46-2, December 1993,
              <http://www.itl.nist.gov/fipspubs/fip46-2.htm>.

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, June 2005.

   [agl-draft]
              Langley, A. and W. Chang, "ChaCha20 and Poly1305 based
              Cipher Suites for TLS", draft-agl-tls-chacha20poly1305-04
              (work in progress), November 2013.

   [standby-cipher]
              McGrew, D., Grieco, A., and Y. Sheffer, "Selection of
              Future Cryptographic Standards",
              draft-mcgrew-standby-cipher (work in progress).

Appendix A.  Examples of the algorithms

A.1.  Example of the block function

   In this example, we show a single run of the ChaCha20 block.  For our
   example, we choose
   o  Key:
      000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f

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   o  Sender ID: 0
   o  Nonce: fedcba9876543210
   o  Block Count: 5

   The block is set up as follows:

      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000005 00000000 76543210 fedcba98

   After running the block function, the result is as follows:

      a435cd80 a16b9b89 9112c0a4 487b4230
      0d98f8cf b5b59396 4cce17a6 d17db31a
      6dd35e45 658dff64 52b615fb b3c17e96
      31d2725f ecd5246f 739bdab7 07cf7593

   The resulting octet string looks like this:

   a435cd80a16b9b899112c0a4487b42300d98f8cfb5b593964cce17a6d17db31a
   6dd35e45658dff6452b615fbb3c17e9631d2725fecd5246f739bdab707cf7593

A.2.  Example of ChaCha20 Encryption in IPsec

   In this example, we show a run of the ChaCha20 encryption function.
   For our example, we chose some arbitrary data.  Also,
   o  Key:
      000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
   o  Sender ID: 0
   o  IV: 0x000000000000004a (74)
   o  Message Length: 80 octets
   o  The message itself:

   35:6f:16:49:d0:2a:7f:19:30:f1:8f:af:e6:d1:69:d3:22:12:1f:76:78:be:6c
   af:90:17:f3:fb:8e:12:d3:f1:f7:dc:7c:31:02:70:36:54:0c:5a:37:aa:31:fd
   8a:e2:31:73:8a:ff:cc:77:8c:ba:c4:7b:6b:d1:17:6c:ce:cc:90:56:ae:65:b9
   c6:af:40:e6:9d:f4:37:8f:4a:a9:f3

   First, we need to apply padding.  We will use an ESP-style padding,
   rounding up the length of the packet to 84 octets, with two padding
   bytes, a pad length, and a Next Header field set to 0x04:

   35:6f:16:49:d0:2a:7f:19:30:f1:8f:af:e6:d1:69:d3:22:12:1f:76:78:be:6c
   af:90:17:f3:fb:8e:12:d3:f1:f7:dc:7c:31:02:70:36:54:0c:5a:37:aa:31:fd
   8a:e2:31:73:8a:ff:cc:77:8c:ba:c4:7b:6b:d1:17:6c:ce:cc:90:56:ae:65:b9
   c6:af:40:e6:9d:f4:37:8f:4a:a9:f3:01:02:02:04

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   For 84 octets, we need two blocks.  We call the block function twice,
   once with the block counter set to 1, and then again with the block
   counter set to two.  The results are as follows:

   Block 1 before rounds:
      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000001 00000000 0000004a 00000000

   Block 1 after rounds:
      9944f9d8 0f69b9cc 9002b600 559b9586
      04579a7b a9a146c0 a601d9dd 8a141b06
      d08a69bb e737527d 0ee7970d ff8512d8
      d959240f 0f09eb18 eb0f2a3a ee0fbcf2

   Block 2 before rounds:
      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000002 00000000 0000004a 00000000

   Block 2 after rounds:
      213bebc0 720ce566 26195c71 84e2ee1d
      511f64c2 b8ed11da ede4e571 d9b57c34
      0aa05765 dd073b1c 22d7dc84 86c91bc0
      a9b89717 dbf8c56f 5822cafd deec62ff

