Robert J. Hansen wrote: >> The thing is, if I create an ECC (ECDSA) secp256k1 primary key with >> Sign, Certify capabilities I can also create a subkey with E >> capability which is also a secp256k1 key. So, they can be used for >> encryption after all, so why can't I just add E capability to the >> primary one. > > You're confusing the field of numbers in which an algorithm operates > with the algorithm itself. It's like confusing a sports car with a tour > bus, thinking that since they run on the same roads they're interchangeable. > > secp256k1 is a certain field of numbers in which elliptical curve > operations may be defined. It is not an algorithm. You do not have a > secp256k1 key. You have an ECDSA key which operates in the curve > defined by secp256k1. > > When you "create a subkey with E capability", you're creating an ECDH > subkey operating in secp256k1. It's a completely different algorithm > that happens to operate in the same numerical space. Different cars, > different capabilities, same roads; different keys, different > capabilities, same curve. > > ECDSA/EdDSA cannot encrypt. ECDH cannot sign or certify. > > Your primary key must be able to make certifications. So that means if > you want to use ECC, your primary key must be ECDSA/EdDSA, and you will > never be able to make it into an encryption-capable primary key.
Thanks for this. Ok, now it's clear why the primary key cannot Encrypt.
Here is a key I have just generated:
sec secp256k1/BF131CA5E1642BE9
created: 2017-08-29 expires: never usage: SC
trust: ultimate validity: ultimate
ssb secp256k1/26882EB702DD7D4B
created: 2017-08-29 expires: never usage: E
[ultimate] (1). Delete Me <del...@me.me>
I understand that the first one is ECDSA and the second is ECDH, but
can't I use the same secp256k1 key (if I import it) but in different two
representations (ECDSA representation for Sign and Certify and ECDH for
Encrypt)? The subkey might have a different fingerprint because it's a
different representation of course but this is not the concern, the
concern is for both to be computed from the same imported private key.
Thanks.
signature.asc
Description: OpenPGP digital signature
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