Converting Password Schemes

Introduction

Through the years computers are being faster and faster, and so with it the encryption of passwords have to more secure. In this example we convert passwords stored in MySQL with basic CRYPT-encryption to SSHA256-encryption (Salted SHA256).

See password schemes for a list of supported password schemes.

We used php to generate the new passwords, but you can use any language you want

Alternative example can be found at: https://kaworu.ch/blog/2016/04/20/strong-crypt-scheme-with-dovecot-postfixadmin-and-roundcube.

Example

Copy the CRYPT-passwords to a new field (newpassword) but with the prefix {CRYPT}. This might start you off in the right direction for mysql: UPDATE 'your_table' SET field_name = CONCAT('{CRYPT}', field_name)

Change dovecot-sql.conf, so it will look at the new fields

Details

# Comment default_pass_scheme so dovecot will look at the prefix
# default_pass_scheme = CRYPT

# update your password_query so it will look at the new field
# AND add a %w field in the query so we have the plain password in our
# Enviroment ($PLAIN_PASS)
password_query = SELECT id as user, newpassword as password, \
    home as userdb_home, uid as userdb_uid, gid as userdb_gid, \
    '%w' as userdb_plain_pass FROM users WHERE id = '%u'

# Alternatively, here is another config that worked for me with
# SHA512-CRYPT (note: uncomment the lines relevant for your setup):
#
# driver = mysql
# connect = host=127.0.0.1 user=mailauth password=secret dbname=postfixadmin
# default_pass_scheme = SHA512-CRYPT
# password_query = SELECT username AS user, password, CONCAT('/var/mail/vdomains/', maildir) as userdb_home, 'vmail' as userdb_uid, 'vmail' as userdb_gid, '%w' as userdb_plain_pass FROM mailbox WHERE username = '%u'
# user_query = SELECT CONCAT('/var/mail/vdomains/', maildir) AS home, 'vmail' AS uid, 'vmail' AS gid, password FROM mailbox WHERE username = '%u' AND active = 1

dovecot.conf:
```
userdb {
  driver = prefetch
}
```
Now reload dovecot, and see everything is still working.
Make the postlogin-script (which is executed after login) and save it as /usr/local/etc/popafter.sh:
sh
```
#!/bin/sh
/usr/local/etc/convertpw.php $USER $PLAIN_PASS
exec "$@"
```

Make the php-script which updates the password and save it as /usr/local/etc/convertpw.php:

Details

php

#!/usr/local/bin/php
<?php
$mysqlhost  = "localhost";
$mysqluser  = "mysqlusername"; // username which is used to connect to the database
$mysqlpass  = "mysqlpassword"; // password which is used to connect to the database
$mysqldb    = "database";      // database where the passwords are stored
$mysqltable = "users";         // table where the passwords are stored
$idfield    = "id";            // fieldname where the userlogin is stored
$passfield  = "newpassword";   // fieldname where the passwords is stored

$user = $argv[1];
$cur_password = $argv[2];
function hexToAscii($hex){
    $strLength = strlen($hex);
    $returnVal = '';
    for($i=0; $i<$strLength; $i += 2) {
        $dec_val = hexdec(substr($hex, $i, 2));
        $returnVal .= chr($dec_val);
    }
    return $returnVal;
}
$link = mysql_connect ("$mysqlhost", "$mysqluser", "$mysqlpass")  or die ("Could not connect");
@mysql_select_db("$mysqldb") or die( "Unable to select database");
$result = mysql_query("SELECT $passfield FROM $mysqltable WHERE $idfield = '$user' AND $passfield like '{SSHA%'");
if (mysql_num_rows($result)==0){
        $salt=substr(sha1(uniqid()),18,8);
        $salt_ascii = hexToAscii($salt);
        $new_query= "UPDATE $mysqltable SET $passfield='{SSHA256.hex}".hash('sha256',$cur_password.$salt_ascii).$salt."' WHERE $idfield='".$user."'";
        $res2 = mysql_query($new_query);
}
exit;
?>

Update your dovecot.conf so it will use the scripts we just made:

# insert these lines so dovecot uses our scripts
service pop3 {
  executable = pop3 pop3-postlogin
}

service pop3-postlogin {
  executable = script-login /usr/local/etc/popafter.sh
  user = $default_internal_user
  unix_listener pop3-postlogin {
  }
}

Reload Dovecot.

As of now, each user which connects through POP will convert their password to SSHA256.

If you look at the database you will see, for example, {SSHA256.hex}fb0e7f39c88c1d7017169f7f6b9cd6977d1e3291149382b90da4a390a31e81bab3cdced8 instead of {CRYPT}$1$.gvrgDqc$Slvoapz5zkpVmmJAxi.0k1.

If you are using IMAP, you will need to add the same kind of commands (i.e. imap-postlogin) to your config, too.

When every record is updated, you can update dovecot.conf (remove the extra lines), and dovecot-sql.conf (remove the %w-part).

