Encryption (xm_crypto)

This module provides encryption and decryption functionality using the AES symmetric encryption algorithm. Decryption of input data is defined within im_file module instances, while encryption of output data is specified within om_file module instances. The functionality of xm_crypto can be combined with other modules providing data conversion such as xm_zlib.

To examine the supported platforms, see the list of installer packages in the Available Modules chapter.

Configuration

The xm_crypto module accepts the following directives in addition to the common module directives.

Password

This optional directive specifies a password to be used by the aes_encrypt and aes_decrypt data converters while processing data. This directive is mutually exclusive with the PasswordFile directive.

PasswordFile

This optional directive specifies a path to a file which stores the password to be used by the aes_encrypt and aes_decrypt data converters while processing data. This directive is mutually exclusive with the Password directive.

UseSalt

This optional Boolean directive specifies whether to use a randomly-generated combination of characters for encryption and decryption. The default value is TRUE.

Iter

This optional directive enhances security by enabling the PBKDF2 algorithm and setting the iteration count during the key generation. For more details, see the EVP_BytesToKey section on the OpenSSL website. The default value is 0.

Data conversion

The xm_crypto module implements data converters to be used with the im_file and om_file modules. These are specified in the InputType and OutputType directives of their respective module and are invoked using dot notation:

<InstanceName>.<DataConverterName>

Where <InstanceName> is the given name of the xm_crypto instance and <DataConverterName> is the name of the converter being invoked.

The following data converters are available to encrypt and decrypt log data.

aes_encrypt

This data converter is used to encrypt log data. It should be specified in the OutputType directive after the output writer function. The encrypted result is similar to running the following OpenSSL command:

openssl enc -aes256 -md sha256 -pass pass:password -in input_filename -out output_encrypted_filename
Rotation of files is done automatically when encrypting log data with the aes_encrypt data converter. The rotation pattern is original_file -→ original_file.1 -→ original_file.2 -→ original_file.n. There is no built-in removal or cleanup of files.
aes_decrypt

This data converter is used to decrypt log data. It should be specified in the InputType directive before the input reader function. The decrypted result is similar to running the following OpenSSL command:

openssl enc -aes256 -d -md sha256 -pass pass:password -in encrypted_filename -out output_decrypted_filename

Examples

The examples below describe various ways of processing logs with the xm_crypto module.

Example 1. Encryption of logs

The following configuration uses the im_file module to read log messages. The aes_encrypt data converter encrypts data at the output and saves the results to a file.

nxlog.conf
<Extension cryptography>
    Module           xm_crypto
    Password         <PASSWORD>
</Extension>

<Input input_file>
    Module           im_file
    File             '/tmp/input'
</Input>

<Output output_file>
    Module           om_file
    File             '/tmp/output'
    OutputType       cryptography.aes_encrypt
</Output>
Example 2. Decryption of Logs

The following configuration uses the aes_decrypt data converter to decrypt log messages at the input. The result is saved to a file.

nxlog.conf
<Extension cryptography>
    Module           xm_crypto
    UseSalt          TRUE
    PasswordFile     passwordfile
</Extension>

<Input input_file>
    Module           im_file
    File             '/tmp/input'
    InputType        cryptography.aes_decrypt
</Input>

<Output output_file>
    Module           om_file
    File             '/tmp/output'
</Output>
Example 3. Decryption and encryption of logs

The configuration below uses the aes_decrypt data converter to decrypt input data. The Exec directive in the input instance runs the to_syslog_ietf() procedure to convert messages to the IETF Syslog format. The result is encrypted with the aes_encrypt converter in the output instance and saved to a file.

<Extension cryptography>
    Module           xm_crypto
    UseSalt          TRUE
    PasswordFile     passwordfile
</Extension>

<Extension syslog>
    Module           xm_syslog
</Extension>

<Input input_file>
    Module           im_file
    File             '/tmp/input'
    InputType        cryptography.aes_decrypt
    Exec             to_syslog_ietf();
</Input>

<Output output_file>
    Module           om_file
    File             '/tmp/output'
    OutputType       cryptography.aes_encrypt
</Output>

Data conversion operations can be chained together to create a workflow. For example, the xm_zlib module functionality can be combined with the xm_crypto module to perform compression and encryption operations on log files.

Data converters are processed sequentially from left to right, thus the order that they are specified in is important. When specifying data converters, decryption should always occur before decompression in input instances, while compression should always precede encryption in output instances, as illustrated in the following table.

Table 1. Sequential order of operations for compression/encryption and decompression/decryption
Directive First Operation Second Operation Third Operation

Compression + Encryption

OutputType

Output writer function

compress

aes_encrypt

Decompression + Decryption

InputType

aes_decrypt

decompress

Input reader function

Example 4. Processing data with multiple data converters

The configuration below processes a zlib-compressed and encrypted log file containing log records in the NXLog Binary format. The input instance decrypts the file using the aes_decrypt converter of the xm_crypto module, and then decompresses it using the decompress converter of the xm_zlib module. Each log record is processed and if it contains the info string it is passed on to the output instance.

The processed log data is written to a file by the output instance in the NXLog Binary format. The data is compressed using the compress converter and finally encrypted using the aes_encrypt converter.

<Extension zlib>
    Module              xm_zlib
    Format              zlib
    CompressionLevel    9
    CompBufSize         16384
    DecompBufSize       16384
</Extension>

<Extension cryptography>
    Module              xm_crypto
    UseSalt             TRUE
    Password            <PASSWORD>
</Extension>

<Input input_file>
    Module              im_file
    File                '/tmp/input'
    InputType           cryptography.aes_decrypt, zlib.decompress, Binary
    Exec                if not ($raw_event =~ /info/) drop();
</Input>

<Output output_file>
    Module              om_file
    File                '/tmp/output'
    OutputType          Binary, zlib.compress, cryptography.aes_encrypt
</Output>
The default input reader and output writer function for the im_file and om_file modules is LineBased. When using the default function, it can be omitted from the respective InputType or OutputType directive.

For more information and examples on combined data conversion operations see Compression and Encryption in the User Guide.