ProFTPD module mod_sql_passwd



Many FTP sites use SQL databases for storing user accounts, including the user name and password. And while the mod_sql module provides support for some formats for the passwords stored in SQL databases, many sites have other formats which are not supported by mod_sql. These other formats often include MD5 or SHA1 passwords, base64-encoded or hex-encoded, without the prefix which is required by mod_sql's "OpenSSL" SQLAuthType.

The mod_sql_passwd module provides support for some of these other formats. When the mod_sql_passwd module is enabled, you can configure SQLAuthTypes of:

as well as the existing types supported by mod_sql.

This module is contained in the mod_sql_passwd.c file for ProFTPD 1.3.x, and is not compiled by default. Installation instructions are discussed here; a discussion on usage is also available.

This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/).

This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).

The most current version of mod_sql_passwd is distributed with ProFTPD.

Author

Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.

Directives


SQLPasswordCost

Syntax: SQLPasswordCost interactive|sensitive
Default: interactive
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.6rc3 and later

The SQLPasswordCost directive configures the high-level cost settings to use for memory-hard algorithms like scrypt and argon2. The supported cost cost values are:


SQLPasswordEncoding

Syntax: SQLPasswordEncoding encoding
Default: hex
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.3rc2 and later

The SQLPasswordEncoding directive configures the encoding that mod_sql_passwd expects when handling password values retrieved from a SQL database.

The following encoding values are currently supported:

If no SQLPasswordEncoding directive is configured, mod_sql_passwd will use "hex" by default.


SQLPasswordEngine

Syntax: SQLPasswordEngine on|off
Default: off
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.3rc2 and later

The SQLPasswordEngine directive enables or disables the module's registered SQLAuthType handlers.


SQLPasswordOptions

Syntax: SQLPasswordOptions opts
Default: None
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.4rc2 and later

The SQLPasswordOptions directive is used to configure various behaviors of mod_sql_passwd. Note: all of the configured SQLPasswordOptions parameters must appear on the same line in the configuration; only the first SQLPassworOptions directive that appears in the configuration is used.

Example:

  SQLPasswordOptions HashEncodeSalt HashEncodePassword

The following options are currently supported:

See the transformations section for a fuller description of how mod_sql_passwd operates on the password and salt data.


SQLPasswordPBKDF2

Syntax: SQLPasswordPBKDF2 digest iterations length
Default: None
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.5rc3 and later

The SQLPasswordPBKDF2 directive configures the input parameters to be used for PBKDF2 (Password-Based Key Derivation Function, version 2) passwords. The digest parameter specifies the digest algorithm to use (e.g. "sha1" or "sha512"); the iterations specifies the number of iterations to use for the key derivation, and length indicates the number of bytes to emit for the derived key.

Note that PBKDF2 requires that a salt be available, e.g. via SQLPasswordSaltFile or SQLPasswordUserSalt.

Per RFC 2898, the salt used should be 8 bytes or longer in length; this RFC also recommends that iterations be 1000 or greater.

Example:

  # Tell mod_sql to use PBKDF2 passwords
  SQLAuthTypes pbkdf2
  ...

  # Use the SHA1 digest algorithm, 200K iterations, and expect an output
  # length of 20 bytes.
  SQLPasswordPBKDF2 sha1 200000 20

  SQLPasswordSaltFile /path/to/salt/file

Use of digest algorithms other than SHA1 for SQLPasswordPBKDF2 requires OpenSSL-1.0.0c or later; earlier versions did not have the necessary APIs.

As of proftpd-1.3.5, the SQLPasswordPBKDF2 directive can instead take a named query, for determining the digest algorithm, iteration count, and output length on a per-user basis. For example:

  SQLNamedQuery get-user-pbkdf2 SELECT "algo, iter, len FROM user_pbkdf2 WHERE
user = '%{0}'
  SQLPasswordPBKDF2 sql://get-user-pbkdf2

SQLPasswordRounds

Syntax: SQLPasswordRounds count
Default: 1
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.4rc2 and later

The SQLPasswordRounds directive configures the number of rounds through which the password (and possibly salt) data will be hashed and encoded. The count parameter must be greater than 1.

See the transformations section for a fuller description of how mod_sql_passwd operates on the password and salt data.


SQLPasswordSaltEncoding

Syntax: SQLPasswordSaltEncoding encoding
Default: none
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.6rc1 and later

The SQLPasswordSaltEncoding directive configures the encoding that mod_sql_passwd expects when handling salt values retrieved either from a SQL database, or from a file.