SHA512-CRYPT

To use SHA512-CRYPT passwords use /usr/local/etc/popafter.sh:

#!/bin/sh
DOVECOTPW=$(doveadm pw -s SHA512-CRYPT -p $PLAIN_PASS)
/usr/local/etc/convertpw.php $USER $DOVECOTPW
exec "$@"

A variant that does not leak the password to the process list:

Details

ScriptAlternate Version/usr/local/etc/convertpw.php

#!/bin/sh
NEWPASSWORD=$(doveadm pw -s SHA512-CRYPT <<EOF
$PLAIN_PASS
$PLAIN_PASS
EOF
)
/etc/dovecot/convert-password.php "$USER" "$NEWPASSWORD"
exec "$@"

bash

#!/usr/local/bin/bash

# Here is an alterate version that I used with SHA512-CRYPT and bash
# (note: uncomment the lines relevant for your setup including the ones
# I added for debugging purposes if needed):
# echo "USER: $USER" >> /tmp/log
# echo "PLAIN-PASS: $PLAIN_PASS" >> /tmp/log
DOVECOTPW=$(/usr/local/bin/doveadm pw -s SHA512-CRYPT -p "$PLAIN_PASS")
# echo $DOVECOTPW >> /tmp/log
/usr/local/etc/convertpw.php $USER $DOVECOTPW
exec "$@"
# note: if enabled, some of the lines above will log passwords to /tmp/log.
# Create the file first, and delete it when no longer needed -
# this while approach is a security risk and should *never* be done in a
# production system. I had to use it for troubleshooting for a very
# limited period of time.

#!/usr/bin/php
<?php
$mysqlhost  = "127.0.0.1";
$mysqluser  = "postfix";     // username which is used to connect to the database
$mysqlpass  = "password";    // password which is used to connect to the database
$mysqldb    = "postfix";     // database where the passwords are stored
$mysqltable = "mailbox";     // table where the passwords are stored
$idfield    = "username";    // fieldname where the userlogin is stored
$passfield  = "password";    // fieldname where the passwords is stored

$usr = $argv[1];
$dov = $argv[2];
function hexToAscii($hex){
    $strLength = strlen($hex);
    $returnVal = '';
    for($i=0; $i<$strLength; $i += 2) {
        $dec_val = hexdec(substr($hex, $i, 2));
        $returnVal .= chr($dec_val);
    }
    return $returnVal;
}
$link = mysql_connect ("$mysqlhost", "$mysqluser", "$mysqlpass")  or die ("Could not connect");
@mysql_select_db("$mysqldb") or die( "Unable to select database");
$result = mysql_query("SELECT $passfield FROM $mysqltable WHERE $idfield = '$usr' AND $passfield like '{SHA%'");
if (mysql_num_rows($result)==0){
    $salt=substr(sha1(uniqid()),18,8);
    $salt_ascii = hexToAscii($salt);
    $new_query= "UPDATE $mysqltable SET $passfield='".$dov."' WHERE $idfield='".$usr."'";
    $res2 = mysql_query($new_query);
}
exit;
?>

selinux

console

$ chcon -u system_u /usr/local/etc/convertpw.php
$ chcon -t bin_t /usr/local/etc/convertpw.php
$ chcon -u system_u /usr/local/etc/popafter.sh
$ chcon -t bin_t /usr/local/etc/popafter.sh

Example for SHA512-Crypt with passwd-files

This example has been tested on Dovecot 2.2.19 in a virtual user setup.

Create a new service for the postlogin script and reference it in the imap service section.

/etc/dovecot/conf.d/10-master.conf:

service imap {
  executable = imap imap-postlogin
  unix_listener imap-master {
    user = dovecot
  }
}

service imap-postlogin {
  executable = script-login /var/vmail/conf.d/scripts/postlogin.sh
  user = vmail
  unix_listener imap-postlogin {
  }
}

Enable the plain_pass variable in the auth-passwdfile configuration.

/etc/dovecot/conf.d/auth-passwdfile.conf.ext:

passdb {
  driver = passwd-file
  args = username_format=%u /var/vmail/auth.d/%d/passwd
}

userdb {
  driver = passwd-file
  args = username_format=%u /var/vmail/auth.d/%d/passwd
  default_fields = plain_pass=%w
}

This script will act on all users for a particular domain specified via the MIGRATE_DOMAIN variable.

/var/vmail/conf.d/scripts/postlogin.sh:

#!/bin/sh
# Split out domain part from $USER user@domain
MAIL_ALIAS=${USER%@*}
MAIL_DOMAIN=${USER#*@}
MIGRATE_DOMAIN="domain.tld"

case "$MAIL_DOMAIN" in
    $MIGRATE_DOMAIN)
    DOVECOTPW=$(/usr/bin/doveadm pw -s SHA512-CRYPT -p "$PLAIN_PASS")
    echo "user: $USER" >> /tmp/log
    echo $DOVECOTPW >> /tmp/log
    ;;
esac

exec "$@"

Exemplary directory permissions (Setup is using vmail context for the users):

console

$ l /var/vmail/conf.d/scripts/
total 4
-r-x------ 1 vmail vmail 322 Nov 23 09:58 postlogin.sh

$  l /tmp/log
-rw------- 1 vmail root 1160 Nov 23 10:27 /tmp/log

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Lua Support

Index Files

Converting Password Schemes

Introduction

Example

SHA512-CRYPT

selinux

Example for SHA512-Crypt with passwd-files

Databases

Mechanisms

Formats

Extensions

Converting Password Schemes ​

Introduction ​

Example ​

SHA512-CRYPT ​

selinux ​

Example for SHA512-Crypt with passwd-files ​

Converting Password Schemes

Introduction

Example

SHA512-CRYPT

selinux

Example for SHA512-Crypt with passwd-files