cipher ID's

David Shaw dshaw at
Wed Jun 25 01:36:54 CEST 2008

On Jun 24, 2008, at 6:10 PM, vedaal at wrote:

> just curious // ? O.T.
> gnupg lists the following cipher ID's for symmetric algorithms:
> Home: ~/.gnupg
> Supported algorithms:
> Pubkey: RSA, RSA-E, RSA-S, ELG-E, DSA
> Cipher: IDEA (S1), 3DES (S2), CAST5 (S3), BLOWFISH (S4), AES (S7),
> AES192 (S8), AES256 (S9), TWOFISH (S10)
> rfc-4880 section 9.2
> lists (S5) and (S6) as "Reserved"
> reserved for what?
> and why couldn't they just be added later in sequence after
> whatever the
> last accepted algorithm is?

They could have been.  In the case of S5 and S6, they're marked as  
reserved because they were actually allocated at one point for SAFER- 
SK128 (S5) and DES/SK (S6).  They're marked as reserved now to make  
sure they're not used by anyone for anything.


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