httpd_payloadshield

mod_payloadshield is an Apache HTTP Server 2.4 module that decrypts the PayloadShield request envelope before the request reaches the application (or mod_proxy upstream) and encrypts the response body before it is returned. It is the Apache counterpart of ngx_payloadshield and shares its crypto providers and wire format.

Wire format

Identical to ngx_payloadshield and ComPyPS/ComPHPPS:

• Body is JSON {"encrypted":"<Base64>"} in both directions.
• aes-gcm-256 / chacha20-poly1305: Base64 of 12-byte nonce || ciphertext || 16-byte tag, shared 32-byte key.
• rsa-hybrid: Base64 of a JSON object with Base64 key (RSA-OAEP-SHA256 wrapped AES key), nonce and data.

The algorithm is static server configuration; it is never taken from the request.

Build

Requires Apache 2.4 development files (apxs) and OpenSSL 1.1.1+ headers.

make                # builds mod_payloadshield.la with apxs
sudo make install   # installs mod_payloadshield.so
make test           # crypto unit tests (no Apache needed)

Configuration

LoadModule payloadshield_module modules/mod_payloadshield.so

<Location "/api">
    PayloadShield On
    PayloadShieldAlgorithm aes-gcm-256
    PayloadShieldKey /etc/payloadshield/server.key
    PayloadShieldMaxBodySize 10485760
</Location>

Directive	Meaning
PayloadShield On|Off	Enable processing. Default Off.
PayloadShieldAlgorithm name	aes-gcm-256, chacha20-poly1305 or rsa-hybrid. Required when enabled.
PayloadShieldKey file	Symmetric key file: 32 raw bytes or Base64 of 32 bytes.
PayloadShieldPrivateKey file	RSA private PEM used to decrypt requests (rsa-hybrid).
PayloadShieldPublicKey file	RSA public PEM used to encrypt responses (rsa-hybrid).
PayloadShieldMaxBodySize bytes	Maximum plaintext request/response size. Default 10 MiB.
PayloadShieldFailOpen On|Off	Pass data through unchanged when PayloadShield fails. Default Off; can expose plaintext.

Directives are valid in server, virtual host, directory and location contexts. Unsupported algorithms and unreadable keys fail apachectl configtest. Set LimitRequestBody high enough for the encrypted JSON request.

Behaviour

• Requests are fully read and decrypted in the fixups phase, so Content-Length seen by handlers and mod_proxy is the plaintext length. Failures return 400 (bad envelope or authentication failure), 413 (too large) or 500.
• Responses are fully buffered, encrypted and sent as application/json with a new Content-Length. Upstream responses with a Content-Encoding other than identity are refused (500) unless fail-open is on.
• Subrequests, internal redirects, HEAD, 1xx, 204 and 304 responses are not processed.

This module is a prototype. Compile and integration-test it against the exact httpd/OpenSSL build used in deployment, and combine it with TLS, replay protection and restrictive key-file permissions.