add support for .(RSA|DSA|EC) PKCS#7 DER files
I've proposed a patch for file(1)
to detect DER Encoded PKCS#7 Signed Data (as well as JAR Manifest & Signature File), as used by e.g. JAR Signature Block Files.
I used the proposed file
/libmagic
output in this MR, but it already works since I added a (unfortunately somewhat short) FILE_TYPE_HEADER_PREFIX
as well (though even without that, fallback recognition would also work).