ProFTPD module mod_sql_passwd

## 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:

- Argon2
- Bcrypt
- MD5
- PBKDF2
- Scrypt
- SHA1
- SHA256
- SHA512

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

- SQLPasswordArgon2
- SQLPasswordCost
- SQLPasswordEncoding
- SQLPasswordEngine
- SQLPasswordOptions
- SQLPasswordPBKDF2
- SQLPasswordRounds
- SQLPasswordSaltEncoding
- SQLPasswordSaltFile
- SQLPasswordScrypt
- SQLPasswordUserSalt

### SQLPasswordArgon2

Syntax: SQLPasswordArgon2 length
Default: 32
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_sql_passwd
Compatibility: 1.3.6rc5 and later

The `SQLPasswordArgon2` directive configures the length of the calculated Argon2 output hash in bytes. The default length is 32 bytes.

### 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:

- interactive

  This cost uses parameters where generating the value is part of an "interactive" session.

  For `scrypt`, depending on the version of `libsodium` used, this cost uses:

          N=16384, r=8, p=1

- sensitive

  This cost uses parameters where the value generated is considered very "sensitive".

  For `scrypt`, depending on the version of `libsodium` used, this cost uses:

          N=1048576, r=8, p=1

### 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:

- base64
- hex (for lowercase hex values)
- HEX (for uppercase hex values)

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:

- `HashPassword`
- `HashEncodePassword`
- `HashSalt`
- `HashEncodeSalt`

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:

- base64
- hex (for lowercase hex values)
- HEX (for uppercase hex values)
- none (use salt value as is)

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.

### SQLPasswordScrypt

Syntax: SQLPasswordScrypt length
Default: 32
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_sql_passwd
Compatibility: 1.3.6rc5 and later

The `SQLPasswordScrypt` directive configures the length of the calculated Scrypt output hash in bytes. The default length is 32 bytes.

### 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
      SQLPasswordUserSalt sql:/get-user-salt Prepend

tells `mod_sql_passwd` to prepend the salt as a prefix, and:

      SQLPasswordUserSalt name Append
      SQLPasswordUserSalt sql:/get-user-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.

## 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:

- sql.passwd

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:

- `HashPassword`

  This option says that `mod_sql_passwd` should use the `HASH()` function on the password data before using it, regardless of whether a salt is used or not. I.e.:

        data = salt + HASH(password)

  which assuming hex and MD5, means:

        data = salt + MD5(password)

- `HashSalt`

  This option says that `mod_sql_passwd` should use the `HASH()` function on the salt data before using it. If no salt is used, this option is silently ignored. Thus:

        data = HASH(salt) + password

  which assuming hex and MD5, means:

        data = MD5(salt) + password

- `HashEncodePassword`

  This option says that `mod_sql_passwd` should use the `HASH()` function and then the `ENCODE()` function on the password data before using it. This option is only useful when salts are also used. Thus:

        data = salt + ENCODE(HASH(password))

  which assuming hex and MD5, means:

        data = salt + hex(MD5(password))

  Note: If no salt is present, this option will be ignored. Without a salt, this option is equivalent to adding another round of transformation, which is not an obvious side effect.

- `HashEncodeSalt`

  This option says that `mod_sql_passwd` should use the `HASH()` function and then the `ENCODE()` function on the salt data before using it. If no salt is used, this option is silently ignored. Thus:

        data = ENCODE(HASH(salt)) + password

  which assuming hex and MD5, means:

        data = hex(MD5(salt)) + password

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 2009-2019 TJ Saunders
All Rights Reserved