What format are they?
Do you mean youve actually opened and extracted stuff from noir with scumm revisited or youve opened a noir file, its come up as unknown block type and you want to find a decrypt value to decrypt it?
As Serge said SCUMM Rev finds the decrypt value itself for SCUMM games (0X69 for most I think, or that might just be bundles)
I suppose you could get SCUMM Rev to decrypt the block if you knew the value but I dont think it'd display the contents because its setup to detect SCUMM blocks.
Of course none of this is fact and is probably wrong, Serge will sort all this out when he replies