why gpg use SHA1 instead of pref???

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David Shaw <dshaw <at> jabberwocky.com> writes:

> > New: Symmetrically Encrypted and MDC Packet(tag 18)(70 bytes)
> > 	Ver 1
> > 	Encrypted data [sym alg is specified in pub-key encrypted session key]
> > 		(plain text + MDC SHA1(20 bytes))
> > 
> > What I must do for using RIPEMD160 hash of encryption??? Its normal because
> > encryption specifications requirements? Or its error of gpg?
> 
> The MDC is always SHA-1.  It is fixed as part of the protocol.
> 
> > Why he will use RSA encryption as other symmetric ciphers like CAST5, 3DES,
> > BLOWFISH,, in prefs, and, RSA its not in prefs list?
> 
> The type of public-key encryption is defined by what type of key you
> are encrypting to.  An RSA key means RSA encryption.  The symmetric
> ciphers are not relevant to this question.

i try to answer this few days before it but it was not post on list so now, i
post again.

but, its confusing output of pgpdump. plain text + SHA1 must be encrypt of
symmetric algorithm and after, its session key is encrypt of public key cipher.
im right or wrong? So why, he will use SHA1 in hash of symmetric key. its
expectation to use SHA1 hash with assymetric public key of receiver. or im not
understand you its really SHA1, with symmetric key its part of protocol??

how its possible to know which symmetric algorithm it was used to encrypt
message?  how i must obtain this informtation from pgpdump?

i think, it will be very good if well have some matrix of prefs, which
assymetric and symmetric algorithm he will use in all this cases. thanks David
to help all peoples of gpg list!!