---
name: "encode_keychange"
section: "1"
platform: "linux"
package: "net-snmp"
version: "5.9.5.2-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/encode_keychange"
---

# encode\_keychange(1)

produce the KeyChange string for SNMPv3

## NAME

encode\_keychange - produce the KeyChange string for SNMPv3

## SYNOPSIS

**encode\_keychange** -t md5\|sha1 \[*OPTIONS*\]

## DESCRIPTION

**encode\_keychange** produces a KeyChange string using the old and new passphrases  as described in Section 5 of RFC 2274 "User-based Security Model (USM) for  version 3 of the Simple Network Management Protocol (SNMPv3)". **-t** option is mandatory and specifies the hash transform type to use.

The transform is used to convert passphrase to master key for a given user (Ku), convert master key to the localized key (Kul), and to hash the  old Kul with the random bits.

Passphrases are obtained by examining a number of sources until success (in order listed):

-

  command line options (see  **-N** and **-O** options below);

-

  the file  **$HOME/.snmp/passphrase.ek** which should only contain two lines with old and new passphrase;

-

  standard input **-or-**  user input from the terminal.

## OPTIONS

- **-E** \[0x\]\<*engineID*\> EngineID used for Kul generation.

  \<*engineID*\> is interpreted as a hex string when preceded by 0x, otherwise it is treated as a text string. If no \<*engineID*\> is specified, it is constructed from the first IP address for the local host.

- **-f**

  Force passphrases to be read from standard input.

- **-h**

  Display the help message.

- **-N** "\<*new\_passphrase*\>"

  Passphrase used to generate the new Ku.

- **-O** "\<*old\_passphrase*\>"

  Passphrase used to generate the old Ku.

- **-P**

  Turn off the prompt for passphrases when getting data from standard input.

- **-v**

  Be verbose.

- **-V**

  Echo passphrases to terminal.

## SEE ALSO

The localized key method is defined in RFC 2274, Sections 2.6 and A.2, and originally documented in

-

  U. Blumenthal, N. C. Hien, B. Wijnen, "Key Derivation for Network Management Applications", IEEE Network Magazine, April/May issue, 1997.