## ContentDigest

Syntax: ContentDigest on|off
Default: `ContentDigest off`
Context: server config, virtual host, directory, .htaccess
Override: Options
Status: experimental
Compatibility: ContentDigest is only available in Apache 1.1 and later

This directive enables the generation of `Content-MD5` headers as defined in RFC1864 respectively RFC2068.

MD5 is an algorithm for computing a "message digest" (sometimes called "fingerprint") of arbitrary-length data, with a high degree of confidence that any alterations in the data will be reflected in alterations in the message digest.

The `Content-MD5` header provides an end-to-end message integrity check (MIC) of the entity-body. A proxy or client may check this header for detecting accidental modification of the entity-body in transit. Example header:

       Content-MD5: AuLb7Dp1rqtRtxz2m9kRpA==

Note that this can cause performance problems on your server since the message digest is computed on every request (the values are not cached).

`Content-MD5` is only sent for documents served by the core, and not by any module. For example, SSI documents, output from CGI scripts, and byte range responses do not have this header.