   84 bytes of key stream:
   99:44:f9:d8:0f:69:b9:cc:90:02:b6:00:55:9b:95:86:04:57:9a:7b:a9:a1:46
   c0:a6:01:d9:dd:8a:14:1b:06:d0:8a:69:bb:e7:37:52:7d:0e:e7:97:0d:ff:85
   12:d8:d9:59:24:0f:0f:09:eb:18:eb:0f:2a:3a:ee:0f:bc:f2:21:3b:eb:c0:72
   0c:e5:66:26:19:5c:71:84:e2:ee:1d:51:1f:64:c2

   XOR'd with the plaintext:
   ac:2b:ef:91:df:43:c6:d5:a0:f3:39:af:b3:4a:fc:55:26:45:85:0d:d1:1f:2a
   6f:36:16:2a:26:04:06:c8:f7:27:56:15:8a:e5:47:64:29:02:bd:a0:a7:ce:78
   98:3a:e8:2a:ae:f0:c3:7e:67:a2:2f:74:41:eb:f9:63:72:3e:b1:6d:45:a5:cb
   ca:4a:26:c0:84:a8:46:0b:a8:47:ee:50:1d:66:c6

A.3.  Example of the AUTH_Poly1305

   In this example, we show a run of the AUTH_Poly1305 message
   authentication function.  For our example, we choose some arbitrary
   data - the same data as in the ENCH_ChaCha20 example above.  Also,
   o  Key:
      000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f

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   o  Replay Counter: 0x0000004a (74)
   o  Message Length: 80 octets
   o  The message itself:

   35:6f:16:49:d0:2a:7f:19:30:f1:8f:af:e6:d1:69:d3:22:12:1f:76:78:be:6c
   af:90:17:f3:fb:8e:12:d3:f1:f7:dc:7c:31:02:70:36:54:0c:5a:37:aa:31:fd
   8a:e2:31:73:8a:ff:cc:77:8c:ba:c4:7b:6b:d1:17:6c:ce:cc:90:56:ae:65:b9
   c6:af:40:e6:9d:f4:37:8f:4a:a9:f3

   First, we run the ChaCha20 algorithm to generate the one-time
   Poly1305 key:

   Key block before the rounds:
      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000000 00000000 0000004a 00000000

   Key block after rounds:
      64345099 66639817 2113da66 371489fa
      091f5ff3 c681552b b0f0a4b5 d0d7e6dd
      5401d1e1 b6ff30e5 25a5a57c b1af2f06
      8a064ae1 39b28c25 9698451b c688b187

   256-bit one-time Poly1305 key:
   64345099666398172113da66371489fa091f5ff3c681552bb0f0a4b5d0d7e6dd

   Tag: 43dc3ef779160bb54943a2279570d679

A.4.  Example of ESP_ChaCha20-Poly1305 in IPsec

   In this example, we encrypt the same data as in Appendix A.2, and
   also authenticate it.  For the purposes of this example, we will
   assume that ESN is not used.
   o  Key:
      000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
   o  Sender ID: 0
   o  SPI: 0x7890abcd
   o  IV: 0x000000000000004a (74)
   o  Message Length: 80 octets
   o  The message itself:

   35:6f:16:49:d0:2a:7f:19:30:f1:8f:af:e6:d1:69:d3:22:12:1f:76:78:be:6c
   af:90:17:f3:fb:8e:12:d3:f1:f7:dc:7c:31:02:70:36:54:0c:5a:37:aa:31:fd
   8a:e2:31:73:8a:ff:cc:77:8c:ba:c4:7b:6b:d1:17:6c:ce:cc:90:56:ae:65:b9
   c6:af:40:e6:9d:f4:37:8f:4a:a9:f3

   First, we repeat the calculations in Appendix A.3 to get the one-time

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   Poly1305 key:

   Key block before the rounds:
      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000000 00000000 0000004a 00000000

   Key block after rounds:
      64345099 66639817 2113da66 371489fa
      091f5ff3 c681552b b0f0a4b5 d0d7e6dd
      5401d1e1 b6ff30e5 25a5a57c b1af2f06
      8a064ae1 39b28c25 9698451b c688b187

   256-bit one-time Poly1305 key:
   64345099666398172113da66371489fa091f5ff3c681552bb0f0a4b5d0d7e6dd

   Next, we need to apply padding.  We will use an ESP-style padding,
   rounding up the length of the packet to 84 octets, with two padding
   bytes, a pad length, and a Next Header field set to 0x04:

