mod_crypto
Support for symmetrical encryption and decryption
Extension
mod_crypto.c
crypto_module
Available in Apache 2.5 and later

This module provides the ability to encrypt and decrypt data on the input and output filter stacks.

Most specifically, it can be used to implement on-the-fly HLS encryption as described by draft-pantos-http-live-streaming-19.

Alternatively, it can be used to deliver secure data over insecure CDN to suitable clients.

The crypto filter may be added to either the input or the output filter stacks, as appropriate, using the SetInputFilter, SetOutputFilter, AddOutputFilter or AddOutputFilterByType directives.

Filters

# Stream Format

The encrypted stream consists of an optional IV block, followed by encrypted blocks using the chosen cipher. The final block is padded before being written. The size of the blocks is governed by the choice of cipher in use.

When the IV is specified with the CryptoIV directive, that IV is used, and is not written to or read from the stream.

# Keys and IVs

The CryptoKey and CryptoIV directives expect binary values which can be specified in a number of ways as below. The most significant bits of the relevant values are used, and if the values are too short, they are padded on the left with zero bits.

file:
  Read the value directly from the given file.
hex:
  Parse the expression as a hex value, which may contain colon separators.
decimal:
  Parse the expression as a decimal value.
base64:
  Parse the expression as a base64 value.
none
  No value is specified.

If the IV is unspecified a random IV will be generated during encryption and written as the first block. During decryption, the first block will be interpreted as the IV.

With the exception of file:, the CryptoKey and CryptoIV directives allow expression syntax to provide flexibility when setting the values. This allows both keys and IVs to be salted with values available to the webserver, such as REMOTE_USER, or the URL.

# Crypto Key Handler

For convenience, the crypto-key handler can be used to serve the key to suitably authorized clients, removing the need to store the key within the directory space of the webserver. This also allows the same expression syntax to be used to derive the key for both the clients and the encrypted content.

## Crypto Key Handler with a File

<Location /key>
SetHandler crypto-key
CryptoCipher aes128
CryptoKey file:/path/to/file.key
AuthType basic
...
</Location>

# HTTP Live Streaming

The HLS protocol supports encrypted streams using the AES-128 cipher and a corresponding key. Access is granted to the stream by sharing the key with the HLS client, typically over a secured connection.

The IV used for encrypting each media segment is specified within HLS in one of two ways:

- Explicitly specified within an IV attribute inside the EXT-X-KEY tag as a hexadecimal value.
- Implicitly specified by interpreting the decimal value of the EXT-X-MEDIA-SEQUENCE tag.

The media sequence value is usually embedded within the media segment filenames, and can be matched by using named regular expressions as per the example below.

## HLS Example - IV from media sequence

<LocationMatch (?<SEQUENCE>[\d]+)[^\d^/]+$>
SetOutputFilter ENCRYPT
CryptoCipher aes128
CryptoKey file:/path/to/file.key
CryptoIV decimal:%{env:MATCH_SEQUENCE}
</LocationMatch>
CryptoDriver
Name of the crypto driver to use
CryptoDriver name
CryptoDriver openssl
server config

The CryptoDriver directive specifies the name of the crypto driver to use. There is usually a recommended default driver on each platform. Possible values include openssl, commoncrypto and nss.

CryptoCipher
Cipher to be used by the crypto filter
CryptoCipher name
CryptoCipher aes256
server config
virtual host
directory
.htaccess

The CryptoCipher directive allows specification of the cipher to be used during encryption or decryption. If not specified, the cipher defaults to `aes256`.

Possible values depend on the crypto driver in use, and could be one of:

- 3des192
- aes128
- aes192
- aes256

CryptoIV
IV (Initialisation Vector) to be used by the crypto filter
CryptoIV value
CryptoIV none
server config
virtual host
directory
.htaccess

The CryptoIV directive allows the IV (initialisation vector) to be specified for the particular URL space. The IV can be read from a file, or can be set based on the expression parser, allowing for flexible scenarios for the setting of keys.

Values can be specified as read from a file, or as a hexadecimal, decimal or base64 value based on the following prefixes:

- file:
- hex:
- decimal:
- base64:

The value 'none' disables setting of the IV. In this case, during encryption a random IV will be generated and inserted as the first block, and during decryption the first block will interpreted as the IV.

CryptoKey
Key to be used by the crypto filter
CryptoKey value
CryptoKey none
server config
virtual host
directory
.htaccess

The CryptoKey directive allows the encryption / decryption key to be specified for the particular URL space. The key can be read from a file, or can be set based on the expression parser, allowing for flexible scenarios for the setting of keys.

Values can be specified as read from a file, or as a hexadecimal, decimal or base64 value based on the following prefixes:

- file:
- hex:
- decimal:
- base64:

The value 'none' disables the key. An attempt to serve a file through the ENCRYPT or DECRYPT filters without a key will cause the request to fail.

CryptoSize
Maximum size in bytes to buffer by the crypto filter
CryptoSize integer
CryptoSize 131072
server config
virtual host
directory
.htaccess

The CryptoSize directive specifies the amount of data in bytes that will be buffered before being encrypted or decrypted during each request. The default is 128 kilobytes.