The following encoding values are currently supported:

If no SQLPasswordSaltEncoding directive is configured, mod_sql_passwd will use "none" by default.


SQLPasswordSaltFile

Syntax: SQLPasswordSaltFile path|"none" ["Prepend"|"Append"]
Default: none
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.3rc2 and later

The SQLPasswordSaltFile directive configures a file which contains salt data. This salt will be added to the digest, along with the password sent by the client. Note that the salt will be used for all users.

Since many editors will automatically add a newline when writing a file, the mod_sql_passwd file will automatically trim the last newline in the salt data, if there is one. This means that if your salt must end in a newline character, then your SQLPasswordSaltFile must contain "salt\n\n".

When using salted passwords, some systems will prepend the salt as a prefix to the data, and others will append the salt as a suffix. The optional second parameter to SQLPasswordSaltFile controls how this module will use the salt:

  SQLPasswordSaltFile /path/to/salt Prepend
tells mod_sql_passwd to prepend the salt as a prefix, and:
  SQLPasswordSaltFile /path/to/salt Append
will cause the salt to be appended as a sufix. Note that the default behavior is to append the salt as a suffix.

If no SQLPasswordSaltFile is configured, then no salting is done.


SQLPasswordUserSalt

Syntax: SQLPasswordUserSalt "name"|source ["Prepend"|"Append"]
Default: none
Context: "server config", <VirtualHost>, <Global>
Module: mod_sql_passwd
Compatibility: 1.3.3 and later

The SQLPasswordUserSalt directive configures a per-user salt that will be added to the digest, along with the password sent by the client.

If "name" is specified, then the per-user salt data will be the name of the user logging in. Alternatively, you can configure a SQLNamedQuery which returns a single column of a single row, containing a string to use as the salt data, e.g.:

  SQLNamedQuery get-user-salt SELECT "salt FROM user_salts WHERE user_name = '%{0}'"
  SQLPasswordUserSalt sql:/get-user-salt

When using salted passwords, some systems will prepend the salt as a prefix to the data, and others will append the salt as a suffix. The optional second parameter to SQLPasswordUserSalt controls how this module will use the salt:

  SQLPasswordUserSalt name Prepend
tells mod_sql_passwd to prepend the salt as a prefix, and:
  SQLPasswordUserSalt name Append
will cause the salt to be appended as a sufix. Note that the default behavior is to append the salt as a suffix.

Installation

The mod_sql_passwd module is distributed with ProFTPD. Simply follow the normal steps for using third-party modules in proftpd. The mod_sql_passwd module requires OpenSSL support, so you must use the --enable-openssl configuration option. In addition, if you have the libsodium library installed, simply include the libsodium headers/libraries in the build command to enable additional algorithms.

NOTE: it is important that mod_sql_passwd appear after mod_sql in your --with-modules configure option:

  $ ./configure --enable-openssl --with-modules=mod_sql:mod_sql_passwd ...
To build mod_sql_passwd as a DSO module:
  $ ./configure --enable-dso --enable-openssl --with-shared=mod_sql_passwd
Then follow the usual steps:
  $ make
  $ make install

For those with an existing ProFTPD installation, you can use the prxs tool to add mod_sql_passwd, as a DSO module, to your existing server:

  $ prxs -c -i -d mod_sql_passwd.c

Usage

The following examples demonstrate how the mod_sql_passwd can be used.

To configure mod_sql_passwd to handle MD5 passwords that are base64-encoded, use:

  <IfModule mod_sql_passwd.c>
    SQLPasswordEngine on
    SQLPasswordEncoding base64
  </IfModule>

  <IfModule mod_sql.c>
    ...

    # Now that mod_sql_passwd is used, we can configure "MD5" as an
    # SQLAuthType that mod_sql will handle.
    SQLAuthTypes MD5
  </IfModule>

To have mod_sql_passwd to handle hex-encoded (and in lowercase) passwords, use:

  <IfModule mod_sql_passwd.c>
    SQLPasswordEngine on
    SQLPasswordEncoding hex
  </IfModule>

And if for some reason your database values are stored as hex values in uppercase, you would use:

  <IfModule mod_sql_passwd.c>
    SQLPasswordEngine on
    SQLPasswordEncoding HEX
  </IfModule>

To use salted passwords, write the salt to use into a file, and configure the mod_sql_passwd module to use it:

  <IfModule mod_sql_passwd.c>
    SQLPasswordEngine on
    SQLPasswordEncoding hex
    SQLPasswordSaltFile /path/to/salt
  </IfModule>

Argon2, Scrypt
When mod_sql_passwd is compiled/linked with the
libsodium library, then the Argon2 and Scrypt algorithms become available for use:

  <IfModule mod_sql_passwd.c>
    SQLPasswordEngine on
    SQLPasswordEncoding hex
    SQLPasswordSaltFile /path/to/salt
  </IfModule>

  <IfModule mod_sql.c>
    ...

