Phar manifest file entry definition
Phar
What makes a phar a phar and not a tar or a zip?
PHP Manual

## Phar Signature format

Phars containing a signature always have the signature appended to the end of the Phar archive after the loader, manifest, and file contents. The two signature formats supported at this time are MD5 and SHA1.

Signature format
Length in bytes | Description
--- | ---
16 or 20 bytes | The actual signature, 20 bytes for an SHA1 signature, 16 bytes for an MD5 signature, 32 bytes for an SHA256 signature, and 64 bytes for an SHA512 signature.
4 bytes | Signature flags. 0x0001 is used to define an MD5 signature, 0x0002 is used to define an SHA1 signature, 0x0004 is used to define an SHA256 signature, and 0x0008 is used to define an SHA512 signature. The SHA256 and SHA512 signature support was introduced with API version 1.1.0.
4 bytes | Magic GBMB used to define the presence of a signature.

Phar manifest file entry definition
Phar
What makes a phar a phar and not a tar or a zip?
PHP Manual