Session Key algorithm

[Funaki, Yasuhiro]

Dear Expert,

I am wondering that which algorithm is used for the session key in GnuPG
1.4.8?
I understand the session key is symmetric key and  used for message
encryption, my concern is the compatibility with PGP commercial.
i.e PGP commercial use IDEA but GnuPG does not have it, then message can
not be decrypted with Gnupg??

Have a nice day.
Yasuhiro 
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