   35:6f:16:49:d0:2a:7f:19:30:f1:8f:af:e6:d1:69:d3:22:12:1f:76:78:be:6c
   af:90:17:f3:fb:8e:12:d3:f1:f7:dc:7c:31:02:70:36:54:0c:5a:37:aa:31:fd
   8a:e2:31:73:8a:ff:cc:77:8c:ba:c4:7b:6b:d1:17:6c:ce:cc:90:56:ae:65:b9
   c6:af:40:e6:9d:f4:37:8f:4a:a9:f3:01:02:02:04

   Step 3, we run the ChaCha20 block twice to create sufficient
   keystream to XOR with all the (padded) plaintext.

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   Block 1 before rounds:
      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000001 00000000 0000004a 00000000

   Block 1 after rounds:
      9944f9d8 0f69b9cc 9002b600 559b9586
      04579a7b a9a146c0 a601d9dd 8a141b06
      d08a69bb e737527d 0ee7970d ff8512d8
      d959240f 0f09eb18 eb0f2a3a ee0fbcf2

   Block 2 before rounds:
      61707865 3320646e 79622d32 6b206574
      03020100 07060504 0b0a0908 0f0e0d0c
      13121110 17161514 1b1a1918 1f1e1d1c
      00000002 00000000 0000004a 00000000

   Block 2 after rounds:
      213bebc0 720ce566 26195c71 84e2ee1d
      511f64c2 b8ed11da ede4e571 d9b57c34
      0aa05765 dd073b1c 22d7dc84 86c91bc0
      a9b89717 dbf8c56f 5822cafd deec62ff

   84 bytes of key stream:
   99:44:f9:d8:0f:69:b9:cc:90:02:b6:00:55:9b:95:86:04:57:9a:7b:a9:a1:46
   c0:a6:01:d9:dd:8a:14:1b:06:d0:8a:69:bb:e7:37:52:7d:0e:e7:97:0d:ff:85
   12:d8:d9:59:24:0f:0f:09:eb:18:eb:0f:2a:3a:ee:0f:bc:f2:21:3b:eb:c0:72
   0c:e5:66:26:19:5c:71:84:e2:ee:1d:51:1f:64:c2

   XOR'd with the plaintext:
   ac:2b:ef:91:df:43:c6:d5:a0:f3:39:af:b3:4a:fc:55:26:45:85:0d:d1:1f:2a
   6f:36:16:2a:26:04:06:c8:f7:27:56:15:8a:e5:47:64:29:02:bd:a0:a7:ce:78
   98:3a:e8:2a:ae:f0:c3:7e:67:a2:2f:74:41:eb:f9:63:72:3e:b1:6d:45:a5:cb
   ca:4a:26:c0:84:a8:46:0b:a8:47:ee:50:1d:66:c6

   next, we construct the AEAD.  As described in Section 3.3.1, the AAD
   is a concatenation of the 4-byte SPI, followed by a 4-byte sequence
   number.  In this case: 78:90:ab:cd:00:00:00:4a.  The Poly1305
   function is run over a concatenation of the AAD, the length of the
   AAD as a 32-bit integer (8), The ciphertext, and the length of the
   ciphertext (84):

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   Buffer to be authenticated:
   78:90:ab:cd:00:00:00:4a:00:00:00:08:ac:2b:ef:91:df:43:c6:d5:a0:f3:39
   af:b3:4a:fc:55:26:45:85:0d:d1:1f:2a:6f:36:16:2a:26:04:06:c8:f7:27:56
   15:8a:e5:47:64:29:02:bd:a0:a7:ce:78:98:3a:e8:2a:ae:f0:c3:7e:67:a2:2f
   74:41:eb:f9:63:72:3e:b1:6d:45:a5:cb:ca:4a:26:c0:84:a8:46:0b:a8:47:ee
   50:1d:66:c6:00:00:00:54

   Tag: 7af839e8f4961cd99f0600dc7b8ad8d6

Author's Address

   Yoav Nir
   Check Point Software Technologies Ltd.
   5 Hasolelim st.
   Tel Aviv  6789735
   Israel

   Email: ynir@checkpoint.com

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