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I need a Documentation to explain in detail the Telnet Fields particularly telnet.enc.type_data

asked 2021-02-02 08:44:04 +0000

khadeeja gravatar image

I need a Documentation to explain in detail the Telnet Fields particularly telnet.enc.type_data

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answered 2021-02-02 17:35:18 +0000

Chuckc gravatar image

updated 2021-02-02 17:57:56 +0000

Looks like the telnet dissector could go a step farther and break out the IV.
Original added here: "updated the TELNET dissector to dissect encryption negotiation commands as specified by RFC 2946"

RFC 2952 - "Telnet Encryption: DES 64 bit Cipher Feedback"

1.  Command Names and Codes

   Encryption Type

      DES_CFB64        1

   Suboption Commands

      CFB64_IV         1
      CFB64_IV_OK      2
      CFB64_IV_BAD     3

2.  Command Meanings

   IAC SB ENCRYPT IS DES_CFB64 CFB64_IV <initial vector> IAC SE

The extra byte (01) before the IV in your data: Type-specific data: 011213141516171819 is the Suboption Command to indicate an IV follows.
I don't see any open issues related to this. Steps to open one here: ReportingBugs

#define TN_ENCTYPE_NULL                 0
#define TN_ENCTYPE_DES_CFB64            1
#define TN_ENCTYPE_DES_OFB64            2
#define TN_ENCTYPE_DES3_CFB64           3
#define TN_ENCTYPE_DES3_OFB64           4
#define TN_ENCTYPE_CAST5_40_CFB64       8
#define TN_ENCTYPE_CAST5_40_OFB64       9
#define TN_ENCTYPE_CAST128_CFB64        10
#define TN_ENCTYPE_CAST128_OFB64        11

The RFCs for currently supported encryption types use the same verbage:

The sender of this command generates a random 8 byte initial
vector, and sends it to the other side of the connection using the
"encryption type"_IV command.
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Thanks very much for this informations. It was helpful.

khadeeja gravatar imagekhadeeja ( 2021-02-03 09:29:57 +0000 )edit

answered 2021-02-02 10:44:52 +0000

Jaap gravatar image

As per RFC 2946 this depends on the selected type of encryption. These are further referenced in the IANA registry.

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These documents don't specify what the telnet.enc.type_data refer to. in my case, the telnet encryption type is DES_CFB64 so the telnet.enc.type_data could be the IV, but the problem is the IV must be 8 bytes and the telnet.enc.type_data is 9 byte (011213141516171819)

here is the entire packet:


Frame 4: 82 bytes on wire (656 bits), 82 bytes captured (656 bits) Ethernet II, Src: xxx, Dst: xxx Internet Protocol Version 4, Src: x.x.x.x, Dst: x.x.x.x Transmission Control Protocol, Src Port: 42818, Dst Port: 23, Seq: 1, Ack: 1, Len: 16 Telnet Suboption Encryption Option Command: Suboption (250) Subcommand: Encryption Option Enc Cmd: IS (0) Enc Type: DES_CFB64 (1) Type-specific data: 011213141516171819 Suboption End Command: Suboption End (240)


any help in what the telnet.enc.type_data ( Type-specific data) refer to?

khadeeja gravatar imagekhadeeja ( 2021-02-02 11:48:32 +0000 )edit

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Asked: 2021-02-02 08:44:04 +0000

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Last updated: Feb 02