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Encrypting User Password Strings

September 10, 2012 Leave a comment Go to comments

Encrypting User Password Strings

The Use Case

User account passwords can be set during systems provisioning in multiple ways. Setting a host’s root password is a common use case. During a FreeBSD 8.x install, one can set root’s password (or other user account password) executing the following within the install.cfg:

/bin/sh -c ‘echo passwd |pw mod user username -h 0’

Unfortunately, doing so exposes the user’s account password. Therefore, the recommendation is to use an encrypted hash as follows:

/usr/bin/chpass -p $1$nPUexUs5$O4JuN.Ed/LqWHJKmf8K0h0 root

Encrypting The Password

The use case begs the question: How does one ascertain an encrypted hash given a string?

On FreeBSD, there are varying methods to ascertain an encrypted hash. Here are just two of the many.

openssl

# openssl passwd -1 MySecret
$1$YRth1v3T$MvGupL8n.VBjvM12JhR4G0

openssl(1) returns the entire encrypted hash. The character between the first and second dollar signs identifies the crypt mechanism. The following eight characters are the salt. The remaining characters following the third dollar sign are the encrypted string.

md5

# md5 -s MySecret
MD5 (“MySecret”) = 4132d75e6cb04073cc7756707057027f

md5(1) returns a partial encrypted hash. In the key-value pair, the key is the crypt mechanism. The first 8 characters of the value are the salt. The remaining characters are the encrypted string.

In this method, one must prepend $1$ to the value before feeding it into chpass(1).

Related Documentation

* Chapter 15, Security, of the FreeBSD handbook explains identifying a host’s crypt mechanism.

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