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Telnet Encryption: CAST-128 64 bit Output Feedback (RFC2949)

IP.com Disclosure Number: IPCOM000005142D
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2001-Aug-16
Document File: 6 page(s) / 9K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Altman: AUTHOR

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.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 35% of the total text.

Network Working Group J. Altman Request for Comments: 2949 Columbia University Category: Standards Track September 2000

Telnet Encryption: 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.

Altman Standards Track [Page 1]

RFC 2949 CAST-128 64 bit Output Feedback September 2000

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 (rece...