Multiple runs of gpg and differing filesizes

Gates, Scott SGates at
Wed Jan 28 09:28:37 CET 2004

That's par for the course. 

The algorithm adds a certain amount of random data, because you're REALLY
just encrypting the session key which encrypted the data. Compression
happens before the encryption, if I'm remembering right; so if you turn off
compression, I'd be willing to bet the size would vary even more.  I
wouldn't guess it would be TOO much, say +- 5%.

Why does it matter that the files be EXACTLY the same size?  

-----Original Message-----
From: Marcus Williams [mailto:marcus at] 
Sent: Tuesday, January 27, 2004 6:52 AM
To: gnupg-users at
Subject: Multiple runs of gpg and differing filesizes

Hi -

If I pick a reasonable sized file (>1mb say) and run something like:

for i in `seq 50`; do cat file.tar | /usr/bin/gpg--symmetric
--passphrase-fd=3 > file.$i 3<pp ; done

I get 50 encrypted copies of the file, but they are not all the same size.
This leads me to three questions :)

1) Is this because of the internal compression?
2) If so, can I guarantee the same filesize if I switch off internal
3) If so, can I pipe the file through gzip _and then_ gpg with no
compression can I guarantee the same filesize?

(I'm using gpg 1.2.4)



Marcus Williams --
Quintic Ltd, 39 Newnham Road, Cambridge, UK
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