This (encrypted) DVDELF.bin-file is necessary (for Homebrew-users yet), to get a valid "encrypted ELF"/"KELF"-Header and build a valid "KELF".
This file isn't necessary, if you have a DVD-Player on ROM.
If you do not have one, on a hardware-based chip in your PS2, you need this DVDELF.bin.
The MCID (and with it the encryption) is different if the filesize of the "KELF" is different. The key varies.
Small, DVDELF.bin's help you to save space on mc and loading-time of FMCB.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux