If you have the key to a particular encryption, you decrypt it with this
action. If you use this on a file, the file becomes decrypted. If you use
this on a node or Matrix traffic, you may access the node or read the
traffic, but it remains encrypted to others.
Pg. 229 SR4A. I'm not arguing the technical sense of the rule, just that the rule exists. On the other hand since SR decryption has nothing to do with real world decryption I suppose it makes as much technical sense as anything in that context.
I think this is being taken out of context. The passage seems to be implying that if you decrypt a node or a file, it is still unencrypted to a random person -- it's not like the file shows up in a 'cracked' state, decryption means you have the key, even nodes. Unwired backs this up, too:
'A hacker may Decrypt the node, after which she can access it, as can anyone else with whom she shares the Decrypted key.' (UW, pg 66)
Coupled with:
'Since technomancers maintain a link with their sprites, as long as they remain online, they are able to communicate and exchange information in terms of text, files, and even impressions.' (UW, pg 154)
It seems clear a sprite could decrypt a node, get the key, then share it with you.