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至顶网网络频道CAST-128 64 bit Output Feedback(1)

CAST-128 64 bit Output Feedback(1)

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This document specifies how to use the CAST-128 encryption algorithm in output feedback mode with the telnet encryption option. Two key sizes are defined: 40 bit and 128 bit.

作者:论坛整理 来源:ZDNet网络安全 2007年12月25日

关键字: telnet命令 opentelnet linux telnet telnet入侵 telnet telnet端口

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  Network Working Group J. Altman

  Request for Comments: 2949 Columbia University

  Category: Standards Track September 2000

  TelnetEncryption: CAST-128 64 bit Output 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 CAST-128 encryption algorithm in output feedback mode with the telnet encryption option. Two key sizes are defined: 40 bit and 128 bit.

  1. Command Names and Codes

  Encryption Type

  CAST5_40_OFB64 9

  CAST128_OFB64 11

  Suboption Commands

  OFB64_IV 1

  OFB64_IV_OK 2

  OFB64_IV_BAD 3

  2. Command Meanings

  IAC SB ENCRYPT IS CAST5_40_OFB64 OFB64_IV IAC SE

  IAC SB ENCRYPT IS CAST128_OFB64 OFB64_IV 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 OFB64_IV command. The initial vector is sent in clear text. Only the side of the connection that is WILL ENCRYPT may send the

  OFB64_IV command.

  IAC SB ENCRYPT REPLY CAST5_40_OFB64 OFB64_IV_OK IAC SE

  IAC SB ENCRYPT REPLY CAST128_OFB64 OFB64_IV_OK IAC SE

  IAC SB ENCRYPT REPLY CAST5_40_OFB64 OFB64_IV_BAD IAC SE

  IAC SB ENCRYPT REPLY CAST128_OFB64 OFB64_IV_BAD IAC SE

  The sender of these commands either accepts or rejects the initial vector received in a OFB64_IV command. Only the side of the connection that is DO ENCRYPT may send the OFB64_IV_OK and OFB64_IV_BAD commands. The OFB64_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 OFB64_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 OFB64_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 CAST128 64 bit Output 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 OFB64_IV command.

  If a new OFB64_IV command is sent (received), and encryption (decryption) is enabled, the encryption (decryption) machine must be re-initialized immediately following the end of the OFB64_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 OFB64_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 OFB64_IV command.

  4. Algorithm

  CAST 64 bit Output Feedback

  key --->+------+

  +->| CAST |--+

  | +------+ |

  +------------+

  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.

  V0 = CAST(iV, key)

  V(n+1) = CAST(Vn, key)

  On = Dn ^ Vn

  5. Integration with the AUTHENTICATION telnet option

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