    # Now that mod_sql_passwd is used, we can configure "SCRYPT" as an
    # SQLAuthType that mod_sql will handle.
    SQLAuthTypes SCRYPT
  </IfModule>

The scrypt algorithm requires 32 bytes of salt data; lack of salt, or salt of the wrong amount, will result in authentication failure. The argon2 algorithm requires 16 bytes of salt data; lack of salt or the wrong amount will result in failure.

The argon2 algorithm requires libsodium-1.0.9 or later.

Logging
The mod_sql_passwd module supports trace logging, via the module-specific log channels:

Thus for trace logging, to aid in debugging, you would use the following in your proftpd.conf:
  TraceLog /path/to/ftpd/trace.log
  Trace sql.passwd:20
This trace logging can generate large files; it is intended for debugging use only, and should be removed from any production configuration.

Processing of Password and Salt Data
The logical description of the processing that mod_sql_passwd does can be expressed as:

  ENCODE(HASH(data))
where data is comprised of the password, and possibly a salt. The function ENCODE() is determined by SQLPasswordEncoding, and the function HASH() by SQLAuthTypes.

Thus if we use a configuration like:

  SQLAuthTypes MD5
  SQLPasswordEncoding hex
Then mod_sql_passwd performs the following processing:
  hex(MD5(data))
in order to calculate the value that it will compare against the password value stored for the authenticating client.

Using Salts
By default, the mod_sql_passwd module uses the password, as sent by the client, as the data on which to perform its processing. In many cases, however, a salt is needed in addition to the password. The SQLPasswordSaltFile and SQLPasswordUserSalt directives are used to tell mod_sql_passwd that it should add a salt to the data before processing it. These directives also specify whether the salt should be prepended to the password, e.g.:

  data = salt + password
or appended to the password, e.g.:
  data = password + salt

Let's show a configuration which uses a prepended salt:

  SQLAuthTypes MD5
  SQLPasswordEncoding hex
  SQLPasswordSaltFile /path/to/salt.data Prepend
This means that mod_sql_passwd would end up checking the following computed value against the value in the database:
  hex(MD5(salt + password))

Some sites will have even more complex requirements for how the data processed by mod_sql_passwd need to be constructed. The salt data may need to be hashed before being used with the password, or may need to be hashed and encoded before use. Or maybe the password data needs to be hashed before use with the salt, or hashed and encoded. The SQLPasswordOptions directive supports options for supporting these use cases.

Each of the following examples assumes the following configuration:

  SQLAuthTypes MD5
  SQLPasswordEncoding hex
  SQLPasswordSaltFile /path/to/salt.data Prepend
Let's look at each of the SQLPasswordOptions in turn:

Of course, these various options can be combined:

  SQLPasswordOptions HashEncodePassword HashEncodeSalt
which would cause the data on which mod_sql_passwd operates to be constructed like so:
    data = ENCODE(HASH(salt)) + ENCODE(HASH(password))
    data = hex(MD5(salt)) + hex(MD5(password))

Rounds
For convenience, let's assume that the function TRANSFORM encompasses the entire ENCODE(HASH()) operation:

  TRANSFORM(data) = ENCODE(HASH(data))
Let's also assume that passwords are stored in your database using something like this:
  hex(MD5(hex(MD5(hex(MD5(data))))))
That means that the data value has gone through multiple rounds of the TRANSFORM function, e.g.:
  TRANSFORM(TRANSFORM(TRANSFORM(data)))
In this case, there are 3 rounds of transformation:
  for (i = 0; i < nrounds; i++) {
    data = TRANSFORM(data)
  }

Using the above example case, you would configure mod_sql_passwd to perform multiple rounds of transformation using the SQLPasswordRounds directive, like so:

  SQLAuthTypes MD5
  SQLPasswordEncoding hex
  SQLPasswordRounds 3
The combination of SQLPasswordOptions and SQLPasswordRounds means that quite few combinations of password values can be supported by the mod_sql_passwd module.



© Copyright 2009-2016 TJ Saunders
All Rights Reserved