Telnet Encryption: DES3 64 bit Cipher Feedback
RFC 2947
| Document | Type |
RFC - Proposed Standard
(September 2000; No errata)
Was draft-altman-telnet-enc-des3-cfb (individual)
|
|
|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | Legacy | ||
| Formats | plain text pdf html bibtex | ||
| Stream | Legacy state | (None) | |
| Consensus Boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | RFC 2947 (Proposed Standard) | |
| Telechat date | |||
| Responsible AD | (None) | ||
| Send notices to | (None) | ||
Network Working Group J. Altman
Request for Comments: 2947 Columbia University
Category: Standards Track September 2000
Telnet Encryption: DES3 64 bit Cipher Feedback
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document specifies how to use the Triple-DES (data encryption
standard) encryption algorithm in cipher feedback mode with the
telnet encryption option.
1. Command Names and Codes
Encryption Type
DES3_CFB64 3
Suboption Commands
CFB64_IV 1
CFB64_IV_OK 2
CFB64_IV_BAD 3
2. Command Meanings
IAC SB ENCRYPT IS DES3_CFB64 CFB64_IV <initial vector> IAC SE
The sender of this command generates a random 8 byte initial vector,
and sends it to the other side of the connection using the CFB64_IV
command. The initial vector is sent in clear text. Only the side of
the connection that is WILL ENCRYPT may send the CFB64_IV command.
Altman Standards Track [Page 1]
RFC 2947 DES3 64 bit Cipher Feedback September 2000
IAC SB ENCRYPT REPLY DES3_CFB64 CFB64_IV_OK IAC SE IAC SB ENCRYPT
REPLY DES3_CFB64 CFB64_IV_BAD IAC SE
The sender of these commands either accepts or rejects the initial
vector received in a CFB64_IV command. Only the side of the
connection that is DO ENCRYPT may send the CFB64_IV_OK and
CFB64_IV_BAD commands. The CFB64_IV_OK command MUST be sent for
backwards compatibility with existing implementations; there really
isn't any reason why a sender would need to send the CFB64_IV_BAD
command except in the case of a protocol violation where the IV
sent was not of the correct length (i.e., 8 bytes).
3. Implementation Rules
Once a CFB64_IV_OK command has been received, the WILL ENCRYPT side
of the connection should do keyid negotiation using the ENC_KEYID
command. Once the keyid negotiation has successfully identified a
common keyid, then START and END commands may be sent by the side of
the connection that is WILL ENCRYPT. Data will be encrypted using
the DES3 64 bit Cipher Feedback algorithm.
If encryption (decryption) is turned off and back on again, and the
same keyid is used when re-starting the encryption (decryption), the
intervening clear text must not change the state of the encryption
(decryption) machine.
If a START command is sent (received) with a different keyid, the
encryption (decryption) machine must be re-initialized immediately
following the end of the START command with the new key and the
initial vector sent (received) in the last CFB64_IV command.
If a new CFB64_IV command is sent (received), and encryption
(decryption) is enabled, the encryption (decryption) machine must be
re-initialized immediately following the end of the CFB64_IV command
with the new initial vector, and the keyid sent (received) in the
last START command.
If encryption (decryption) is not enabled when a CFB64_IV command is
sent (received), the encryption (decryption) machine must be re-
initialized after the next START command, with the keyid sent
(received) in that START command, and the initial vector sent
(received) in this CFB64_IV command.
Altman Standards Track [Page 2]
RFC 2947 DES3 64 bit Cipher Feedback September 2000
4. Algorithm
DES3 64 bit Cipher Feedback
key1 key2 key3
| | |
v v v
+-------+ +-------+ +-------+
+->| DES-e |->| DES-d |->| DES-e |-- +
| +-------+ +-------+ +-------+ |
| v
INPUT --(-------------------------------->(+)+---> DATA
| |
+------------------------------------+
Given:
iV: Initial vector, 64 bits (8 bytes) long.
Dn: the nth chunk of 64 bits (8 bytes) of data to encrypt (decrypt).
On: the nth chunk of 64 bits (8 bytes) of encrypted (decrypted) output.
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