Questions about particular use cases (integrity verification w/o private key, add E flag to primary key, import secp256k1 key)

[Mario Castelán Castro]

On 29/08/17 02:09, s7r wrote:
> 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.

You can use hash(private_key_1) to seed a cryptographically secure
pseudo-random number generator (E.g.: AES in CTR mode with the seed as
the key), and then use that random stream to generate (private_key_2,
pubic_key_2.

This is a method applicable in general. The algorithms of private_key_1
and private_key_2 need not be the same, nor do they need to be defied
over the same curve.

The only problem is that I do not know of a program to do they key
generation from a user-provided seed.

-- 
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